JPH04263526A - Optical receiver - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a circuit connected to a following step and to prolong the service life of a photodetector by suppressing the amplification factor of the photodetector and the gain of a variable gain amplifier when an inputted optical signal is lower than a reference value set in advance. CONSTITUTION:A beam splitter 102 branches the optical signal inputted from an optical cable 101 into first and second optical signals and outputs those signals. A photodetector 104 converts the first optical signal to an electric signal and outputs it. A variable gain amplifier 106 outputs the electric signal at a fixed level. An optical power detector 111 lowers the outputs of the photodetector 104 and the variable gain amplifier 106 when the second optical signal is lower than the reference value set in advance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver, and more particularly to an optical receiver used in an optical communication device.

0002

2. Description of the Related Art Generally, an optical receiver, as shown in FIG.
It has a conversion section 301 that converts an optical signal into an electrical signal, an equalization amplification section 302, an identification section 303, and a timing extraction amplification section 304.

The equalizing amplifier of a conventional optical receiver includes a light receiving element (APD element) 202 that receives an optical signal, as shown in FIG.
A preamplifier 203, a variable gain amplifier 204, a peak detector 205 that detects the equalized output amplitude, two feedback amplifiers 206 and 207, and a multiplication factor controller 208 that controls the multiplication factor of the light receiving element. has been done. The received optical signal is converted into an electrical signal by a light receiving element 202, amplified by a preamplifier 203, and further amplified by a variable gain amplifier 204 to obtain an electrical signal large enough to be processed. Also, the amplitude of the output signal is determined by the peak detector 20.
5 becomes a DC voltage, which is amplified by feedback amplifiers 206 and 207, and by controlling the gain of variable gain amplifier 204 and the multiplication factor of light receiving element 202 with its output, the output signal amplitude of equalizing amplifier 302 is kept constant. There is. Therefore, when the input power of the optical signal is relatively high, the light receiving element 20
2 and the gain of the variable gain amplifier 204. Conversely, when the power is weak, both the multiplication factor and the gain of the amplifier are increased, so that the input power of the optical signal fluctuates within a predetermined range. It is possible to output an electrical signal of constant amplitude even if the

0004

In this conventional equalizing amplifier for an optical receiver, when the input signal decreases, the multiplication factor of the light receiving element and the gain of the variable gain amplifier increase in order to obtain a signal output with a predetermined amplitude. When the input of the optical signal is cut off, the multiplication factor and gain become maximum. When the multiplication factor reaches its maximum value, due to the characteristics of the photodetector, an excessive current may flow and destroy the photodetector, and a high level of noise is emitted, which is amplified by the maximum gain amplifier in the subsequent stage. There is a problem in that the timing extraction section causes the identification section to malfunction.

[0005]

[Means for Solving the Problems] The optical receiver of the present invention includes an optical splitter that branches and outputs an input optical signal into first and second optical signals, and converts the first optical signal into an electrical signal. a light-receiving element that outputs the second optical signal; a variable gain amplifier that outputs the electric signal at a constant level; and a variable gain amplifier that outputs the electric signal when the second optical signal becomes lower than a preset reference value; and a photopower detector that reduces the output.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention.

[0007] Optical branching device 102 branches and outputs the optical signal from optical cable 101 to optical cables 103 and 112. The optical power detector 111 outputs a control signal a when the level of the optical signal from the optical cable 112 becomes lower than a preset reference value. The light receiving element 104 converts the optical signal from the optical cable 103 into an electrical signal and outputs it.

The variable gain amplifier 106 has a light receiving element 104.
The electric signal input from the preamplifier 105 is adjusted to a constant level and output. Peak detector 107 and feedback amplifier 108 control the gain of variable gain amplifier 106. The feedback amplifier 109 and the multiplication factor controller 110 are
The optical-to-electrical conversion gain of the light receiving element 104 is controlled. When the control signal a is output from the optical power detector 111, the multiplication factor of the light receiving element 104 and the gain of the variable gain amplifier 106 are suppressed via the feedback amplifiers 108 and 109.

[0009] In this way, the optical branching device 102 and the optical power detector 111 are added, and when the input level of the optical signal is higher than a preset value, normal operation is performed, and when it is lower, 2 By forcibly lowering the output voltages of the two feedback amplifiers 108 and 109 and suppressing both the gain of the variable gain amplifier 106 and the multiplication factor of the light receiving element 104, it is possible to prevent noise from being output at an excessive level.

0010

As explained above, the present invention suppresses the multiplication factor of the light receiving element and the gain of the variable gain amplifier when the input optical signal becomes lower than a preset reference value. It is possible to prevent malfunctions of circuits caused by

Furthermore, since an excessive voltage is not applied, the life of the light receiving element can be extended.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of an example of an optical receiver.

FIG. 3 is a block diagram showing an example of an equalizing amplifier of a conventional optical receiver.

[Explanation of symbols]

101, 103, 112 Optical cable 102
Optical splitter 104 Light receiving element 105 Preamplifier 106 Variable gain amplifier 107 Peak detectors 108, 109 Feedback amplifier 110 Multiplication factor controller 111 Optical power detector

Claims (1)

[Claims] 1. An optical splitter that branches and outputs an input optical signal into a first and a second optical signal; a light receiving element that converts the first optical signal into an electrical signal and outputs the electrical signal; and an optical power detector that reduces the output of the light receiving element and the variable gain amplifier when the second optical signal becomes lower than a preset reference value. An optical receiver comprising: