JP2010080665A - Device and method for receiving light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for receiving light without requiring a large bit resolution and capable of accurately numerical-converting the received signal light. <P>SOLUTION: Light receivers 7a to 7d convert the received signal light to a first electric signal. Automatic gain control amplifiers 11a to 11d amplify the first electric signal output from the light receivers 7a to 7d, convert it to a constant level second electric signal for output to AD converters 13a to 13d, and further output amplification coefficients 14a to 14d at amplification. The AD converters 13a to 13d convert the second electric signal to the digital signal. A digital signal processing circuit 16 converts the output of the AD converters 13a to 13d to the level proportional to the first electric signal by the amplification coefficients 14a to 14d. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical fiber transmission system, and more particularly to an optical receiving apparatus and an optical receiving method using a coherent reception method.

The configuration and operation of the optical receiver 1 using the digital coherent reception method will be described with reference to FIGS.
In FIG. 3, the received signal light 2 is separated into two orthogonal polarization components by a polarization beam splitter 3a. Similarly, the local light 4 from the local light source is separated into two orthogonal polarization components by the polarization beam splitter 3b. The signal light and local light divided into orthogonal polarization components are input to the 90-degree optical hybrids 6a and 6b. The signal light and local light mixed by the 90-degree optical hybrids 6a and 6b are input to the optical receivers 7a to 7d, and the beat components are output as received signals 10a to 10d. The reception signals 10a to 10d are input to the AD converters 13a to 13d, converted into digital signals by the AD converters 13a to 13d, and input to the digital signal processing circuit 16 as digitized reception signals 15a to 15d. The digital signal processing circuit 16 performs signal processing on the reception signals 15 a to 15 d and outputs the result as an output signal 17.
The following documents are known as prior art documents related to the present invention.
JP 2001-168748 A Japanese Patent Publication No. 07-104539 JP-T-2006-524462 JP-T-2007-513558

  FIG. 4 shows signal waveforms at various parts in the optical receiver 1 described above. As shown in this figure, in the optical receiver 1 using the digital coherent reception method, the received signals 10a and 10b (see FIGS. 4A and 4C) output from the optical receivers 7a and 7b are as follows. The signals are input to the AD converters 13a and 13b as they are and converted into digitized received signals 15a and 15b (see FIGS. 4B and 4D). As a result, in order to accurately quantify the received signal having a small amplitude as in the signal 10b (FIG. 4C), the AD converter 13b needs to have a very large bit resolution.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical receiving apparatus and an optical receiving method capable of accurately digitizing received signal light without requiring a large bit resolution. There is to do.

 The present invention provides an optical receiver that converts received signal light into a first electrical signal by an optical receiver and then converts it into a digital signal by an AD converter, and amplifies the first electrical signal output from the optical receiver Then, it is converted into a second electric signal of a constant level and output to the AD converter, and an automatic gain control amplifier that outputs an amplification coefficient at the time of amplification, and the output of the AD converter is converted into the first electric signal by the amplification coefficient. An optical receiver comprising a digital signal processing circuit for converting to a level proportional to an electrical signal.

 The present invention also provides a first polarization beam splitter that separates received signal light into two orthogonal polarization components, and a second polarization beam splitter that separates local light from a local light source into two orthogonal polarization components. The first and second 90 degree optical hybrids that mix the light from the first and second polarization beam splitters, and the outputs of the first and second 90 degree optical hybrids are converted into first electric signals. And an automatic gain for amplifying the first electric signal output from the optical receiver, converting it to a second electric signal at a constant level, and outputting an amplification coefficient at the time of amplification A control amplifier; an AD converter that converts the second electrical signal into a digital signal; and a digital signal that converts the output of the AD converter to a level proportional to the first electrical signal by the amplification coefficient. An optical receiving apparatus characterized by comprising a processing circuit.

 According to another aspect of the present invention, there is provided an optical receiving method for converting received signal light into a first electric signal, and then converting the received signal light into a digital signal. The first electric signal is amplified and converted into a second electric signal having a constant level. And converting the second electric signal into a digital signal, and converting the converted digital signal into a level proportional to the first electric signal by an amplification coefficient at the time of amplification. is there.

According to the present invention, the level of the electric signal input to the AD converter is constant, and a small level signal is also input after being greatly enlarged, so that the bit resolution required by the AD converter can be reduced. . In general, an AD converter has a circuit scale that exponentially increases as the bit resolution increases, and the cost increases accordingly, and the operation speed is limited.
Further, according to the present invention, since the electric signal level input to the AD converter is constant regardless of the signal light level, there is an effect that stable signal reception can be performed even when the signal light level fluctuates.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an optical receiver 21 according to an embodiment of the present invention. The optical receiver 21 shown in this figure is an optical receiver using a so-called digital coherent reception scheme.

  In FIG. 1, reference numeral 2 is signal light, 4 is local light from a local light source, the signal light 2 is applied to the polarization beam splitter 3a, and the local light 4 is applied to the polarization beam splitter 3b. The polarization beam splitter 3a separates the signal light 2 into two orthogonal polarization components and outputs them to the 90-degree optical hybrids 6a and 6b. The polarization beam splitter 3b separates the local light 4 into two orthogonally polarized components and outputs them to the 90-degree optical hybrids 6a and 6b. The 90-degree optical hybrid 6a mixes the input signal light and the polarization components of the local light, and outputs beat components obtained thereby to the optical receivers 7a and 7b. Similarly, the 90-degree optical hybrid 6b mixes the input signal light and the polarization components of the local light, and outputs the beat components obtained thereby to the optical receivers 7c and 7d. The optical receiver 7a converts the input optical signal into an electric signal 10a and outputs it to the automatic gain control amplifier 11a. Similarly, the optical receivers 7b to 7d convert the input optical signals into electric signals 10b to 10d, respectively, and output them to the automatic gain control amplifiers 11b to 11d.

  The automatic gain control amplifier 11a amplifies the electric signal output from the optical receiver 7a so that the output amplitude becomes a predetermined constant value A, and outputs the amplified signal to the AD converter 13a as a signal 12a. The gain control signal is digitized and output to the digital signal processing circuit 16 as an amplification coefficient 14a. Similarly, the automatic gain control amplifiers 11b to 11d amplify the electric signals output from the optical receivers 7b to 7d so that the output amplitude becomes the constant value A, respectively, and the signals 12b to 12d are AD converters 13b to 13d. The gain control signal at the time of amplification is digitized and output to the digital signal processing circuit 16 as amplification coefficients 14b to 14d. The AD converters 13a to 13d convert the input signals 12a to 12d into digital signals and output the digital signals to the digital signal processing circuit 16 as received signals 15a to 15d. The digital signal processing circuit 16 converts the received signals 15a to 15d to levels proportional to the signals 10a to 10d using the amplification coefficients 14a to 14d, performs predetermined processing on the converted signals, and outputs the result as an output signal. 17 is output.

Next, the operation of the above-described optical receiver will be described.
The received signal light 2 is separated into two orthogonal polarization components by the polarization beam splitter 3a and input to the 90-degree optical hybrids 6a and 6b. Further, the local light 4 from the local light source is separated into two orthogonal polarization components by the polarization beam splitter 3b and input to the 90-degree optical hybrids 6a and 6b. The 90-degree optical hybrids 6a and 6b mix the input signal light and local light, respectively, and output beat components obtained thereby to the optical receivers 7a to 7d. The optical receivers 7a to 7d convert the input optical signals into electric signals 10a to 10d, respectively, and output them to the automatic gain control amplifiers 11a to 11d.

  The automatic gain control amplifiers 11a to 11d amplify the respective output amplitudes so as to have a constant value A, and output the signals 12a to 12d as signals 12a to 12d to the AD converters 13a to 13d. And output to the digital signal processing circuit 16 as amplification coefficients 14a to 14d. The AD converters 13a to 13d convert the input signals 12a to 12d into digital signals and output the digital signals to the digital signal processing circuit 16 as received signals 15a to 15d. The digital signal processing circuit 16 converts the received signals 15a to 15d to a level proportional to the signals 10a to 10d using the amplification coefficients 14a to 14d, performs predetermined processing on the converted signals, and outputs the result to the output signal 17 Output as.

FIG. 2 shows signal waveforms at various parts of the optical receiver 1 shown in FIG. However, in FIG. 2, only two of the four signal systems are picked up and described.
In FIG. 2, the amplitudes of the reception signals 10 a and 10 b (FIG. 2A and FIG. 2E) output from the optical receivers 7 a and 7 b depend on the polarization state of the signal light 2 and take various values. Also, this amplitude varies with time. In the optical receiver 1, the amplitudes of the reception signals 10a and 10b output from the optical receivers 7a and 7b are converted into AD by the automatic gain control amplifiers 11a and 11b as shown in FIGS. Convert to a constant value suitable for input to the converter. The AD converters 13a and 13b convert the received signals 12a and 12b into numerical data, and output them as digitized received signals 15a and 15b (FIGS. 2C and 2G). In FIG. 2, the received signals 15a and 15b are schematically described, but the actual received signals 15a and 15b are bit strings. The digitized received signals 15a and 15b are corrected by the amplification factors 14a and 14b notified from the automatic gain control amplifiers 11a and 11b in the digital signal processing circuit 16, and are shown in FIGS. 2 (d) and 2 (h). Converted to the original amplitude. Predetermined signal processing is performed on the received signal converted into the original amplitude and digitized.

  The present invention is mainly applied to an optical receiver using a digital coherent reception method.

It is a block diagram which shows the structure of the optical receiver by one Embodiment of this invention. It is a wave form diagram which shows the waveform of each part of the optical receiver. It is a block diagram which shows the structural example of the conventional optical receiver. It is a wave form diagram which shows the waveform of each part of the optical receiver shown in FIG.

Explanation of symbols

3a, 3b ... Polarizing beam splitters 6a, 6b ... 90 degree optical hybrids 7a-7c ... Optical receivers 11a-11d ... Automatic gain control amplifiers 13a-13d ... AD converter 16 ... Digital signal processing circuit

Claims (3)

In an optical receiver that converts received signal light into a first electrical signal by an optical receiver and then converts it into a digital signal by an AD converter,
An automatic gain control amplifier that amplifies the first electric signal output from the optical receiver, converts the first electric signal into a second electric signal at a constant level, outputs the second electric signal to the AD converter, and outputs an amplification coefficient upon amplification; ,
A digital signal processing circuit for converting the output of the AD converter to a level proportional to the first electric signal by the amplification coefficient;
An optical receiver characterized by comprising: A first polarization beam splitter that separates received signal light into two orthogonal polarization components;
A second polarizing beam splitter that separates the local light from the local light source into two orthogonal polarization components;
First and second 90-degree optical hybrids for mixing light from the first and second polarization beam splitters;
An optical receiver for converting the output of the first and second 90-degree optical hybrids into a first electrical signal;
An automatic gain control amplifier that amplifies the first electric signal output from the optical receiver, converts it into a second electric signal of a certain level and outputs it, and outputs an amplification coefficient at the time of amplification;
An AD converter for converting the second electric signal into a digital signal;
A digital signal processing circuit for converting the output of the AD converter to a level proportional to the first electric signal by the amplification coefficient;
An optical receiving apparatus comprising: In an optical receiving method for converting a received signal light into a first electrical signal and then into a digital signal,
The first electric signal is amplified and converted into a second electric signal of a certain level, the second electric signal is converted into a digital signal, and the converted digital signal is converted into the first electric signal by an amplification coefficient at the time of amplification. An optical receiving method characterized by converting to a level proportional to one electrical signal.

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