JPS6236929A - Optical communication light receiving circuit - Google Patents

Abstract

PURPOSE:To simplify the transmission system and to obtain an inexpensive optical communication system with high reliability by inputting a part of a reception light at the reception side in optical communication to a semiconductor laser and obtaining a local oscillation light so as to obtain a beat. CONSTITUTION:A part of an optical signal sent from a transmitter through an optical fiber 11 is inputted to a distributed feedback type laser diode 13 via a beam splitter 12 and a condenser lens. An output of the diode 13 enters a beam splitter 14, a part of the light is inputted to a photodiode 15 and its electric output is given to a temperature adjusting device 16. An output of the temperature adjusting device 16 is fed back to the local oscillation diode 13 and an output current of the diode 15 applies temperature control in interlocking with the temperature adjusting device 16 to maximize the local oscillation light. Further, most output of the beam splitter 14 is inputted to a mixer 18 via a reflection mirror 17 and a signal is obtained via a photodetector 19 and a demodulator 20. Thus, no local oscillation line is required by providing the local oscillating device at the reception side.

Description

[Detailed Description of the Invention] [Summary] The present invention is a semiconductor light receiving circuit for coherent optical communication, which is a semiconductor light receiving circuit for use in coherent optical communication. However, in the present invention, a simple optical communication system is realized by inputting a part of the received light into a semiconductor laser to obtain local light and obtain a beat.

[Industrial Field of Application] The present invention relates to a semiconductor light-receiving circuit, and particularly to a method for generating local light in a light-receiving circuit.

In recent years, coherent optical communication systems have rapidly come into use in optical communications due to the development of optical devices and optical fibers.

Conventionally, optical transmission methods have been based on pulse code conversion (PCM), which transmits signals by turning on/off the laser light of an optical circuit.
) method, but in the PCM method, the laser output is about 5 to 20 mW, and the maximum transmission distance is 1100 K to transmit 400 Mbit, and the transmission distance is 1100 K to transmit 1.6 Gbit. Since the limit is 30 km, a coherent communication system is required to transmit 10 gigabit over a long distance of 400 km, for example.

Normally, in the receiving circuit of coherent optical communication, the S/N is large.
In addition to the heterogain method, the homodyne method can further improve the S/H.

However, in the homodyne type receiving circuit of coherent optical communication, it is difficult to generate stable local light, so conventionally the local light is transmitted separately from the transmitting side to the receiving side, and the receiving side transmits it. Since the method of detecting waves by using the same method is adopted, the line cost is high, and improvements are desired.

[Prior Art] FIG. 2 is a schematic circuit block diagram of the main parts of a conventional optical transmission system.

On the transmitting side, there is a laser light emitting device 1, and the laser light emitted from this device is input to a beam splinter 2 as shown by the arrow, where it is split into carrier light and local light.

The carrier light is modulated by a modulator 4 modulated by a signal from a signal device 3 and transmitted to the receiving side via an optical fiber 5. Similarly, the local light is also transmitted to the receiving side via an optical fiber 6.

On the receiving side, the carrier light and the local light transmitted through the optical fiber are input to the mixer 7, and the generated beat signal is detected by the detection device 8 and the signal is extracted.

Conventional optical transmission circuits have the disadvantage that local light needs to be separately transmitted from the transmitting side to the receiving side through an optical fiber, which makes the installation of the optical fiber expensive.

[Problems to be solved by the invention] In conventional optical communication light receiving circuits, in order to perform homodyne detection, it is necessary to transmit local light from the transmitting side to the receiving side through separate fibers, making the system complicated. Therefore, there is a problem that the line cost becomes expensive.

[Means for Solving the Problems] The present invention provides a semiconductor light-receiving circuit for solving the above-mentioned problems. When detecting on the receiving side, a part of the received light is input into a laser diode, and the temperature of the laser diode is changed and adjusted to tune the optical wavelength of the input light and the oscillation wavelength. The system generates light and detects and reproduces the signal by taking the beat between the local light and the signal light.

[Function] The present invention is a light receiving circuit for coherent communication. In order to obtain stable local light, the present invention utilizes the fact that the emission wavelength of a laser diode changes depending on temperature changes. Input a part of the emitted light into a laser diode with a stable oscillation wavelength, tune it to the frequency of the optical signal, generate stable local light on the receiving side, and keep the beat between the signal light and the local light. This problem was solved by performing homodyne detection.

Detection of the optimum state of tuning can be performed by detecting the maximum light from a local light laser diode using a photodiode.

[Embodiment] FIG. 1 is a block diagram of a schematic main circuit of an optical communication light receiving circuit of the present invention.

An optical signal (
(shown by a dotted line in the figure) is incident on the beam splitter 12, and at this part, the input optical output of about 175 is inputted to the laser diode 13 via a condensing lens. is 0.51, the optical input to the local laser diode 13 is 0.11.

The types of laser diodes are distributed feedback lasers (DF
BLD) is best used and has the best frequency stability.

In particular, when the optical signal is amplitude shift keyed (ASK), frequency locking is sufficiently possible because the carrier frequency component is large.

The output from the laser diode 13 enters a beam splint 14, where some of the light is input as a photodiode 15, for example a germanium photodiode.
Its electrical output is connected to a temperature regulating device 16.

The output of the temperature adjustment device 16 is the local laser diode 13.
However, so that the photodiode 15 always obtains the maximum amount of light received, the output current of the photodiode 15 is temperature controlled in conjunction with the temperature control device 16, and the local light is maximized. The temperature control device is operating as follows.

Most of the output of the beam splitter 14 is input to a mixer 18 via a reflecting mirror 17, and a signal is obtained via a photoreceiver 19 and a demodulator 20.

By providing a local oscillation device independently on the receiving side of the optical communication system in this way, the transmission system becomes extremely simple as no local oscillator line is required.

[Effects of the Invention] As explained above in detail, by providing a local oscillator in the receiving circuit in optical communication according to the present invention, the transmission method is simplified and becomes less expensive, and a highly reliable device is provided. This is a great benefit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of the optical communication receiving circuit of the present invention, and FIG. 2 is a block diagram of the main parts of the circuit of the conventional optical communication method. In the figure, 11 is an optical fiber, 12 is a beam splitter 13
14 is a laser diode, 14 is a beam splint 15 is a photodiode, 16 is a temperature adjustment device, 17 is a reflecting mirror,
18 is a mixer, 19 is a light receiver,
Reference numeral 20 indicates a demodulator. In the unlikely event that an invention occurs within the scope of the invention,
Figure I11

Claims (1)

[Claims] When detecting modulated light optically modulated by a receiving device in a coherent optical communication system, a part of the received modulated light is transmitted to a laser diode (13).
The output of the laser diode is input to the photodiode (15).
and a temperature control device (16) to tune the oscillation wavelength of the laser diode (13) to the carrier wavelength of the modulated light, and then by taking the beat between the modulated light and the local light. An optical communication light receiving circuit characterized in that it detects and reproduces modulated light.