JPH09312615A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical receiver by which an automatic gain adjustment function at a receiver side is realized in order to compensate a difference from a transmission loss in the case of different optical fiber transmission line length or output fluctuation at a transmitter side even in an optical fiber transmission system for analog communication where a transmission signal level is not certain. SOLUTION: This optical receiver detects a DC current flowing through a photoelectric conversion element 1, a pilot signal generator 3 generates a pilot signal having a level proportional to the level of the DC current, the pilot signal is superimposed on a reception signal detected by the photoelectric conversion element 1 and the resulting signal is inputted to a variable gain amplifier 4. A pilot signal level detector 5 separates a pilot signal component from the output of the variable gain amplifier 4 and a controller 6 controls a gain of the variable gain amplifier 4 so that the level of the pilot signal component is made constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, for transmitting an arbitrary modulation signal in CATV, mobile communication, radar, satellite communication, etc., intensity-modulates laser light with the modulation signal, and modulates the laser light. The present invention relates to an optical receiver in an optical fiber transmission system that transmits an optical fiber over a predetermined distance and converts the transmitted laser light into an original electric signal.

[0002]

Optical fiber transmission systems are widely used as a means of digital communication in the field of data transmission. On the other hand, with recent improvements in the performance of semiconductor lasers and photodiodes, CATV, mobile communications, radar,
The application of the optical fiber transmission system is spreading as a means of high quality analog communication for transmitting an arbitrary modulated signal in satellite communication.

[0003]

In the optical fiber transmission system of this type, in order to compensate for the difference in transmission loss when the optical fiber transmission path lengths are different, output fluctuations on the transmission side, etc. It is necessary to have an automatic gain adjustment function.

As a means for achieving this, conventionally, in an optical fiber transmission system for digital communication, a received signal is input to a variable gain amplifier and the gain of the variable gain amplifier is controlled so that its output level becomes constant. In general, feedback control is performed. This presupposes that the level of the transmission signal is constant in digital communication.

On the other hand, in an optical fiber transmission system for analog communication for transmitting an arbitrary modulated signal, the level of transmission vibration is not constant unlike digital communication. It is obvious that the signal level fluctuates when the transmission signal is an amplitude modulation signal. Further, even in the case of frequency-modulated signals, when handling frequency-multiplexed signals, the amplitude ratio of each carrier is not always constant, so the average signal level also fluctuates.

An object of the present invention is to compensate for a difference in transmission loss when the optical fiber transmission path length is different, an output fluctuation on the transmitting side, and the like even in an optical fiber transmission system for analog communication in which the transmission signal level is not constant. Therefore, it is an object of the present invention to provide an optical receiver capable of realizing an automatic gain adjustment function on the receiving side.

[0007]

According to the present invention, a direct current flowing through a photoelectric conversion element is detected, a pilot signal having an amplitude proportional to its level is generated, and a received signal detected by the photoelectric conversion element is generated. An optical device characterized in that a pilot signal is superimposed and input to a variable gain amplifier, a pilot signal component is separated from the output of the variable gain amplifier, and the gain of the variable gain amplifier is controlled so that the level becomes constant. A receiver is obtained.

Further, according to the present invention, a photoelectric conversion element, a DC level detector for extracting a DC component and a gradually varying component from the output of the photoelectric conversion element, a predetermined frequency, and an amplitude of the DC A pilot signal generator for generating a pilot signal proportional to the output of the level detector; a variable gain amplifier; a pilot signal level detector for extracting the pilot signal from the output of the variable gain amplifier to detect its amplitude; A controller for adjusting the gain of the variable gain amplifier, superimposing the output of the pilot signal generator on the output of the photoelectric conversion element and inputting it to the variable gain amplifier, and the output of the pilot signal level detector is predetermined. An optical receiving device is obtained in which the gain of the variable gain amplifier is adjusted so as to match the reference level of.

According to the present invention, the pilot signal level detector further comprises a bandpass filter for extracting a pilot signal from the output of the variable gain amplifier, a rectifying circuit for rectifying the pilot signal extracted by the bandpass filter, The optical receiving device is provided, which is provided with a smoothing circuit that smoothes an output of the rectifier circuit.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An optical receiver according to an embodiment of the present invention will be described below.

First, in a transmitter of an optical fiber transmission system for analog communication, it is general that a constant direct current is passed through a light emitting element and a transmission signal is superposed on it.

In the optical receiver according to the present embodiment, a direct current flowing through the light receiving element (photoelectric conversion element) is detected and a pilot signal having an amplitude proportional to its level is generated. The pilot signal is superimposed on the received signal detected by the photoelectric conversion element and input to the variable gain amplifier, the pilot signal component is separated from the output, and the gain of the variable gain amplifier is controlled so that the level becomes constant.

FIG. 1 is a block diagram showing the configuration of an optical receiver according to an embodiment of the present invention.

In FIG. 1, the present optical receiver comprises a photoelectric conversion element 1, a DC level detector 2, a pilot signal generator 3, a variable gain amplifier 4, a pilot signal level detector 5, and a controller 6. And have.

The photoelectric conversion element 1 is composed of a PIN photodiode, an avalanche photodiode, or the like.

The DC level detector 2 is for extracting a DC component and a component that fluctuates gently from the output of the photoelectric conversion element 1, and is composed of, for example, a low pass filter.

The pilot signal generator 3 has a predetermined frequency and generates a pilot signal whose amplitude is proportional to the output of the DC level detector 2. For example, a DC signal having a predetermined frequency is detected by the DC level detector. This is a configuration for multiplying two outputs.

The pilot signal level detector 5 extracts a pilot signal from the output of the variable gain amplifier 4 and detects its amplitude, and is equipped with, for example, a bandpass filter.

The controller 6 adjusts the gain of the variable gain amplifier 4.

In the present apparatus, the output of the pilot signal generator 3 is superimposed on the output of the photoelectric conversion element 1 and input to the variable gain amplifier 4, and the controller 6 controls the output of the pilot signal level detector 5 to a predetermined value. The gain of the variable gain amplifier 4 is adjusted so as to match the reference level (set and stored in the controller 6).

The pilot signal level detector 5 includes, for example, in addition to the bandpass filter, a rectifier circuit that rectifies the pilot signal component extracted by the bandpass filter and a smoothing circuit that smoothes the output. .

[0022]

The optical receiving apparatus according to the present invention detects a direct current flowing through a photoelectric conversion element, generates a pilot signal having an amplitude proportional to the level, and outputs a pilot signal to the reception signal detected by the photoelectric conversion element. For superimposing and inputting to the variable gain amplifier, separating the pilot signal component from the output of the variable gain amplifier, and controlling the gain of the variable gain amplifier so that the level becomes constant, for analog communication where the transmission signal level is not constant In the above optical fiber transmission system as well, the automatic gain adjustment function on the receiving side can be realized in order to compensate for the difference in transmission loss when the optical fiber transmission path length is different, output fluctuation on the transmitting side, and the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical receiving device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Photoelectric conversion element 2 DC level detector 3 Pilot signal generator 4 Variable gain amplifier 5 Pilot signal level detector 6 Controller

Claims (3)

[Claims] 1. A variable gain amplifier which detects a direct current flowing through a photoelectric conversion element, generates a pilot signal having an amplitude proportional to its level, and superimposes the pilot signal on a reception signal detected by the photoelectric conversion element. An optical receiving apparatus, characterized by inputting, separating a pilot signal component from an output of the variable gain amplifier, and controlling a gain of the variable gain amplifier so that a level thereof becomes constant. 2. A photoelectric conversion element, a DC level detector for extracting a DC component and a component that changes gently from the output of the photoelectric conversion element, a predetermined frequency, and an amplitude of the output of the DC level detector. , A variable gain amplifier, a pilot signal level detector for extracting a pilot signal from the output of the variable gain amplifier and detecting its amplitude, and a gain of the variable gain amplifier. And a controller for adjusting the output of the pilot signal generator is superimposed on the output of the photoelectric conversion element and input to the variable gain amplifier, and the output of the pilot signal level detector matches a predetermined reference level. The optical receiving device is characterized in that the gain of the variable gain amplifier is adjusted so that 3. The pilot signal level detector comprises a bandpass filter for extracting a pilot signal from an output of a variable gain amplifier, a rectifier circuit for rectifying the pilot signal extracted by the bandpass filter, and an output of the rectifier circuit. The optical receiver according to claim 2, further comprising a smoothing circuit that smoothes