JPH0591201A - Optical relay transmitter - Google Patents

Abstract

PURPOSE:To prevent an avalanche photodiode from generating intermittent noise because the operation of the avalanche photodiode enters an unstable region when an optical input to the avalanche photodiode is low. CONSTITUTION:The transmitter is provided with an automatic gain control amplifier 13 operated when a level of an optical signal is a prescribed level or over to keep the amplitude of an output characteristic of a mark signal in the signal presence state constant through the reception of an optical signal and with a avalanche photodiode 41 to change a multiple factor when the level of the optical signal is a prescribed level or below. An optical input of white noise inputted to one of the avalanche photodiode whose level is lower than the level of the optical signal is generated by a light emitting diode 42 and fed to the other terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal, which is a transmission medium, which is affected by noise and distortion in addition to being attenuated during transmission, and is reproduced in a transmission line in order to reproduce the same signal as a transmission signal without distortion. The present invention relates to an optical repeater transmission device arranged at fixed intervals. Particularly, it is an object of the present invention to prevent the avalanche photodiode from generating intermittent noise when it enters an unstable region when the light input to the avalanche photodiode becomes low.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a conventional optical repeater transmission apparatus. The optical repeater transmission apparatus shown in this figure uses a 3R system and amplifies and shapes the received waveform that is distorted and distorted to form an equalized waveform with a good signal-to-noise ratio (S / N). And a timing reproducing section 2 for reproducing phase information from a received signal in order to transmit a transmission pulse at correct time intervals,
An identification / reproduction unit 3 for identifying binary information from the equalized waveform from the equalization amplification unit 1 and reproducing a pulse corresponding to the binary information.

The equalizing and amplifying section 1 receives an optical signal Pin consisting of a mark signal in a signal state and a space signal in a non-signal state, and an avalanche photodiode (APD) 11
And a preamplifier (PREAMP) 12 of the APD 11
And an automatic gain control amplifier (AGCAMP) 13 which operates automatically to keep the amplitude of the output characteristic of the signal essentially constant irrespective of the change in its characteristic at the input from the signal of the PREAMP 12. , The AG
A distributor (DIS) 14 that distributes the output signal of the CAMP 13 according to a plurality of purposes, and a DC feedback unit that detects a DC component from a space signal from the DIS 14 and feeds it back to the PREAMP 12 to remove an offset ( DCFB) 15 and an automatic gain control feedback unit (AGCF) for detecting the peak level of the space signal from the DIS 14 and forming a feedback signal.
B) 16, a switch 17 that supplies the output level to the AGCAMP 13 as an electric AGCFB signal as shown in the figure when the output level of the AGCFB 16 is higher than the reference voltage Vref1, and the switch 17
When the output level of B16 is lower than the reference voltage Vref1, the output level is supplied as an optical AGCFB signal as shown in the figure and a DC / DC converter (D) for supplying a bias voltage to the APD 11 to change the multiplication factor is supplied. / D c
18).

Although some of the light receiving elements use ordinary photodiodes, the present invention is premised on the APD having a photoelectric multiplication function. The timing reproducing unit 2 is, for example, S
A clock extraction circuit 21 configured by an AW filter for nonlinearly extracting a clock signal from the output signal from the DIS 14, and an output blocking signal when the output signal of the clock extraction circuit 21 is smaller than a reference voltage Vref2. And an input disconnection detection unit 22 for transmitting

The identification reproduction section 3 compares the output signal from the DIS 14 with a reference voltage Vref3 to determine whether the level is 1 or 0, the output signal of the comparator 31 and the clock. The flip-flop 32 that reproduces a signal according to the reproduction clock signal of the extraction circuit 21 and the output signal of the reference flip-flop 32 are input to the input disconnection detection unit 2
It includes a comparator 33 for blocking by the output signal of 2, a laser diode driving device 34 connected to the output of the comparator 33, and a laser diode 35 for sending an optical output Po by the laser diode driving device 34.

Next, the operation will be described. When the APD 11 receives a normal light input, the DCFB 15 and the A
After the GCFB 16 operates normally and the clock is extracted, the clock is regenerated, converted to electrical / optical, and the optical output is transmitted. Figure 4
FIG. 4 is a diagram illustrating a control operation of the equalization amplification unit in FIG. 3. As shown in the figure, during normal optical input reception, at a high optical input level, the amplification factor (M) of the APD 11 is fixed to 1 or 2, and a constant output amplitude is maintained by changing the gain of the AGCAMP 13. At a low level of optical input, the gain of the AGCAMP 13 is maximized and the amplification factor of the APD 11 is made variable to maintain a constant output amplitude. When the light input further decreases, the APD 11 enters an unstable region as shown in the figure, and the APD 11 emits intermittent noise, so that the control operation becomes unstable. Conventionally, in order to prevent this unstable operation, when the clock component falls below a certain threshold level, the input disconnection detection unit 2
2 to disconnect the signal and output the optical output signal when there is no signal
There was a function to do F.

[0007]

However, in the conventional optical repeater transmission apparatus, it becomes difficult to detect the clock component as the transmission speed of the main signal increases, that is, as the frequency becomes higher, and the input break detection unit 22 itself becomes unstable. Further, since the output of the optical repeater transmission device becomes unstable via the comparator 33, the number of systems having a circuit configuration in which the input disconnection detection unit 22 is deleted is increasing. However, in this configuration, noise is relayed even when there is no input. When the optical input becomes low, the APD
There is a problem in that it is impossible to prevent the noise from being generated intermittently by 11.

Therefore, in view of the above problems, the present invention provides an optical repeater transmission device for preventing an unstable operation of the equalization amplification section and ensuring stability against an increase in transmission speed when the optical input is low. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for controlling the level of an optical signal in order to keep the amplitude of the output characteristic of a mark signal in a signal state by receiving an optical signal. In an optical repeater transmission device having an automatic gain control amplifier that operates when the optical signal level is above a predetermined level and an avalanche photodiode that changes the multiplication factor when the level of the optical signal is below a predetermined level, the optical signal input to one of the avalanche photodiodes. An optical input with white noise lower than the level of is supplied to the other.

[0010]

According to the optical repeater transmitter of the present invention, the level of the optical signal is lowered by adding the optical input of white noise lower than the level of the optical signal input to one of the avalanche photodiodes to the other and supplying it. However, it is possible to prevent the control operation from becoming unstable because the avalanche photodiode emits intermittent noise when it enters the unstable region of the avalanche photodiode. Further, the input disconnection detecting section is not required, and the stability can be secured against the increase of the transmission rate.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an equalizing / amplifying unit in an optical repeater transmission apparatus according to an embodiment of the present invention. In this figure, FIG.
The difference from the configuration of the equalizing / amplifying unit is the APD4 for two inputs
1 and a light emitting diode 4 for supplying a constant low noise optical signal to the other input with respect to the optical input Pin of the APD 41.
2 and a power supply 4 for driving the light emitting diode 42
It is 3.

FIG. 2 is a diagram for explaining the operation of the light receiving element according to this embodiment. As shown in this figure, the light emitting diode 4
2, the white noise component Pin2 is always input to the APD 41. The input signal component Pin1 to the APD 41 is reduced to a level (12 to 15) sufficiently lower than the minimum light receiving level Pmin at which the APD 41 generates intermittent noise.
Since white noise of about dB) can be input from the light emitting diode 42, it is possible to prevent the occurrence of intermittent noise because the white noise does not enter the unstable operation range. Therefore, the input break detection unit 22 shown in FIG. 3 is not required, and the stability of the output of the optical repeater transmission apparatus can be secured even when the transmission speed increases.

[0013]

As described above, according to the present invention, A
Since white noise of a sufficiently low level is input to one optical input of the PD from the other, it is possible to prevent intermittent noise from occurring due to unstable operation even when the optical input level to the APD becomes low. The equalizing and amplifying unit can be operated stably.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an equalization amplification unit in an optical repeater transmission apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the light receiving element according to the present embodiment.

FIG. 3 is a diagram showing a conventional optical repeater transmission device.

FIG. 4 is a diagram illustrating a control operation of the equalization amplification unit in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Equalization amplification part 2 ... Timing reproduction part 3 ... Identification reproduction part 11, 41 ... APD 42 ... Light emitting diode 43 ... Supply power supply 12 ... Preamplifier 13 ... Automatic gain control amplifier 14 ... Distributor 15 ... DC feedback part 16 ... Automatic gain control feedback unit 17 ... Switch 18 ... DC / DC converter

Claims (1)

[Claims] 1. An automatic gain control amplifier which operates when a level of an optical signal is equal to or higher than a predetermined level in order to keep an amplitude of an output characteristic of a mark signal in a signal state by receiving the optical signal, and an optical gain control amplifier for the optical signal. In an optical repeater transmission device having an avalanche photodiode that changes the multiplication factor when the level is below a predetermined level, an optical input of white noise lower than the level of the optical signal input to one of the avalanche photodiodes is added to the other to supply. An optical repeater transmission device characterized by: