JPH1184153A - Optical waveguide functional element - Google Patents

Abstract

(57) [Problem] To provide an optical waveguide functional element which can reduce the influence of a manufacturing process error and can be easily manufactured. SOLUTION: An input optical waveguide (25), a branch portion for splitting light from the input optical waveguide, a plurality of optical waveguides (27) for propagating respective lights split by the split portion, and a plurality of optical waveguides In the optical waveguide functional element including the multiplexing unit that multiplexes the light from the multiplexing unit and the output optical waveguide (28) that propagates the light from the multiplexing unit, the multimode interference coupler (26 ) Is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide functional device, and more particularly to a technology effective when applied to an optical waveguide functional device used for optical communication, optical switching, optical information processing and the like.

[0002]

2. Description of the Related Art Conventionally, in an optical waveguide functional element (hereinafter simply referred to as an optical waveguide functional element) for once branching light, passing through a plurality of optical waveguides, and then multiplexing the light, the light is split into a plurality of optical waveguides. The Y branch circuit shown in FIG. 9 or the directional coupler shown in FIG. 10 is used as a branching unit for branching into a plurality of optical waveguides or a combining unit for combining light from a plurality of optical waveguides. 9 and 10, reference numerals 1 and 2 indicate optical waveguides.

[0003]

However, if the dimensions of the Y-branch circuit or the directional coupler deviate from the design values due to a process error in manufacturing the optical waveguides (1, 2), the light is equally divided. There were problems such as non-distribution and large loss. Further, in the Y branch circuit, the demultiplexed mode is unstable, and when the demultiplexed light is multiplexed again, there is a problem that a higher-order mode is lost.

For this reason, an optical waveguide functional element using a Y-branch circuit or a directional coupler in the branching and multiplexing sections has disadvantages such as an increase in circuit loss and an unstable function. There has been a problem in improving the performance and stabilizing the optical waveguide function element.

In a conventional directional coupler, an optical waveguide having a ridge structure shown in FIG. 11 is used. This is because the mode coupling of light between two optical waveguides is required when splitting or combining light, and a high-mesa type optical waveguide in which the mode coupling of light between the two optical waveguides is weak. This was because it could not be realized in the wave path. In FIG. 11, reference numerals 3 and 5 denote optical waveguide cladding layers, and reference numeral 4 denotes an optical waveguide core layer.

However, in the optical waveguide having the ridge type structure, since etching for forming the optical waveguide must be stopped before the optical waveguide core layer 4, a high-precision control requiring precise control in the depth direction is required. Etching technology was required, and fabrication was difficult. Furthermore, the ridge-type optical waveguide requires a high-precision etching technique that requires precise controllability in the depth direction for insulation between the light-receiving elements even when the light-receiving elements are monolithically integrated into the optical waveguide. It was difficult to manufacture as required.

In the prior art, when coupling light from a plurality of optical waveguides to one optical waveguide, a plurality of optical multiplexing circuits (15a to 15g) are used as shown in FIG. Therefore, there was a problem that the loss increased. In FIG. 12, reference numerals 16a to 16o denote optical waveguides.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to reduce the influence of manufacturing process errors in an optical waveguide functional device and to easily manufacture the device. It is to provide a technology that makes it possible.

Another object of the present invention is to provide an optical waveguide functional device which can reduce light loss when light from a plurality of optical waveguides is coupled to one optical waveguide. Is to provide.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0011]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

[0012] An input optical waveguide, a branching portion for branching light from the input optical waveguide, a plurality of optical waveguides for propagating each of the light branched by the branching portion, and a light from the plurality of optical waveguides. In an optical waveguide functional element including a multiplexing unit that multiplexes and an output optical waveguide that propagates light from the multiplexing unit, a multimode interference coupler is used for the branching unit and the multiplexing unit. .

[0013] At least a part of the optical waveguide is constituted by an optical waveguide having a high mesa structure.

That is, according to the present invention, there is provided an optical waveguide function element for once splitting light, passing the light through a plurality of optical waveguides, and then multiplexing the light again.
Alternatively, a main feature is that a multi-mode interference type coupler is used in a multiplexing unit that multiplexes light from a plurality of optical waveguides, and at least a part of the optical waveguide is formed of an optical waveguide having a high-mesa structure.

Thus, it is possible to realize a stable branching ratio and low-loss light multiplexing / demultiplexing irrespective of manufacturing process errors. Further, by using a high mesa structure optical waveguide, Becomes easier.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments, parts having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

[First Embodiment] FIG. 1 is a top view schematically showing a schematic configuration of an optical waveguide functional element according to a first embodiment of the present invention. The optical waveguide function element of the present embodiment has a branching portion that splits the light from the input optical waveguide 25 into two optical waveguides 27 and combines the light from the two optical waveguides 27 into two outputs. This is a Mach-Zehnder type optical interferometer using a multi-mode interference type coupler 26 in a multiplexing unit for outputting to an optical waveguide 28.

FIG. 2 is a graph showing the relationship between the length of the interference area of the multi-mode interference coupler 26 and the distribution ratio of the optical power. In the graph shown in FIG. 2, the horizontal axis represents the length of the multimode interference coupler in the light propagation direction, and the vertical axis represents the output light intensity.
This figure shows the relationship between the light intensity distributed to the output optical waveguide 1 and the output optical waveguide 2 when light is incident from one input optical waveguide 1 in a two-input multi-mode interference coupler.

FIG. 2 shows that the length of the interference area is about 19
An enlarged view around 5 μm is also shown. In the enlarged view, reference numeral 21 denotes output light power from the output optical waveguide 1, and reference numeral 22 denotes output light power from the output optical waveguide 2.

As is apparent from FIG. 2, when the length of the interference region of the multimode interference type coupler 26 is about 195 μm, the light is split into two by the output optical waveguide 1 and the output optical waveguide 2. Further, even when there is an error of ± 1 μm in the length of the interference region of the multi-mode interference type coupler 26, the light loss in the output optical waveguide 1 and the output optical waveguide 2 is 0.1 dB or less. Furthermore, the length of the interference area is
Even if it is shifted from the optimal length, the length of the interference area
In the case of 185 μm to 200 μm, the distribution ratio of the divided light is constant at 1: 1.

Therefore, the multi-mode interference type coupler 2
By using 6 for the light branching and multiplexing parts, high-performance multiplexing / demultiplexing of light can be easily achieved. Thus, in the present embodiment, stable operation and a high extinction ratio can be realized without being affected by manufacturing process errors.
A low-loss, high-performance Mach-Zehnder optical interferometer can be realized.

[Embodiment 2] FIG. 3 is a top view showing a schematic configuration of an optical waveguide functional element according to Embodiment 2 of the present invention. The optical waveguide functional device of the present embodiment is configured to convert the light from the input optical waveguide 25 into two asymmetric optical waveguides (30, 3).
1) and two asymmetric optical waveguides (3
0, 31) to form two output optical waveguides 28.
And a temperature-independent wavelength filter using a multi-mode interference type coupler 26 in a multiplexing unit that outputs a signal. The two asymmetric optical waveguides (30, 31) differ from each other in the composition and length of the optical waveguide material.

In this temperature independent wavelength filter, when the temperature changes, the refractive index of the asymmetric optical waveguide (30, 31) changes, and the phase of the propagating light changes. However, 2
The relationship between the difference in refractive index change and the difference in length of the asymmetric optical waveguides (30, 31) is such that the phase relationship does not change when two lights are multiplexed at the multiplexing unit. , The phase relationship of the transmitted light passing through the temperature-independent wavelength filter is constant without depending on the temperature.

Also in this embodiment, since the multimode interference type coupler 26 is used for the light branching and multiplexing parts, low power and uniform distribution of optical power can be achieved, and the power is affected by the manufacturing process error. Without this, a stable operation and a high extinction ratio can be realized, and a low-loss and high-performance temperature-independent wavelength filter can be realized.

[Embodiment 3] FIG. 4 is a top view schematically showing the configuration of an optical waveguide functional element according to Embodiment 3 of the present invention. The optical waveguide functional device according to the third embodiment is the same as the output optical waveguide 2 of the temperature-independent wavelength filter according to the second embodiment.
8 is a temperature-independent wavelength filter in which the light receiving element 32 is integrated.

FIG. 5 is a graph showing the output signal of the light receiving element 32 according to the third embodiment as a function with respect to the wavelength. As can be seen from FIG. 5, the optical power output from the temperature-independent wavelength filter according to the present embodiment is incident on the two light receiving elements 32 with phases opposite to each other with respect to the wavelength. Have been.

At this time, if the characteristics of the two light receiving elements 32 vary, accurate differential detection becomes difficult. However, in the present embodiment, the light coupling with the optical waveguide is achieved by monolithically integrating the light receiving elements 32. Is omitted, and a temperature-independent wavelength filter having uniform performance can be realized without the optical characteristics after branching being affected by the mounting accuracy.

Fourth Embodiment FIG. 6 is a diagram showing a schematic configuration of an optical waveguide function element according to a fourth embodiment of the present invention.
2A is a schematic top view, and FIG. 2B is a cross-sectional view showing a cross section taken along a broken line A and B shown in FIG. The optical waveguide function element according to the fourth embodiment of the present invention is a temperature-independent wavelength filter using a high-mesa type optical waveguide as the optical waveguide. In FIG. 6B, 40 is p-
Type semiconductor optical waveguide cladding layer, 41 is an optical waveguide core layer,
42 is an n- type semiconductor optical waveguide cladding layer, 43 is a p- type semiconductor optical waveguide cladding layer, and 44 is a light absorbing layer.

The light receiving element 32 of the present embodiment is constituted by a light receiving element having a layered structure in which a light absorbing layer 44 is laminated on the optical waveguide core layer 41.

It has been impossible to realize a directional coupler with an optical waveguide having a high mesa structure because of the weak interaction between the optical waveguides. By using 26, an optical waveguide having a high mesa structure can be used as the optical waveguide.

In an optical waveguide having a high-mesa structure, the etching for forming the optical waveguide can be performed to the lower portion of the optical waveguide layer. Therefore, the etching for forming the optical waveguide requires precise controllability in the depth direction. No high-precision etching technology is required. Therefore, it is easy to manufacture the temperature-independent wavelength filter, and it is easy to electrically insulate the plurality of light receiving elements 32 when the light receiving elements 32 are integrated.

FIG. 7 is a cross-sectional view showing a cross section of an optical waveguide section and a light receiving element section when a ridge type optical waveguide is used in the temperature independent wavelength filter according to the embodiment of the present invention.

In the temperature independent wavelength filter of the present embodiment, when an optical waveguide having a ridge structure is used,
In order to electrically insulate the plurality of light receiving elements 32 from each other, it is necessary to completely separate the light absorbing layers 44 of the plurality of light receiving elements 32, and the surface of the optical waveguide core layer 41 cannot be exposed. It is necessary to stop the etching for forming the optical waveguide in the middle of the light absorbing layer 44 and the optical waveguide core layer 41. For this reason, a high-precision etching technique that requires precise controllability in the depth direction is required for etching for forming an optical waveguide, and it is difficult to manufacture the optical waveguide.

As described above, in the present embodiment, the manufacturing process is simplified and the light-receiving element 3 having good performance is compared with the case where an optical waveguide having a ridge structure is used as the optical waveguide.
2 can be realized as a temperature-independent wavelength filter.

[Fifth Embodiment] FIG. 8 is a top view showing a schematic configuration of an optical waveguide functional device according to a fifth embodiment of the present invention. The optical waveguide function element according to the fifth embodiment is a temperature-independent wavelength filter using a multi-input two-output multi-mode interference coupler 46 at a light branching portion.

The multi-input two-output multi-mode interference type coupler 46 is, for example, an LBSoldano et al., J. Lightwave Te.
chnol., vol. 13, (4), pp. 615-627, 1995. This multi-input two-output multi-mode interference type coupler 46 has
Light from a plurality of input optical waveguides 45 can be split by one interferometer, and the light can be split stably with low loss.

Accordingly, the temperature-independent wavelength filter of the present embodiment has a lower loss and a lower loss than the case where a number of conventional optical multiplexing circuits (15a to 15g) shown in FIG.
In addition, a high-performance temperature-independent wavelength filter can be realized.

As described above, the invention made by the present inventor is:
Although a specific description has been given based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the invention.

[0040]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the present invention, since a multi-mode interference coupler is used for the light branching and multiplexing parts, low loss and uniform distribution of optical power can be achieved. As a result, a low-loss, high-performance optical waveguide functional element can be realized without being affected by the manufacturing process error.

(2) According to the present invention, as an optical waveguide,
Since an optical waveguide having a high-mesa structure can be used, a high-precision etching technique that requires precise controllability in the depth direction is not required for the etching for forming the optical waveguide. , Can be easily created.

(3) According to the present invention, a multi-mode interference type coupler having a plurality of input ports is used as a light branching unit. It is possible to realize a low-loss, high-performance optical waveguide functional element.

[Brief description of the drawings]

FIG. 1 is a top view showing a schematic configuration of an optical waveguide functional element according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the length of an interference region and the distribution ratio of optical power in a two-input two-output multimode interference coupler.

FIG. 3 is a top view showing a schematic configuration of an optical waveguide functional element according to a second embodiment of the present invention.

FIG. 4 is a schematic top view showing a schematic configuration of an optical waveguide functional element according to Embodiment 3 of the present invention.

FIG. 5 is a graph showing output signals of two light receiving elements integrated in the optical waveguide function element according to the third embodiment as a function with respect to wavelength.

FIG. 6 is a schematic top view showing a schematic configuration of an optical waveguide functional element according to a fourth embodiment of the present invention, and a cross-sectional view showing a cross section taken along a broken line A or B.

FIG. 7 is a cross-sectional view showing a cross section of an optical waveguide section and a light receiving element section when an optical waveguide having a ridge structure is used in the optical waveguide functional element according to the fourth embodiment of the present invention.

FIG. 8 is a top view showing a schematic configuration of an optical waveguide functional element according to a fifth embodiment of the present invention.

FIG. 9 is a top view showing a schematic configuration of a branch circuit used for multiplexing / demultiplexing light.

FIG. 10 is a top view schematically showing a schematic configuration of a directional coupler used for multiplexing / demultiplexing light.

FIG. 11 is a cross-sectional view showing a cross section of an optical waveguide having a ridge structure used in a directional coupler.

FIG. 12 is a schematic top view showing a schematic configuration of a light multiplexing unit that couples light from a plurality of optical waveguides to one optical waveguide using a plurality of optical multiplexing circuits.

[Explanation of symbols]

1, 2, 16a to 16o, 27, 30, 31: optical waveguide, 3, 5: optical waveguide clad layer, 4, 41: optical waveguide core layer, 15a to 15g: optical multiplexing circuit, 25, 45: input optical waveguide 26, a multimode interference type coupler, 28, an output optical waveguide, 32, a light receiving element, 40, 43, a p- type semiconductor optical waveguide cladding layer, 42, an n- type semiconductor optical waveguide cladding layer, 44, a light absorbing layer, 46 ... Multi-input 2-output multi-mode interference coupler.

Claims (5)

[Claims] 1. An input optical waveguide, a branch portion for splitting light from the input optical waveguide, a plurality of optical waveguides for propagating each light branched by the split portion, and a plurality of optical waveguides from the plurality of optical waveguides. In an optical waveguide functional element including a multiplexing unit that multiplexes light and an output optical waveguide that propagates light from the multiplexing unit, a multimode interference coupler is used for the branching unit and the multiplexing unit. An optical waveguide functional element. 2. The optical waveguide functional element according to claim 1, wherein the plurality of optical waveguides are different from each other in at least one of an optical waveguide length and a composition. 3. The optical waveguide functional device according to claim 1, wherein at least a part of the optical waveguide is formed of a high-mesa type optical waveguide. 4. The optical waveguide functional element according to claim 1, comprising a plurality of input optical waveguides or a plurality of output optical waveguides. 5. The optical waveguide functional device according to claim 1, wherein the output optical waveguide has a light receiving element integrated in a part thereof.