JPS5834423A - Optical branching and coupling circuit - Google Patents

Abstract

PURPOSE:To make a branching ratio variable without giving any change to the distribution of transmission mode of an optical fiber and at the same time to assure high accuracy, by having a fan-shaped reflective film to divide a light. CONSTITUTION:Optical fibers 1 and 2 are set opposite to each other on the same optical axis, and refractive index distribution type lenses 4 and 5 are attached to the tips of the fibers 1 and 2, respectively. A cubic prism 8 is set so that the optical axes of the lenses 4 and 5 pass the center point P of a fan-shaped reflective film 8b of the prism 8 and that the surface of the film 8b forms a 45 deg. angle to the optical axis. At the same time, the optical axis of the fiber 1 containing the lens 4 at its tip is set so that said optical axis passes the center point P of the film 8b and forms a 45 deg. angle to the film 8b. Furthermore, the center axis of a refractive index distribution type lens containing a reflective film 7a at its end of one side passes through the point P and is put on the extended line of the optical axis of an optical fiber 3. Thus optical connection is possible with high accuracy among optical fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical branching/coupling circuit (used, for example, for extracting or coupling an optical data bus in a fiber-optic transmission).

Conventionally, this (as the city's device, No. 11) A1. What is shown in Figure 2? In Fig. 1, 1.2°3 is) Y: fiber, 4, 5, 6.7 are collimating gradient index lenses (hereinafter simply referred to as gradient index lenses), and 7a is the above-mentioned loop. (C attached to the end face of the gradient index lens 7)
8 is a Y-split body (hereinafter referred to as ``Gubup 117'j\\''), and as shown in the perspective view in Fig. 2, there is a small part of the joint surface of the VC gube prism 8. A reflective film 8a is not provided.

A data bus is a system in which many terminal devices share one transmission path for data transmission, and only one direction of signals is transmitted.
When transmitting data using separate transmission paths for each direction,
Shares one transmission line and transmits signals in both directions +rIf? It may be transmitted. Bidirectional transmission as an optical data bus -44
If you think about it when transmitting , you will need a 9T type branching and coupling device. Each terminal device is connected to the trunk optical fiber via an optical T-type branching/coupling device.

A conventional optical T-type branching/coupling circuit used in this manner will be explained.

Opposing optical fiber 1.2 has the same light i11+ l Vc
At the tip of the lens, gradient index lenses 4 and 5 (lens length is approximately 1/4 of the period) are placed at the tip, and a cube is placed on the optical axis -1-. The prism 8 is arranged so that the upper edge of the reflective film 8a is on the prism 8, and the surface of the reflective film 8a forms an angle t!- of 45 degrees with respect to the round axis. The optical fiber 30 optical axis is
The upper edge of the reflective film 8a is J:ru, 1:tsuni, and
The original fiber 3 is aligned so as to form a 45 degree angle with the reflective film 8a surface.
is located. Further, a gradient index lens I having a reflective film 7a surface at one end is inserted through a cube prism B,
They are arranged in one direction along the optical fiber 3, and their optical axes are placed on the same line. Light 11 emitted by optical fibers 1 and 2;
[Also, the surface of the cube prism 80 reflective film 8a is perpendicular to the lower surface so that the optical axes are on the same plane.
Each one is arranged so that

Therefore, the T light emitted from the optical fiber 3 is converted into a substantially parallel light beam by the gradient index lens 6, and is then converted into a parallel light beam by the reflection film 8a of the cube prism 8.
The reflected light from the IA is collected by the gradient index lens 5 and coupled to the optical fiber 2 for propagation. On the other hand, the remaining half of the light that has passed through the cube prism 8 enters the gradient index lens 7Vc and returns to its reflective film 7a, but is not aligned with the optical axis of the gradient index lens I. Since the light beam is converted into a symmetrical light beam, it is reflected by 8alC on the reflection 11 of the cube prism B, focused by the gradient index lens 4, and coupled and propagated to the optical fiber 1.

The light emitted from the honey fiber 1 is made into almost parallel light by the gradient index lens 4, and half of the light is reflected by the reflective film 8a.
The remaining half of the light is reflected by the gradient index lens 4 and condensed into the optical fiber 3, and the remaining half of the light is not reflected and is coupled and propagated to the optical fiber 2. f, optical fiber 2
The light emitted from the lens is also converted into almost parallel light by the gradient index lens 5.

Half of it is reflected by the reflective film 8& and returns to the original fiber 3.
The remaining half of the light is reflected! (The light is condensed by the index distribution lens 4 and coupled and propagated to the optical fiber 1. From this, the optical fibers 1, 2, and 3 are used as a three-terminal optical T-type branching and coupling circuit with mutual coupling relationships. You can see that it is functional.

When using an optical T-type branching/coupling circuit for a loop-shaped optical data bus, the optimal value of the amount of bypass by the optical T-type branching/coupling circuit varies depending on the number of terminals kc, so the branching ratio is changed according to the number of terminals. I feel safe.

For example, let the number of terminals be N, and let the ratio of light extraction from the data bus to the terminal and the coupling of light from the terminal to the data bus be η. The transmission loss between the optical transmitter and the receiver between the ends of one frame is expressed as L=-10]ogη2(177)N-2, and the optimal branching ratio is expressed as η=2/N.

In the conventional example, the bypass blade can be changed by adjusting the insertion sleeve of the reflective film surface into the optical path. However, in the case of a branch other than 3 dB, the optical There is a problem that it is difficult to maintain a constant amount of bypass due to mode dependence depending on the fiber length, etc.

This invention was developed in order to eliminate the drawbacks of conventional ones such as the above N+2, and even if the optical fiber length changes or the mode distribution propagating through the optical fiber changes,
It is an object of the present invention to provide an optical branching/coupling circuit that can maintain a bypass amount with high accuracy.

Hereinafter, this invention will be explained with reference to the drawings.

FIG. 3 shows a perspective view of the cube prism 8 in one embodiment of the invention. In FIG. 3, 81) is a fan-shaped reflective film attached to the joint surface of the cube prism 8;
is the center point of the fan shape, and the reflective film 8b is formed with a central angle θ with the center point P as the apex.

Next, its operation will be explained.

The configuration of this invention is the same as that of the conventional optical branching and coupling circuit shown in FIG. 1, except that the shape of the reflective film 8b attached to the joint surface of the cube prism 8 shown in FIG. 3 is fan-shaped. It is. Therefore, the operation will be explained using FIGS. 1 and 3.

Opposing optical fibers 1 and 2 are on the same optical axis (167'J)
A gradient index lens 4.5 is attached to the tip of the cube prism 8, and its optical axis passes through the center point P of the fan-shaped reflective film 8b of the cube prism 8, and the surface of the fan-shaped reflective film 8b reflects this light. Cube prisms 8 are arranged so as to make an angle of 45 degrees with respect to the axis, 8 h, an optical fiber 10 having a tip layer gradient index lens 4, and a reflecting film 8b whose element axis is fan-shaped.
45 for the fan-shaped reflective film 8b, taking the center point P of 1.)
It is set so that the angle in degrees is f[. Further, the central axis of the gradient index lens 7 having a reflective film 7a surface at one end passes through the center point P of the fan-shaped reflective film 8b and is on an extension of the optical axis of the optical fiber 30.

Therefore, if the central angle of the fan shape of the reflective film 8b of the cube prism 80W4.11 is 0, the light from the optical fiber 3 is
Suouji J), Hikaru, Aiba 2. No 2 π
They are combined at a ratio of 2π.

Light from optical fiber 1 is coupled to fiber 2 at a rate of -h'' to optical fiber 3, t7 to fiber 1 (carrier, 2 π θ).

If the optical fiber 3.2 is the original fiber for the data bus and the optical fiber for connecting the other fiber to the terminal, the branching ratio is expressed as η-32), and θ is changed by 2π. Bypass can be adjusted. Since the light beam is split so that the center point of the light beam collimated by the gradient index lens coincides with the center point P of the fan-shaped reflective film 8b, the light beam propagating through the original fibers 1 to 3 is divided. There is no change in mode distribution.

Figure 2p4 shows an embodiment of this invention.
A total reflection M-angle prism 9 is used in place of the gradient index lens T in the second embodiment, and the same effects as in the above embodiment are expected.

FIG. 5 shows still another embodiment of the present invention, in which one of the optical fibers 1 to 3 is not used, and the light emitting device 11. It is directly coupled to the light receiving element 12, and this example shows the case where no optical fiber is used. That is, 10
13.14 is a beam splitter for light division, and 13.14 is a collimator 2. It is a gradient index lens for focusing and charging.

In the above embodiment, the reflector is composed of the axially symmetrical gradient index lenses 4 to 6 and the reflective film 7IL.
A similar effect can be expected by using a slab lens with a plane-symmetric tx refractive index distribution and a reflective film.

Further, in the above embodiment, a case was described in which a gradient index lens is used as the 1/lens, but the same effect can be expected even if a normal optical lens and a reflecting mirror are used.

Furthermore, in Example 1, the case was described in which the reflection film 8b of the junction surface VCP@ shape of the cube prism B was formed as the light splitting body, but the same effect can be obtained even if the reflection film is formed on a plate-like transparent body. There is expected. Furthermore, if a wavelength-selective film is used as the fan-shaped reflective film 8b, a branching/coupling circuit can be formed only for optical signals of a specific wavelength.

As explained above, according to the present invention, the simple configuration in which the reflective film for dividing light is made into a fan shape allows
It is possible to change the distribution of the propagation mode of the optical fiber, first of all, to change the one-branching ratio, which has the effect of obtaining a high-precision product at low cost.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional plan view showing a conventional TS; branching and coupling circuit;
FIG. 2 is a schematic perspective view of the conventional cube prism of the above-mentioned Vt.
FIG. 3 is a schematic perspective view of a cube prism according to an embodiment of the present invention, FIG. 4 is a sectional plan view showing another embodiment of the invention, and FIG. 5 is a schematic perspective view of a cube prism according to an embodiment of the invention. It is a cross-sectional plane good. In 1, 1, 2.3 are optical fibers, 4, 5, and 6.7 index gradient lenses, 7a is a reflective film, 8 is a cube prism, 8b is a fan-shaped reflective film, and 9 is a total reflection right angle. prism,
11 is a light emitting element, and 12 is a light receiving element. t"Oh, the same reference numerals in the figures indicate the same or equivalent parts. Agent authentication 'ljF letter - (1 other person) Figure 1'/a Figure 2 Figure 3/ Figure 5

Claims (1)

[Claims] (1) A first lens having a collimating oil gradient index lens at opposing tips. A light splitting body having a fan-shaped reflective film attached to a transparent body is arranged between the second optical fibers so that the center point of the fan-shaped reflective film passes over the light beam 111 of the optical fiber. On one side of the light reflected by the splitting body, a third original fiber having a collimating filter 111 gradient index lens at its tip is inserted so that its optical axis passes through the center point of the fan-shaped reflective film. further on the extension line of the optical axis of the third optical fiber and opposite to the light splitting body.
An optical branching and coupling circuit characterized in that a reflector is arranged to convert a VC light beam into plane symmetry or angle symmetry and return it. (2) The light according to claim 1, wherein the light splitting body is a gup prism having a quadrilateral cross section and a fan-shaped reflective film attached to its diagonal joint surface. Branch-coupling circuit. (3) The optical branching/coupling circuit according to claim 1 or 2, wherein the reflective film has wavelength selectivity. (4) The optical branching/coupling circuit according to claim (1) or (2); ii-'+, wherein the reflector is constituted by a lens and a reflecting mirror. (5) Claim (1) or j'J characterized in that the reflector is constituted by a total reflection right angle prism.
(The optical branching and coupling circuit described in item 21. 11'! Arrange the attached light splitting body so that the center point of the sector-shaped reflective film passes on the optical axis of the optical fiber, and add a collimator to one of the light beams reflected by the light splitting body at the tip. A third optical fiber having an oil gradient index lens is arranged so that its optical axis passes through the center point of the sector-shaped reflective film, and further on an extension line of the optical axis of the third optical fiber. , and a reflector for converting the light beam into plane symmetry or point symmetry and returning the light beam is arranged on the opposite side of the light splitting body.
Instead of using any one of the third optical fibers, a light emitting element and a light receiving element are coupled to the light splitting body via a coupling lens and a beat splitter, respectively. - Optical branching and coupling circuit. (7) The light dividing body is 1 [but is it a quadrilateral? Claim No. 6 is characterized in that it is a cube prism with a fan-shaped reflection 11U on the diagonal joint surface of rL, t.
) Optical branching/coupling circuit described in section 2. (8) Claim (6), I, and (), characterized in that the reflective film is wavelength selective.
7) The optical branching and coupling circuit described in section 7). (9) Claim No. (6) Yamaji Etake No. (7) characterized in that the reflector is constituted by a lens and a reflecting mirror.
) Optical branching/coupling circuit described in section 2. (10) The optical branching and coupling circuit according to claim (6) and (7), characterized in that the reflector is a total reflection right-angle prism.