JPH0618731A - Waveguide type optical branch unit - Google Patents

Abstract

PURPOSE:To raise the degree of freedom of a branching ratio by adjusting an angle of a branch slit and enlarging a branch angle. CONSTITUTION:An optical waveguide 1 consists of a core 3 and a clad 4 for covering it, and is constituted on a plane substrate 2 so that its cross section is roughly rectangular. The core 3 is constituted of a branch line 3A being an incident part, and branch lines 3B and 3C being emitting parts. On the way of the optical waveguide 1, a branch slit 5 formed by having an inclination of an angle theta1 against the branch lines 3A, 3B is provided. By the angle theta1 made by the branch lines 3A, 3B and the branch slit 5, and an angle theta2, a branch angle of the waveguide type optical branch unit is determined. The branch slit 5 consists of a structure cut in the height direction to the halfway of the core 3, in a branch part 6. This connected part L1 of the optical waveguide 1, and the part L2 which is connected without being cut exist, and by an area ratio (area ratio of the branch slit) of these L1 and L2, a branching ratio of light in this branch waveguide is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical branching device for branching propagating light, and more particularly to an optical branching device having improved branching characteristics.

[0002]

2. Description of the Related Art As optical communication systems become more sophisticated,
There is an increasing need for a high-performance waveguide that has functions such as demultiplexing characteristics, amplification characteristics, and branching characteristics in addition to simply propagating light with respect to a waveguide as a light propagation path. In particular,
A star coupler having an optical waveguide as shown in FIG. 4 is realized as one having a branching characteristic function. This is an optical waveguide 3 consisting of a core and a clad on a substrate 32.
3 is formed by patterning 3 in a star shape using a so-called Y-branch waveguide having a desired branch angle, and shows a state in which the optical fiber 34 is connected to the input / output end of the coupler.

[0003]

However, in the star coupler shown in FIG. 4, if the branching angle is made larger than the optimum value, a component that does not couple to the branching path occurs due to the straightness of light, which causes an increase in loss. Since the branch angle is small and the so-called Y-branch structure is adopted, the degree of freedom of the branch ratio is limited.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a waveguide type optical branching device capable of obtaining a desired branching angle and branching ratio.

[0005]

A waveguide type optical branching device of the present invention is provided on a plane substrate, and has a core for propagating light having an optical waveguide covered with a clad having a lower refractive index. ,
The optical waveguide has at least a branch as a light incident part and two branches as a light emitting part, and these branches are applied to a waveguide type optical branching device that is branched and arranged at a certain branching angle. To be done. For branching where the optical waveguide branches into a branching part where the depth reaches part of the core in the direction that intersects the light propagation direction and a light reflection surface is formed at the boundary with the core due to the difference in refractive index. A slit is provided. This slit is
It is obtained by cutting an appropriate amount of the incident light propagating through the waveguide in the height direction of the waveguide in order to branch the light into branches.

This branching slit is required at the branching part to obtain a desired branching angle and a desired branching ratio with respect to the optical paths propagating in the cores of the respective branching paths. It is provided to form a depth. The width of the branch slit is not particularly limited,
In order to reduce the loss of the transmitted light output, the width of the slit is preferably narrow. Also, especially to have a switch function,
It is also possible to put a substance for matching the refractive index between the cores of the branches into and out of the branch slit.

[0007]

Since the waveguide is cut to the middle of the core in the height direction by the branch slit provided at the branch portion of the waveguide, the waveguide has a reflection surface due to the part cut in the branch slit. And a transmissive part composed of a non-cut part. A part of the light propagating from the branch path as the light incident part and hitting the transmitting part is reflected as it is to one branch path as the light exiting part, and the rest of the light hitting the reflecting part is reflected there. It branches to the other branch as a light emitting part. At that time, the light propagating in the waveguide is branched according to the ratio of the reflecting portion and the transmitting portion (branching slit area ratio). Therefore, a desired optical branching ratio can be obtained by adjusting the depth of the branching slit when the waveguide type optical branching device is manufactured. Further, by adjusting the angle of the branch slit, the desired branch angle direction of the light propagating through the waveguide can be obtained.

[0008]

The following EXAMPLES Examples illustrate the invention illustrated examples in detail. FIG. 1 is a perspective view of an optical waveguide having slits showing the principle of the present invention, and a plan view of a waveguide type optical branching device according to this embodiment, and FIG. 2 is its configuration diagram and an enlarged section aa '. It is a figure. In FIG. 1A, an optical waveguide 1 is formed in a substantially rectangular cross section on a flat substrate 2 made of single crystal silicon or a quartz substrate. The waveguide 1 is formed of silicon oxide (SiO ₂ ) having a different refractive index, and has a core 3 (refractive index n _w ) through which light propagates and a low refractive index clad 4 (refractive index n _c ) that covers the core 3. Have and. The gist of the present invention is to provide the optical waveguide 1 with the slit 5 as shown in the figure.

In FIG. 1B, the core 3 on the substrate 2
Has three branches formed by straight branches 3A, 3B and branches 3C arranged at an angle θ ₂ therewith, and each axis 14, 15, 16 of which is shown in FIG. 1 (B). Of these, the branch path 3A serves as a light incident portion for the core 3 and the remaining two branch paths 3A are included.
B and 3C function as emission parts of the branched light. here,
In contrast to the branch 3A on the side of the light entrance 11 side, the branch 3B on the side of the exit 12 of the branched light is on an extension of the branch 3A, and on the side of the other branch light exit 13 side. 3C is arranged at the position of the angle θ ₂ described above.

In the middle of the optical waveguide 1 thus constructed, as shown in FIG. 1 (B), an angle θ ₁ is formed in the branches 3A and 3B.
There is a branching slit 5 formed with an inclination of. Angle θ ₁ formed by the branches 3A, 3B and the slit 5 for branching
If, branch 3A, the angle theta ₂ of 3B and branch passages 3C, branch angle theta ₃ of the waveguide type optical branching device is determined. If the branch 3C is not at a right angle to the branch 3A, the branched light is the branch 3C.
As you go straight, change θ ₁ accordingly. That is, θ ₁ = (180 ° −θ ₂ ) / 2 (1) Further, as shown in FIG. 2 (A), this branching slit 5 is provided with the optical waveguide 1 at the branching portion 6 of the optical waveguide 1. The structure is cut in the height direction from the top to the middle of the core 3. Here, the height direction is the Z direction perpendicular to the plane XY when the plane XY is the plane of the plane substrate 2. In FIG. 2A, the optical waveguide 1 is partially cut by the branch slit 5 in the aa ′ cross-sectional enlarged view, but it is connected to the cut core portion L1 without being cut. There is a core part L2
And the area ratio of L2 (branch slit area ratio) determines the branching ratio of light in this waveguide optical branching device. That is, assuming that the core width W is the waveguide width, and the cutting depth d ₁ of the core 3 and the remainder d ₂ are as shown in FIG. 2B, L ₁ = W × d ₁ L ₂ = W × d ₂ (2) and L ₁ / L ₂ = d ₁ / d ₂ determines the branching ratio.

In the waveguide type optical branching device configured as described above, the light incident on the branch 3A propagates through the optical waveguide 1 and reaches the reflecting surface by the slit 5 for branching. Since the optical waveguide 1 is partially cut by the branching slit 5, the propagated light is transmitted as it is in the portion where the optical waveguide 1 is connected, and is output from the branch 3B to the emission port 12. In the cut portion of the optical waveguide 1, a part of the propagating light is reflected by the refractive index difference between the branching slit 5 and the core 3, is coupled to the branch 3C, and is output to the emission port 13. The branch angle is the angle θ ₂ described above with respect to the branch path 3A, and the branch angle θ ₃ , that is, the angle formed by the branch path 3B and the branch path 3C is
It is obtained by designing the reflection surface angles θ ₁ and θ ₂ and the arrangement of the optical waveguide 1.

The branching ratio of the light is adjusted by the cutting amount of the optical waveguide by the branching slit 5, and the area ratio between the area L ₁ where the optical waveguide is connected and the area L ₂ which functions as a reflecting surface. Determined by. This area ratio is variable depending on the branch slit forming conditions, and an effective area ratio can be obtained by adjusting the depth of the branch slit 5. In particular, if this is applied, it is useful as an optical tap component in which only a part of the light coming from the input fiber is detected by the photodetector for monitoring, and most of the light is coupled again to the output fiber.

Modification Example FIG. 3 shows a modification example of the waveguide type optical branching device shown in FIGS. In this example, the index matching liquid 7 is inserted into the above-mentioned branch slit 5 to provide a switch function. This index matching liquid 7
Uses a liquid whose refractive index is equal to that of the core at the wavelength of the light to be branched. That is, when the refractive index matching liquid 7 is inserted into the branching slit 5, the optical waveguide 1 is divided by the branching slit 5, but there is no difference in the refractive index on the reflecting surface. Goes straight, and all the incident light is output to the emission port 22 (total transmission state).

Next, when the refractive index matching liquid 7 is removed from the inside of the slit 5 for branching, the reflecting surface by the slit 5 for branching becomes effective again, and due to the large difference in refractive index between the core and the slit 5 for branching, all the light is emitted. The light is reflected and branched to the emission port 22 and the emission port 23 (light branching state). In this way, it is possible to switch between a state in which all the incident light is transmitted and a state in which the light is branched by moving the refractive index matching liquid in and out of the branch slit provided for the light branch. . Instead of the index matching liquid, gas or solid may be used.

[0015]

As described above, according to the present invention, the following effects can be obtained.

(1) According to the optical waveguide type branching device of the first aspect, a desired optical branching angle can be obtained by setting the arrangement of the branching slit and the waveguide. In particular, since total reflection of light is used as the branching principle, it is possible to increase the branching angle as compared with the conventional method. Moreover, since the branch angle can be increased, the size of the branch device can be reduced. Further, the light splitting ratio can be freely set by the area ratio of the reflecting surface by the splitting slit.

(2) According to the optical waveguide branching device of the second aspect, it is possible to switch between a state where all the incident light is transmitted and a branching state.

[Brief description of drawings]

FIG. 1 is a plan view of an optical waveguide having slits for explaining the principle of the present invention and a waveguide type optical branching device according to an embodiment of the present invention.

FIG. 2 is a perspective view and a sectional view of a waveguide type optical branching device according to the present embodiment.

FIG. 3 is a perspective view showing a modified example in which a waveguide type optical branching device has a switching function.

FIG. 4 is a perspective view showing a conventional optical waveguide type star coupler.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Substrate 3 Core 3A, 3B, 3C Branch 4 Cladding 5 Optical branching slit 6 Branching part of waveguide 7 Index matching liquid 11 Inlet port 12, 13 Outlet port 21 Inlet port 22 Outlet port 23 Outlet port

Claims (2)

[Claims] 1. A light guide provided on a plane substrate, wherein a core for propagating light has an optical waveguide covered with a clad having a lower refractive index than the core, and the optical waveguide has at least a branch as an incident part of light. In a waveguide type optical branching device, which is provided with two branch paths as light emitting parts, and these branch paths are branched at a branching angle with respect to each other, a branching part where the optical waveguide branches is provided with a propagation direction of light. The depth reaches a part of the core in the intersecting direction,
A branching slit that forms a light reflecting surface formed by a refractive index difference is provided at the boundary with the core, and the branching slit has a desired optical path that propagates in the core of each branch at the branching portion. And a depth required to obtain a desired branching ratio, and a waveguide type optical branching device. 2. The waveguide type optical branching device according to claim 1, wherein a material for matching the refractive index between the cores of the branch path can be put into and taken out from the slit for branching.