JPH02116208A - Optical signal receiving part - Google Patents

Abstract

PURPOSE:To attain the automatic gain control of the total range of an optical input level without using an optical fixed attenuator or even when the optical input level is not forecasted by providing a fixed attenuator with a switch at the front stage of a pre-amplifier. CONSTITUTION:A fixed attenuator 4 with a switch capable of inserting or passing through the fixed attenuator of 12dB with the control of a switch to the front step of a pre-amplifier 2 without using an optical fixed attenuator is provided, and a switch control part 5 to detect and control and AGC voltage to control the gain of the pre-amplifier 2 is provided in order to insert and pass through the fixed attenuator of 12dB. Namely, when an input level is <=-12dBm, the fixed attenuator of 12dB of the fixed attenuator 4 with a switch is passed through, and when the input level is >=-12dBm, the fixed attenuator of the 12dB of the fixed attenuator 4 with the switch is inserted. Thus, the range of 0dBm to -25dBm can be applied with AGC.

Description

[Detailed Description of the Invention] [Summary] This invention relates to an optical signal receiving section that varies the gain in response to changes in the optical input level due to the length of the optical transmission path, without using a fixed optical attenuator, and with the prediction of the optical input level. The purpose of the present invention is to provide an optical signal receiver capable of automatically controlling the gain over the entire range of optical input levels without having to perform automatic gain control over the entire range of optical input levels. In an optical signal receiving section having an automatic gain control circuit for varying the gain and keeping the output level constant, a fixed attenuator with a switch capable of inserting or passing the fixed attenuator is provided before the preamplifier, Further, a switch control unit is provided that detects the value of a control voltage for varying the gain of the preamplifier of the automatic gain control circuit, controls the switch of the fixed attenuator with a switch, and inserts or passes the fixed attenuator. composition.

[Industrial application field]

The present invention relates to an improvement in an optical signal receiving section that changes gain in response to changes in optical input level due to the length of an optical transmission path.

[Conventional technology]

Normally, the distance of an optical transmission line varies depending on the route, and therefore the loss also varies depending on the route. For example, the width of the pre-input curve of the optical signal receiving section is
~-37dBm and wide.

Since it takes time and effort to adjust the gain of the optical signal receiving section one by one in response to this input level, a method is used in which a certain range is set as an automatic gain control (hereinafter referred to as AGC) range.

Furthermore, the range from OdBm to -37dBm is determined by the AG of the optical signal receiving section.
C range may be sufficient, but since it is technically difficult to widen the range to this extent, AGC is usually performed in two stages using a fixed optical attenuator.

FIG. 3 is a block diagram of a conventional optical signal receiving section, and FIG. 4 is a diagram showing an example of an optical input level range and an AGC range.

The optical signal receiving section in Fig. 3 has an optical input level of OdBm~-
If it is 25 dBm, as shown in Fig. 4, a 12 dB fixed optical attenuator 8 is used to lower the level to a range of -12 dBm to -37 dBm, and AGC is performed to reduce the input level to 112 dBm.
If the range is from dBm to -37 dBm, the fixed optical attenuator 8 is removed and AGC is performed.

The configuration consists of a 12 dB fixed optical attenuator 8 at the beginning, followed by an avalanche photodiode (with variable multiplication factor).
(hereinafter referred to as APD) ■, then a preamplifier 2 whose gain can be varied, then a main amplifier 6, and then a waveform equalizer 7, and the output of the waveform equalizer 7 is applied to the automatic gain control circuit 3. , the outputs are respectively input to the APDI and the preamplifier 2, and the APD 1 outputs the range (-25 dBm to -37 dBm) shown in FIG.
The output level of the waveform equalizer 7 is kept constant by performing gain control in the range (3) shown in the figure.

Note that when the input level is in the range of 112 dBm to -37 dBm, the fixed optical attenuator 8 is removed to keep the output level constant.

In these cases, the multiplication factor of A I) is 1 when the input level is from OdBm to -25 dBm, and when the input level is below, A
The GC voltage is about +IOV ~ → -32V, and the multiplication factor is 1 ~
The gain of the preamplifier 2 is constant when the input level is between OdBm and -12dBm and below -25d, Brn, and the AGC voltage is between -2V and -25dBm between -12dBm and -25dBm. At about +3v, the gain is 13dB
It changes by about m.

[Problem to be solved by the invention]

However, when the distance of the optical transmission path is short, a fixed optical attenuator is almost always required, but the fixed optical attenuator 8 is expensive, and there is a problem that the optical signal receiving section becomes expensive. In addition, the worst-case loss for optical cables is generally indicated in the specifications, and the input level is calculated based on this, but in reality, the loss may be about half, making it difficult to predict the input level. There is a problem in that it is difficult to predict the value of an optical fixed attenuator.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal receiving section that can perform automatic gain control over the entire range of optical input levels without using a fixed optical attenuator or predicting the optical input level.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

As shown in FIG. 1, there is a light-receiving element 1 that can at least vary the multiplication factor, a preamplifier 2 that can vary the gain, and an automatic gain control circuit 3 that makes the output level constant by varying the multiplication factor and gain. In the optical signal receiving section having a switch, a fixed attenuator 4 with a switch is provided upstream of the preamplifier 2, allowing the fixed attenuator to be inserted or passed through.

Further, the value of the control voltage for varying the gain of the preamplifier 2 of the automatic gain control circuit 3 is detected, and the fixed attenuator 4 with switch is detected.
A switch control unit 5 is provided to control the switch and insert or pass the fixed attenuator.

[For production]

According to the present invention, if the value of the control voltage for varying the gain of the preamplifier 2 is less than -2 dBm, which corresponds to less than -12 dBm of the optical input level, the switch control unit 5 , and controls the switch of the fixed attenuator 4, for example, l 2 (by turning the fixed attenuator of IB through, as shown in A in FIG. 4, for example -12
AGC is performed in the range of d 13m to 37 d 13m.

If the optical input level is less than 2V, which corresponds to 112 dBm or more, the switch control unit 5 detects this and controls the switch of the fixed attenuator 4 with a switch to
A fixed dB attenuator is inserted to perform AGC in the range of, for example, OdBm to -25 dBm, as shown at the beginning of FIG.

In this way, AGC can be performed over the entire optical input level range of OdBm to -37d 13m without using an expensive optical fixed attenuator, and A, G C can be performed over the entire range.
Therefore, there is no need to particularly predict the optical input level.

〔Example〕

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a block diagram of an optical signal receiving section according to an embodiment of the present invention.

The difference between FIG. 2 and FIG. 3 is that the fixed optical attenuator 8 in FIG. 3 is not used, but a fixed attenuator of 12 This 12dB
In order to insert or pass through the fixed attenuator, a switch control section 5 is provided to detect and control the AGC voltage that controls the gain of the preamplifier 2.

In this way, if the input level is below 112 dBm, the gain of the preamplifier 2 will be controlled by the 0C voltage.
Since it is larger than V, the switch control unit 5 allows the 12 dB fixed attenuator of the fixed attenuator with switch 4 to pass through, so that AGC can be performed in the range of -12 dBm to -37 dBm shown in A of Fig. 4. .

If the human power level is 112 dBr or more, the AGC voltage that controls the gain of the preamplifier 2 is smaller than 12 V, so in switch plagiarism 1 part 5, the 12 dB fixed attenuator of the fixed attenuator 4 with switch is Since it is inserted, AGC can be performed in the range of OdBm to -25 dBm shown at the beginning of FIG.

Therefore, AGC can be performed over the entire optical input level range of OdBm to -37dBrn without using an expensive fixed optical attenuator, and AGC can be performed over the entire range.
In particular, there is no need to predict the level of human power.

In order to prevent the fixed attenuator 4 with a switch from fluttering when the fixed attenuator is inserted or through, the time constant of the operation of the switch control section 5 should be lengthened, or the fixed attenuator should be inserted. This is done when the AGC voltage becomes less than 12 V, which corresponds to 112 dBm, and the fixed attenuator is turned on.
It is sufficient to provide a hysteresis characteristic by making a difference in the dark value voltage, as is done when the GC voltage becomes larger than →-3■ corresponding to 25 dBm.

Since this fixed attenuator is through in the low level range, it does not cause a decrease in human S/N.

C) Effects of the Invention As explained in detail above, according to the present invention, AGC can be performed over the entire range of optical input levels without using an expensive optical fixed attenuator, and the optical signal receiving section can be made inexpensive. ,
In addition, since AGC can be performed over the entire range, there is no need for particularly human-powered predictions.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of an optical signal receiving section according to an embodiment of the present invention, Fig. 3 is a block diagram of a conventional optical signal receiving section, and Fig. 4 is an example. FIG. 3 is a diagram showing a range of optical input levels and a range of Acc. In the figure, 1 is a light receiving element, an avalanche photodiode, 2 is a preamplifier, 3 is an automatic gain control circuit, 4 is a fixed attenuator with a switch, 5 is a switch control section, 6 is a main amplifier, and 7 is a waveform vase. , 8 indicates an optical fixed attenuator.

Claims (1)

[Claims] A light receiving element (1) capable of varying at least a multiplication factor, a preamplifier (2) capable of varying a gain, and an automatic gain for making the output level constant by varying the multiplication factor and gain. In an optical signal receiving section having a control circuit (3), a fixed attenuator (4) with a switch capable of inserting or through-setting a fixed attenuator is provided in front of the preamplifier (2), and the automatic gain control circuit (3) A switch control unit that detects the value of the control voltage that varies the gain of the preamplifier (2), controls the switch of the fixed attenuator with switch (4), and inserts or passes through the fixed attenuator. An optical signal receiving section characterized in that (5) is provided.