JPH0314322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In an optical fiber communication system, an element called an access coupler is important because it branches part of the information from the main line, sends a signal to the terminal, and merges the data reprocessed at the terminal with the main line.

Conventionally, access couplers have been constructed by combining a focusing lens, a prism, a mirror, etc., or by processing the optical fiber itself. This type of device was complicated to manufacture and had problems with reliability. Therefore, an access coupler has been proposed in which an optical waveguide is formed in a transparent substrate such as glass or plastic, and the optical waveguide is branched and merged. There were problems such as large optical loss.

The present invention has been made in consideration of such conventional technical problems, and proposes an optical waveguide type access coupler that has low insertion loss at branching and merging sections and is also easy to connect to optical fibers.

Methods for forming optical waveguides in glass substrates include ion exchange method, ion diffusion method using electric field, and CVD used for manufacturing optical fibers.
When using plastic substrates, there are photopolymerization methods, diffusion methods, etc.
The present invention is not limited to either.

A method of forming a branch circuit by forming an optical waveguide in a planar substrate is as shown in FIG. 1, by keeping the optical waveguide width W constant and changing the branch angle θ.
It is possible to change the ratio of the light outputs of output ends 1 and 2, ie po2/po1. For example, if θ is set to 1° or less, po2/po1≈1, that is, a two-branch circuit. However, the branching ratio used in the access coupler is po2/po1, which is small at 1/5 to 1/20, so in order to obtain this ratio, it is necessary to increase θ.
Increasing θ increases extra optical loss at the branching portion, which increases insertion loss (po1+po2)/pi, which is not practical.

Therefore, as shown in FIG. 2, a conventional method has been proposed in which the insertion loss is reduced by reducing the branching angle θ and changing the guide width. For example, by making the guide widths w 1 and _{w 2} at the output ends 1 and ₂ smaller than w ₀ and w ₁ > w ₂ with respect to the guide width w ₀ on the input side, the output ratio can be increased.
This is a method to reduce po2/po1. However,
With this method, it is difficult to set po2/po1 to the desired value, especially in multimode fiber systems, because the branch output ratio po2/po1 can vary widely even if the connection position of the optical fiber connected to the input end is slightly different. It was hot.

The purpose of the present invention is to solve the above-mentioned conventional problems and provide a new optical waveguide type access coupler that can set the branch output ratio from the main line to a desired value with high precision and has less loss at the branch section. It is intended to.

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 3 is a plan view of an access coupler shown as a reference for explaining the structure and function of the main parts of the product of the present invention. A light guide path having a substantially circular cross section is provided.
The light guide path is a main light path 11 that is approximately V-shaped in plan view.
and an input path 11A that constitutes this main optical path 11,
Of the output paths 11B, a branch light guide path 12 for input is provided, which branches from the output path 11B and reaches the side surface of the substrate 10.

As an example, the above-mentioned light guide path has a refractive index distribution such that the refractive index is maximum at the center in a cross section perpendicular to the optical axis, and the refractive index decreases parabolically toward the outer periphery.

The diameter of the optical fiber groups 20A, 20B, 20C, 20d connected to this access coupler is
The diameter is approximately the same throughout the entire optical path.

Further, the V-shaped bottom portion 13 of the main optical path 11 is exposed on the side surface 10A of the substrate 10, and the shape of this exposed portion is also circular to approximately match the core diameter of the optical fiber 20C connected to this portion.

The entrance path 11A and the exit path 11B that constitute the main optical path 11 have the same angle θ ₁ with the normal to the substrate side surface 10A, and on the substrate side surface of the V-shaped bottom 13 where the optical paths 11A and 11B intersect, Injection path 11A
A dielectric filter film 14 is provided which transmits a part of the transmitted light and reflects the remaining part.

The angle θ ₁ is set to a value sufficiently smaller than the critical angle of total reflection of the filter film 14. The branch light guide path 12 for input is arranged so that it merges with the main light path in the middle of the output path 11B.
The axis is provided at the merging portion so as to form an acute angle θ ₂ toward the V-shaped bottom portion 13 with respect to the axis. If this angle θ ₂ is too large, merging loss will occur, so it is generally 4° or less, preferably 2° or less. By setting θ ₂ within this range, the confluence loss can be made so small that it can be ignored.

The light transmittance of the filter film 14 is generally 20% to 5% so that the output optical power has a desired branching ratio under the condition of angle θ ₁ formed by the optical axis of the incident path 11A.
The transmittance is selected so that the transmittance is as follows.

Instead of being formed on the substrate side surface 10A, the filter film 14 can also be provided on the end surface side of the optical fiber 20C connected here.

A trunk optical fiber 20A is connected to the end 15 (board side surface 10B) of the input path 11A of the access coupler described above.
is connected, and another trunk optical fiber 20B is connected to the end 16 of the output path 11B exposed on the same side surface 10B of the substrate.

Further, on the opposing side surface 10A of the substrate, an optical fiber 20d for transmitting optical signal information reprocessed by a terminal device is connected to the end 17 of the branch light guide path 12, for example.

As a result, after the optical signal information transmitted by the optical fiber 20A is transmitted through the input path 11A of the access coupler, a part of it passes through the filter film 14 at the V-shaped bottom 13, and the optical signal information transmitted by the optical fiber 20C is connected thereto. The data is transmitted to terminals, etc. through

Alternatively, instead of connecting the fiber 20C, a photodetector can be connected to monitor the trunk transmission light.

The remaining transmission light reflected by the filter film 14 passes through the output path 11B in the access coupler and is transmitted to the trunk fiber 20B connected to the end portion 16.

In addition, the data signal reprocessed by the terminal and transmitted through the optical fiber 20d enters the branch light guide path 12 in the access coupler, passes through this optical path 12, and merges with the main signal transmitted through the output path 11B. .

The above access coupler can be manufactured with high precision, for example, by the method described below. First, the upper surface of the glass substrate is covered with a mask made of a substance that has a permeation blocking effect on diffused ions, and a portion of the mask is removed in accordance with the planar pattern of the light guide path to form an opening.

Next, this mask surface is brought into contact with a molten salt containing ions that greatly contribute to increasing the refractive index of the glass, such as thallium (Tl) ions, and an electric field is applied using the mask surface as a positive electrode to move the ions in the salt onto the mask of the substrate glass. When it is diffused into areas where it is not present, a high refractive index area with a substantially semicircular cross section is formed, with a distribution in which the refractive index is maximum at the mask opening and gradually decreases toward the inside of the substrate.

Next, the mask on the surface of the glass substrate is removed, and the surface of the substrate on which the high refractive index portion is formed is treated with nitrates or sulfates containing ions such as sodium ions and potassium ions, which have a relatively small contribution to increasing the refractive index of the substrate glass. When the ions are brought into contact with the substrate and a DC voltage is applied in the same manner as above to diffuse the ions into the substrate, a substantially circular light guide path is formed in a cross section perpendicular to the substrate surface.

FIG. 5 shows an embodiment of the present invention.

In this example, in order to save the effort of processing the ends of the main fiber connected to the access coupler into slopes, the vicinity of the ends of the input path 11A and the output path 11B of the main optical path are formed as curved paths with a gentle radius R of the substrate. It has a structure in which the optical axes at the ends of both optical paths 11A and 11B are perpendicular to the side surface 10B, and the rest is the same as that in FIG. 3.

In addition, instead of making the entrance path 11A and the exit path 11B curved paths near the ends, the entrance path 11A and the exit path 11B are made straight paths as shown in FIG. Both optical paths 11A, 1
A similar effect can be obtained by forming a slope perpendicular to the optical axis of 1B.

As described above in the embodiments, the present invention provides a continuous main optical path 11 formed in a transparent substrate, which is approximately V-shaped in plan view and has a higher refractive index than the substrate, and is formed in the V-shaped bottom portion 13 and Both ends 15 and 16 are exposed on the side surfaces of the substrate facing each other, and an input branch light guide path 12 that branches from the output path of the main optical path and reaches the side surface of the substrate is connected to the main optical path at the V
The main optical path is provided in such a way that it is a straight path that intersects at an acute angle toward the bottom, and its axis is perpendicular to the side edge of the substrate, and the axis of the optical path is also perpendicular to the side surface of the substrate at the input and output ends of the main optical path. By cutting the side surface of the board at an angle or by providing a curved path part in the middle of each V-shaped side of the main optical path, the optical path is made parallel to the side edge of the board near the input/output end, and the light transmitted through the main optical path is made parallel to the side edge of the board. This is an optical waveguide type access coupler in which a part of the light is outputted through a filter film 14 provided in contact with the V-shaped bottom part 13 of the main optical path, and the remaining part of the light is reflected by the filter film. By simply selecting the transmittance of the membrane 14, the main signal can be branched and outputted with high precision at a large branching ratio of, for example, 5:1 or more, while keeping the diameter of the light guide path uniform throughout the coupler.

In this way, it is possible to make the diameter of the light guide path in the access coupler the same throughout the entire access coupler.As mentioned above, it is possible to make the diameter of the light guide path the same throughout the access coupler. When fabricating by applying a mask with patterned openings and diffusing a monomer that forms a polymer with a high refractive index through the openings, or by CVD
This is especially important when manufacturing using the PCVD method.

In other words, if the width of the mask aperture is unequal, the depth of diffusion and penetration of diffused ions, resin monomers, or particles,
Alternatively, variations may occur in the deposition thickness, resulting in distortion of the cross-sectional shape of the light guide, resulting in a large loss of transmitted light.However, according to the present invention, the above-mentioned problems can be avoided.

Furthermore, branched output light can always be obtained at a constant branching ratio regardless of the alignment between the light guide and the input fiber.

Furthermore, since the axes of all input and output ends of the light guide path that are integrally formed in the board are perpendicular to the side edge of the board, it is necessary to cut the fiber ends diagonally when connecting optical fibers to them. This makes the fiber end less likely to be damaged during the connection process, making the connection process very easy. Furthermore, since the connection interface between the waveguide end face and the fiber end face is perpendicular to the optical axis of the transmitted light, connection loss due to reflection at the interface can be suppressed to a lower level than when the connection interface is a slope.

The access coupler according to the present invention is also useful as a single mode access coupler by selecting the shape and refractive index of the main optical path 11 and the input branch optical guide path 12 so as to propagate only a single mode.

[Brief explanation of drawings]

1 and 2 are plan views showing a conventional access coupler, FIG. 3 is a plan view showing a reference example of a flat type access coupler, and FIG. 4 is a plan view of a conventional access coupler.
5 is a plan view showing an embodiment of the present invention, and FIG. 6 is a plan view showing still another embodiment of the present invention. 10... Transparent substrate, 11... Main optical path, 11A
...Input path, 11B...Output path, 12...Branch light guide for input, 13...V-shaped bottom, 14...Filter film.

Claims (1)

[Claims] 1. A continuous main optical path is provided in a transparent substrate, which is approximately V-shaped in plan view and is composed of a region having a higher refractive index than the substrate, with the bottom and both ends of the V-shape exposed on the opposing side surfaces of the substrate. In addition, among the main optical paths, an input branch light guide branching from the output path and extending to the side surface of the substrate is a straight path so as to intersect with the main optical path at an acute angle toward the bottom of the V-shape, and has an axis at the side edge of the substrate. are provided perpendicularly to each other, and at the input and output ends of the main optical path, so that the axis of the optical path is perpendicular to the side surface of the board, the side surface of the board at this portion is obliquely cut, or the main optical path is provided at the center of each V-shaped side. By providing a curved path portion, the optical path is made parallel to the side edge of the substrate near the input/output end, and a part of the light transmitted through the main optical path is outputted through a filter film provided in contact with the V-shaped bottom of the main optical path, An optical waveguide type access coupler in which the remaining light is reflected by the filter film.