JPH02271727A - Optical transmission/reception level adjusting circuit - Google Patents

Abstract

PURPOSE:To suppress a maximum value of an optical input level to a light receiving element and to attain stable operation for a reception electric circuit by inserting an optical attenuation element whose attenuation is variable between an optical signal input output terminal and a light receiving element and light emitting element. CONSTITUTION:An optical signal inputted from an optical signal input terminal A is reproduced into an electric signal and outputted from an electric signal output terminal B. On the other hand, a peak value of an electric signal amplified by an equalizing amplifier 14 is detected in an AGC circuit 16 and a control signal proportional to the quantity of the input level is sent to an optical attenuation control circuit 17. The circuit 17 generates a control voltage in a direction to increase the optical attenuation of an optical attenuation element 11 when the input level is larger than the specified value to control the element 11. On the other hand, in the case of the signal transmission direction (from a terminal C to a terminal D), the optical attenuation of an optical attenuation element 23 is varied by a control voltage outputted from the circuit 17. When the distance up to an opposite station is short, the light receiving level of the opposite station is suppressed below the specified value by reducing the optical output level at an optical signal output terminal D automatically.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic adjustment circuit for advance/reception levels in an optical communication system, and in particular, a circuit for automatically adjusting excessive light reception levels and excessive optical output levels during short distance transmission. The present invention relates to a circuit configuration that is adjusted manually.

[Conventional technology]

Conventionally, this type of optical level adjustment circuit has been used to control the gain of an electrical circuit after optical-to-electrical conversion, since the received light level on the receiving side varies greatly depending on the transmission distance.
The output level of the optical receiver circuit is kept constant by controlling the bias voltage of the light receiving element.

[Problem to be solved by the invention]

In the conventional optical level adjustment circuit described above, when the transmission distance is short and the received light level is large, the optical power input to the photodetector becomes excessive, and it is necessary to design the input dynamic range of the downstream amplifier to be sufficiently large. It is difficult to ensure stable characteristics over a wide range of light reception levels because the photocurrent generated in the light receiving element is excessive and may cause deterioration of the characteristics of the light receiving element. There is a drawback.

[Means to solve the problem]

The optical transmission/reception level adjustment circuit of the present invention includes an optical attenuation element whose optical attenuation can be varied by an external control voltage between the optical signal input terminal and the light receiving element, and between the semiconductor laser and the optical output signal terminal. By inserting a similar optical attenuation element, when the optical reception level to the optical signal input terminal is large during short distance transmission, the optical attenuation amount of the optical attenuation element is increased and the optical input level to the light receiving element is increased. Adjust appropriately and attenuate the optical output level of the optical signal output terminal for transmission in the reverse direction.
This circuit appropriately adjusts the optical reception level at the other end.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

The optical signal input from the optical signal input terminal A is transmitted to the optical attenuation element 1.
1, is converted into an electrical signal by the light receiving element 12,
Next, the preamplifier 13. After being amplified to a predetermined level by the equalizing amplifier 14, the output electric signal is regenerated by the discrimination regenerator 15 and output from the electric signal output terminal B. On the other hand, the electric signal amplified by the equalization amplifier 14 is
The peak value is detected in the circuit 16, and a control signal proportional to the magnitude of the optical signal input level is transmitted to the optical attenuation amount control circuit 17. The control circuit 17 controls the optical attenuation element 11 by generating a control voltage that increases the amount of optical attenuation of the optical attenuation element 11 when the optical signal input level is higher than a specified value. On the other hand, for transmission in the reverse direction, the electrical signal input from the electrical signal input terminal C is applied to the semiconductor laser 22 via the semiconductor laser drive circuit 21, converted into an optical signal, and then It passes through the attenuation element 23 and is sent out to the optical signal output terminal. Here, the amount of optical attenuation of the optical attenuation element 23 is varied by the control voltage output from the optical attenuation amount control circuit 17, and when the distance to the opposite station is short, the optical attenuation element 23 automatically outputs the signal from the optical signal output terminal. By reducing the light output level,
The light reception level at the opposing station can be suppressed to a specified value or less.

〔Effect of the invention〕

As explained above, by inserting an optical attenuation element that can adjust the light level between the optical signal maximum/output terminal and the light receiving element 2 and the light emitting element, the present invention can be used even when the transmission distance is short. Since the optical input level to the light receiving element on the station side does not become excessive and can be suppressed to a relatively narrow input dynamic range, stable operation of the receiving electric circuit can be expected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. 11... Attenuation variable type optical attenuation element, 12...
. . . Photodetector, 13 . . . Preamplifier, 14.
... Equalization amplifier, 15 ... Discrimination regenerator,
16... AGC circuit, 17... Optical attenuation control circuit, 21... Semiconductor laser drive circuit,
22...Semiconductor laser, 23...Variable attenuation type optical attenuation element, A...Optical signal input terminal,
B: Electric signal output terminal, C: Electric signal input terminal, D: Optical signal output terminal. Agent Patent Attorney Susumu Nai

Claims (1)

[Claims] In optical communication systems, forward transmission/reception level adjustment circuits are equipped with optical signal input/output terminals and optical reception An optical transmission/reception level adjustment circuit characterized by suppressing the maximum value of the optical input level to a light receiving element by inserting an optical attenuation element capable of varying the amount of attenuation between the light emitting element and the light emitting element.