JPS59131903A - Light guide type access coupler - Google Patents

Abstract

PURPOSE:To set a branch output ratio to a desired value with high precision and to reduce branch part loss by forming a V-shaped pattern in a transparent substrate and providing a main light guide path which has a larger refractive index than the substrate, and leading out branch paths from the V-shaped bottom part through a filter and from the middle of a projection path. CONSTITUTION:A light guide path which is circularly sectiolned has such a refraction index distribution that the refractive index is maximum at the center part and decreases parabolically toward the outer circumference in a section perpendicular to an optical axis. The light transmittivity of a filter film 14 is so selected that outputs are at the desired branch ratio on the condition of an angle theta1. A light signal transmitted by an optical fiber 20A is transmitted through an incidence path 11A, transmitted partially through the filter film 14 at the V-shaped bottom part 13, and transmitted to a terminal equipment, etc., through an optical fiber 20C. The remaining transmitted light reflected by the filter film 14 passes through a projection path 11B and is transmitted to a trunk line fiber 20B. A signal which is processed again by the terminal equipment and transmitted through an optical fiber 20d is incident to a branch light guide path 12 and mixed with the trunk-line signal in the projection path 11B.

Description

[Detailed description of the invention] In an optical fiber communication system, an element called a coupler is an important element that 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. It is.

Conventionally, access couplers have been constructed by combining focusing lenses, prisms, mirrors, etc., or by processing the optical fiber itself. This type of device was complicated to manufacture and had reliability problems.

Therefore, an access coupler has been proposed in which an optical waveguide is formed in a transparent substrate such as glass or plastic, and its branches are merged, but the insertion loss at the branching and merging sections is large, and the connection with the optical fiber 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 can be easily connected to optical fibers.

Methods for forming optical waveguides in glass substrates include ion exchange method, ion diffusion method using electric field, and optical method.
There are CVD methods, POVD methods, etc. that are used for manufacturing eyeglasses, and when using a plastic substrate, there are photopolymerization methods, diffusion methods, etc., and the present invention is not limited to either method.

(,2) Form a leading wavepath in a flat substrate and form a branch circuit at the output end/
It is possible to change the ratio of the light outputs of and -, ie po, 2/po/. For example, if - is set to 10 or less, it becomes pop/pO/middle/, that is, it becomes a one-branch circuit. However, since the number of branches used in the access coupler increases, the insertion loss (po/+p0.2)/pi increases, which is not practical.

Therefore, as shown in FIG. 2, methods that have been proposed in the past include reducing the insertion loss by reducing the branch angle and changing the guide width. For example, with respect to the guide width WO on the input side, the output end guide width W1+W2 is made smaller than W(, and Wl>W2, thereby reducing the output ratio po2/po/.4 However, this method In particular, in multimode fiber systems, the branch output ratio po, 2/po/ can vary greatly even if the connection position of the optical fiber connected to the input (3) end is slightly different.
It was difficult to set j/po/ to a desired value.

The purpose of the present invention is to solve the above-mentioned conventional problems, and to be able to set the branch output ratio from the main line to a desired value with high precision.
Moreover, it is an object of the present invention to provide a novel optical waveguide type access coupler with less loss at the branching portion.

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

FIG. 3 is a plan view of the access coupler according to the present invention, in which a transparent substrate IO made of glass or synthetic resin,
A light guide path having a substantially circular cross section and consisting of a region having a refractive index lower than that of the substrate is provided.

The light guide path includes a main optical path l/ which is approximately V-shaped in plan view, and an incident path //A that constitutes the main optical path l/.

The output path //B branches from the output path //B to the substrate 10
It is equipped with a branch light guide path for input that reaches the side of the

(4()) The above-mentioned light guide path has, for example, a refractive index distribution such that the refractive index is maximum at the center within a cross section perpendicular to the optical axis, and the refractive index decreases unevenly toward the outer periphery.

Further, its diameter is approximately the same as the core diameter of the optical fiber group 201.20B, 20G, and Od connected to this access coupler, and the diameter is approximately the same throughout the entire optical path.

Further, the V-shaped bottom 13 of the main optical path l/ is connected to the side surface 10 of the substrate 10.
It is exposed at point A, and the shape of this exposed portion is also circular, approximately matching the core diameter of the optical fiber 20G connected to this portion.

Input path 1/A and exit path //B that constitute the main optical path //
The angle θ1 formed with the normal line of the substrate side surface 10IL is the same, and the bottom of the v-shape where both optical paths //A and //B intersect is /.
A dielectric filter film /V is provided on the side surface of the substrate 3, which transmits a part of the light transmitted through the input path //A and reflects the remaining part.

The angle θ1 is set to a value sufficiently smaller than the critical angle of total reflection of the filter film /9.

The input branch light guide path /C is arranged so that it merges with the output path //B of the main optical path in the middle, and its axis is at an acute angle θ2 toward the bottom of the V-shape /3 at the merging point with respect to the axis of the output path //B. It is set up so as to accomplish the following.

, If this angle θ2 is too large, confluence loss will occur, so it is generally less than II0, preferably ! It is better to set it to 0 or less. By setting θ2 within this range, the confluence loss can be made so small that it can be ignored.

The light transmittance of the filter film /+ used in the present invention is the incident path //
Under the condition of the angle θ1 formed by the optical axis of A, the transmittance is generally selected to be 20% to 5% so that the output optical power has a desired branching ratio.

Instead of being formed on the substrate side surface IOA, the filter film III can also be provided on the end surface side of the optical fiber 200 connected here.

The trunk optical fiber JOA is connected to the end lj (side surface 10B of the board) of the input path //A of the access coupler described above, and the end lb of the output path //H exposed on the same side surface 10B of the board is connected to the main optical fiber JOA. is connected to another trunk optical fiber 20B.

Further, a branch light guide path 12 is provided on the opposite side surface IOA of the substrate.
For example, an optical fiber 20 (l) for transmitting optical signal information reprocessed by a terminal is connected to the end 17 of the terminal.

As a result, the optical signal information transmitted to the optical fiber 20 is transmitted through the input path //A of the access coupler, and a part of it is transmitted through the filter film IQ at the V-shaped bottom 13.
The data is transmitted to a terminal device etc. through the 20G optical fiber connected here.

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

The remaining transmitted light reflected by the filter film /& passes through the output path //B in the access coupler and is transmitted to the main fiber 20B connected to the end /B.

In addition, the data signal that has been reprocessed by the terminal and transmitted through the optical fiber 20C1 enters the branch light guide saw in the access coupler, passes through this optical path 12, and becomes the main signal transmitted through the output path //B. join together.

For example, in the access coupler of the present invention, the upper surface of a glass substrate is first covered with a mask made of a substance having a transmission blocking effect, and a part of the mask is removed in accordance with the planar pattern of the light guide path to form an opening. will be established.

Next, this mask surface is brought into contact with a molten salt containing ions, such as thallium (Tl) ions, which greatly contribute to increasing the refractive index of the glass, and an electric field is applied with the mask surface as a positive electrode to direct the ions in the salt to 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 the side where the high refractive index portion is formed is treated with a nitrate or nitrate containing ions such as IJium ions and potassium ions, which have a relatively small contribution to increasing the refractive index of the substrate glass. When brought into contact with sulfate and carried out in the same manner as described above (7), a substantially circular light guide path is formed in a cross section perpendicular to the substrate surface.

Another embodiment of the present invention is shown in FIG.

In this example, the input path of the main optical path is
The vicinity of the ends of /A and output path //B are curved paths with a gentle radius of curvature R, and both optical paths //A are connected to the side surface 10B of the substrate.
, //A structure in which the optical axis at the end of B is vertical,
The rest is the same as the previous embodiment.

Also, instead of making the vicinity of the ends of the entrance path //A and the exit path //B curved paths, the entrance path //A and the exit path //B are made straight paths as shown in the figure. A similar effect can be obtained by forming the side surface of the substrate at the end as a slope perpendicular to the optical axes of the optical paths //A and //B.

As explained above in the embodiments, the present invention provides
A continuous main optical path //, which is approximately V-shaped in plan view and is composed of a region having a higher refractive index than the substrate, is connected to the V-shaped bottom portion 13 and both ends /! ; and /4 are provided exposed on the side surfaces of the opposing substrates, respectively, and an input branch light guide path /2 that branches from the output path and reaches the side surface of the substrate among the main optical paths is used as the main optical path. On the other hand, they are provided near the bottom of the V-shape so as to intersect at an acute angle, and a part of the light transmitted through the main optical path is outputted through a filter film L provided in contact with the bottom 13 of the V-shape of the main optical path; This is an optical waveguide type access coupler in which the remaining light is reflected by the filter film, and according to the present invention, the diameter of the light guide path can be maintained uniform throughout the coupler by simply selecting the transmittance of the filter film. , the trunk signal can be branched and outputted with high precision at a large branching ratio of, for example, j to 1 or more.

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. This method is manufactured 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 method.

///IX This is particularly important when manufacturing using the PCVD method.

In other words, if the width of the mask opening is unequal, there will be variations in the depth of diffusion and penetration of diffused ions, resin monomers, or particles, or in the thickness of the deposit, which will distort the cross-sectional shape of the light guide and cause a large loss of transmitted light. However, according to the present invention, the above problem 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.

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 /l and the input branch optical path 7.2 so as to propagate only a single mode.

[Brief explanation of the drawing]

Fig. 1 and Fig. 2 are plan views showing a conventional access cover; Fig. 3 is a plan view showing an embodiment of the present invention; Fig. 4 is a cross-sectional view taken along the line ■-■ in Fig. 3; FIG. 5 is a plan view (/l) showing another embodiment of the invention, and FIG. 6 is a plan view showing still another embodiment of the invention. IO・・・・・・・Transparent substrate //・・・・・・・・・・
Leading optical path //A...Incidence path //B...
・・・・・・Output path/K・・・・・・Input branch light guide path/3・・・・・・V-shaped bottom lII・・・・
...Filter membrane (/ko) Figure 1 ＼ Figure 2 Figure 3 is also the 4th prisoner

Claims (1)

[Claims] l) In a transparent substrate, a continuous main optical path formed in a substantially V-shape in plan view and consisting of a region having a higher refractive index than the substrate is exposed at the bottom and both ends of the V-shape on the opposing side surfaces of the substrate. Further, an input branch light guide branching from the output path of the main light path and extending to the side surface of the substrate is provided so as to intersect with the main light path at an acute angle toward the bottom of the V-shape, so that the main light path is used for transmission. An optical waveguide type access coupler in which a part of the light is output through a filter film provided in contact with the V-shaped bottom of the main optical path, and the remaining light is reflected by the filter film.