JPH08163029A - Optical reception circuit - Google Patents

Abstract

PURPOSE: To suppress deterioration due to distortion even in the case of an optical signal with a high input by receiving optical signals with small optical power at separate light receiving circuits simultaneously and adding outputs of all the light receiving circuits electrically. CONSTITUTION: This optical reception circuit is provided with an optical branch circuit 5 branching an optical signal received from an optical fiber 1, plural light receiving circuit, that is, two sets of light receiving elements 2 and electric amplifiers 3 converting the branched optical signals into electric signals respectively, and an adder circuit 6 adding output signals of the plural light receiving circuits. Then the optical signal received from the optical fiber 1 is branched into two at the optical branch circuit 5 and received by the two light receiving elements 2, in which the optical signal is converted into an electric signal respectively. The output of the light receiving element 2 is amplified by the electric amplifier 3 with low noise and the two electric signals are analogically summed by the adder circuit 6 and the sum signal is outputted to an output terminal 4. Thus, optical power twice in comparison with a conventional circuit when viewing from the optical fiber 1 is received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used for receiving optical signals. In particular, the present invention relates to an optical receiving circuit that can convert an optical signal of high power into an electric signal without causing distortion deterioration.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional optical receiving circuit. This optical receiving circuit includes an optical fiber 1 for inputting an optical signal, a light receiving element 2, a low noise electric amplifier 3, and an output terminal 4 of an electric signal. As the light receiving element 2, a photodiode or an avalanche photodiode is used.

In this optical receiving circuit, when a high power optical signal is input from the optical fiber 1, distortion may occur in the light receiving element 2 or the electric amplifier 3 and the electric signal may not be converted correctly. Further, in the light receiving element 2, the maximum light receiving power is limited from the viewpoint of reliability, and in the present technology, the upper limit is about 1 mW.

[0004]

SUMMARY OF THE INVENTION In an optical transmission system,
The received power value at which the optical power transmitted from the transmission side is received by the reception side greatly differs depending on the line configuration and the transmission distance. For this reason, in the case of a large input, a measure such as inserting a fixed attenuator having an appropriate value between the receiving side optical fiber and the receiving device is taken. In this case, it is necessary to measure each received light power value at the time of system construction, select a fixed attenuator with an appropriate attenuation amount and insert it, and the fixed attenuator causes a problem that the device cost increases. .

Particularly when the AM-FDM signal is transmitted by the SCM (subcarrier multiplex) transmission system, a desired CNR is obtained.
The received light power value for realizing the above is about -1 to -5 dBm,
The value is higher than that of other transmission systems. For this reason,
Due to variations in line loss, the received light power on the receiving side is several dB.
Frequent occurrences of m or more frequently occur. Therefore, the fixed optical attenuator is essential when using the conventional optical receiving circuit.

An object of the present invention is to solve the above problems and to provide an optical receiving circuit capable of obtaining a good electric signal without causing distortion deterioration even for a large input optical signal. To do.

[0007]

The optical receiving circuit of the present invention comprises:
An optical branching circuit for branching the input optical signal, a plurality of light receiving circuits for converting the optical signals branched by the optical branching circuit into electric signals, respectively, and a combining circuit for adding the output signals of the plurality of light receiving circuits It is characterized by that.

The light receiving circuit may include an opto-electric conversion element for converting an optical signal into an electric signal and an electric amplifier for amplifying the output of the opto-electric conversion element with low noise.

[0009]

The input optical signal is branched to reduce the individual optical power, and the individual optical signals having the small optical power are simultaneously received by the different light receiving circuits. Further, the outputs of all the light receiving circuits are electrically added. As a result, it is possible to obtain a good electric signal without causing distortion deterioration even for a large input optical signal.

[0010]

1 is a circuit diagram showing an optical receiving circuit according to a first embodiment of the present invention. The optical receiving circuit includes an optical branching circuit 5 for branching an input optical signal from the optical fiber 1 and a plurality of light receiving circuits for converting the optical signals branched by the optical branching circuit 5 into electric signals, that is, two sets of light receiving circuits. The light receiving element 2 and the electric amplifier 3 are provided, and a combining circuit 6 for adding the output signals of the plurality of light receiving circuits.

An optical signal input from the optical fiber 1 is split into two by an optical branching circuit 5, and is input to two light receiving elements 2 to be converted into an electrical signal. The output of the light receiving element 2 is amplified by the electric amplifier 3 with low noise, and the two electric signals are analogically added by the combining circuit 6 and output to the output terminal 4.

With this configuration, since the received light power of the same level as in the conventional case can be received by each system of the two sets of receiving circuits, the optical fiber 1 can receive twice the optical power as compared with the conventional case.

FIG. 2 is a circuit diagram showing an optical receiving circuit according to the second embodiment of the present invention. This embodiment differs from the first embodiment in that the input optical signal is split into four. That is, the optical fiber 1
An optical branching circuit 7 for branching an input optical signal from the optical receiver, four sets of light receiving circuits including a light receiving element 2 and an electric amplifier 3, and a combining circuit 8 for adding electric signals of four systems.

The optical signal input from the optical fiber 1 is branched into four by the optical branching circuit 7, and each of them is converted into an electric signal by the light receiving element 2. The output of the light receiving element 2 is amplified by the electric amplifier 3 with low noise, and the four electric signals are analogically added by the synthesizing circuit 8 and output to the output terminal 4.

In this configuration, when viewed from the optical fiber 1,
It is possible to receive optical power four times that of the conventional one.

FIG. 3 shows a light receiving surface of a light receiving element suitable for use in the present invention. The light receiving surface of the light receiving element is divided into four. If this is used in the second embodiment, the optical branch circuit 7 becomes unnecessary and the input optical fiber 1 to the light receiving element 2
The configuration up to is simple.

A light receiving element having a plurality of light receiving surfaces has already been put to practical use for DAD (digital audio disc) or VD (video disc). Such examples are, for example, optoelectronic devices NECROC series; NEC data book,
p112-113, 1998. Such a structure may be used in an element for a communication wavelength band, that is, a band of 1 to 1.6 μm.

[0018]

As described above, the optical receiving circuit of the present invention has an effect that the maximum value of received light power can be increased with a simple circuit configuration and that the dynamic range of a receiving device can be easily expanded. is there.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an optical receiver circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a light receiving circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a light receiving surface of a light receiving element suitable for use in the present invention.

FIG. 4 is a circuit diagram of a conventional optical receiver circuit.

[Explanation of symbols]

 1 optical fiber 2 light receiving element 3 electric amplifier 4 output terminal 5, 7 optical branching circuit 6, 8 combining circuit 9 light receiving surface

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04B 10/26 10/14 10/04 10/06 H04B 9/00 Y

Claims (2)

[Claims] 1. An optical receiving circuit for converting an optical signal into an electric signal, an optical branching circuit for branching an input optical signal, and a plurality of light receiving circuits for respectively converting the optical signals branched by the optical branching circuit into electric signals. An optical receiving circuit comprising: a combining circuit for adding output signals of the plurality of light receiving circuits. 2. The optical receiving circuit according to claim 1, wherein the light receiving circuit includes an opto-electric conversion element that converts an optical signal into an electric signal, and an electric amplifier that amplifies an output of the opto-electric conversion element with low noise. .