JP4888779B2 - Optical fiber coupler - Google Patents

Description

  The present invention relates to an optical fiber coupling device that optically couples a plurality of optical fibers used in an optical fiber communication system and an optical sensor such as a magnetic field sensor.

  A plurality of optical fibers used in an optical fiber communication system and an optical sensor are optically coupled to each other. As an apparatus for optically coupling optical fibers, an optical fiber coupling device as shown in FIG. 4 has been devised. (For example, refer to Patent Document 1).

JP-A-2005-37731 (page 2-3, FIG. 4)

  In FIG. 4, 100 is an adapter, 101 and 102 are optical fibers, 103 and 104 are plugs, 105 and 106 are spherical lenses, 107 is a beam waist, and C1 and C2 are the centers of the spherical lenses 105 and 106.

  The signal light and excitation light emitted from the optical fiber 101 are radiated into the space system (in the air) within the plug 103 and then collimated by the spherical lens 105 installed adjacent to the optical fiber 101.

  Conversely, signal light and excitation light emitted from the optical fiber 102 are radiated into the space system (in the air) within the plug 104 and then collimated by the spherical lens 106 installed adjacent to the optical fiber 102. .

  The collimated signal light and excitation light are collected on an optical fiber in the other plug by a spherical lens in the other plug of the plug pair.

Further, the end face of the optical fiber in the plug facing the spherical lens is subjected to oblique processing for reducing the reflected light at the end face. By this end face oblique processing, the light reflected by the end face of the optical fiber is incident on the optical fibers 101 and 102 again and becomes return light so as not to affect the stability of a light source (not shown).

In the optical fiber coupling device of FIG. 4, the end faces of the optical fibers 101 and 102 are obliquely processed as described above, and the pair of optical fibers 101 and 102 are disposed on the same fiber shaft 107.

  However, in order to meet the market demands for reducing the number of components and miniaturization and cost of optical fiber couplers, the number of lenses is reduced from two to one, and a pair of optical fibers is optically connected by one lens. An optical fiber coupling device has been devised (see, for example, Patent Document 2).

63-88805 (1st page, Fig. 1)

  An optical fiber coupling device disclosed in Patent Document 2 is shown in FIG. As shown in FIG. 5, optical fibers 111 and 112 are inserted into holes provided at the centers of cylindrical ferrules 109 and 110 to form a pair of plugs 113 and 114. Further, the plugs 113 and 114 are fitted into the sleeve 115, respectively, and one rod lens 116 is brought into contact with the end surfaces of the plugs 113 and 114. With this structure, an optical fiber coupling device 108 in which a pair of optical fibers 111 and 112 are optically coupled via a single rod lens 116 is configured.

In an optical fiber communication system, a magnetic field sensor, or the like in which such an optical fiber coupling device is used, the required functions may be different between the incident side optical fiber and the output side optical fiber that are optically coupled.

  For example, in a magnetic field sensor, a single mode optical fiber is used for the optical transmission fiber on the output side, and the low birefringence light having the Faraday effect is used for the optical fiber arranged near the magnetic field measurement target on the incident side. Fiber is used. In such an optical fiber coupling system that couples optical fibers having different characteristics, optical fibers having different refractive indexes are optically coupled.

  Even in such a coupling system between optical fibers having different refractive indexes, the end face of the optical fiber is obliquely processed to reduce reflected light. However, since the end face of the optical fiber is obliquely processed, the optical path direction of the light emitted from the optical fiber is inclined with respect to the fiber axis of the optical fiber.

  Further, if the end faces of a plurality of optical fibers having different refractive indexes are obliquely processed at the same angle, the refractive index is different, so that a difference occurs in the angle of the optical path of incident / exit light with respect to the fiber axis. Accordingly, if the fiber axes of a pair of optical fibers and the optical axis of one lens are arranged parallel to each other and on one axis, the coupling loss becomes about several dB level.

Therefore, in order to improve the coupling efficiency, it has been devised that the fiber axis of one of the optical fibers is inclined by the angle difference. When assembling such an optical fiber coupling system, after adjusting the fiber axis of one optical fiber, the lens and the other optical fiber are placed, and then the lens and the other optical fiber are aligned by a dedicated device for alignment. The optical axis of the fiber and the fiber axis alignment are performed.

However, a dedicated device is very expensive. If such a device is introduced into the assembly process of an optical fiber coupler, the introduction cost is reflected in each optical fiber coupler. Incurs high costs. However, even if the alignment operation is performed without using a dedicated device, the operation is time-consuming and the accuracy of the operation is also lacking, leading to a decrease in the yield of the optical fiber coupling device.

  Therefore, the present invention has a high coupling efficiency while enabling easy assembly by arranging the fiber axes of the optical fibers and the optical axes of the lenses in parallel and on one axis in order to simplify the alignment work. Another object of the present invention is to provide an optical fiber coupling device for optical fibers having different refractive indexes.

An optical fiber coupling device according to claim 1 of the present invention includes a first optical fiber, a second optical fiber, and one lens,
The first optical fiber is an optical fiber made of a quartz material having a single mode,
The second optical fiber is a single-mode optical fiber having lead silicate glass;
The refractive index n1 of the core of the first optical fiber and the refractive index n2 of the core of the second optical fiber are different from each other,
The end portion of the first optical fiber and the end portion of the second optical fiber are arranged to face each other, and the lens is disposed between the end portion of the first optical fiber and the end portion of the second optical fiber. Is placed,
Furthermore, the fiber axis of the first optical fiber, the fiber axis of the second optical fiber, and the optical axis of the lens are arranged on one axis,
The lens is arranged as an optical coupling lens for each core of the optical fiber;
An angle α1 with respect to the fiber axis direction of the optical path of the light incident / exited at the end of the first optical fiber, and an angle α2 with respect to the fiber axis direction of the optical path of the light incident / exited at the end of the second optical fiber. The optical fiber coupling device is characterized in that the inclination angles θ1 and θ2 of the end portion of the first optical fiber and the end portion of the second optical fiber are set different from each other so as to be equal to each other. .

In the optical fiber coupling device of the present invention, the inclination angle θ1 of one optical fiber is determined, and then the inclination angle θ2 of the other optical fiber is adjusted, thereby satisfying α1 = α2. This α1 = α2 is set in a coupling system of optical fibers having different refractive indexes , such as an optical fiber made of a quartz material having a single mode and an optical fiber having a lead silicate glass having a single mode . The angle difference between the optical paths of the incoming and outgoing light with respect to the fiber axes fa1 and fa2 is eliminated. Accordingly, it is possible to improve the coupling efficiency between optical fibers having different refractive indexes while arranging the fiber axes fa1 and fa2 and the optical axis oa of the lens in parallel on one axis.

  As a result, the optical fiber coupling device of the present invention has an effect that the coupling efficiency can be improved while the alignment work can be simplified and easy assembly can be performed without tilting each optical fiber.

  The best mode of the optical fiber coupling device according to the present invention will be described below in detail with reference to FIGS. 1 is a conceptual diagram showing the configuration of the optical fiber coupling device of the present invention, FIG. 2 is a conceptual diagram showing an optical path between optical fibers in FIG. 1, and FIG. 3 is the vicinity of the end face of each optical fiber in FIG. It is the elements on larger scale which expanded partially.

The optical fiber coupling device 1 in FIG. 1 includes a first optical fiber 2, a second optical fiber 3, and a single lens 4.

The first optical fiber 2 is an optical fiber made of a quartz material having a single mode (SM). The refractive index n1 of the core 2a is set to 1.4492. Furthermore, the end surface is subjected to oblique processing in order to reduce reflected light. From FIG. 3, the inclination angle θ1 of the oblique machining is
It is set to 12.5 degrees (θ1 = 12.5 degrees) from the direction perpendicular to the fiber axis fa1. The obliquely processed end surface is formed facing the lower right direction from FIG. Further, the end surface is subjected to an optical polishing process and an AR (Anti-Reflection) coat.

  The second optical fiber 3 is a single mode optical fiber mainly composed of lead silicate glass. Accordingly, the refractive index n2 of the core 3a is set to 1.833, so that the refractive index n1 of the core 2a of the first optical fiber 2 and the refractive index n2 of the core 3a of the second optical fiber 3 are different from each other. Composed. Further, the end face is subjected to oblique processing in order to reduce the reflected light, like the first optical fiber 2. The inclination angle θ2 for the oblique processing is set to 6.85 degrees (θ2 = 6.85 degrees) from the direction perpendicular to the fiber axis fa2. The obliquely processed end face is formed facing the lower left direction from FIG. Further, the end surface is subjected to an optical polishing process and an AR coating.

  The lens 4 is a GRIN (Gradient Index) lens, and its lens length L4 is set to 0.25P (P: the pitch of the lens 4). The outer shape is formed in a cylindrical shape, and the optical surface is formed perpendicular to the optical axis oa. By setting the lens length L4 to 0.25P, as shown in FIG. 2, the lens 4 is arranged as an optical convergence coupling lens to the cores 2a and 3a of the optical fibers 2 and 3, respectively. .

  As described above, the end of the first optical fiber 2 and the end of the second optical fiber 3 are disposed to face each other, and the lens 4 is disposed between the ends of the optical fibers 2 and 3. Thus, an optical fiber coupling device is configured. Furthermore, the fiber axis fa1 of the first optical fiber 2, the fiber axis fa2 of the second optical fiber 3, and the optical axis oa of the lens 4 are arranged in parallel and on one axis. Accordingly, the fiber axes fa1 and fa2 coincide with the optical axis oa of the lens 4.

Light such as signal light and pumping light propagating through the core 2a and emitted from the end of the first optical fiber 2 is emitted into the space system (in the air) within the optical fiber coupler 1, and then the optical fiber. 2 is incident on the lens 4 installed adjacent to the lens 2. When light is emitted from the optical fiber 2, the light emission direction is deviated from the fiber axis fa1, and is coupled to the lens 4 in the direction of the angle α1. Angle α
Reference numeral 1 denotes an angle of the optical path of light incident / exited (exited in this description) at the end of the first optical fiber 1 with respect to the fiber axis fa1 as shown in FIG.

  The light incident on the lens 4 is propagated while meandering by the refractive index gradient inside the lens 4. As described above, since the lens length L4 is set to 0.25P, light is emitted from the lens 4 to the space system (in the air) while drawing a gentle curved optical path as shown in FIG.

The light emitted from the lens 4 is then optically coupled to the second optical fiber at an angle α2 as shown in FIG. The angle α2 is an angle with respect to the fiber axis fa2 direction of the optical path of the light incident / exited (incident in this description) at the end of the second optical fiber 3 as shown in FIG. The light incident on the second optical fiber 3 propagates through the core 3a.

  The angle α1 and the angle α2 are set to be equal to each other. This setting is performed by setting the inclination angles θ1 and θ2 of the end portion of the first optical fiber 2 and the end portions of the second optical fiber 3 to be different. Specifically, the θ2 is

  Is set to satisfy. The propagating light has a single wavelength of wavelength λ: 1.55 μm.

On the other hand, it goes without saying that the same thing can be said for the configuration in which the light emitted from the optical fiber 3 propagates in the lens 4 and enters the optical fiber 2 in the reverse direction.

  Next, the background for setting the inclination angles θ1 and θ2 will be described. As described above, the refractive indexes n1 and n2 of the cores 2a and 3a, the inclination angles θ1 and θ2, the fiber axes fa1, so that the first optical fiber axis fa1 and the fiber axis fa2 of the second optical fiber coincide on the same axis. Installation angle around fa2 is specified.

  As shown in FIG. 3, when the core refractive index of the first optical fiber 2 is n1 (= 1.4492), the inclination angle of the end face is θ1 (= 12.5 degrees), and the refractive index of air is n0 (= 1), The light incident / exit angle α1 at the end of one optical fiber 2 is derived as follows from Snell's law.

  Similarly, when the core refractive index of the second optical fiber 3 is n2 (= 1.833), the inclination angle of the end face is θ2, and the refractive index of air is n0 (= 1), the end of the second optical fiber 3 The light incident / exit angle α2 is derived as follows.

  Here, in order to improve the coupling efficiency of the one-time optical fiber coupling system using one lens 4, the incident / exit angles α1 and α2 are set to be the same. Selection of the incident and outgoing angles α1 and α2 is such that light incident on the optical fibers 2 and 3 is refracted at the ends of the optical fibers 2 and 3 according to Snell's law, and is parallel to the fiber axes fa1 and fa2 of the optical fibers 2 and 3 This is done by refracting the optical fiber 2 or 3 in any direction. Therefore, from α1 = α2, θ2 is

  Is required. Substituting n1 = 1.4492, n2 = 1.833, and θ1 = 12.5 degrees, θ2 is derived as 6.85 degrees.

  As described above, in the optical fiber coupling device 1 of the present embodiment, the optical path directions of the light refracted at the ends of the optical fibers 2 and 3 are made parallel to the fiber axes fa1 and fa2, so The coupling efficiency between the three is improved. For this purpose, after determining θ1, the inclination angle θ2 of the other optical fiber 3 is determined so that α1 = α2.

  As described above, the optical fiber coupling device 1 of the present invention satisfies α1 = α2 by determining the inclination angle θ1 of one optical fiber 2 and adjusting the inclination angle θ2 of the other optical fiber 3. Yes. Setting α1 = α2 eliminates the angle difference between the optical paths of the incoming and outgoing light with respect to the fiber axes fa1 and fa2 in a coupling system of optical fibers having different refractive indexes. Therefore, it is possible to improve the coupling efficiency of optical fibers having different refractive indexes while arranging the fiber axes fa1 and fa2 and the optical axis oa of the lens 4 in parallel on one axis. Thereby, the optical fiber coupling device 1 of the present invention has the effect that the coupling efficiency can be improved while the alignment work can be simplified and easy assembly can be performed without tilting the optical fiber 2 or 3. Play.

  Although the components for holding the optical fibers 2 and 3 and the lens 4 have not been described, general plugs, ferrules, capillaries, adapters, sleeves, etc. may be used.

  Since the return return light loss at the end of the optical fiber 2 or 3 depends on the inclination angles θ1 and θ2, the target return return light loss is included by including the AR coating in the set inclination angle θ1 or θ2. Needless to say,

  The angle tolerance of θ1 and θ2 depends on the required coupling efficiency, but there is no practical problem if it is about ± 1 degree.

  If the tilt angles θ1 and θ2 are sufficiently small and can be approximated as sin θ1≈θ1 and sin θ2≈θ2, the calculation can be performed more easily. The calculation of θ2 by approximation is shown below.

  If the core refractive index of the first optical fiber 2 is n1, the tilt angle of the end face is θ1, and the refractive index of air is n0, the light incident / exit angle α1 at the end of the first optical fiber 2 is Snell's From the law, it is derived as follows.

  Similarly, if the core refractive index of the second optical fiber 3 is n2, the inclination angle of the end face is θ2, and the refractive index of air is n0, the light incident / exit angle α2 at the end of the second optical fiber 3 is Is derived as follows.

  From α1 = α2, θ2 is obtained as follows.

  By substituting n1 = 1.4492, n2 = 1.833, and θ1 = 12.5 degrees, θ2 is derived as 6.74 degrees. Although there is a slight difference from 6.85 degrees as a result derived from Equation 5, there is no practical problem because it is within the angle tolerance (about ± 1 degree) of θ1 and θ2.

  The wavelength λ of the propagating light may be 1.31 μm, 0.85 μm, and 0.63 μm in addition to 1.55 μm. Generally, the refractive index of the core of the optical fiber is determined according to the wavelength. The corresponding θ2 may be derived from the equation (5).

  The optical fiber coupling device of the present invention can be used for an optical fiber communication system and an optical fiber coupling system in an optical sensor such as a magnetic field sensor.

The conceptual diagram which shows the structure of the optical fiber coupling device of this invention. The conceptual diagram which shows the optical path between the optical fibers in FIG. FIG. 3 is a partially enlarged view in which the vicinity of the end face of each optical fiber in FIG. 2 is partially enlarged. The block diagram of the conventional optical fiber coupling device. The block diagram of the other conventional optical fiber coupling device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber coupling device 2 1st optical fiber 3 2nd optical fiber 4 Lens

Claims (1)

The optical fiber coupling device includes a first optical fiber, a second optical fiber, and one lens,
The first optical fiber is an optical fiber made of a quartz material having a single mode,
The second optical fiber is a single-mode optical fiber having lead silicate glass;
The refractive index n1 of the core of the first optical fiber and the refractive index n2 of the core of the second optical fiber are different from each other,
The end portion of the first optical fiber and the end portion of the second optical fiber are arranged to face each other, and the lens is disposed between the end portion of the first optical fiber and the end portion of the second optical fiber. Is placed,
Furthermore, the fiber axis of the first optical fiber, the fiber axis of the second optical fiber, and the optical axis of the lens are arranged on one axis,
The lens is disposed as an optical coupling lens for each core of the optical fiber, and an angle α1 with respect to a fiber axis direction of an optical path of light incident / exited at an end of the first optical fiber, and the second Inclination of each of the end of the first optical fiber and the end of the second optical fiber so that the angle α2 with respect to the fiber axis direction of the optical path of the light incident / exited at the end of the optical fiber becomes equal An optical fiber coupling device, wherein the angles θ1 and θ2 are set differently.

Images