JPS6055801B2 - optical circuit element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical circuit elements, particularly to a splitter for optical fibers in optical information transmission.

A conventional device of this type is shown in FIG. In the figure, 1, 2, 3 are multimode optical fiber bundles, 4
, 5 and 6 are glass optical mixers for mixing the lights of these optical fibers, 4a, 5a and 6a are their core parts, 4b
, 5b, 6b are cladding parts, 7 is a branch part of the optical fiber bundle, 7c, 7d, 7e are part bundles of the branch parts, 8, 9
, 10, 11, 12, and 13 are optical fiber bundle connectors. The conventional three-terminal bidirectional optical fiber distributor is configured as described above. For example, when a part of the optical fiber bundle entering the optical fiber bundle connector 8 is excited by a light source, the optical fiber is connected to the optical fiber through the connector 9. Light is propagated in part of the bundle 1.

Next, the light is guided to a glass optical mixer 4, and this core part 4a
The light is mixed to propagate throughout the optical fiber bundle within the optical fiber bundle 7 and enters the branched optical fiber bundle 7. Here, the optical fiber bundle 7 is branched into optical fiber bundles 7c and 7d, and the separated light is guided to the next optical mixer 5, 6.
The mixture is mixed so as to excite the entire optical fiber bundles 2 and 3, and supplied to the other two terminals through the optical fiber bundle connectors 10 and 11 or 12 and 13. Connectors 8, 11
, 13 and onwards, and connect them to the light source section and the light receiving section, bidirectional optical information transmission between the three terminals is possible.
Conventional three-terminal bidirectional optical fiber distributors are configured as described above, so they cannot be applied to single-core optical fibers, and because they use a large number of multimode optical fiber bundles, There were disadvantages such as the ratio of the area of the entire optical fiber core to the area of the fiber bundle was low, making it difficult to keep the loss at the connection portion low.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and by using a gradient index lens at the branching part, a low-loss optical splitter that can be applied to a single-core optical fiber is created. is intended to provide.

An embodiment of the present invention will be described below with reference to FIG.

In the figure, 21, 22, and 23 are single-core step type optical fibers, 21a, 22a, and 23a are the core portions of these fibers, 2↑B, 22b, and 23b are the folded portions of these fibers, and 20 is a light beam; 25 and 26 are π12 long refractive index profile shapes having identical refractive index distribution constants and diameters, which are polished with two surfaces forming an angle of 600 degrees with the central axis in the two directions of reflection from the central axes 24c, 25c, and 26c, respectively. Lenses 27, 28, 29 have their central axes 27c, 28c
, 29c, with the same refractive index distribution constant, which has a total reflection layer on both end faces and polished so as to form an angle of 30 degrees with respect to the central axis. Fig. 3, Fig. 4, and Fig. 5 are cross-sectional views of the I-1 section, ■-■ section, and ■-■ section of Fig. 2, respectively.
The figure is a diagram for explaining the progression of light rays through the π12 long gradient index lenses 24, 25, and 26. This invention will be explained in detail below using an embodiment of the invention shown in FIG.

A medium with a distribution in which the refractive index decreases in proportion to the square of the radius in the radial direction from the central axis of the lens toward the outer diameter has a lens action, and like the normal four optical lenses, it has an imaging action. .

The relationship between the geometrical characteristics within the gradient index lens will be explained below.

For the sake of simplicity, let us consider a dimensional lens-like medium and assume that its refractive index distribution is expressed by the following equation. Here, h is the refractive index at the central axis, a is the refractive index distribution constant, and x is the distance from the central axis.

It is known that a ray in this medium can be described by the following ray determinant (2) using paraxial ray approximation. However, x is the position of the ray from the central axis of the lens, ? represents the inclination of the light ray with respect to the central axis of the lens, z represents the direction of the central axis of the lens, and l represents the length of the lens. Next, the operation of the embodiment shown in FIG. 3 of the present invention will be explained. For example, the light 20 emitted from the optical fiber 21 enters the gradient index lens 24 having a central axis length of π12 (=1i1).

The reflection end face of lens 24 is polished so as to form an angle of 60 degrees with the central axis in the two directions of reflection from the central axis 24c, so the position of the light on the exit surface! and the slope are, respectively.
From equation (2), at the plane of incidence,
Letting the positional inclination of the θx light with respect to the central axis of the lens be X, l2θz, it is expressed as follows.

Figure 6 shows their positional relationship. Next, the light is centered on the central axis 27c,
In 28c, 11 lenses each enter π-length (=1i1) gradient index lenses 27 and 28 with reflective surfaces, but (2)
From the formula, the exit position and inclination are the central axes 27c and 28c of the lens.
, the incident position and inclination are the same. Therefore, the light passing through those lenses 27 and 28 passes through the gradient index lenses 25 and 2, which have the same shape as the lenses 24 and have a central axis length of π12.
The light is reflected from the central axes 25c and 26c of the lens 6 under the same conditions as the exit conditions for the central axis 24c of the lens 24, and from equation (2), it passes through the opposite path to the central axis 24c of the lens 24. The light inside the lens 25 is focused on the end face. Therefore, the coupling portions of the lenses 24, 25, and 26 with the fibers are in a 1:1 imaging relationship with each other. Therefore, half of the power of the light entering the lens 24 is transmitted to the lenses 25 and 26, resulting in a 6B distributor with low loss. Similarly, the light emitted from the optical fiber 22 can be distributed to the optical fibers 21 and 23, and the light emitted from the optical fiber 23 can be distributed to the optical fibers 21 and 22, respectively. By providing branch portions at the distributor portion and the reflection end of the optical fibers 21, 22, and 23 and connecting them to the light emitting source and the light receiving source, it is possible to mutually transmit and receive light from three locations. In order to prevent reflection loss at the joint between an optical fiber and a gradient index lens, or between gradient index lenses, it is not recommended to use a matching liquid or adhesive that has a refractive index close to that of the lens or optical fiber. It is effective in reducing the

In the above embodiment, it is assumed that the optical fibers 21, 22, and 23 have the same core body and numerical aperture, and the gradient index lenses 24, 25, and 26 have the same refractive index distribution constant and diameter. However, when connecting different optical fibers,
It is possible to combine gradient index lenses with different characteristics depending on the characteristics of the optical fiber.

FIG. 7 shows another embodiment in which normal optical convex lenses are used instead of the gradient index lenses 24, 25, and 26. For example, the optical fiber 21, the optical lens 33, and the π-long refractive index The positional relationship between the distributed lenses 27 and 28, the optical fiber 22, the optical lens 34, and the π long refractive index distributed lens 27,
Alternatively, if the optical fiber 23, the optical lens 35, and the π-long gradient index lenses 28 and 29 are kept in the same positional relationship, the same effects as in the embodiments of the present invention can be expected.

In this case, optical fibers 21, 22, 23 and lenses 33, 3
4 and 35 is the focal length of the lens. Figure 8 shows π-long gradient index lenses 27, 28, 2.
9 has a curvature, it is not necessary to polish the π12 long gradient index lenses 24, 25, and 26, and furthermore, in the above embodiment, the light is transmitted through the gradient index lenses 24, 25, and 26. Although an optical path difference occurs depending on the position where the light exits from 24, in this case, no optical path difference occurs.

9 and 10 are π-long gradient index lenses 27, 2.
This shows another example in which the total reflection layers No. 8 and 29 are placed on the inside, and the same effects as the above example can be expected.

FIG. 10 is a cross-sectional view taken along the line ■-■ in FIG. 9. FIG. 11 shows yet another embodiment in which the gradient index lens is replaced with gradient index lenses 33, 34, and 35 of 2π length without a total reflection layer, and these refractive index lenses are By making the index center axes 33c, 34c, and 35c deviate from the center axes 24c, 25c, and 26c of the π12 long gradient index lens, the same effects as in the above embodiment can be expected.

Although the above embodiment describes a three-terminal bidirectional optical splitter, if six π-long gradient index lenses are used and arranged to form a regular tetrahedron, a four-terminal bidirectional optical splitter can be created. It can also be configured.

Further, the optical fiber can be used in either a refractive index distribution type or a stepped type, and furthermore, it does not matter if it is a single mode or multimode type. It can also be applied to optical fiber bundles. As explained above, by using a gradient index lens, this invention enables a small and inexpensive optical splitter that can be applied to single-core optical fibers to be constructed with low loss and high precision. There is an effect that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing a conventional optical distributor, and FIG. 2 is a 5 side sectional view showing an embodiment of the optical distributor according to the present invention.
Figures 3, 4, and 5 are part I-1 of Figure 2, respectively.
■Part 1, ■Part 1, sectional view, Fig. 6 is a diagram for explaining the behavior of the light beam, Fig. 7 is a sectional view showing another embodiment of the present invention, Fig. 8 is a sectional view of this invention. 9 is a cross-sectional view showing another embodiment of the invention, FIG. 10 is a cross-sectional view along the line ■-■,
FIG. 11 is a side sectional view showing yet another embodiment of the present invention. In the figure, 21, 22, 23 are optical fibers, 24, 2
5, 26 are π12 long gradient index lenses, 27, 28,
29 is a π-long gradient index lens; 30, 31, and 32 are total reflection layers; and 33, 34, and 35 are 2π-long gradient index lenses.

Claims (1)

[Claims] 1. Three graded index lenses are arranged in abutting fashion to form a triangular shape, and each apex has an optical waveguide and the light from the optical waveguide has the two abutted refractive indexes. An optical circuit element characterized in that a distributed lens and another lens are arranged. 2 Set the length of the three gradient index lenses to nπ length (n=1
, 2...), and a total reflection layer is provided at the central axis portion of the optical circuit element, and the reflection layer is directed to the outside of the triangle. 3 Set the length of the three gradient index lenses to nπ length (n=1
, 2...), and a total reflection layer is provided at the central axis portion of the optical circuit element, and the reflection layer is directed inside the triangle. 4 Set the length of the three gradient index lenses to 2nπ length (n=
1, 2...). The optical circuit element according to claim 1. 5. The optical circuit element according to any one of claims 1 to 4, wherein the three gradient index lenses have curvature. 6. The light according to any one of claims 1 to 6, wherein the apex lens is a π/2 (2n-1) long refractive index gradient lens (n=1, 2...) circuit element. 7. The optical circuit element according to any one of claims 1 to 5, wherein the lens at the apex portion is an optical convex lens, and the distance between the optical fiber and the lens is the length of its focal length.