JPH06104670A - Optical receiver - Google Patents

Abstract

PURPOSE:To provide the optical receiver keeping a frequency characteristic at an input terminal of an identification circuit of the optical receiver constant. CONSTITUTION:In the optical receiver having a light receiving element 100, an equalization amplifier section 200 provided with an automatic gain controlled amplifier 600, and an identification circuit 300, the equalization amplifier section 200 is provided with an equal error rate curve measurement means 120 receiving part of an output signal of the automatic gain controlled amplifier 600 and measuring and outputting data of an equal error rate curve by using an error rate as a parameter, and an arithmetic operation processing means 130 applying inverse Fourier transformation to an output of the equal error rate curve measurement means 120 to obtain a frequency characteristic corresponding to an input optical signal and outputting a control signal to the automatic gain controlled amplifier 600 so as to keep a frequency characteristic of the output signal from the equalization amplifier section 200 constant with the control signal being the output of the arithmetic operation processing means 130.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an optical receiver of an optical transmission device.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing the configuration of an example of an optical repeater. FIG. 10 is a block diagram showing a configuration of a conventional equalization amplification unit.

FIG. 11 is a gain-frequency characteristic diagram obtained by automatic gain control (hereinafter referred to as AGC) of the output of the equalizing amplifier of the conventional example. In FIG. 9, an avalanche photodiode (APD) 1 converts an optical input signal from the optical transmission line into an electric signal and then applies the electric signal to the equalization amplification unit 2. The preamplifier 5 of the equalization amplification unit 2 shown in FIG. 10 converts a current signal into a voltage signal, and this output is subjected to automatic gain control by a feedback loop of the AGC amplifier 6, the postamplifier 7, and the gain control unit 8, A signal having a gain-frequency characteristic as shown in 11 is output from the post amplifier 7.

The output of the equalizing / amplifying unit 2 is branched and added to the discrimination circuit 3 and the timing circuit 4. The timing circuit 4 generates a clock for identifying and reproducing the input signal, and the identifying circuit 3 performs identification and reproduction for the input signal by this clock.

[0005]

However, in the conventional optical receiver,
As shown in 11, the gain was controlled uniformly over a predetermined frequency range. For this reason, in high-speed optical communication in which the individual variations in the frequency characteristics of the optical transmitter are large, the waveform at the input end of the identification circuit of the optical receiver varies, which causes deterioration of the minimum receiving sensitivity in the optical receiver. There was a problem.

Therefore, an object of the present invention is to provide an optical receiver in which the deterioration of the minimum receiving sensitivity does not occur even with a high-speed input optical signal.

[0007]

The above problems can be solved by the circuit configuration shown in FIG. (Claim 1) A light receiving element 100 for converting an input optical signal into an electric signal and outputting the electric signal, and an automatic gain control amplifier 60 for amplifying and outputting the output of the light receiving element by an automatic gain control loop.
In the optical receiver including the equalization amplification unit 200 including 0 and the identification circuit 300 that performs identification reproduction on the output signal of the equalization amplification unit 200 by the clock extracted by the equalization amplification unit 200, 120 is It is an equal error rate curve measuring means for inputting a part of the output signal of the automatic gain control amplifier 600 and measuring and outputting data of the equal error rate curve using the value of the error rate as a parameter.

Reference numeral 130 denotes an inverse Fourier transform for the output of the equal error rate curve measuring means 120 to obtain a frequency characteristic corresponding to the input optical signal and obtain a control signal as an automatic gain control amplifier.
It is an arithmetic processing means for outputting to 600. The above 120 and 130 are provided in the equalization amplification section 200.

Then, the signal frequency characteristic of the output of the equalizing and amplifying section 200 is kept constant by the control signal of the output of the arithmetic processing means 130. (Claim 2) A light receiving element 100 which converts an input optical signal into an electric signal and outputs the electric signal, and an automatic gain control amplifier 60 which amplifies and outputs the output of the light receiving element by an automatic gain control loop.
In an optical receiver including an equalization amplification unit 200 including 0 and an identification circuit 300 that performs identification reproduction with a clock extracted by the equalization amplification unit with respect to an output signal of the equalization amplification unit,
Is an equal error rate curve measuring means for inputting a part of the output signal of the automatic gain control amplifier 600 and measuring and outputting data of the equal error rate curve using the value of the error rate as a parameter.

135 receives a part of the output signal of the automatic gain control amplifier 600 and outputs the first control signal to the automatic gain control amplifier 600 so that the amplitude of the output signal of the automatic gain control amplifier 600 becomes constant. An arithmetic process of outputting the second control signal to the automatic gain control amplifier 600 by performing the inverse Fourier transform on the output of the equal error rate curve measuring means 120 while obtaining the frequency characteristic corresponding to the input optical signal. It is a means. The above 120 and 135 are provided in the equalization amplification section 200.

Then, the signal frequency characteristic of the output of the equalizing and amplifying section 200 is kept constant by the first and second control signals of the output of the arithmetic processing means 135.

[0012]

In FIG. 1, (claim 1) the data of the equal error rate curve measured by the equal error rate curve measuring means 120,
The inverse Fourier transform is performed by the arithmetic processing means 130 to obtain the frequency characteristic corresponding to the input optical signal. Then, the control signal for canceling this frequency characteristic and obtaining the ideal frequency characteristic is output to the automatic gain control amplifier 600.

As a result, the equalization amplification unit 2 of the optical receiver always corrects the frequency characteristic of the signal sent from the optical transmitter (not shown), and maintains the frequency characteristic close to ideal at the output end. This makes it possible to prevent deterioration of the minimum receiving sensitivity.

(Claim 2) In the arithmetic processing means 135, a part of the output signal of the automatic gain control amplifier 600 is input and the first control is performed so that the amplitude of the output signal of the automatic gain control amplifier 600 becomes constant. The signal is output to the automatic gain control amplifier 600.

At the same time, the data of the equal error rate curve output from the equal error rate curve measuring means 120 is subjected to an inverse Fourier transform by the arithmetic processing means 135 to obtain the frequency characteristic corresponding to the input optical signal. Then, the second control signal for canceling this frequency characteristic and obtaining the ideal frequency characteristic is output to the automatic gain control amplifier 600.

Since the control by the first control signal is performed faster than the control operation by the second control signal, the control by the second control signal requires fine adjustment, and the response of the entire automatic gain control loop is required. Speed up. As a result, it is possible to respond to the fluctuation of the input signal level at high speed.

[0017]

2 is a block diagram showing the structure of an equalizing / amplifying unit according to an embodiment of the present invention. FIG. 3 is an equal error rate curve diagram of the output waveform of the optical transmitter (LD) in the example.

FIG. 4 is a frequency characteristic diagram of the output of the optical transmitter obtained by inverse Fourier expansion of the data of FIG. FIG. 5 is a frequency characteristic diagram required at the input end of the identification circuit of the embodiment.

FIG. 6 is a frequency characteristic diagram of the optical receiver for canceling the frequency characteristic of FIG. FIG. 7 is a frequency characteristic diagram of each AGC amplifier for satisfying the frequency characteristic of FIG.

FIG. 8 is a block diagram showing the structure of the equalizing / amplifying unit according to the second embodiment of the invention. The same reference numerals denote the same objects throughout the drawings. In FIG. 2, 9-1 to 9-n are band pass filters (hereinafter referred to as BPFs) whose band center frequencies are slightly different from each other. 6-1 to 6-n are each BPF9-1 to
AG that amplifies the signal that has passed 9-n by the AGC loop
It is a C amplifier. Reference numeral 11 is an adder for adding the outputs of these AGC amplifiers 6-1 to 6-n.

Reference numeral 12 denotes an equal error rate curve measuring section for measuring an equal error rate curve using the value of the error rate as a parameter for the signal waveform of the output of the post amplifier 7 (that is, the output of the equalization amplifying section 2). .

When a part of the output of the post-amplifier 7 is added to the equal error rate curve measuring section 12, the equal error rate curve measuring section 12 receives the optical signal waveform transmitted from the optical transmitter (not shown). For example, an equal error rate curve as shown in FIG. 3 is measured. This measurement data is subjected to inverse Fourier expansion processing by the CPU 13 to obtain the frequency characteristic as shown in FIG.

On the other hand, in order to prevent the deterioration of the minimum receiving sensitivity, even if the frequency characteristic of the optical signal due to the optical transmitter (not shown) varies, the ideal frequency as shown in FIG. It has to be a characteristic. For this reason,
In order to cancel the frequency characteristic (see FIG. 4) of the output of the optical transmitter (not shown), the optical receiver needs to have the frequency characteristic as shown in FIG.

Therefore, the CPU 13 calculates the frequency characteristic required for the optical receiver from the frequency characteristic subjected to the inverse Fourier expansion process. In the embodiment of the present invention, the equalizing / amplifying unit includes a plurality of AGC amplifiers 6-1 to 6-1 whose frequency domain is divided as shown in FIG.
Since it is composed of 6-n, the gain of each AGC amplifier 6-1 to 6-n is calculated by the CPU 13 so as to obtain the frequency characteristic required for the optical receiver, and the result as shown in FIG. 7 is obtained, for example. . According to this calculation, CPU13 to each AGC amplifier
The control signals are output to 6-1 to 6-n, and the optical receiver is shown in FIG.
The frequency characteristics shown in are obtained.

By the above operation, the equalization amplification section 2 of the optical receiver
Thus, by constantly correcting the frequency characteristic of the signal sent from the optical transmitter (not shown) and maintaining the frequency characteristic close to the ideal at the output end, the deterioration of the minimum receiving sensitivity can be prevented.

Next, a second embodiment of the present invention shown in FIG. 8 will be described. The difference from the embodiment of FIG. 2 described above is that a part of the output of the postamplifier 7 is branched and added to the equal error rate curve measuring section 12 and also to the CPU 13, and the equal error rate curve measuring section 12 is included. This is because there is a double loop configuration of an AGC loop which does not include an AGC loop and an equal error rate curve measuring unit 12.

That is, A that does not include the equal error rate curve measuring unit 12
In the GC loop, the CPU 13 detects the "H" and "L" level values of the output pulse of the postamplifier 7 and initializes these values, and the postamplifier 7 does not change even if the input signal to the preamplifier 5 changes. The same control signal is output to the AGC amplifiers 6-1 to 6-n so as to output a pulse signal having a constant amplitude. The amplitude of the output pulse of the post-amplifier 7 (output of the equalizing / amplifying unit 2) is kept constant to give an average frequency characteristic. After that, the AGC loop including the equal error rate curve measuring unit 12 finely adjusts the frequency characteristic of the output signal of the post amplifier 7 (output of the equalizing amplification unit 2) according to the same operation principle as described in FIG. .

As a result, the gain adjustment of each of the AGC amplifiers 6-1 to 6-n need only be finely adjusted, and the response speed of the entire AGC loop becomes faster. As a result, it is possible to respond to the fluctuation of the input signal level at high speed.

[0029]

As described above, according to the present invention, it is possible to prevent deterioration of the minimum receiving sensitivity even for a high-speed input optical signal. Further, it is possible to respond at high speed to the fluctuation of the input signal level.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of an equalizing / amplifying unit according to an embodiment of the invention of claim 1;

FIG. 3 is an equal error rate curve diagram of an optical transmitter (LD) output waveform in the embodiment,

FIG. 4 is a frequency characteristic diagram of an optical transmitter output obtained by performing an inverse Fourier expansion on the data of FIG.

FIG. 5 is a frequency characteristic diagram required at the input end of the identification circuit of the embodiment,

6 is a frequency characteristic diagram of an optical receiver for canceling the frequency characteristic of FIG. 4,

FIG. 7 is each AGC for satisfying the frequency characteristic of FIG.
Amplifier frequency characteristic diagram,

FIG. 8 is a block diagram showing a configuration of an equalizing / amplifying unit according to an embodiment of the invention of claim 2;

FIG. 9 is a block diagram showing a configuration of an example optical repeater,

FIG. 10 is a block diagram showing a configuration of a conventional equalization amplification unit,

FIG. 11 is a gain-frequency characteristic diagram by AGC of the equalization amplification unit output of the conventional example.

[Explanation of symbols]

 100 is a light receiving element, 120 is an equal error rate curve measuring means, 130 and 135 are arithmetic processing means, 200 is an equalizing amplifier, 300 is an identification circuit, and 600 is an automatic gain control amplifier.

Claims (2)

[Claims] 1. A light receiving element (100) for converting an input optical signal into an electric signal and outputting the electric signal, and an automatic gain control amplifier (600) for amplifying and outputting the output of the light receiving element by an automatic gain control loop. An optical receiver having an equalization amplification section (200) provided and an identification circuit (300) for performing identification reproduction with respect to an output signal of the equalization amplification section by a clock extracted by the equalization amplification section, An equal error rate curve measuring means (120) for inputting a part of the output signal of the automatic gain control amplifier (600) and measuring and outputting data of the equal error rate curve using the error rate value as a parameter.
And an operation for performing an inverse Fourier transform on the output of the equal error rate curve measuring means (120) to obtain a frequency characteristic corresponding to the input optical signal and outputting a control signal to the automatic gain control amplifier (600). A processing means (130) is provided in the equalization amplification section (200), and a signal frequency characteristic of the output of the equalization amplification section (200) is kept constant by a control signal of the output of the arithmetic processing means (130). An optical receiver characterized in that 2. A light receiving element (100) which converts an input optical signal into an electric signal and outputs the electric signal, and an automatic gain control amplifier (600) which amplifies and outputs the output of the light receiving element by an automatic gain control loop. An optical receiver having an equalization amplification section (200) provided and an identification circuit (300) for performing identification reproduction with respect to an output signal of the equalization amplification section by a clock extracted by the equalization amplification section, An equal error rate curve measuring means (120) for inputting a part of the output signal of the automatic gain control amplifier (600) and measuring and outputting data of the equal error rate curve using the error rate value as a parameter.
And a part of the output signal of the automatic gain control amplifier (600) is input, and the first control signal is input to the automatic gain control so that the amplitude of the output signal of the automatic gain control amplifier (600) becomes constant. In addition to outputting to the amplifier (600), inverse Fourier transform is performed on the output of the equal error rate curve measuring means (120) to obtain the frequency characteristic corresponding to the input optical signal, and the second control signal is automatically transmitted. An arithmetic processing unit (135) for outputting to the gain control amplifier (600) is provided in the equalization amplification unit (200), and the equalization is performed by the first and second control signals output from the arithmetic processing unit (135). An optical receiver characterized in that the signal frequency characteristic of the output of the amplification section (200) is kept constant.