JPH10177117A - Light combiner and transmitter for optical communications - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light combiner including an input waveguide having a structure capable of easing the positioning precision of a semiconductor laser or the like. SOLUTION: The light combiner consists of a clad 2 laminated on a substrate 3, an input waveguide core 11, a slab waveguide core 12, and an output waveguide core 13. The cross section of the core 11 on the end part of the input waveguide opposed to a semiconductor laser or the like is set up to a large area, the diameter of the core 11 is narrowed in accordance with separation from the end part and the core diameter is finally narrowed up to a single mode condition. Consequently positioning precision between the semiconductor laser or the like and the input waveguide of the light combiner can be eased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler required for an optical element used in the field of optical communication and the like, and a transmitter for optical communication including the optical coupler.

[0002]

2. Description of the Related Art Conventionally, in order to perform wavelength division multiplexing optical communication, there is a need for a technique of combining outputs of a plurality of semiconductor lasers into one and coupling them to an optical fiber. At this time, the method of causing the outputs of the plurality of semiconductor lasers to be incident on the optical fiber using the respective lenses requires the adjustment of the optical axis individually, which is complicated and lacks reliability.

Several proposals have been made to solve this drawback. U.S. Pat. No. 5,394,489 is an example (see FIG. 8). The feature of this proposal is to provide a merger using the slab waveguide CO1. Semiconductor lasers LA1 to LA having different oscillation wavelengths
Input waveguides W1 to W8 extending from the semiconductor laser array in which A8 is arrayed are connected to the slab waveguide CO1,
They merge at a relatively short distance in the slab waveguide CO1 and are output to the output waveguide OW1 on the opposite side of the input waveguide.

[0004]

However, this proposal has the following problems. Since the optical coupler requires a relatively large substrate area, it cannot be monolithically integrated with the semiconductor laser on an expensive semiconductor laser substrate from the viewpoint of cost. Further, in order to reduce the waveguide loss caused by light absorption, the same substrate cannot be used because the optical combiner must be formed with a different layer configuration from the semiconductor laser portion. However, in hybrid integration in which the merger and the semiconductor laser are manufactured on separate substrates, and then combined and mounted, high precision is required for adjusting the position of the semiconductor laser and the input waveguide of the optical merger. This has led to a drop in productivity and yield. The core size of the waveguide of the optical coupler is designed based on the refractive index difference between the core and the clad, but both the width and height are on the order of several microns, and the position adjustment accuracy of the semiconductor laser and the optical coupler is specifically, Within 1 micron was required.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the first to third aspects of the present invention is to provide an optical device having an input waveguide having a structure capable of relaxing the alignment accuracy with a semiconductor laser or the like. An object of the present invention is to provide a merger (corresponding to claims 1 to 3 of the claims). For this purpose, the core cross-sectional area at the end of the input waveguide of the optical combiner facing the semiconductor laser or the like is increased, the core diameter is reduced as the distance from the end increases, and finally the core diameter is reduced to the single mode condition. Thereby, the alignment accuracy between the semiconductor laser or the like and the input waveguide of the optical coupler is reduced. Further, since the core cross-sectional area is increased only for a short distance (for example, several tens to several hundreds of microns), the deterioration of the transmission signal waveform due to multi-mode waveguide is small. That is, the optical coupler includes a plurality of input waveguides, a single branch / merge section (for example, a slab waveguide) connected to the input waveguides, and a single or a plurality of couplers connected to the branch / merge section. The input waveguide is characterized in that the core cross-sectional area gradually and smoothly increases from a predetermined position toward the end surface from the end surface not connected to the branching / converging portion. I do.

It is another object of the fourth to sixth aspects of the present invention to provide an optimum material for an optical coupler (corresponding to the inventions according to claims 4 to 6 of the claims). For that purpose, specific examples of waveguide materials (semiconductor materials, dielectric materials,
Polyimide). This makes it possible to manufacture an optical combiner.

[0007] Further, an object of a seventh invention according to the present application is as follows.
A transmitter for wavelength multiplexing optical communication is provided (corresponding to the invention according to claim 7 of the claims). For this purpose, a plurality of semiconductor lasers (semiconductor laser element groups or semiconductor laser arrays) having different wavelengths and the optical coupler of the present invention are integrated.
As a result, a transmitter for wavelength multiplexing optical communication is obtained.

The object of an eighth invention according to the present application is as follows.
A wavelength multiplexing optical communication system is provided (corresponding to the invention according to claim 8 of the claims). For this purpose, a communication system using the transmitter for wavelength division multiplexing optical communication of the present invention, an optical fiber, a wavelength discriminator, and a photodetector is constructed. As a result, a wavelength division multiplexing optical communication system is obtained. That is, this wavelength multiplexing optical communication system uses the optical communication transmitter of the present invention on the transmission side, and outputs the output light of each laser of the optical communication transmitter.
Each laser is modulated according to each input signal by a control circuit for controlling and driving each laser, and these modulated signals are transmitted to a receiving side via an optical fiber.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a perspective view of a first embodiment of an optical coupler using an optical waveguide according to the concept of the present invention as an input waveguide. In FIG. 1, 3 is a substrate, 11 is a plurality of input waveguide cores whose cross-sectional shape is changed at least in part, 12 is a single slab waveguide core, 13 is one output waveguide core,
Reference numeral 2 denotes a clad surrounding these cores. The clad 2 is drawn transparent in FIG. 1 so that the configuration of the inner cores 11, 12, and 13 can be easily understood.

The manufacturing method of this embodiment is as follows.
First, the clad 2 is laminated on the substrate 3. Next, a material for a core having a higher refractive index than the cladding 2 is laminated, and the core material is patterned and etched to form the input waveguide core 11, the slab waveguide core 12, and the output waveguide core 13 shown in FIG. Take shape. Finally, the clad 2 is laminated thereon again so that any of the cores 11, 12, and 13 is covered with the clad 2.

A characteristic of the optical coupler shown in FIG. 1 is the shape of the input waveguide core 11. FIG. 2 is a three-view drawing showing the structure of the input waveguide portion of FIG. 2A is a top view, FIG. 2B is a side view, and FIG. 2C is a front view at a position A. As can be seen from these figures, the cross-sectional area of the core 11 near the end of the input waveguide on the side opposite to the slab waveguide side is large. The cross-sectional area of the core 11 is the largest at the input waveguide end (position A), decreases as the distance from the outer input waveguide end to the slab waveguide core 12 increases, and decreases from the middle position B. The cross-sectional area of the core 11 is constant in the direction C.

In FIGS. 1 and 2, the cross-sectional shape of the core 11 at the end of the input waveguide from the position A to the position B is horizontally long. In other words, the length may be increased in the direction of the adjustment axis with low accuracy of position adjustment (that is, difficult to perform accurate positioning). That is, FIGS. 1 and 2 show the cross-sectional shape of the core 11 used when the accuracy of the adjustment axis in the horizontal direction with respect to the surface of the substrate 3 is low.

FIG. 3 is a cross-sectional view of the core 11 used when the precision of the adjustment axis in the vertical direction with respect to the substrate surface is low (for example, when the adjustment in the horizontal direction with respect to the substrate 3 surface can be accurately performed by a guide). 3 is shown. Here, the cross-sectional shape of the core 11 at the end of the input waveguide from the position A to the position B is vertically elongated, and the degree of the vertically elongated shape is gradually reduced. For example, such a core 11 is provided on a substrate 3 having a gentle V-shaped groove as shown in FIG.
As shown in (d), when the clad 2 and the core 11 are laminated, the core 11 is laminated in a direction to reduce the step of the groove. After laminating the clad 2, the core 11, and the clad 2, patterning and etching are performed as described above,
Then, by cutting at the position indicated by the chain line in FIG.
A structure in which the length of the core 11 at the end of the input waveguide is reduced from the position B to the position B can be manufactured.

FIG. 4 shows a sectional shape of the core 11 used when the accuracy of the adjustment axis is low both in the horizontal direction and the vertical direction with respect to the surface of the substrate 3. Here, the cross-sectional shape of the core 11 at the end of the input waveguide from the position A to the position B is a rounded square, and the vertical and horizontal lengths are gradually reduced.
The fabrication of this cross-sectional shape may be performed according to a method of manufacturing a vertically long and a horizontally long cross-sectional shape.

Next, an example of manufacturing the optical coupler shown in FIG. 1 using polyimide will be described. On the substrate 3, UR5 is used as the core material.
100FX (Toray), PIX-L110 for clad 2
(Manufactured by Hitachi Chemical). The width of the core 11 from the position B to the direction C was 3 μm in order to form a single mode waveguide. The width of the core 11 at the position A is 10 μm
The distance from the position A to the position B was 40 to 60 μm, and the core width was gently changed. The height of the core 11 is constant at 3 μm throughout. These numerical values are appropriately determined in relation to the material and the purpose of use. At this time, the distance from the position A to the position B, which does not become a single mode waveguide, is as small as possible and the change angle of the core width is as shallow as possible. This is preferable for preventing power loss of guided light.

For comparison, an optical coupler having an input waveguide having a constant core diameter (3 μm) in both width and height was manufactured.
An experiment was performed in which semiconductor laser light was input to the input waveguide of the optical combiner thus manufactured, and the output from the output waveguide was measured. The semiconductor laser used in the experiment is current-controlled so that the output is constant. This is placed at the end of the input waveguide, and after adjusting the position in the vertical direction with respect to the substrate surface, the semiconductor laser is moved in the horizontal direction, and the amount of movement and the change in output from the output waveguide. Is a graph of FIG.

According to this, the output when the position adjustment is optimized is larger in the conventional optical combiner having the input waveguide having a fixed core diameter, but is smaller than the output when the position adjustment is optimized. In the present embodiment, the amount of positional deviation until the position is reduced by 3 dB is larger. This indicates that the position adjustment of this embodiment can be tolerated even if it is roughly performed.

In this embodiment, the materials of the cores 11, 12, and 13 and the cladding 2 may be InP, InGaAs, I
Numerous semiconductor materials such as nGaAsP, AlGaAs, SiO ₂ , and Si ₃ N ₄ (in this case, if other materials are also semiconductor materials, the manufacturing process can be simplified) and dielectric materials (inorganic, organic) are used It is possible. As described above, by using the optical coupler of the present embodiment, the tolerance of position adjustment when connecting optical components such as a semiconductor laser is reduced.

Second Embodiment FIG. 6 is a perspective view of an optical communication transmitter having an optical coupler according to the present invention using a characteristic optical waveguide as an input waveguide. In FIG. 6, 3 is a substrate, 11 is an input waveguide core, 12 is a slab waveguide core, 13 is an output waveguide core, 2 is a clad, and 16 is a semiconductor laser array. The clad 2 is drawn transparent so that the internal core configuration can be easily understood. Each of the semiconductor lasers constituting the semiconductor laser array 16 has a wavelength variable mechanism individually, and can oscillate at any different wavelength. The configuration may be any.

An example of the manufacturing method of this embodiment is as follows. First, the clad 2 is laminated on the substrate 3. Next, a material for a core having a higher refractive index than the cladding 2 is laminated, and a plurality of input waveguide cores 11 and one slab waveguide core 1 are stacked.
2. One output waveguide core 13 is formed by patterning and etching. Next, the clad 2 is laminated thereon again so that all the cores 11, 12, and 13 are wrapped by the clad 2. Finally, an end face is formed on the input waveguide side of the optical coupler, and the semiconductor laser array 1 formed on another substrate is formed.
6 is mounted on the optical combiner.

Another example of the manufacturing method is as follows.
The substrate 3 provided with the semiconductor laser array 16 is prepared in advance. The semiconductor laser array 16 may be monolithically made of the same material as the substrate 3 or may be mounted on the substrate 3 of a different material by soldering or the like. Here, the clad 2 is laminated. At this time, the semiconductor laser array 16 is covered with a mask. Next, a material for a core having a higher refractive index than the cladding 2 is laminated, and a plurality of input waveguide cores 1 are formed.
1, one slab waveguide core 12 and one output waveguide core 13 are formed. Finally, the clad 2 is laminated thereon again so that all the cores 11, 12, and 13 are covered with the clad 2.

The characteristic of FIG. 6 is the shape of the input waveguide. The dimension of the core 11 near the entrance of the input waveguide is large. This shape varies depending on the component form of the optical communication transmitter or the mounting form of the semiconductor laser array.
The shape may be any of the shapes described in the embodiments.

The transmitter for optical communication according to the present embodiment operates as follows. Light from each of the semiconductor lasers constituting the semiconductor laser array 16 is oscillated and modulated at an arbitrary different wavelength by the wavelength variable mechanism, and is incident from the corresponding input waveguide and guided. The light guided by the input waveguide enters the slab waveguide, merges, is guided to one output waveguide, and is output from the end face of the output waveguide. That is, it functions as an optical communication transmitter that emits a plurality of signals having different wavelengths from one output waveguide.

As described above, the optical communication transmitter according to the present embodiment is an integrated light source most suitable for wavelength division multiplexed optical communication.
By devising the shape of the input waveguide, the tolerance of the positional adjustment accuracy between the semiconductor laser and the input waveguide is relaxed.

Third Embodiment FIG. 7 is a block diagram of a wavelength division multiplexing communication system constituted by an optical communication transmitter using an optical waveguide according to the present invention. From the optical communication transmitter 17, each channel 256Mb
/ S, wavelength interval 0. The optical signal multiplexed at 1 nm passes through the optical fiber 20 and is discriminated into an optical signal for each wavelength by a wavelength discriminator 18 such as a filter.
The photodetector 19 converts the signal into an electric signal as an Mb / s signal. In this way, wavelength multiplexing optical communication becomes possible.

[0026]

As described above, according to the first to third aspects of the present invention, it is possible to obtain an optical coupler in which the positioning accuracy of a semiconductor laser or the like and the input optical waveguide of the optical coupler is reduced. . According to the fourth to sixth aspects of the present invention, it is possible to obtain an optimum material for an optical waveguide and to manufacture an optical coupler. According to the seventh aspect of the present invention, a suitable wavelength multiplexing optical communication transmitter can be obtained. Further, according to the eighth aspect of the present application, a suitable wavelength division multiplexing optical communication system can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention.

FIG. 2 is a view showing the first embodiment of the present invention as viewed from the top, side, and front.

FIG. 3 is a diagram illustrating a state of a modification of the first embodiment of the present invention viewed from the top, side, and front, and a method of manufacturing an input waveguide core.

FIG. 4 is a diagram showing a state of another modification of the first embodiment of the present invention viewed from the top, side, and front.

FIG. 5 is a graph comparing an embodiment of the present invention with a conventional example.

FIG. 6 is a perspective view of a second embodiment of the present invention.

FIG. 7 is a block diagram of a third embodiment of the present invention.

FIG. 8 is a diagram for explaining a conventional example.

[Description of Signs] 2 Cladding 3 Substrate 11 Input waveguide core 12 Slab waveguide core 13 Output waveguide core 16 Semiconductor laser array 17 Transmitter for optical communication 18 Wavelength discriminator 19 Photodetector 20 Optical fiber

Claims (8)

[Claims] A plurality of input waveguides, a single branching / junction section connected to the input waveguides, and a single or plural output waveguides connected to the branching / junction sections; The optical coupler according to claim 1, wherein the input waveguide has a core whose cross-sectional area gradually and smoothly increases from a predetermined position toward the end face from an end face that is not connected to the branching / joining part. 2. The optical coupler according to claim 1, wherein said branching / converging section is a slab waveguide. 3. The input waveguide, wherein a core cross-sectional area gradually increases from a position several tens to several hundreds microns from an end face not connected to the branching / joining portion toward the end face. The optical combiner according to claim 1 or 2, wherein: 4. The optical coupler according to claim 1, wherein the waveguide of the optical coupler is made of a semiconductor material. 5. The optical coupler according to claim 1, wherein the waveguide of the optical coupler is made of a dielectric material. 6. The optical coupler according to claim 1, wherein the waveguide of the optical coupler is made of polyimide. 7. A semiconductor laser device group or a semiconductor laser array is connected to an end face of the input waveguide of the junction device according to any one of claims 1 to 6 which is not connected to the branching / converging portion. Characteristic transmitter for optical communication. 8. An optical communication transmitter according to claim 7, wherein the output side of each laser of the optical communication transmitter is modulated by a control circuit for controlling and driving each laser in accordance with each input signal. A wavelength division multiplexing optical communication system wherein these modulated signals are transmitted to a receiving side via an optical fiber.