JPH0591049A - Optical circuit - Google Patents

Abstract

PURPOSE:To drastically improve the S/N in an output of a semiconductor photodetector receiving a signal when the optical circuit is provided to a 2-way optical communication transmitter-receiver. CONSTITUTION:A waveguide type wavelength filter 8 is installed to an optical guide path 2c connecting optically to a semiconductor detector 5. Thus, a reflection return optical wave outputted from the semiconductor light source 4 in a specific oscillation wavelength is interrupted and the quantity of the return light reaching the semiconductor photodetector 5 is much reduced in comparison with a conventional structure and the S/N of the output of the semiconductor detector 5 is drastically improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transceiver in an optical communication network, and more particularly to an optical transceiver using an optical waveguide.

[0002]

2. Description of the Related Art At the same time as the capacity of optical communication systems is increasing, the demand for multifunctional advanced systems is increasing.
There is a strong demand for cost reduction of optical fiber networks. Among them, downsizing, high integration, and cost reduction of optical devices such as optical transmitters and optical receivers are essential. Optical transmitters and optical receivers currently in practical use have a structure in which a lens is installed between a semiconductor light source or a semiconductor photodetector and an optical fiber to perform optical connection spatially. The structure for spatially optical connection using this lens is called micro-optics. The micro-optics structure is limited in the shape of the lens, the shape of the package of the semiconductor light source and the package of the semiconductor photodetector, etc., and thus there is a limit to miniaturization. Further, in order to efficiently couple the light propagating in the space to the optical fiber or the photodetector, accurate optical axis adjustment is required, and a large number of man-hours are required for the work, which does not reduce the cost. Is the current situation. It goes without saying that it is completely unsuitable for high integration of the same function or different functions.

Recently, the need for a two-way communication system has increased, and it is desired to introduce this system into homes. At this time, an optical transmitter and a receiver are required as an optical device that enables bidirectional communication. However, if they are individually configured, the optical transmitter / receiver becomes large, which hinders the spread of the system. Therefore, an optical device (optical transceiver) that integrates two functions is desired, but it is difficult to use the microoptics structure for the reasons described above. Against this background, the structure using an optical waveguide as a structure aiming at downsizing, high integration, and low cost is described by Henry et al.
Eye Triple Elite Wave Technology 1530
Pp. 1539 (1989) and the like. FIG. 3 shows a plan view of an optical circuit having a conventional structure.

In the optical circuit shown in FIG. 3, an optical waveguide 2 having a coupling / branching function is formed on a substrate 1, and the optical waveguide 2, the optical fiber 3, the semiconductor light source 4 and the semiconductor photodetector 5 for signal detection are formed.
Each a is directly optically coupled on the same substrate 1. In FIG. 3, the semiconductor photodetector 5b for monitoring the optical output of the semiconductor light source 4 is also integrated on the same substrate 1, and the optical waveguide 2
However, even if the semiconductor photodetector 5b for monitoring the optical output of the semiconductor light source 4 is not provided, there is no problem in the function of the transceiver for bidirectional optical communication. Also,
Electronic device 6 for receiving circuit of semiconductor photodetectors 5a and 5b
Are integrated on the same substrate 1, but there is no problem in the function of the transceiver for bidirectional optical communication whether this electronic device is on the same substrate 1 or not. If an optical transmitter / receiver is configured using the optical waveguide 2 shown in FIG. 3, not only downsizing but also coupling with the guided light propagating in the optical waveguide whose optical axis is fixed by the lithography process and constant is performed. Since it is good, the optical axis adjustment is simplified, and the cost can be reduced because the optical waveguide itself is mass-produced in a lithographic process.

[0005]

In this optical transceiver for two-way optical communication, when the wavelength multiplexing two-way communication system in which the wavelengths of the transmission signal and the reception signal are made different is used, as described above, the semiconductor light source and the semiconductor optical detection are used. Since the device is formed on the same substrate, the reflected return light of the light wave output from the semiconductor light source, which is a transmission signal with a wavelength different from that of the reception signal, enters the semiconductor photodetector and deteriorates the SN ratio of the photodetector. There is a drawback that makes it.

An object of the present invention is to provide an optical circuit which obtains a high SN ratio at the output of a semiconductor photodetector for signal reception.

[0007]

The optical circuit according to the present invention comprises:
An optical waveguide having a light splitting or multiplexing / demultiplexing function is formed on a substrate, and a semiconductor light source and a semiconductor photodetector are near the respective end faces of the first and second optical waveguides of the optical waveguides which are close to each other. Installed on the substrate of, and
In an optical circuit optically connected to each of the first and second optical waveguides, a waveguide type wavelength filter that blocks light having an oscillation wavelength of the semiconductor light source is installed in the second optical waveguide. It is characterized by

[0008]

By using an optical circuit in which the optical waveguide, the semiconductor light source and the semiconductor photodetector according to the present invention are integrated on the same substrate, a high SN ratio can be obtained as the output of the photodetector. That is, in the present invention, unlike the conventional structure, a wavelength of a waveguide type that cuts off the oscillation wavelength of a semiconductor light source that outputs a transmission signal to an optical waveguide (second optical waveguide) optically connected to a semiconductor photodetector. A filter is installed. Therefore, the reflected return light of the light wave output from the semiconductor light source at a specific oscillation wavelength is blocked, and the amount of return light reaching the semiconductor photodetector is greatly reduced compared to the conventional structure, and the semiconductor photodetector 5 Output SN
The ratio is greatly improved.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing the structure of an optical circuit according to an embodiment of the present invention. In FIG. 1, Si is used for the substrate 1, and the optical waveguide 2 including the optical power branching or optical wavelength demultiplexing function optical circuit 7 is made of a silica-based material. Optical waveguides 2a, 2
b and 2c are included in the optical waveguide 2. As the optical power branching or optical wavelength demultiplexing function optical circuit 7, for example, a Y branching optical circuit or a directional coupler is used in the case of an optical power branching function optical circuit, and in the case of an optical wavelength demultiplexing function optical circuit. , Directional couplers, branch interferometers, etc. are used. The optical fiber 3, the semiconductor light source 4, and the semiconductor photodetector 5 are optically connected to the optical waveguides 2a, 2b, and 2c, respectively, and the optical waveguide 2, the semiconductor light source 4, and the semiconductor photodetector 5 are on the substrate 1. Are collected in. In FIG. 1, a waveguide-type wavelength that cuts an oscillation wavelength component of a semiconductor light source 4 that outputs a transmission signal to an optical waveguide 2c optically connected to a semiconductor photodetector 5 (hereinafter referred to as a detector-side optical waveguide). A filter 8 is installed. With this structure, the optical power branching or optical wavelength demultiplexing function optical circuit 7 portion of the light wave output from the semiconductor light source 4 at a specific oscillation wavelength, the optical coupling portion between the optical waveguide 2a and the optical fiber 3, and the optical signal The reflected return light from the optical connector 9 connecting the optical fibers 3 provided in the transmission path is blocked by the waveguide type wavelength filter 8, and the amount of light reaching the semiconductor photodetector 5 is significantly larger than that of the conventional structure. As a result, the SN ratio of the output of the semiconductor photodetector 5 is significantly improved. The waveguide type wavelength filter 8 has a detector-side optical waveguide 2b.
A grating, a branch interference type filter, or the like formed above is used. FIG. 1 shows a plan view of an optical circuit using a grating as the waveguide type wavelength filter 8.
FIG. 2 shows a plan view of an optical circuit which is another embodiment of the present invention using a branch interference type filter as the waveguide type wavelength filter 8. Note that the effects in FIGS. 1 and 2 are the same,
An improvement in SN ratio of about 20 dB was obtained as compared with the conventional structure. The waveguide type wavelength filter 8 may be anything as long as it blocks the oscillation wavelength of the semiconductor light source 4, and the structure is not limited. In the case of a grating, the waveguide type wavelength filter 8 is manufactured by using a lithography process after forming the optical waveguide 2, and in the case of a branch interference type filter, it is manufactured simultaneously with the formation of the optical waveguide 2. It is obvious that the materials of the substrate 1 and the optical waveguide 2 are not limited.

[0010]

By using the optical circuit in which the optical waveguide, the semiconductor light source and the semiconductor photodetector according to the present invention are integrated on the same substrate, a high SN ratio can be obtained as the output of the photodetector. That is, in the present invention, unlike the conventional structure, a waveguide-type wavelength filter that cuts off the oscillation wavelength of the semiconductor light source that outputs a transmission signal is installed in the optical waveguide that is optically connected to the semiconductor photodetector. Therefore, the reflected return light of the light wave output from the semiconductor light source at a specific oscillation wavelength is blocked, and the amount of light reaching the semiconductor photodetector is greatly reduced compared to the conventional structure, and the SN of the output of the semiconductor photodetector 5 is reduced. The ratio is greatly improved.

[Brief description of drawings]

FIG. 1 is a plan view showing a structure of an optical circuit according to an embodiment of the present invention.

FIG. 2 is a plan view showing the structure of an optical circuit according to another embodiment of the present invention.

FIG. 3 is a plan view showing the structure of a conventional optical circuit.

[Explanation of symbols]

 1 substrate 2 optical waveguide 3 optical fiber 4 semiconductor light source 5, 5a, 5b semiconductor photodetector 6 electronic device 7 optical power branching or optical wavelength demultiplexing function optical circuit 8 waveguide type wavelength filter 9 optical connector

Claims (1)

[Claims] 1. A first optical waveguide and a second optical waveguide in which an optical waveguide having a function of multiplexing or demultiplexing light is formed on a substrate, and a semiconductor light source and a semiconductor photodetector are close to each other. Of the waveguide type for blocking the light of the oscillation wavelength of the semiconductor light source in the optical circuit installed on the substrate near the respective end faces of the optical circuit and optically connected to the first and second optical waveguides, respectively. An optical circuit in which the wavelength filter of is installed.