JP5831403B2 - Coupling optical system and coupling method - Google Patents

Description

  The present invention relates to a coupling optical system and a coupling method for coupling optical elements used for optical communication and the like.

  With the spread of smartphones and tablet terminals, communication of data having an enormous amount of information is required. Accordingly, further increase in capacity of optical communication is desired.

  Conventional optical communication is performed using a single core fiber in which one core is provided in a clad. However, since there is a capacity limit when communication is performed using one single core fiber, means for performing data communication with a capacity exceeding the capacity is required.

  In this regard, for example, a multi-core fiber that is an optical fiber in which a plurality of cores are provided in one clad can be used (see Patent Documents 1 and 2). Since the multi-core fiber has a plurality of cores, it is possible to perform large-capacity data communication compared to the single-core fiber.

  In optical communication, such a multi-core fiber may be used by being optically coupled with, for example, a fiber bundle in which a plurality of single-core fibers are bundled, a light emitting element such as a laser diode, or a light receiving element such as a photodiode. is there. Hereinafter, all or part of the multi-core fiber, the fiber bundle, the light emitting element, and the light receiving element may be referred to as “optical element”.

JP-A-10-104443 JP-A-8-119656

  Here, when optically coupling the multi-core fiber and another optical element, securing coupling efficiency becomes a problem.

  When multicore fibers having the same number of cores are coupled, the cores can be reliably coupled by aligning the multicore fibers. Therefore, it is difficult to cause coupling loss, and high coupling efficiency can be achieved.

  On the other hand, when the multi-core fiber and another optical element are coupled, there is a problem that coupling efficiency is lowered. For example, in general, the cores of the multi-core fiber are arranged at a distance narrower than the diameter of each single-core fiber of the fiber bundle. Therefore, when the fiber bundle and the multi-core fiber are coupled, it is difficult to reliably couple the cores. Therefore, the coupling efficiency between the multi-core fiber and the fiber bundle is reduced.

  The present invention solves the above problems, and provides a coupling optical system capable of suppressing a decrease in coupling efficiency when coupling a multi-core fiber and another optical element, and a coupling method using the same. With the goal.

In order to solve the above-described problem, the coupling optical system according to claim 1 includes a plurality of light sources, a plurality of light receiving elements, and any one of a plurality of optical elements bundled with a plurality of single core fibers and a plurality of light elements. The core is disposed between the multi-core fiber covered with the clad and optically couples the optical element and the multi-core fiber. In the coupling optical system, the numerical aperture of each of the plurality of lights incident from the incident side element consisting of one of the optical element and the multi-core fiber is equal to the numerical aperture of each of the plurality of lights exiting toward the exit side element consisting of the other. It is comprised so that it may become. The coupling optical system includes a first optical system and a second optical system. The first optical system converges each of the plurality of lights. The second optical system changes the interval between the plurality of lights. The first optical system has a configuration in which a plurality of lenses are arranged in an array. The second optical system is a double-sided telecentric optical system.
In order to solve the above problem, the coupling optical system according to claim 2 is the coupling optical system according to claim 1, wherein the first optical system is disposed closer to the optical element than the second optical system. ing.
In order to solve the above problem, the coupling optical system according to claim 3 is the coupling optical system according to claim 1 or 2, wherein the magnification of the first optical system and the magnification of the second optical system are as follows: Is a value satisfying
βm × βr = 1
However,
βm: magnification of the first optical system βr: magnification of the second optical system In order to solve the above problem, the coupling optical system according to claim 4 is a coupling optical system according to any one of claims 1 to 3. The pitch between the plurality of lenses is equal to any of the pitch between the plurality of light sources, the pitch between the plurality of light receiving elements, and the pitch between the plurality of single core fibers.
Moreover, in order to solve the said subject, the coupling optical system of Claim 5 is a coupling optical system in any one of Claims 1-4, Comprising: The magnification of a 2nd optical system is between several light sources. Is equal to the ratio of the pitch between the plurality of light receiving elements and the pitch between the single core fibers to the pitch between the cores of the multicore fiber.
Further, in order to solve the above problem, a coupling optical system according to claim 6, wherein, there is provided a coupling optical system according to any one of 請 Motomeko 1-5, an incident-side element, and the coupling optical system, emission The side element means that each principal ray of light from the incident side element enters perpendicularly to the incident surface of the coupling optical system, and each principal ray of light emitted from the exit surface of the coupling optical system corresponds to the emission side element. It is arranged to enter perpendicularly to the light receiving surface.
Further, in order to solve the above described problems, binding method of Claim 7, wherein, using a coupling optical system according to any of claims 1 to 6, a plurality of light each numerical aperture incident from incident-side element And the optical element and the multi-core fiber are coupled so that the numerical apertures of the plurality of lights emitted toward the emission side element are equal.

  In the coupling optical system that optically couples the optical element and the multi-core fiber, the numerical apertures of the plurality of lights incident from the incident side element are equal to the numerical apertures of the plurality of lights emitted toward the emission side element. Designed to be Accordingly, it is possible to suppress a decrease in coupling efficiency when coupling the multi-core fiber and another optical element.

It is a figure which shows the multi-core fiber common to embodiment. It is a figure which shows the coupling optical system which concerns on 1st Embodiment. It is a figure which shows the coupling optical system which concerns on 2nd Embodiment. It is a figure which shows the deflection optical system which concerns on 2nd Embodiment. It is a figure which shows another example of the deflection | deviation optical system which concerns on 2nd Embodiment. It is a figure which shows another example of the deflection | deviation optical system which concerns on 2nd Embodiment. It is a figure which shows the coupling optical system which concerns on 3rd Embodiment. It is a figure which shows the deflection optical system which concerns on 3rd Embodiment. It is a figure which shows the coupling member which concerns on the modification 2 common to 3rd Embodiment from 1st Embodiment. It is a figure which shows the coupling member which concerns on the modification 3 common to 3rd Embodiment from 1st Embodiment. It is a figure which shows the coupling member which concerns on the modification 4 common to 3rd Embodiment from 1st Embodiment. It is a figure which shows the coupling member which concerns on the modifications 2-4 common to 3rd Embodiment from 1st Embodiment. It is a figure which shows the multi-core fiber which concerns on the modifications 2-4 common to 3rd Embodiment from 1st Embodiment. It is a figure which shows the multi-core fiber and coupling member which concern on the modifications 2-4 common to 3rd Embodiment from 1st Embodiment.

[Configuration of multi-core fiber]
The configuration of the multicore fiber 1 will be described with reference to FIG. The multi-core fiber 1 is generally a long cylindrical member having flexibility. FIG. 1 is a perspective view of the multi-core fiber 1. In FIG. 1, only the tip portion of the multi-core fiber 1 is shown.

The multi-core fiber 1 is made of a material having a high light transmittance such as quartz glass or plastic. The multicore fiber 1 includes a plurality of cores C _k (k = 1 to n) and a clad 2.

The core C _k is a transmission path for transmitting light from a light source (not shown). Each of the cores C _k has an end face E _k (k = 1 to n). From the end surface E _k, the light source light emitted by the (not shown) is emitted. In order to increase the refractive index as compared with the clad 2, the core C _k is made of a material in which germanium oxide (GeO ₂ ) is added to, for example, quartz glass. Although FIG. 1 shows a configuration having _seven cores C _{1 to} C ₇ , the number of cores C _k may be at least two.

The clad 2 is a member that covers the plurality of cores _Ck . Cladding 2 has a function to confine light from a light source (not shown) in the core C _k. The clad 2 has an end face 2a. The end surface _Ek of the core _Ck and the end surface 2a of the clad 2 form the same surface (the end surface 1b of the multicore fiber 1). The cladding 2 material, a low refractive index material is used than the core C _k material. For example, when the material of the core C _k is made of quartz glass and germanium oxide, quartz glass is used as the material of the clad 2. Thus, by making the refractive index of the core C _k higher than the refractive index of the cladding 2, the light from the light source (not shown) is totally reflected at the interface between the core C _k and the cladding 2. Therefore, light can be transmitted in the core _Ck .

<First Embodiment>
Next, a configuration example of the coupling optical system 20 according to the first embodiment will be described with reference to FIG. In the present embodiment, a case where the fiber bundle 10 and the multi-core fiber 1 are coupled will be described. FIG. 2 is a sectional view in the axial direction of the coupling optical system 20, the fiber bundle 10, and the multicore fiber 1.

[Configuration of fiber bundle]
The fiber bundle 10 includes a plurality of single core fibers 100. In the fiber bundle 10, the same number of single core fibers 100 (seven in this embodiment) as the number of cores of the multi-core fibers 1 to be coupled (seven in this embodiment) are bundled. In FIG. 2, only three single core fibers 100 are shown. The single core fiber 100 includes a core C inside a clad 101. The core C is a transmission path for transmitting light from a light source (not shown). The light emitted from the end surface Ca of the core C is incident on the incident surface (described later) of the coupling optical system 20 with a predetermined numerical aperture NA. The numerical aperture NA is defined by N sin θ (NA = N sin θ). N is a refractive index. θ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the end face Ca enters the coupling optical system 20.

[Configuration of coupling optical system]
The coupling optical system 20 according to the present embodiment includes a first optical system 21 and a second optical system 22. The first optical system 21 has a function of converging each of the plurality of lights. The second optical system 22 has a function of changing the interval between the plurality of lights.

The first optical system 21 in the present embodiment has a function of converging each of a plurality of lights from the fiber bundle 10. The first optical system 21 includes a plurality of convex lenses 21a arranged in an array. The plurality of convex lenses 21 a are provided in the same number as the single core fibers 100 included in the fiber bundle 10. The first optical system 21 (convex lens 21a) is disposed at a position where each light (principal ray Pr) emitted from each end face Ca of the fiber bundle 10 enters perpendicularly to the surface of the corresponding convex lens 21a. (In this case, the end face Ca functions as a stop). The plurality of convex lenses 21a has a pitch P _m (a distance between optical axes of adjacent convex lenses 21a). A pitch P _out between a plurality of single core fibers 100 (a distance between optical axes of adjacent single core fibers 100. For example, a fiber bundle. The distance between the optical axis of the core C of the fiber disposed at the center of the fiber 10 and the optical axis of the core C of the fiber disposed at the periphery thereof is disposed. Note that the first optical system 21 is disposed closer to the fiber bundle 10 than the second optical system 22. In the present embodiment, the surface of the convex lens 21a on which the light from the fiber bundle 10 is incident is an example of an “incident surface”. The plurality of convex lenses 21a in the present embodiment is an example of “a plurality of lenses”.

  The magnification of the first optical system 21 (each convex lens 21a) is designed to be a predetermined magnification βm. The first optical system 21 (each convex lens 21a) is designed so that the numerical aperture NA ′ (= N sin θ ′) of the emitted light is smaller than the numerical aperture NA of the incident light. θ ′ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the first optical system 21 reaches the imaging point IP.

The second optical system 22 in the present embodiment has a function of narrowing the interval between the plurality of lights from the first optical system 21. The second optical system 22 is constituted by a double-sided telecentric optical system including two convex lenses 22a and 22b. The second optical system 22 is arranged at a position where each of the plurality of lights (principal rays Pr) from the first optical system 21 is perpendicularly incident on the end face E _k of each core C _k of the corresponding multi-core fiber 1. ing. The second optical system 22 is designed so that light (light flux) emitted from the second optical system 22 has a predetermined numerical aperture NA ″ (= Nsin θ ″). θ'', the light (light beam) emitted from the second optical system 22 is an angle principal ray Pr and marginal rays Mr forms as they enter the multi-core fiber 1 (end surface E _k of each core C _k). In the present embodiment, the surface of the convex lens 22b from which the light from the first optical system 21 is emitted is an example of an “emission surface”. In the present embodiment, the end surface E _k is an example of a “light receiving surface”.

In the present embodiment, the second optical system 22 has a magnification βr of the pitch P _out between the single core fibers 100 and the pitch P _in between the cores C _{k of the} multi-core fiber 1 (adjacent cores in the multi-core fiber 1). C _k of the distance between the optical axes. for example, are designed to be equal to the ratio of the distance) between the optical axes of the periphery of the core C ₂ of the center of the core C ₁ of the multi-core fiber 1. Note that the ratio of the magnification βr and the pitch P _out to the pitch P _in does not necessarily have to be equal depending on the tolerance of the optical element used and variations in design. Any value that can secure at least the coupling efficiency necessary for optical transmission, for example, a value satisfying the following expression (1) may be used.

0.9βr <P _in / P _out <1.1βr (1)

  Further, if the numerical aperture NA of the light incident on the first optical system 21 and the numerical aperture NA ″ of the light emitted from the second optical system 22 are different, the coupling efficiency is lowered. Therefore, in this embodiment, the coupling optical system 20 is designed so that the numerical aperture NA is equal to the numerical aperture NA ″.

  Furthermore, in the present embodiment, the magnification βm of the first optical system 21 and the magnification βr of the second optical system 22 are designed so as to satisfy the following expression (2).

  βm × βr = 1 (2)

  It should be noted that the relationship between the magnification βm and the magnification βr does not necessarily satisfy the condition of the expression (2) due to the tolerance of the optical element used and variations in design. Any value that can secure at least the coupling efficiency necessary for optical transmission, for example, a value satisfying the following expression (3) may be used.

  0.9 <βm × βr <1.1 (3)

  In the above description, the configuration of the coupling optical system 20 arranged so that the light emitted from the first optical system 21 enters the second optical system 22 has been described. However, the first optical system 21 and the second optical system 21 The arrangement of the system 22 may be reversed. Also in this case, the magnification βm of the first optical system 21 and the magnification βr of the second optical system 22 need only satisfy the relationship of Expression (2) or Expression (3).

[About how light travels]
Next, how light travels according to the present embodiment will be described with reference to FIG. In the present embodiment, a configuration in which light is emitted from the fiber bundle 10 will be described. That is, the fiber bundle 10 in the present embodiment is an example of an “incident side element”. On the other hand, the multi-core fiber 1 in the present embodiment is an example of an “emission side element”.

  First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Light emitted from each end face Ca enters the first optical system 21 (convex lens 21a) with a predetermined numerical aperture NA while being diffused. As described above, in the present embodiment, each light (principal ray Pr) emitted from the end face Ca is incident on the first optical system 21 (the surface of the convex lens 21a) perpendicularly.

  Each of the plurality of lights (principal rays Pr) incident on the first optical system 21 is perpendicularly incident on the second optical system 22 (surface of the convex lens 22a) with the imaging point IP as a secondary light source. The numerical aperture (equal to NA ′) when each of the plurality of lights enters the second optical system 22 is smaller than the numerical aperture NA. Therefore, the configuration of the second optical system 22 can be simplified.

  The second optical system 22 is formed by a double-sided telecentric optical system. Accordingly, the plurality of light beams (principal rays Pr) incident perpendicularly to the second optical system 22 are emitted vertically from the second optical system 22 (surface of the convex lens 22b) in a state where the distance between them is narrowed.

At this time, in the present embodiment, the magnification βm of the first optical system 21 and the magnification βr of the second optical system 22 satisfy the relationship of Expression (2). Accordingly, the light (principal ray Pr) corresponding to the plurality of cores C _k (end faces E _k ) of the multi-core fiber 1 without changing the numerical aperture NA of the light emitted from each end face Ca (NA = NA ″). ) Can be incident vertically. Therefore, it is possible to transmit light while maintaining a high coupling efficiency between the optical elements.

As a specific example, a fiber bundle 10 of pitch _{P out} is 120μm between the plurality of single-core fiber 100 will be described a case where the pitch _{P in} between the core _{C k} are attached to the multi-core fiber 1 of 40 [mu] m. In this case, since the pitch is reduced to 1/3, if the magnification βm of the first optical system 21 is 3 and the magnification βr of the second optical system 22 is 1/3, the numerical aperture NA is not changed ( NA = NA ″) The corresponding light (principal ray Pr) can be vertically incident on the plurality of cores C _k of the multi-core fiber 1.

The pitch P _in and the pitch P _out can be arbitrarily set when the multi-core fiber 1 and the fiber bundle 10 are optically designed. For example, the pitch P _out can be set between about 100 to 150 μm. The pitch _{P in,} for example, can be set anywhere between about 30 to 50 [mu] m.

[Modification 1]
In the present embodiment, the example in which a plurality of lights emitted from the fiber bundle 10 are guided to the multicore fiber 1 via the coupling optical system 20 has been described. However, the target for emitting the light is not limited thereto. For example, a plurality of light sources can be used instead of the fiber bundle 10. In this case, the light source is an example of an “incident side element”. In this case, the above-mentioned “P _out ” is the pitch between adjacent light sources (for example, the distance between the center of the exit surface of the light source disposed at the center and the center of the exit surface of the light source disposed around the center). )

[Modification 2]
Alternatively, it is also possible to guide each of a plurality of lights emitted from the multi-core fiber 1 (a plurality of cores C _k ) to the fiber bundle 10 or a light receiving element (not shown) using the above-described coupling optical system 20. In this case, the multi-core fiber 1 is an example of an “incident side element”. Further, the fiber bundle 10 or the light receiving element is an example of the “outgoing side element”. Hereinafter, an example in which each light emitted from the multicore fiber 1 is guided to the fiber bundle 10 will be described.

  The second optical system 22 in this modification has a function of widening the interval between a plurality of lights emitted from the multicore fiber 1. In the present modification, the surface of the convex lens 22b on which the light from the multicore fiber 1 is incident is an example of an “incident surface”.

  The first optical system 21 in this modification has a function of converging each of the plurality of lights from the second optical system 22. Each converged light (principal ray Pr) is perpendicularly incident on the end face Ca of the corresponding core C. In the present modification, the surface of the first optical system 21 (convex lens 21a) from which the light from the second optical system 22 is emitted is an example of an “emission surface”. In the present embodiment, the end surface Ca is an example of a “light receiving surface”.

  Θ in this modification is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light flux) emitted from the first optical system 21 enters the fiber bundle 10 (each single core fiber 100). θ ′ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the second optical system 22 reaches the imaging point IP. θ ″ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the multicore fiber 1 enters the second optical system 22.

When the light receiving element hits the “outgoing side element”, the above “P _out ” is arranged at the pitch between adjacent light receiving elements (for example, the center of the light receiving surface of the light receiving element arranged at the center and the periphery thereof). Distance from the center of the light receiving surface of the light receiving element.

[Action / Effect]
The operation and effects of the present embodiment (including modifications) will be described.

The coupling optical system 20 according to the present embodiment includes an optical element including any one of a plurality of light sources, a plurality of light receiving elements, and a fiber bundle 10 in which a plurality of single core fibers 100 are bundled, and a plurality of cores C _k are clad 2. The optical element and the multi-core fiber 1 are optically coupled to each other. The coupling optical system 20 includes a numerical aperture of each of a plurality of lights incident from an incident side element composed of one of the optical element and the multi-core fiber 1, and a numerical aperture of each of the plurality of lights emitted toward an output side element composed of the other. Are designed to be equal.

  More specifically, the coupling optical system 20 according to the present embodiment includes a first optical system 21 and a second optical system 22. The first optical system 21 converges each of the plurality of lights. The second optical system 22 changes (narrows / expands) the interval between the plurality of lights.

The magnification βm of the first optical system 21 and the magnification βr of the second optical system 22 are designed to satisfy the following formula (2).
βm × βr = 1 (2)

  Thus, the coupling efficiency is obtained by combining the first optical system 21 and the second optical system 22 so that the numerical aperture of the light incident on the coupling optical system 20 and the numerical aperture of the light emitted from the coupling optical system 20 do not change. Light can be transmitted without dropping light. That is, according to the coupling optical system 20 in the present embodiment, the optical element and the multicore fiber 1 can be optically coupled while suppressing a decrease in coupling efficiency.

  In the coupling optical system 20 according to the present embodiment, the first optical system 21 is arranged on the optical element side with respect to the second optical system 22.

  By arranging the optical system in this way, the numerical aperture NA ′ of light incident on the second optical system 22 from the first optical system 21 (or the aperture of light incident on the first optical system 21 from the second optical system 22). The number NA ′) can be kept small, so that the configuration of the optical system can be simplified.

  The first optical system 21 according to this embodiment has a configuration in which a plurality of lenses 21a are arranged in an array.

  In this case, the first optical system 21 can be designed with a simple configuration using a single lens of the same shape.

The coupling optical system 20 according to this embodiment, the pitch Pm between the plurality of lenses 21a are between the plurality of light sources pitch, the pitch P _out between pitch and a plurality of single-core fiber 100 between the plurality of light receiving elements Designed to be equal to either.

  In this case, for example, each of the light (principal ray Pr) from the plurality of single core fibers 100 can be perpendicularly incident on the surface of the corresponding plurality of lenses 21a (that is, the light beam from the single core fiber 100 is axially coupled). Can be treated as the upper luminous flux). Alternatively, each of the plurality of lights (principal rays Pr) emitted from the plurality of lenses 21a can be perpendicularly incident on the end surfaces Ca of the plurality of single core fibers 100 and the surfaces of the plurality of light receiving elements. Accordingly, it is possible to suppress a decrease in coupling efficiency.

  The second optical system 22 according to the present embodiment is a both-side telecentric optical system.

In addition, the magnification βr of the second optical system 22 according to the present embodiment is any of the pitch between the plurality of light sources, the pitch between the plurality of light receiving elements, and the pitch P _out between the plurality of single core fibers 100, and the multicore fiber 1. It is designed to be equal to the ratio of the pitch P _in between the cores C _{k of the} two.

In this case, each of the plurality of lights (principal rays Pr) from the coupling optical system 20 may be perpendicularly incident on the core C _k (or the corresponding plurality of light receiving elements, the fiber bundle 10) of the corresponding multicore fiber 1. It becomes possible. Accordingly, it is possible to suppress a decrease in coupling efficiency.

Second Embodiment
Next, a configuration example of the coupling optical system 30 according to the second embodiment will be described with reference to FIGS. In the present embodiment, a case where the fiber bundle 10 and the multi-core fiber 1 are coupled will be described. FIG. 3 is a sectional view in the axial direction of the coupling optical system 30, the fiber bundle 10, and the multicore fiber 1. A detailed description of the configuration similar to that of the first embodiment, such as the configuration of the fiber bundle 10, may be omitted.

[Configuration of coupling optical system]
The coupling optical system 30 according to the present embodiment includes a collimating optical system 31, a deflection optical system 32, and an imaging optical system 33.

The collimating optical system 31 has a function of collimating each of a plurality of lights from the fiber bundle 10. The collimating optical system 31 includes a plurality of collimating lenses 31a arranged in an array. The plurality of collimating lenses 31 a are provided in the same number as the single core fibers 100 included in the fiber bundle 10. The collimating optical system 31 (collimating lens 31a) is disposed at a position where light (principal ray Pr) emitted from each end face Ca enters perpendicularly to the surface of the corresponding collimating lens 31a. In this case, the end face Ca functions as a diaphragm). The plurality of collimating lenses 31a has a pitch P _cl (the distance between the optical axes of adjacent collimating lenses 31a. For example, the lens center of the collimating lens 31a disposed at the center and the lens center of the collimating lens 31a disposed at the periphery thereof. Is arranged to be equal to the pitch P _out between the plurality of single core fibers 100 (the distance between the optical axes of adjacent single core fibers 100). The collimating optical system 31 is arranged on the fiber bundle 10 side with respect to the deflection optical system 32. In the present embodiment, the surface of the collimating lens 31a on which the light from the fiber bundle 10 is incident is an example of an “incident surface”.

  The deflection optical system 32 has a function of individually deflecting a plurality of incident light (in this embodiment, light from the fiber bundle 10). The deflection optical system 32 in this embodiment includes a first deflection prism 32a and a second deflection prism 32b. The first deflection prism 32a in the present embodiment is an example of a “first deflection optical system”. The second deflection prism 32b in the present embodiment is an example of a “second deflection optical system”.

  The first deflecting prism 32a in the present embodiment has a function of deflecting each of a plurality of lights collimated by the collimating optical system 31 (collimating lens 31a) in a predetermined direction while being collimated. As shown in FIG. 3, the first deflection prism 32a is designed so that light passing through the center thereof is not deflected. The first deflection prism 32a has an incident surface 321a and an exit surface 322a corresponding to the number of incident light. The first deflecting prism 32a in the present embodiment is designed such that each of the plurality of lights (principal rays Pr) from the collimating optical system 31 is incident on the corresponding incident surface 321a perpendicularly.

  In the present embodiment, the incident surface 321a is a flat surface. The emission surface 322a is formed as a convex surface corresponding to the number of light beams. Here, the emission surface 322a is designed to be inclined by a predetermined angle γ.

This inclination angle γ is determined as follows, for example. FIG. 4A is an enlarged view of a part of the cross section of the first deflection prism 32a. Here, the incident angle of light incident on the exit surface 322a of the first deflecting prism 32a (only the principal ray Pr is shown in the figure) is γ _in , and the light deflected by the first deflecting prism 32a and emitted (the principal ray Pr is shown in the figure). emission angle gamma _out only shown), a pitch between the plurality of single-core fiber 100 _{P out,} the pitch between the cores _{C k} of the multicore fiber 1 _{P in,} the first deflecting prism 32a and the second deflecting prism 32b Let the interval be t. The incident angle γ _in is equal to the tilt angle γ.

At this time, the emission angle γ _out is determined by the following equation (4).

Tan [γ _out ] = (P _out −P _in ) / t (4)

Further, when the refractive index of the base material of the first deflecting prism 32a is N and the refractive index of the medium on the exit side is N ′, the incident angle γ _in satisfies the relationship of the following equation (5).

Nsin [γ _in ] = N′sin [γ _out ] (5)

For example, when P _out is designed to be 120 μm, P _in is 40 μm, and t is 0.3 mm, the emission angle γ _out is about 14.9 °. Here, the medium on the emission side is assumed to be air (N ′ = 1). When the first deflecting prism 32a is formed of a material having a base material refractive index of 1.6 with respect to the emission angle γ _out , the incident angle γ _in is about 9.25 °. Therefore, the emission surface 322a of the first deflecting prism 32a can be designed so that the inclination angle γ is about 9.25 °.

Note that the incident surface 321a may be a convex surface. In this case, the inclination angle γ ′ is determined as follows, for example. FIG. 4B is an enlarged view of a part of the cross section of the first deflecting prism 32a. Here, the incident angle of light incident on the incident surface 321a of the first deflecting prism 32a (only the principal ray Pr is shown in the figure) is γ ′ _in , the deflection angle of the incident light is γ ′ ₁ , and the perpendicular to the incident surface 321a The angle of the incident light is γ ′ ₂ , the emission angle of the light that is deflected and emitted by the first deflecting prism 32 a (only the principal ray Pr is shown in the figure) is γ ′ _out , and the pitch between the single core fibers 100 is P _out , the pitch between the cores C _k of the multi-core fiber 1 is P _in , and the interval between the first deflection prism 32a and the second deflection prism 32b is t. The incident angle γ ′ _in is equal to the inclination angle γ ′.

At this time, the emission angle γ _out is determined by the above equation (4).

Further, the incident angle γ ′ _in , the deflection angle γ ′ ₁ , and the angle γ ′ ₂ have the relationship of the following formula (6).

γ ′ ₂ = γ ′ _in −γ ′ ₁ (6)

  Further, when the base material refractive index of the first deflecting prism 32a is N and the refractive index of the exit side medium is N ′, the following expression (7) is established.

Nsin [γ ′ ₁ ] = N′sin [γ ′ _out ] (7)

Further, the incident angle γ ′ _in and the angle γ ′ ₂ have the relationship of the following expression (8) according to Snell's law.

N′sin [γ ′ _in ] = N′sin [γ ′ ₂ ] (8)

For example, when P _out is designed to be 120 μm, P _in is 40 μm, and t is 0.3 mm, the emission angle γ _out is about 14.9 °. Here, the medium on the emission side is assumed to be air (N ′ = 1). When the first deflecting prism 32a is formed of a material having a base material refractive index of 1.6 with respect to the emission angle γ _out , the incident angle γ _in is about 24 °. Therefore, the incident surface 321a of the first deflection prism 32a can be designed so that the inclination angle γ ′ is about 24 °.

  The second deflection prism 32b in the present embodiment has a function of further deflecting each light deflected by the first deflection prism 32a. In the present embodiment, each of the plurality of lights (principal rays Pr) from the second deflecting prism 32 b is deflected in a direction perpendicularly incident on the imaging optical system 33. Even when the light is deflected by the second deflecting prism 32b, the state in which each of the plurality of lights is collimated does not change. As shown in FIG. 3, the second deflection prism 32b is designed so that light passing through the center thereof is not deflected. The second deflection prism 32b has an incident surface 321b and an exit surface 322b corresponding to the number of incident light. In the present embodiment, the incident surface 321b is formed as a concave surface corresponding to the number of light beams. The emission surface 322b is formed in a plane. Further, the emission surface 322b can be a concave surface. The inclination angle of the concave surface of the second deflection prism 32b can be obtained by a method similar to the method for obtaining the inclination angle of the first deflection prism 32a described above.

  In the present embodiment, the configuration in which the first deflection prism 32a and the second deflection prism 32b are separate from each other has been described. However, the deflection optical system 32 may be configured by one deflection prism 32 ′. An example is shown in FIG. FIG. 5 is a side view of the deflection prism 32 ′. The deflecting prism 32 ′ is formed with an incident surface 32 ′ a on which light from the collimating optical system 31 is incident and an output surface 32 ′ b that emits light to the imaging optical system 33. The incident surface 32′a is formed, for example, in the same manner as the emission surface 322a of the first deflection prism 32a described above. The exit surface 32'b is formed, for example, in the same manner as the entrance surface 321b of the second deflection prism 32b described above.

  The deflection optical system 32 has a predetermined degree of deflection R. The degree of deflection R is the amount of change in the angle of the principal ray Pr incident on the deflection optical system 32 and the angle of the principal ray Pr emitted from the deflection optical system 32. The degree of deflection can also be expressed by the ratio of the light flux height of light incident on the deflection optical system 32 (the distance from the central light flux to another light flux) and the light flux height of light emitted from the deflection optical system 32.

  When the deflection optical system 32 includes the first deflection prism 32a and the second deflection prism 32b, the degree of deflection R depends on the angle of the principal ray Pr incident on the first deflection prism 32a and the principal ray Pr emitted from the second deflection prism 32b. The amount of change in the angle. In this case, it can be said that the degree of deflection R is a combination of the degree of deflection R1 of the first deflection prism 32a and the degree of deflection R2 of the second deflection prism 32b.

In the present embodiment, the degree of deflection R1 of the first deflection prism 32a is designed to be equal to the degree of deflection R2 of the second deflection prism 32b. In the present embodiment, the degree of deflection R (R1 + R2) is designed to be equal to the ratio of the pitch P _out between the plurality of single core fibers 100 and the pitch P _in between the cores C _k of the multi-core fiber 1. Yes.

The imaging optical system 33 has a function of imaging each of a plurality of lights (light beams) deflected by the deflection optical system 32 on each core C _k of the multi-core fiber 1. The imaging optical system 33 includes a plurality of imaging optical lenses 33a arranged in an array. The plurality of imaging optical lenses 33a are provided in the same number as each core C _k of the multi-core fiber 1. An imaging optical system 33 (the imaging optical lens 33a), the light emitted from the deflecting optical system 32 (main beam Pr) is disposed in a position that is incident perpendicularly to the end face E _k of each core C _k corresponding Has been. The plurality of image forming optical lenses 33a are arranged at the pitch P _im (the distance between the optical axes of adjacent image forming optical lenses 33a. For example, the center of the image forming optical lens 33a disposed at the center and the periphery thereof. distance between the lens center of the image-forming optical lens 33a) is arranged to be equal to the pitch P _in between the core C _k. The imaging optical system 33 is designed so that the emitted light (light beam) has a predetermined numerical aperture NA ″ (= Nsin θ ″). θ'', the light (light beam) emitted from the imaging optical system 33 is an angle principal ray Pr and marginal rays Mr forms as they enter the multi-core fiber 1 (end surface E _k of each core C _k). In the present embodiment, the surface of the imaging optical lens 33a from which the light from the deflection optical system 32 is emitted is an example of an “emission surface”. In the present embodiment, the end surface E _k is an example of a “light receiving surface”.

  Further, if the numerical aperture NA of the light incident on the collimating optical system 31 is different from the numerical aperture NA ″ of the light emitted from the imaging optical system 33, the coupling efficiency is lowered. Therefore, in this embodiment, the coupling optical system 30 is designed so that the numerical aperture NA and the numerical aperture NA ″ are equal.

In this embodiment, in order to make the numerical aperture NA equal to the numerical aperture NA ″, the focal length f _{cl of} the collimating optical system 31 (collimating lens 31a) and the imaging optical system 33 (imaging optical lens 33a) are set. The coupling optical system 30 is designed so that the focal length f _im becomes equal.

Note that the relationship between the focal length f _cl and the focal length f _im is not necessarily equal due to tolerances of optical elements used and variations in design. Any value that can secure at least the coupling efficiency necessary for optical transmission, for example, a value that satisfies the following equation (9) may be used.

0.9 <f _im / f _cl <1.1 (9)

[About how light travels]
Next, how light travels according to the present embodiment will be described with reference to FIG. In the present embodiment, a configuration in which light is emitted from the fiber bundle 10 will be described. That is, the fiber bundle 10 in the present embodiment is an example of an “incident side element”. On the other hand, the multi-core fiber 1 in the present embodiment is an example of an “emission side element”.

  First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Light emitted from each end face Ca enters the collimating optical system 31 (collimating lens 31a) with a predetermined numerical aperture NA while being diffused. In the present embodiment, each light (principal ray Pr) emitted from the end face Ca is incident perpendicularly to the collimating optical system 31 (the surface of the collimating lens 31a).

  Each of the plurality of lights incident on the collimating optical system 31 is collimated and enters the first deflecting prism 32a. The first deflection prism 32a individually deflects each of the plurality of lights with a predetermined degree of deflection R1. Each deflected light is incident on the second deflecting prism 32b.

The second deflection prism 32b individually deflects a plurality of lights with a predetermined degree of deflection R2. Each light deflected by the second deflection prism 32 b enters the imaging optical system 33. Each light incident on the imaging optical system 33 is incident on the core C _k of the corresponding multi-core fiber 1.

At this time, in this embodiment, the focal length f _cl and the focal length f _im are equal. Accordingly, the light (principal ray Pr) corresponding to the plurality of cores C _k (end faces E _k ) of the multi-core fiber 1 without changing the numerical aperture NA of the light emitted from each end face Ca (NA = NA ″). ) Can be incident vertically. Therefore, it is possible to transmit light while maintaining a high coupling efficiency between the optical elements.

As a specific example, a fiber bundle 10 of pitch _{P out} is 120μm between the plurality of single-core fiber 100 will be described a case where the pitch _{P in} between the core _{C k} are attached to the multi-core fiber 1 of 40 [mu] m. In this case, since the pitch is reduced to 1/3, if the design is made such that the value obtained by combining the deflection degree R1 of the first deflection prism 32a and the deflection degree R2 of the second deflection prism 32b is 3, the numerical aperture NA Without changing (NA = NA ″), the corresponding light (principal ray Pr) can be vertically incident on the plurality of cores C _k of the multi-core fiber 1. In this case, it is desirable that the pitch P _cl is 120 μm and the pitch P _im is 40 μm.

Note that the pitch P _in and the pitch P _out can be arbitrarily set when the multi-core fiber 1 or the fiber bundle 10 is optically designed. For example, the pitch P _out can be set between about 100 to 150 μm. The pitch _{P in,} for example, can be set anywhere between about 30 to 50 [mu] m.

[Modification 3]
In the present embodiment, the example in which a plurality of lights emitted from the fiber bundle 10 are guided to the multicore fiber 1 via the coupling optical system 30 has been described. However, the target for emitting the light is not limited thereto. For example, a plurality of light sources can be used instead of the fiber bundle 10. In this case, the light source is an example of an “incident side element”. In this case, the above-mentioned “P _out ” is a pitch between adjacent light sources.

[Modification 4]
Alternatively, it is also possible to guide each of a plurality of lights emitted from the multi-core fiber 1 (a plurality of cores C _k ) to the fiber bundle 10 or a light receiving element (not shown) using the above-described coupling optical system 30. In this case, the multi-core fiber 1 is an example of an “incident side element”. Further, the fiber bundle 10 or the light receiving element is an example of the “outgoing side element”. Hereinafter, an example in which each light emitted from the multicore fiber 1 is guided to the fiber bundle 10 will be described.

The imaging optical system 33 in this modification has a function of collimating each of a plurality of lights emitted from the multicore fiber 1. That is, in the present modification, the imaging optical system 33 corresponds to the “collimating optical system”. In the present modification, the surface of the imaging optical lens 33a on which the light from the multicore fiber 1 is incident is an example of an “incident surface”. In addition, the pitch between the imaging optical lenses 33 a in this modification is equal to the pitch between the cores C _k of the multicore fiber 1.

  The deflection optical system 32 in this modification has a function of deflecting each of a plurality of lights from the imaging optical system 33. Each deflected light (principal ray Pr) enters the collimating optical system 31 perpendicularly.

  The collimating optical system 31 in the present modification has a function of imaging each of a plurality of lights emitted from the deflection optical system 32 on the core C of the corresponding single core fiber 100. That is, in this modification, the collimating optical system 31 corresponds to the “imaging optical system”. In the present modification, the surface of the collimating optical system 31 (collimating lens 31a) from which the light from the deflection optical system 32 is emitted is an example of an “exiting surface”. In the present modification, the end surface Ca is an example of a “light receiving surface”. Further, in this modification, the pitch between the collimating lenses 31 a is equal to the pitch between the cores C of the single core fiber 100.

  In the present modification, when a plurality of deflection optical systems (first deflection prism 32a and second deflection prism 32b) are used as the deflection optical system 32, the first deflection prism 32a is the “second deflection optical system”. An example. The second deflection prism 32b is an example of the “first deflection optical system”.

  Θ in this modification is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light flux) emitted from the collimating optical system 31 enters the fiber bundle 10 (each single core fiber 100). θ ″ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the multicore fiber 1 enters the imaging optical system 33.

When a light receiving element is used as the “emission side element”, the degree of deflection R in the present modification is equal to the ratio between the pitch between the plurality of light receiving elements and the pitch between the cores C _k of the multicore fiber 1. In this case, the pitch between the collimating lenses 31a is equal to the pitch between the light receiving elements.

[Action / Effect]
The operation and effects of the present embodiment (including modifications) will be described.

  The coupling optical system 30 according to the present embodiment includes a deflection optical system 32 that individually deflects a plurality of incident light.

  Thus, even when the deflection optical system 32 is used for the coupling optical system 30, light can be transmitted without reducing the coupling efficiency. That is, according to the coupling optical system 30 in the present embodiment, the optical element and the multicore fiber 1 can be optically coupled while suppressing a decrease in coupling efficiency.

  Further, the coupling optical system 30 according to the present embodiment includes a collimating optical system 31. The collimating optical system 31 (collimating lens 31a) collimates light from any of the incident side elements. The deflecting optical system 32 deflects the light collimated by the collimating optical system 31.

  By disposing the collimating optical system 31 in this way, the configuration of the coupling optical system 30 can be simplified.

  The collimating optical system 31 according to this embodiment has a configuration in which a plurality of collimating lenses 31a are arranged in an array.

  In this case, the collimating optical system 31 can be designed with a simple configuration using a single lens of the same shape.

In addition, the pitch P _cl between the plurality of collimating lenses 31a according to the present embodiment is equal to any of the pitch between the plurality of light sources, the pitch P _out between the plurality of single core fibers, and the pitch P _in between the cores of the multicore fibers. Designed to be

  In this case, for example, each of the light (principal ray Pr) from the plurality of single core fibers 100 can be perpendicularly incident on the surface of the collimating lens 31a (that is, the light flux from the single core fiber 100 is treated as an axial light flux. be able to). Alternatively, each of the plurality of lights (principal rays Pr) emitted from the collimator lens 31a can be perpendicularly incident on the end surfaces Ca of the plurality of single core fibers 100 and the surfaces of the plurality of light receiving elements. Accordingly, it is possible to suppress a decrease in coupling efficiency.

  The deflection optical system 32 according to the present embodiment includes a first deflection optical system (first deflection prism 32a) and a second deflection optical system (second deflection prism 32b). The first deflection optical system deflects a plurality of incident light. The second deflection optical system further deflects the plurality of lights deflected by the first deflection optical system.

  As described above, even when a plurality of deflection optical systems are used, light can be transmitted without reducing the coupling efficiency. That is, according to the coupling optical system 30 in the present embodiment, the optical element and the multicore fiber 1 can be optically coupled while suppressing a decrease in coupling efficiency.

  In the first deflection optical system and the second deflection optical system according to the present embodiment, one side is formed in a convex shape and the other side is formed in a concave shape.

  Further, the deflection optical system 32 according to the present embodiment is designed so that the degree of deflection R1 of the first deflection optical system is equal to the degree of deflection R2 of the second deflection optical system.

In addition, the deflection degree R of the deflection optical system 32 according to the present embodiment is any of the pitch between the plurality of light sources, the pitch between the plurality of light receiving elements, and the pitch P _out between the plurality of single core fibers, and the multicore fiber 1. It is designed to be equal to the ratio between the pitch P _in between the core C _k.

  By configuring the deflection optical system 32 in this way, it is possible to make each of the light (principal ray Pr) incident from the incident side element enter perpendicularly to the surface of the output side element. That is, it is possible to suppress a decrease in coupling efficiency.

  Further, the coupling optical system 30 according to the present embodiment includes an imaging optical system 33 (imaging optical lens 33a). The imaging optical system 33 forms an image of the light deflected by the deflection optical system 32 on one of the emission side elements.

  Further, the imaging optical lens 33a according to the present embodiment has a configuration in which a plurality of lenses are arranged in an array.

Further, the pitch P _im between the imaging optical lenses 33a according to the present embodiment is the pitch P _out between the plurality of single core fibers 100, the pitch between the light receiving elements, and the pitch P _in between the cores C _{k of the} multi-core fiber 1. Designed to be equal to either.

  In this way, by forming the imaging optical system 33, it is possible to make each light (principal ray Pr) emitted from the imaging optical system 33 enter perpendicularly to the surface of the emission side element. That is, it is possible to suppress a decrease in coupling efficiency.

In the present embodiment, the focal length f _cl of the collimating lens 31a is designed to be equal to the focal length f _im of the imaging optical lens 33a.

  With this configuration, the numerical aperture of the light incident on the coupling optical system 30 and the numerical aperture of the light emitted from the coupling optical system 30 can be kept unchanged, so that light can be transmitted without reducing the coupling efficiency. I can do it. That is, according to the coupling optical system 30 in the present embodiment, the optical element and the multicore fiber 1 can be optically coupled while suppressing a decrease in coupling efficiency.

<Third Embodiment>
Next, with reference to FIGS. 6 and 7, a configuration example of the coupling optical system 30 ′ according to the third embodiment will be described. In the present embodiment, a case where the fiber bundle 10 and the multi-core fiber 1 are coupled will be described. FIG. 6 is a cross-sectional view in the axial direction of the coupling optical system 30 ′, the fiber bundle 10, and the multicore fiber 1. Note that detailed description of the configuration of the fiber bundle 10 and the like similar to those of the first and second embodiments may be omitted.

[Configuration of coupling optical system]
The coupling optical system 30 ′ according to the present embodiment includes a collimating optical system 31, a deflection optical system 34, and an imaging optical system 33. The collimating optical system 31 and the imaging optical system 33 have the same configuration as in the second embodiment.

  The deflection optical system 34 in the present embodiment includes a first diffractive optical system 34a and a second diffractive optical system 34b. The first diffractive optical system 34a in the present embodiment is an example of a “first deflection optical system”. The second diffractive optical system 34b in the present embodiment is an example of a “second deflecting optical system”.

  The first diffractive optical system 34a in this embodiment has a function of deflecting each of the plurality of lights collimated by the collimating optical system 31 (collimating lens 31a) in a predetermined direction by diffraction while being collimated. As shown in FIG. 6, the first diffractive optical system 34a is designed so that light passing through the center thereof is not deflected. The first diffractive optical system 34a has an incident surface 341a and exit surfaces 342a and 343a corresponding to the number of incident light. In addition, the first diffractive optical system 34a in the present embodiment is designed such that each of a plurality of lights (principal rays Pr) from the collimating optical system 31 is incident perpendicularly to the corresponding incident surface 341a.

  The incident surface 341a is formed in a plane. Light from the collimating optical system 31 is incident on the incident surface 341a.

  The exit surface 342a is formed as a diffraction grating composed of serrated projections. On the other hand, no diffraction grating is formed on the exit surface 343a. Therefore, the light passing through the emission surface 343a is not deflected by diffraction.

FIG. 7 is a view of the emission surface 342a and the emission surface 343a as seen from the direction of arrow A in FIG. As shown in FIG. 7, the emission surface 342 a and the emission surface 343 a in this embodiment have seven surfaces F _k (F _{1 to} F ₇ ) that emit light from the seven single core fibers 100. Among these, the surface F ₁ (the emission surface 343a) transmits the light from the single core fiber 100 without being deflected. Diffraction gratings are formed on the surfaces F _{2 to} F ₇ (outgoing surface 342a) with a pitch d (interval between protrusions). In this embodiment, the pitches d of the diffraction gratings are all equal.

This pitch d is determined as follows, for example. Here, the incident angle of light incident on the exit surface 342a is ε _in , the exit angle of light deflected by the exit surface 342a is ε _out , the base material refractive index of the first diffractive optical system 34a is N, and the exit side The refractive index of the medium is N ′, the diffraction order is m, and the wavelength of incident light is λ.

  At this time, the pitch d is determined by the following equation (10).

N sin [ε _in ] −N ′ sin [ε _out ] = mλ / d (10)

  Here, as shown in FIG. 6, the light enters perpendicularly to the emission surface 342 a. At this time, if the diffraction order to be used is 1, the pitch d is determined by the following equation (11). Note that the medium on the emission side is air (N ′ = 1).

N-sin [ε _out ] = λ / d (11)

  The second diffractive optical system 34b in the present embodiment has a function of further deflecting each light deflected by the first diffractive optical system 34a. In the present embodiment, each of the plurality of lights (principal rays Pr) from the second diffractive optical system 34 b is deflected in a direction perpendicularly incident on the imaging optical system 33. Even when the light is deflected by the second diffractive optical system 34b, the state in which each of the plurality of lights is collimated does not change. As shown in FIG. 6, the second diffractive optical system 34b is designed so that light passing through the center thereof is not deflected. The second diffractive optical system 34b has incident surfaces 341b and 342b and an emission surface 343b corresponding to the number of incident light.

  The incident surface 341b is formed as a diffraction grating composed of a sawtooth projection. On the other hand, no diffraction grating is formed on the incident surface 342b. Therefore, the light passing through the incident surface 342b is not deflected by diffraction. Light from the first diffractive optical system 34a is incident on the incident surfaces 341b and 342b.

  The emission surface 343b is formed in a plane. Each of the plurality of lights (principal rays Pr) emitted from the emission surface 343b is perpendicularly incident on the imaging optical system 33 (imaging optical lens 33a). The pitch in the second diffractive optical system 34b can be obtained by a method similar to the method for obtaining the pitch d in the first diffractive optical system 34a.

[About how light travels]
Next, with reference to FIG. 6, how the light travels according to the present embodiment will be described. In the present embodiment, a configuration in which light is emitted from the fiber bundle 10 will be described. That is, the fiber bundle 10 in the present embodiment is an example of an “incident side element”. On the other hand, the multi-core fiber 1 in the present embodiment is an example of an “emission side element”.

  First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Light emitted from each end face Ca enters the collimating optical system 31 (collimating lens 31a) with a predetermined numerical aperture NA while being diffused. In the present embodiment, each light (principal ray Pr) emitted from the end face Ca is incident perpendicularly to the collimating optical system 31 (the surface of the collimating lens 31a).

  Each of the plurality of lights incident on the collimating optical system 31 is collimated and enters the first diffractive optical system 34a. The first diffractive optical system 34a individually deflects a plurality of incident light beams by a diffraction grating. Each deflected light enters the second diffractive optical system 34b.

The second diffractive optical system 34b deflects a plurality of incident light individually. Each light deflected by the second diffractive optical system 34 b enters the imaging optical system 33. Each light incident on the imaging optical system 33 is incident on the core C _k of the corresponding multi-core fiber 1.

At this time, in this embodiment, the focal length f _cl and the focal length f _im are equal. Accordingly, the light (principal ray Pr) corresponding to the plurality of cores C _k (end faces E _k ) of the multi-core fiber 1 without changing the numerical aperture NA of the light emitted from each end face Ca (NA = NA ″). ) Can be incident vertically. Therefore, it is possible to transmit light while maintaining a high coupling efficiency between the optical elements.

[Modification 5]
In the present embodiment, the example in which a plurality of lights emitted from the fiber bundle 10 are guided to the multicore fiber 1 via the coupling optical system 30 ′ has been described, but the target for emitting the light is not limited thereto. For example, a plurality of light sources can be used instead of the fiber bundle 10. In this case, the light source is an example of an “incident side element”. In this case, the above-mentioned “P _out ” is a pitch between adjacent light sources.

[Modification 6]
Alternatively, it is possible to guide each of a plurality of lights emitted from the multi-core fiber 1 (a plurality of cores C _k ) to the fiber bundle 10 or a light receiving element (not shown) using the above-described coupling optical system 30 ′. In this case, the multi-core fiber 1 is an example of an “incident side element”. Further, the fiber bundle 10 or the light receiving element is an example of the “outgoing side element”. Hereinafter, an example in which each light emitted from the multicore fiber 1 is guided to the fiber bundle 10 will be described.

The imaging optical system 33 in this modification has a function of collimating each of a plurality of lights emitted from the multicore fiber 1. That is, in the present modification, the imaging optical system 33 corresponds to the “collimating optical system”. In the present modification, the surface of the imaging optical lens 33a on which the light from the multicore fiber 1 is incident is an example of an “incident surface”. In addition, the pitch between the imaging optical lenses 33 a in this modification is equal to the pitch between the cores C _k of the multicore fiber 1.

  The deflection optical system 34 in this modification has a function of deflecting each of a plurality of lights from the imaging optical system 33 by a diffraction grating. Each deflected light (principal ray Pr) enters the collimating optical system 31 perpendicularly.

  The collimating optical system 31 in the present modification has a function of imaging each of a plurality of lights emitted from the deflection optical system 34 on the core C of the corresponding single core fiber 100. That is, in this modification, the collimating optical system 31 corresponds to the “imaging optical system”. In this modification, the surface of the collimating optical system 31 (collimating lens 31a) from which the light from the deflection optical system 34 is emitted is an example of an “exiting surface”. In the present modification, the end surface Ca is an example of a “light receiving surface”. Further, in this modification, the pitch between the collimating lenses 31 a is equal to the pitch between the cores C of the single core fiber 100.

  In the present modification, when a plurality of deflection optical systems (first diffractive optical system 34a and second diffractive optical system 34b) are used as the deflecting optical system 34 as in the embodiment, the first diffractive optical system 34a is “second deflecting optical system 34a”. An example of “optical system”. The second diffractive optical system 34b is an example of a “first deflecting optical system”.

  Θ in this modification is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light flux) emitted from the collimating optical system 31 enters the fiber bundle 10 (each single core fiber 100). θ ″ is an angle formed by the principal ray Pr and the marginal ray Mr when the light (light beam) emitted from the multicore fiber 1 enters the imaging optical system 33.

When a light receiving element is used as the “emission side element”, the degree of deflection R in the present modification is equal to the ratio between the pitch between the plurality of light receiving elements and the pitch between the cores C _k of the multicore fiber 1. In this case, the pitch between the collimating lenses 31a is equal to the pitch between the light receiving elements.

[Action / Effect]
The operation and effects of the present embodiment (including modifications) will be described.

  In the first deflecting optical system (first diffractive optical system 34a) and the second deflecting optical system (second diffractive optical system 34b) according to the present embodiment, at least a part of each side is formed as a diffraction grating.

  As described above, even when the diffractive optical system (the first diffractive optical system 34a and the second diffractive optical system 34b) is used as the deflection optical system, light can be transmitted without reducing the coupling efficiency. That is, according to the coupling optical system 30 ′ in this embodiment, the optical element and the multicore fiber 1 can be optically coupled while suppressing a decrease in coupling efficiency.

[Modification 1 common to the first to third embodiments]
In the above embodiment, the case _where the intervals of the cores C _k of the multi-core fiber 1 are the same has been described. However, when the intervals of the cores C _k are different from each other, some of the intervals of the cores C _k are equal, and the other intervals The above configuration can also be applied when there are a plurality of interval settings for the intervals of the cores C _k such as different. In this case, it is sufficient to design the coupling optical system 20 according to the position of each of the cores C _k. For example, in the first embodiment may be performed first magnification setting of the optical system 21 and second optical system 22 in accordance with the position of the core C _k. In this case, according to the position of each core C _k, at a magnification relationship in Equation (2) or formula (3), to design the optical system for each of the core C _k. At this time, for example, if the second optical system 22 shown in FIG. 2 is configured in an array, desired requirements can be satisfied. In the second embodiment the optical system may be performed setting the degree of deflection depending on the position of the core C _k. In this case, according to the position of each core C _k, deflecting prism 32a, 32b or the incident surface of 32 ', the angle of the exit surface, at each side, the same method as described in the second embodiment, To set the degree of deflection. In the third embodiment, the pitch d of the diffraction gratings on the surfaces F _k of the first diffractive optical system 34a and the second diffractive optical system 34b may be changed according to the position of the core C _k .

[Variation 2 common to the first to third embodiments]
It is also possible to fill the space between the fiber bundle 10 and the multi-core fiber 1 with a medium.

[Composition of coupling member]
FIG. 8 is a conceptual diagram showing an axial cross section of the coupling member 20, the fiber bundle 10, and the multicore fiber 1. The coupling member 20 according to this modification has one end in contact with the fiber bundle 10 and the other end in contact with the multicore fiber 1. The coupling member 20 is filled with a predetermined medium. The predetermined medium is a medium other than air, and for example, quartz glass or BK7 is used. The coupling member 20 and the fiber bundle 10 (multi-core fiber 1) are fixed to each other at their opposite end surfaces with an adhesive or the like. The adhesive has a refractive index comparable to that of the core C (core Ca).

Further, the coupling member 20 changes the mode field diameter of each light from each optical path (single core fiber 100) of the fiber bundle 10 and changes the interval of the light whose mode field diameter has been changed. Lead to each core (core C _k ). The mode field diameter refers to the diameter of light actually emitted from a certain target. For example, light passing through the core C of the single core fiber 100 slightly leaks to the cladding 101 side around the core C. Therefore, the light emitted from the single core fiber 100 is emitted not only from the core C but also from the cladding 101 around the core C. That is, the diameter of light emitted from the single core fiber 100 is larger than the diameter of the core C. This “diameter of light emitted from the single core fiber 100” is an example of a mode field diameter.

The coupling member 20 in the present modification includes a first optical system 21 and a second optical system 22. The first optical system 21 changes the mode field diameter of each light incident from the single core fiber 100 and causes the light to enter the second optical system 22. The second optical system 22 changes the interval of light incident from the first optical system 21 to match the interval of the cores C _k of the multicore fiber 1. Note that the refractive index of the medium A2 constituting the lens portion of the first optical system 21 and the second optical system 22 is different from that of the medium A1 constituting the other portion. The medium A1 is an example of a “first medium”. The medium A2 is an example of a “second medium”. In addition, the first optical system 21 and the second optical system 22 in this modification are integrally formed via the medium A1 (the first optical system 21 and the second optical system 22 are formed continuously). ).

Refractive index of the medium A1 is desirably equal material and the refractive index of the core C _k of the refractive index or the multi-core fiber of the core C of single-core fiber 100. For example, when the core C _k of the multi-core fiber 1 is formed of a material in which germanium oxide (GeO ₂ ) is added to quartz glass, the same material in which germanium oxide is added to quartz glass is used as the medium A1 ( Alternatively, another material having the same refractive index as the core C _k may be used.

  The first optical system 21 in this modification is an expansion optical system that expands the mode field diameter of each light from each single core fiber 100 of the fiber bundle 10. The first optical system 21 includes a plurality of convex lens portions 21a arranged in an array. The plurality of convex lens portions 21a are made of the medium A2, and are arranged in the medium A1. Since it is necessary to change the mode field diameter of each light from the fiber bundle 10, the plurality of convex lens portions 21 a is provided in the same number as the single core fibers 100 included in the fiber bundle 10. The first optical system 21 (convex lens portion 21a) is disposed at a position where each principal ray Pr of light emitted from each end face Ca of the fiber bundle 10 is perpendicularly incident on the surface of the corresponding convex lens portion 21a. (The convex lens portion 21a is disposed on the same optical axis as each core C). The convex lens portion 21a has a diameter larger than the mode field diameter of the core C, and condenses light from the core C. The plurality of convex lens portions 21a in the present modification is an example of “a plurality of lenses”.

The second optical system 22 in this modified example reduces the distance of the light from the first optical system 21 (a plurality of lights having an enlarged mode field diameter) and leads to the cores C ₁ to C ₇ of the multicore fiber 1. It is an optical system. The second optical system 22 is configured by a double-sided telecentric optical system including two convex lens portions (a convex lens portion 22a and a convex lens portion 22b). Convex lens part 22a and convex lens part 22b consist of medium A2, and are arranged in medium A1. The reason why only one set of the convex lens portion 22a and the convex lens portion 22b is provided is to change the interval of light from the plurality of convex lens portions 21a. The second optical system 22 is disposed at a position where each principal ray Pr of the light from the first optical system 21 is perpendicularly incident on the end face E _k of each core C _k of the corresponding multi-core fiber 1.

[About how light travels]
Next, how light travels according to the present embodiment will be described with reference to FIG. In this modification, a configuration in which light is emitted from the fiber bundle 10 will be described.

  First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Each light emitted from each end face Ca enters the convex lens portion 21a with a predetermined mode field diameter while diffusing in the medium A1. As described above, in the present embodiment, the principal ray Pr of each light emitted from the end face Ca is incident perpendicularly to the convex lens portion 21a. Each light transmitted through the convex lens portion 21a forms an image at the image point IP with the mode field diameter being enlarged.

  Each light transmitted through the convex lens portion 21a enters the convex lens portion 22a while diffusing in the medium A1 with the imaging point IP as a secondary light source.

The convex lens portion 22a and the convex lens portion 22b are formed as a both-side telecentric optical system. Accordingly, each of the principal rays Pr of light incident perpendicularly to the convex lens portion 22a passes through the medium A1 in a collimated state and enters the convex lens portion 22b. Each principal ray Pr of the light is emitted perpendicularly from the convex lens portion 22b in a state where the distance therebetween is narrowed, incident perpendicularly to the plurality of cores C _k of the multi-core fiber 1 passes through the medium A1.

  Moreover, it is also possible to form the coupling member 20 by creating the first optical system 21 and the second optical system 22 separately and combining them. Specifically, the first optical system 21 and the second optical system 22 are respectively made of the medium A1 and the medium A2. Then, the end face of the first optical system 21 and the end face of the second optical system 22 are fixed with an adhesive, thereby forming an integral coupling member 20. The adhesive has a refractive index comparable to that of the medium A1.

[Variation 3 common to the first to third embodiments]
FIG. 9 is a conceptual diagram illustrating a cross section in the axial direction of the coupling member 20, the fiber bundle 10, and the multicore fiber 1. In this modification, an example in which a GRIN lens is used as the first optical system 21 and the second optical system 22 constituting the coupling member 20 shown in Modification 2 common to the first to third embodiments will be described.

[Composition of coupling member]
The coupling member 20 in this modification has a GRIN lens. The GRIN lens is a refractive index distribution type lens that collects light by adjusting the refractive index distribution in the lens by bending the medium that constitutes the lens, and bending the diffused light. The refractive index distribution can be adjusted by the ion exchange processing method. As the GRIN lens, for example, a SELFOC lens (“SELFOC” is a registered trademark) can be used.

  The first optical system 21 has a GRIN lens SL1. The GRIN lens SL1 is formed of a medium whose refractive index is adjusted so as to change the mode field diameter of light from the fiber bundle 10 (single core fiber 100). In the present embodiment, a plurality of GRIN lenses SL1 are provided corresponding to the number of single core fibers 100 forming the fiber bundle 10. The GRIN lens SL1 is an example of a “first GRIN lens”.

  In addition, each of the plurality of GRIN lenses SL1 in this modification includes a first optical member SL1a and a second optical member SL1b. The first optical member SL1a is in contact with the fiber bundle 10 at one end, and the refractive index distribution is adjusted so as to collimate light that is incident from the single core fiber 100 and diffuses. One end of the second optical member SL1b is in contact with the other end of the first optical member SL1a, and the refractive index distribution is adjusted so that the light collimated by the first optical member SL1a is converged. The mode field diameter of the light (light at the imaging point IP) converged by the second optical member SL1b is larger than the mode field diameter of the light from the single core fiber 100. The first optical member SL1a and the second optical member SL1b constitute an integral GRIN lens SL1 by being fixed by an adhesive or the like. The adhesive has a refractive index comparable to that of the medium.

  The second optical system 22 has a GRIN lens SL2. The GRIN lens SL2 is formed of a medium whose refractive index is adjusted so as to change the interval of light whose mode field diameter has been changed. In this modification, only one GRIN lens SL2 is provided so that light from the plurality of GRIN lenses SL1 enters. The GRIN lens SL2 is an example of a “second GRIN lens”.

In addition, the GRIN lens SL2 in the present modification includes a third optical member SL2a and a fourth optical member SL2b. The third optical member SL2a has one end in contact with the other end of the second optical member SL1b, and the refractive index distribution is adjusted so as to collimate each light from the plurality of second optical members SL1b. The fourth optical member SL2b has one end in contact with the other end of the third optical member SL2a and the other end in contact with the multi-core fiber 1. The refractive index distribution of the fourth optical member SL2b is adjusted so as to converge the light from the third optical member SL2a. Light converged by the fourth optical member SL2b is incident on each core C _k of the multi-core fiber 1 corresponds. The third optical member SL2a and the fourth optical member SL2b constitute an integral GRIN lens SL2 by being fixed by an adhesive or the like. Then, the second optical member SL1b and the third optical member SL2a are fixed with an adhesive or the like, so that the coupling member 20 is integrally formed.

  Note that the GRIN lens SL1 and the GRIN lens SL2 do not need to be formed by a plurality of optical members. The GRIN lens SL1 and the GRIN lens SL2 only need to be formed from a medium whose refractive index is adjusted so that the respective functions can be achieved. That is, the GRIN lens SL1 and the GRIN lens SL2 may each be formed by one optical member. Alternatively, the GRIN lens SL1 and the GRIN lens SL2 can be formed from a single optical member.

[About how light travels]
Next, with reference to FIG. 9, how the light travels according to this modification will be described. In this modification, a configuration in which light is emitted from the fiber bundle 10 will be described.

  First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Each light emitted from each end face Ca is collimated by the first optical member SL1a and enters the second optical member SL1b. The light incident on the second optical member SL1b is converged by the refractive index distribution of the medium constituting the second optical member SL1b. Each of the lights transmitted through the second optical member SL1b forms an image at the image point IP with the mode field diameter being enlarged.

  Each light transmitted through the second optical member SL1b is incident on the third optical member SL2a using the imaging point IP as a secondary light source (in this embodiment, the imaging point IP is between the GRIN lens SL1 and the GRIN lens SL2). The refractive index of each GRIN lens is adjusted so that it is located at the boundary).

Each light incident on the third optical member SL2a passes through the third optical member SL2a in a state of being collimated based on the refractive index distribution of the medium constituting the third optical member SL2a, and enters the fourth optical member SL2b. . Then, the light incident on the fourth optical member SL2b is converged based on the refractive index distribution of the medium constituting the fourth optical member SL2b, and the plurality of cores C of the multi-core fiber 1 are narrowed with each other being narrowed. Incident to _k .

[Modification 4 common to the first to third embodiments]
FIG. 10 is a conceptual diagram illustrating a cross section in the axial direction of the coupling member 20, the fiber bundle 10, and the multicore fiber 1. In this modification, an example in which a plurality of fibers _Fk are used as the first optical system 21 constituting the coupling member 20 and a GRIN lens SL2 is used as the second optical system 22 will be described.

[Composition of coupling member]
The coupling member 20 in this modification includes a first optical system 21 and a second optical system 22.

The first optical system 21 has a plurality of fibers F _k (k = 1 to n) as a medium. One end of the fiber F _k is in contact with the single core fiber 100 constituting the fiber bundle 10 and changes the mode field diameter of each light from the single core fiber 100. The fiber F _k includes a core C _f that transmits light and a clad 3 that covers the core C _f . The diameter of the core C _f at the incident end in contact with the single core fiber 100 is substantially the same as the diameter of the core C of the single core fiber 100. The number of the fibers F _k equal to the number of the single core fibers 100 constituting the fiber bundle 10 is provided.

Further, the fiber F _k has a different core diameter at the entrance end and the exit end. Specifically, the fiber F _k is formed such that the diameter of the core C _f at the exit end in contact with the GRIN lens SL2 is larger than the diameter of the core C _f at the entrance end in contact with the single core fiber 100. The light passing through the core C _f of the fiber F _k has a mode field diameter that increases as it approaches the exit end.

The fiber F _k is manufactured by the following method, for example. First, heat is applied to a part of one fiber to cut the fiber. By performing the further heat treatment to the end face of the cut fiber may be a core diameter of one end to obtain a larger fiber F _k than the core diameter of the other end.

In this modification, the example in which the fiber F _k constituting the first optical system 21 and the single core fiber 100 are separate is described. However, by manufacturing the single core fiber 100 by the above manufacturing method, a single core fiber 100 is manufactured. It is also possible to manufacture the core fiber 100 and the fiber _Fk integrally. In this way, by producing integrally the single-core fiber 100 and fiber Fk, it becomes unnecessary alignment with a single core fiber 100 and the fiber F _k.

The second optical system 22 in the present modification uses the GRIN lens SL2 shown in the third modification common to the first to third embodiments. GRIN lens SL2 has one end in contact with the other end of the fiber F _k, is formed from a medium refractive index is adjusted to change the spacing of a plurality of fibers F _k light mode field diameter was changed in each.

[About how light travels]
Next, with reference to FIG. 10, how the light travels according to this modification will be described. In this modification, a configuration in which light is emitted from the fiber bundle 10 will be described.

First, light is emitted from the end face Ca of the core C provided in each of the plurality of single core fibers 100. Each light emitted from the end surfaces Ca, the mode field diameter at the fiber F _k is enlarged, and enters the GRIN lens SL2.

Each of the lights incident on the GRIN lens SL2 is converged based on the refractive index distribution of the medium constituting the second optical system 22, and is spaced from each other with respect to the plurality of cores C _k of the multicore fiber 1. Incident.

  In Modifications 2 to 4 common to the first to third embodiments, when the multi-core fiber 1 and the fiber bundle 10 are connected via the coupling member 20, the alignment adjustment in the rotational direction is performed at each connection portion. Is required. In this modification, a configuration that does not require alignment adjustment will be described. Hereinafter, although the connection between the multi-core fiber 1 and the coupling member 20 will be described, the same configuration can be used for the connection between the coupling member 20 and the fiber bundle 10.

  FIG. 11A is a diagram illustrating an end surface of the coupling member 20. FIG. 11B is a diagram illustrating an end face of the multi-core fiber 1. FIG. 11C is a diagram illustrating a cross section taken along line AA in FIGS. 11A and 11B.

As shown in FIGS. 11A and 11C, a fitting portion M <b> 1 is provided on the end surface of the coupling member 20 (the end surface on the side connected to the multi-core fiber 1). As the fitted part M1, for example, at least two hole parts H _k (k = 1 to n) are provided on the end face of the coupling member 20. In this modification, three holes H ₁ to H ₃ are provided.

As shown in FIGS. 11B and 11C, a fitting portion M <b> 2 is provided on the end face 2 a (end face on the side connected to the coupling member 20) of the clad 2 of the multicore fiber 1. As the fitting portion M2, for example, at least two protrusions P _k (k = 1 to n) are provided on the end surface 2a. In the present modification, _three projections P ₁ to P ₃ corresponding to the hole H ₁ to the hole H ₃ are provided. The size of the protrusion _Pk is formed to be approximately the same as the size of the hole _Hk .

As shown in FIG. 11C, when connecting the coupling member 20 and the multicore fiber 1, the multicore fiber 1 with respect to the end surface of the coupling member 20 is connected by fitting so that the protrusions P _k and the holes H _k are fitted. The position of the end face 1b is uniquely determined. That is, alignment adjustment in the rotation direction is not necessary. It is also possible to provide the fitting portion M2 on the end surface of the coupling member 20 and provide the fitted portion M1 on the end surface 2a of the clad 2.

  Further, the first optical system 21 and the second optical system 22 in Modifications 2 to 4 common to the first to third embodiments can be arbitrarily combined. For example, the coupling member 20 has the GRIN lens SL1 in the second embodiment as the first optical system 21, and the both-side telecentric optical system (convex lens portion 22a, convex lens portion 22b) in the first embodiment as the second optical system 22. It is also possible to have.

DESCRIPTION OF SYMBOLS 1 Multi-core fiber 1b End surface 2 Clad 2a End surface 10 Fiber bundle 20 Coupling optical system 21 1st optical system 21a Convex lens 22 2nd optical system 22a, 22b Convex lens 100 Single core fiber 101 Cladding C, C _k core Ca, E _k End surface

Claims (7)

The optical element is arranged between any one of a plurality of light sources, a plurality of light receiving elements, and a fiber bundle obtained by bundling a plurality of single core fibers, and a multi-core fiber in which a plurality of cores are covered with a cladding. A coupling optical system for optically coupling an element and the multi-core fiber, each of a plurality of light incident from an incident-side element composed of one of the optical element and the multi-core fiber, and an exit side composed of the other It is configured so that the numerical aperture of each of the plurality of lights emitted toward the element is equal,
The coupling optical system includes:
A first optical system for converging each of the plurality of lights;
A second optical system for changing an interval between the plurality of lights;
Including
Wherein the first optical system, Ri configuration der in which a plurality of lenses are arranged in an array,
It said second optical system, the coupling optical system, wherein both-side telecentric optical system der Rukoto.   The coupling optical system according to claim 1, wherein the first optical system is disposed closer to the optical element than the second optical system. The coupling optical system according to claim 1 or 2, wherein the magnification of the first optical system and the magnification of the second optical system are values satisfying the following expressions.
βm × βr = 1
However,
βm: magnification of the first optical system βr: magnification of the second optical system   The pitch between the plurality of lenses is equal to any of a pitch between the plurality of light sources, a pitch between the plurality of light receiving elements, and a pitch between the plurality of single core fibers. The coupling optical system according to any one of the above. The magnification of the second optical system is a ratio of a pitch between the plurality of light sources, a pitch between the plurality of light receiving elements, or a pitch between the plurality of single core fibers, and a pitch between the cores of the multicore fiber. The coupling optical system according to claim 1, wherein the coupling optical system is equal to: The incident-side element, the coupling optical system, and the exit-side element are configured such that each principal ray of light from the incident-side element is incident perpendicularly to an incident surface of the coupling optical system, and the coupling optical system The coupling according to any one of claims 1 to 5, wherein each of the principal rays of the light emitted from the light emitting surface of the light is incident perpendicularly to the light receiving surface of the light emitting side element. Optical system. Using the coupling optical system according to any one of claims 1 to 6, the numerical aperture of each of the plurality of lights incident from the incident side element and the respective apertures of the plurality of lights output toward the emission side element A coupling method comprising coupling the optical element and the multi-core fiber so that the numbers are equal.

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