JPH0591054A - Optical circuit - Google Patents

Abstract

PURPOSE:To obtain the optical circuit in which a duplex optical communication use optical transmitter-receiver is realized with completely stable operation. CONSTITUTION:Two optical guide lines 2b, 2d are formed with a semiconductor light source 4 inbetween and the semiconductor light source 4 and the two optical guide lines 2b, 2d are connected optically. Moreover, a photodetector 5a is installed to an end face 8 of the end faces of the light source side optical guide path 2d not optically in connection to the semiconductor light source 4 to monitor an optical output of the semiconductor light source 4. Since the deterioration in the semiconductor light source itself being a cause of the fluctuation in the transmission level or a change in the optical coupling efficiency due to a secular optical axis deviation between the semiconductor light source and the optical guide path are simultaneously measured the transmission level is always kept constant.

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 micro-optics 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 in the article of Henry et al. Eye Triple Lightwave Technology 1530-
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 bidirectional optical communication, the semiconductor light source and the semiconductor photodetector are formed on the same substrate as described above. At this time, the fluctuation of the transmission level occurs due to the deterioration of the semiconductor light source itself or the change of the optical coupling efficiency due to the shift of the optical axis of the semiconductor light source and the optical waveguide over time. There is no structure that constantly obtains a constant transmission level by controlling the injection current to the semiconductor light source of the optical output power of
There is a drawback that stable operation cannot be obtained.

An object of the present invention is to provide an optical circuit for realizing an optical transceiver for bidirectional optical communication, which can obtain a completely stable operation.

[0007]

The optical circuit according to the present invention comprises:
An optical waveguide having a function of splitting / multiplexing light is formed on a substrate, and a semiconductor light source and a first semiconductor photodetector are first and second optical waveguides close to each other among the optical waveguides. In the optical circuit that is installed on the substrate near each end face and is optically connected to the first and second optical waveguides, two optical waveguides are formed with the semiconductor light source interposed therebetween. One of these two optical waveguides is the first optical waveguide, and a second semiconductor photodetector is provided on an end face of the other optical waveguide of the optical waveguides. And

[0008]

When 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 is used, an optical circuit for realizing an optical transceiver for bidirectional optical communication in which completely stable operation can be obtained. Is obtained. That is, in the present invention, unlike the conventional structure, two optical waveguides are formed so as to sandwich the semiconductor light source, and semiconductor optical detection for monitoring the transmission level on the end face of one of the two optical waveguides. Equipped with a vessel. Therefore, it is possible to simultaneously measure the deterioration amount of the semiconductor light source itself, which is a factor that changes the transmission level, or the change amount of the optical coupling efficiency due to the time-dependent shift of the optical axis of the semiconductor light source and the optical waveguide. By controlling the injection current to the semiconductor light source by using the output of the semiconductor photodetector, the transmission level can be always maintained at a constant value. That is, it is possible to obtain an optical circuit that realizes an optical transceiver for bidirectional optical communication that can obtain a completely stable operation.

[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
The optical waveguide 2 is formed by b, 2c and 2d. If the optical power branching or optical wavelength demultiplexing function optical circuit 7 is, for example, an optical power branching function optical circuit, a Y branching optical circuit or a directional coupler is used for the circuit 7. If the optical power branching or optical wavelength demultiplexing function optical circuit 7 is, for example, an optical wavelength demultiplexing function optical circuit, a directional coupler, a branching interferometer or the like is used for the circuit 7. The optical fiber 3, the semiconductor light source 4, and the semiconductor photodetector 5 are optically connected to the optical waveguide 2, and the optical waveguide 2, the semiconductor light source 4, and the semiconductor photodetectors 5 and 5a are integrated on the substrate 1. Has been done. In FIG. 1, an optical waveguide 2c is optically coupled to the semiconductor photodetector 5,
Two optical waveguides 2b and 2d (hereinafter referred to as light source side optical waveguides) are formed so as to sandwich the semiconductor light source 4, and the semiconductor light source 4 and the two light source side optical waveguides 2b and 2d are optically connected. There is. Further, a photodetector for monitoring the optical output of the semiconductor light source 4 is provided on the end face 8 of one of the light source side optical waveguides 2d which is not optically connected to the semiconductor light source 4 (hereinafter referred to as the monitor optical waveguide end face). 5a (hereinafter referred to as a monitor photodetector) is installed. At this time, since the two light source side optical waveguides 2b and 2d are normally formed at the same time by using a lithography process, the optical axes are exactly the same, and the optical axes of the light emitting end faces on both sides of the semiconductor light source 4 are also natural. Since they are the same, the optical connection structure of the semiconductor light source 4 and the two light source side optical waveguides 2b and 2d are exactly the same. Therefore, the deterioration amount of the output level of the semiconductor light source 4 itself, which is a factor of the variation of the transmission level, or the change amount of the optical coupling efficiency due to the time-dependent shift of the optical axes of the semiconductor light source 4 and the optical waveguide 2b, is simultaneously monitored. Since it can be measured by the detector 5a, by controlling the injection current to the semiconductor light source 4 by using the output of the monitoring photodetector 5a, the transmission level can always be maintained at a constant value.

When the semiconductor light source 4 is optically coupled to the optical waveguide 2b, the monitor photodetector 5a previously installed on the optical circuit and the light source side optical waveguide 2d optically connected thereto. Since it can be performed using an optical system, the productivity is significantly improved compared to the conventional structure in which each semiconductor optical element must be installed while being individually measured.

FIG. 2 is a plan view showing the structure of another embodiment of the optical circuit according to the present invention. In FIG. 2, the end face 8 of the monitor optical waveguide is optically connected to the monitor photodetector 5a after being inclined by 45 degrees with respect to the optical axis. The effect is the same as in FIG. 1, but the optical axis incident on the monitor photodetector 5a is
Since it is not parallel to the optical axis of the semiconductor light source 4 or the optical waveguide 2,
When the semiconductor light source 4 is optically coupled to the optical waveguide 2b, reflected light or leakage light generated as coupling loss and leakage light from the optical waveguide 2 that appears as propagation loss are incident on the monitor photodetector 5a in a small amount. Become. Therefore, more accurate transmission level monitoring is possible. In the structure shown in FIG. 2, the monitor optical waveguide end face 8 may be tilted any number of times, or the optical axis may be changed by using a curved optical waveguide or the like.

Obviously, the materials of the substrate 1 and the optical waveguide 2 are not limited. The waveguides 2b and 2c in FIGS. 1 and 2 correspond to the above-described first and second optical waveguides, respectively, and the semiconductor photodetectors 5 and 5a correspond to the above-described first and second semiconductor photodetectors, respectively. To do.

[0013]

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, an optical transceiver for bidirectional optical communication can be realized in which a completely stable operation can be obtained. An optical circuit is obtained. That is, in the present invention, unlike the conventional structure, a semiconductor photodetector in which two optical waveguides are formed so as to sandwich a semiconductor light source, and a transmission level is monitored at an end face of one of the two optical waveguides. It has. Therefore, it is possible to simultaneously measure the deterioration amount of the semiconductor light source itself, which is a factor that changes the transmission level, or the change amount of the optical coupling efficiency due to the time lag of the optical axis of the semiconductor light source and the optical waveguide. By controlling the injection current to the semiconductor light source by using the output of the semiconductor photodetector, the transmission level can be always maintained at a constant value. That is, it is possible to obtain an optical circuit that realizes an optical transceiver for bidirectional optical communication that can obtain a completely stable operation. Further, when the semiconductor light source is optically coupled to the optical waveguide, it can be performed by using the monitor semiconductor photodetector previously installed on the optical circuit and the optical system of the optical waveguide optically connected thereto. Therefore, the productivity is significantly improved as compared with the conventional structure in which each semiconductor optical element has to be installed while being individually measured.

[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 reference signs] 1 substrate 2, 2a optical waveguide 2b, 2d light source side optical waveguide 2c photodetector side optical waveguide 3 optical fiber 4 semiconductor light source 5 semiconductor photodetector 5a monitor photodetector 6 electronic device 7 optical power branch Or optical wavelength demultiplexing function Optical circuit 8 Optical waveguide end face for monitor

Claims (1)

[Claims] 1. An optical waveguide having a function of multiplexing / branching or multiplexing / demultiplexing light is formed on a substrate, and a semiconductor light source and a first semiconductor photodetector are provided in a first and a second of the optical waveguides which are close to each other. In an optical circuit installed on the substrate near each end face of the second optical waveguide and optically connected to the first and second optical waveguides, two semiconductor optical sources are sandwiched between the two optical circuits. An optical waveguide is formed and these 2
One of the two optical waveguides is the first optical waveguide, and a second semiconductor photodetector is provided on an end face of the other optical waveguide of the two optical waveguides. And optical circuit.