JPH04136803A - Optical coupling method for optical fiber - Google Patents

Abstract

PURPOSE:To easily, securely, and stably perform optical coupling between optical fibers or between an optical fiber and an optical element provided on a substrate by arranging the core of an optical fiber and an optical waveguide or the cores of two optical fibers in parallel to specific coupling length. CONSTITUTION:When the optical fiber 3 and substrate 1 are connected, the optical fiber 3 which has a flat surface at its end part is arranged on the surface of the optical substrate 1 so that its core 5 is parallel to the optical waveguide 2. Then light with constant intensity is inputted to this optical fiber 3. The length of the overlap part between the core 5 and the optical waveguide 2 on the substrate 1, i.e. coupling length is so adjusted that the output of light projected from the end part of the optical fiber 3 on the substrate 1 becomes minimum. Then the optical fiber 3 is connected to the substrate 1 and fixed at the position where the output of the light projected from the end part of the optical fiber 3 becomes minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is used in the fields of optical switches, optical modulators, optical computing, etc. to connect optical fibers to each other or to connect optical elements and optical fibers formed on a substrate. The present invention relates to an optical coupling method with an optical fiber for optically coupling and transmitting an optical signal or inputting and outputting an optical signal to an optical element.

[Prior Art] FIG. 5 is an assembly diagram showing a conventional optical coupling method between an optical fiber and an optical element provided on a substrate.

A predetermined optical element (not shown) is formed on the substrate 20, and a plurality of optical waveguides (not shown) connected to this optical element are formed on the substrate 20.
(not shown) are formed to extend to both ends of the substrate 2o. The optical input/output ends of these optical waveguides are connected to the substrate 2.
They are arranged at both ends of o with a constant interval between them.

Connecting members (V l+'♂
.

A substrate (substrate) 21 is to be bonded. This coupling member 21 is provided with a plurality of V grooves parallel to each other and separated in a direction perpendicular to the end surface.

The spacing between these grooves corresponds to the spacing between the optical waveguides at the end of the substrate 20. The optical fiber 22 to be connected to the optical element of the substrate 20 is connected to these V
It is placed in a groove.

The end of each optical fiber 22 is connected to each optical waveguide arranged at the end of the substrate 20. For example, the signal light enters an optical waveguide provided on the substrate 20 from the optical fiber 22 of one of the coupling members 21, reaches the optical element through this leading waveguide, and is modulated or switched by the optical element. , and is emitted to the optical fiber 22 of the other coupling member 21.

The coupling portion vJ21 provided with this groove is also used for coupling optical fibers together.

FIG. 6 is a perspective view showing another conventional optical coupling method.

A predetermined optical element and a leading waveguide 26 connected to the optical element are formed on the substrate 25. The surface of this substrate 25”
Second, a pair of prisms 27a are aligned with the leading waveguide 26.
, 27b are provided.

Input and output ends of optical fibers (not shown) are arranged on the surfaces of the prisms 27a and 27b that are inclined with respect to the substrate 25.

The signal light incident from one prism 27a (27b) via the optical fiber is transmitted to this prism 27a (27b).
The light is refracted by the waveguide 25 and introduced into the leading waveguide 26 provided on the substrate 25. Then, the signal light reaches the optical element along this leading waveguide 26, is switched by this optical element, and then passes from the waveguide 26 below the other prism 27b (27a) via the prism 27b (27a). and outputs it to the other optical fiber.

[Problems to be Solved by the Invention] However, the conventional optical coupling method described above has the following problems.

In the case of an optical coupling method using a coupling member 21 provided with a V-groove as shown in FIG. Since it is necessary to join the V-groove of the joining member 21 with extremely high precision. In addition, when fixing this coupling member 21 to the substrate 20, the position of the end of the optical fiber in the vertical (X-axis) direction, the position in the horizontal (Y-axis) direction, the thickness (
It is necessary to precisely align the optical axis of the optical fiber 22 and the optical axis of the leading waveguide by adjusting the position and angle (0) in the Z-axis direction, which makes the adjustment work complicated. Furthermore, for example, when coupling a plurality of optical fibers 22 to a plurality of leading waveguides, it takes an extremely long time to adjust the optical axis, and it is extremely difficult to couple all the optical fibers 22 and the leading waveguides with high precision. It is. Furthermore, since the bonding area between the optical fiber 22 and the substrate 20 is small, the bond is easily broken by temperature changes or mechanical stress, resulting in low durability.

On the other hand, when the optical fiber and the optical waveguide are coupled using prisms 27a and 27b as shown in FIG. 6, there is a drawback that the coupling loss is large.

Furthermore, this optical coupling method has the disadvantage that adjustment of the incident angle and output angle of light is complicated.

The present invention has been made in view of such problems, and includes:
Optical coupling with optical fibers that allows easy optical coupling between optical fibers or between optical fibers and an optical element provided on a substrate, and also enables reliable and stable optical coupling with low coupling loss. This is the purpose of providing a method.

[Means for Solving the Problems] A method for optical coupling with an optical fiber according to the first invention of the present application includes attaching an optical fiber to the surface of a substrate on which an optical element and an optical waveguide connected to the optical element are formed. The core of the optical fiber and the leading waveguide are arranged in parallel over a predetermined coupling length.

The method for optical coupling with an optical fiber according to the second invention of the present application is as follows:
In the present invention, the optical fiber is bonded so that the cores of both optical fibers are arranged in parallel over a predetermined coupling length. or two optical fibers are arranged with their ends parallel to each other over a predetermined coupling length. It is joined.

In this case, the overlapping portion between the cores of the optical fibers or between the cores of the optical fibers and the leading waveguide has a predetermined length (perfect coupling length), thereby forming a directional coupler. Therefore, the signal light can be almost completely transferred from the optical fiber to the optical waveguide, from the optical waveguide to the optical fiber, or from one optical fiber to the other optical fiber.

In other words, in the present invention, two optical fibers or an optical waveguide provided on a substrate and an optical fiber are arranged parallel to each other, and the length of the coupling portion is adjusted so that the optical fibers are connected to each other or provided on the substrate. A directional coupler is formed between the optical waveguide and the optical fiber. In this case, since the length of the joint between the optical fibers or between the substrate and the optical fiber is relatively long, the joint area between the optical fibers or between the optical fiber and the substrate is large. Therefore, the strength of the joint between the optical fibers or between the optical fiber and the substrate is high, the joint can be prevented from being destroyed by temperature changes and mechanical stress, and the durability of the joint is high. Also, when configuring a directional coupler with a desired bond length, the length (X-axis) direction and width (
Since position adjustment is only required in the (Y-axis) direction, optical coupling between optical fibers or between an optical fiber and an optical waveguide is extremely easy. Therefore, even when there are a large number of optical fibers and optical waveguides to be coupled, each optical fiber and optical waveguide can be optically coupled with low loss.

Note that in order to obtain a perfect coupling length, for example, light with a constant intensity is input into an optical fiber, and a coupling length at which the intensity of light output from this optical fiber is minimized at the coupling portion is determined. The bond length at this time is the complete bond length. Also,
For example, light with a constant intensity is input into an optical fiber, and the coupling length is adjusted so that the intensity of the light output from the leading waveguide of the substrate or other optical fiber coupled to this optical fiber is maximized. The complete bond length may also be determined.

In addition, when joining optical fibers or optical fibers and a substrate, for example, by partially polishing or etching the peripheral surface of the optical fiber at the joint part to provide a flat surface.
The optical fibers or the optical fibers and the substrate can be easily joined on this flat surface.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a front cross-sectional view showing an optical coupling method according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view thereof. In this embodiment, an optical fiber and an optical element provided on a substrate are optically coupled.

The optical fiber 3 includes a core 5 and a cladding 4 arranged around the core 5.

The peripheral surface of the end of the optical fiber 3 is partially polished or etched to be flattened until the core 5 is exposed, thereby providing a flat surface at the end.

On the other hand, a guide waveguide 2 is provided on the substrate 1, and this optical waveguide 2 is connected to an optical element (not shown) formed on the substrate 1.

The optical fiber 3 has the flat surface in contact with the substrate 1, and the core 5 is aligned and parallel to the optical waveguide 2, so that the optical fiber 3 is connected to the substrate 1.
bonded on the surface of the A filler material 6, such as silicone resin, having a refractive index similar to that between the cladding 4 and the path is filled between the end surface of the joint portion of the substrate 1 and the end portion of the flat surface of the optical fiber 3. .

The width of the optical waveguide 2 is, for example, 10 μm. Further, the optical fiber 3 has an outer diameter of 125 μm, for example, and a core 5
The diameter is θμm. In this case, by polishing or etching the optical fiber 3 by about 60 μm from the outer peripheral surface toward the center in the radial direction, the width is reduced to about 124 μm.
A flat surface of m can be obtained. Core 5 is on this flat surface.
is exposed, and the width of the exposed portion of the core 5 is about 8 to 9 μm. This flat surface has a wavelength similar to that of the light to be input into the optical fiber 3, more preferably l/1 of this wavelength.
Mirror polished to a surface roughness of about 0.

Note that the substrate 1 and the optical fiber 3 are bonded to each other using a UV crosslinkable organic adhesive, glass, or the like. For this reason, the distance between the optical waveguide 2 and the core 5 is about 1 to 5 μm since the joint is inserted therebetween, but it is preferable that this distance is as narrow as possible.

However, even if the distance between the optical waveguide 2 and the core 5 is outside this range, by adjusting the length and width of the coupling portion between the optical waveguide 2 and the core 5, the complete coupling length can be achieved as described later. The signal light can be almost completely transferred from the optical fiber 3 to the optical waveguide 2 or from the optical waveguide 2 to the optical fiber 3.

The optical fiber 3 and the substrate 1 are bonded as shown below. First, an optical fiber 3 having a flat surface at its end is
is placed on the surface of the substrate 1 with its core 5 parallel to the waveguide 2. Next, light with constant intensity is input into this optical fiber 3.

Then, the length of the overlapping portion between the core 5 and the optical waveguide 2 of the substrate 1, that is, the coupling length, is adjusted so that the output of light emitted from the end of the optical fiber 3 on the substrate 1 is minimized. Next, the optical fiber 3 is bonded and fixed to the substrate 1 at a position where the output of light emitted from the end of the optical fiber 3 is minimized.

FIG. 3 is a graph showing the relationship between the length of the coupling portion between the substrate 1 and the optical fiber 3 on the horizontal axis and the optical output on the vertical axis. In FIG. 3, the solid line indicates that light having a constant intensity is input to the optical fiber 3, and the output from the end of the optical fiber 3 to the outside at the coupling portion side is investigated. The broken line indicates the optical output output from the optical waveguide 2. Therefore, when the output of the light output from the coupling part side end of the optical fiber 3 becomes O, the light is completely transmitted from the optical fiber 3 to the optical waveguide 2. As a result, the output from the leading waveguide 2 becomes maximum. On the contrary, when the output of the light emitted from the end of the optical fiber 3 is the maximum, almost no light transfers to the optical waveguide 2, and the output of the light of the optical waveguide 2 is the minimum.

That is, it is difficult to adjust the coupling length between the core 5 of the optical fiber 3 and the optical waveguide 2 of the substrate 1, and from the leading waveguide 2 provided on the substrate 1 to the optical fiber 3 or from the optical fiber 3 to the optical waveguide 2. , the signal light can be selectively and almost completely transferred. The length in this case, that is, the complete bond length, is
Usually, it is several mm to 2 cm.

In this way, conventional techniques have been used to reduce coupling loss by adjusting the length (X-axis), lateral (Y-axis), and height (Z-axis) of the end of the optical fiber.
Whereas it was necessary to adjust the axis) direction and angle (θ), in this example, the vertical (X-axis) direction and horizontal (Y-axis)
Since only the direction adjustment is required, the optical waveguide 2 and optical fiber 3
Optical coupling with is extremely easy. In this example, the coupling loss is about 1 dB or less when each dimension and shape are within the above-mentioned ranges.

In addition, the joint side where the conventional V groove is provided (see Figure 5)
In this system, it is extremely difficult to couple, for example, 80 optical fibers and 80 leading waveguides with good accuracy. However, with the structure of this embodiment, even in such a large number of optical connections, the coupling loss of each coupling part can be suppressed. Furthermore, in this example,
For example, as mentioned above, the joint between the optical fiber and the substrate has a width of about 124 μm and a length of several mm to 2 cm, and because the joint area is significantly wider than that of the conventional method, the strength of the joint between the optical fiber and the substrate is increased. High and durable.

FIG. 4 is a front sectional view showing a second embodiment of the invention. This embodiment is for optically coupling optical fibers together.

In this embodiment, the peripheral surfaces of the two optical fibers 11 and 12 are polished or etched to provide a flat surface. Then, the two are joined by bringing their flat surfaces into contact with each other. Furthermore, the exposed portions of the cores 13, 14 at the ends of the optical fibers 11, 12 are filled with a filler 15.

In this case, as in the first embodiment, by adjusting the coupling length of the cores 13.14 of both optical fibers 11.12, the light of one optical fiber 11 (12) is almost completely transferred to the other. It can be transferred to the optical fiber 12 (11). In this embodiment, when the dimensions of the optical fibers 11 and 12 are the same as in the first embodiment, the coupling loss is about 0.
It is 3dB.

This embodiment has the advantage that optical fibers can be easily coupled together and that the coupling loss is small. Furthermore, since the bonding area between the optical fibers is large, the durability of the bonded portion is high.

Note that the above-mentioned embodiments are for the case where the core of the optical fiber and the leading waveguide of the substrate or the core of one optical fiber and the core of the other optical fiber are in contact with each other, but there is a gap between them. cladding material may occupy the space between them.

[Effects of the Invention] As explained above, according to the present invention, when the cores of an optical fiber core optical waveguide or two optical fibers are arranged in parallel with each other with a predetermined coupling length, it is possible to achieve this by simply adjusting the length of the coupling part. Signal light can be almost completely transferred from an optical fiber to an optical waveguide, from an optical waveguide to an optical fiber, or from one optical fiber to another optical fiber. Furthermore, even when a large number of optical fibers and optical waveguides are to be joined, the joining is easy because only the length and width of the joining portions need to be adjusted. Furthermore, since the bonding area between the optical fibers or between the optical fibers and the substrate is large, the bonding strength of the bonded portion is high and the durability is excellent.

[Brief explanation of the drawing]

FIG. 1 is a front cross-sectional view showing the optical coupling method according to the first embodiment of the present invention, FIG. 2 is a cross-sectional view thereof, and FIG. 4 is a front sectional view showing the second embodiment of the present invention, and FIG. 5 is an assembly diagram showing the conventional optical coupling method.
FIG. 6 is a perspective view showing another conventional optical coupling method.

Claims (4)

[Claims] (1) An optical fiber is bonded to the surface of a substrate on which an optical element and an optical waveguide connected to the optical element are formed, and the core of the optical fiber and the optical waveguide are arranged in parallel over a predetermined coupling length. A method for optical coupling with an optical fiber, characterized by: (2) A method for optical coupling with optical fibers, characterized in that two optical fibers are joined so that the cores of both optical fibers are arranged in parallel over a predetermined coupling length. (3) The predetermined coupling length is set so that the intensity of light output from the end of the optical fiber on the coupling section side is minimized when light is input to the optical fiber. An optical coupling method with an optical fiber according to claim 1 or 2, characterized in that: (4) The predetermined coupling length is such that when light is input to the optical fiber, the intensity of the light output from the optical waveguide coupled to this optical fiber or another optical fiber coupled to the optical fiber is determined by the predetermined coupling length. 3. The optical coupling method with an optical fiber according to claim 1, wherein the optical coupling method is set so as to maximize the optical fiber.