JP2010136146A - Optical receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiving device which requires a smaller number of optical components than the conventional technology. <P>SOLUTION: Provided is a device for receiving transmitted optical signals including a plurality of subcarriers from an optical transmission device. The device includes a laser diode for generating local light and a reception means. The reception means includes: a first means which receives transmitted optical signals by coherent reception using the local light and outputs in-phase and orthogonal optical signals; a second means which converts the optical signals output from the first means into electrical signals and outputs them; a third means which converts the output of the second means into digital signals; a fourth means which compensates for dispersion of the resulting digital in-phase and orthogonal signals; and a fifth means which Fourier-transforms the in-phase and orthogonal signals compensated for dispersion. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiver of an optical communication system using a plurality of subcarriers.

  Currently, a 40 Gb / s optical transmission system has been put into practical use, and a 100 Gb / s system has been studied (for example, see Non-Patent Document 1).

  According to Non-Patent Document 1, on the transmission side, a Mach-Zehnder modulator (MZM) generates two subcarriers from continuous light generated by a laser diode, and a filter (MZI) using a Mach-Zehnder interferometer has two subcarriers. Are output to a differential quadrature phase shift keying (DQPSK) modulator having a modulation rate of 25 GBaud, and the outputs of the DQPSK modulators are combined to generate an optical signal of 100 Gb / s. It has gained.

  On the receiving side, after dispersion compensation, the received optical signal is demodulated using a discrete Fourier transform circuit (for example, see Non-Patent Document 2) including a Mach-Zehnder delay interferometer (MZDI) and an optical gate formed by MZM. ing.

A. Sano, et al. “30 × 100-Gb / sall-optical OFDM transmission over 1300 km SMF with 10 ROADMModes”, Hiroaki Sanjoh, et al. , “Optical orthogonal frequency division multiplexing using frequency / time domain filtering for high spectral up to 1 bit / s / Hz2”, FC2

  The present invention is applicable to an optical transmission system of 100 Gb / s, and an object of the present invention is to provide an optical receiver capable of reducing necessary optical components from the prior art. It is another object of the present invention to provide an optical receiver that can suppress the occurrence of errors in reception and demodulation processing from the prior art.

According to the optical receiver of the present invention,
An apparatus for receiving a transmission optical signal including a plurality of subcarriers from an optical transmission apparatus, comprising a laser diode for generating local light and a receiving means, wherein the receiving means uses local light A first means for coherently receiving a transmission optical signal and outputting in-phase and quadrature optical signals; a second means for converting an optical signal output from the first means into an electrical signal; and a second means Third means for converting the output of the means into a digital signal, fourth means for performing dispersion compensation on the in-phase and quadrature signals after digital conversion, and Fourier transform processing of the in-phase and quadrature signals after dispersion compensation And a fifth means.

According to another embodiment of the optical receiver of the present invention,
It is also preferable to further include means for generating local light to be input to each receiving means from continuous light output from the laser diode.

According to another embodiment of the optical receiver of the present invention,
The receiving means preferably further comprises sixth means for performing polarization mode dispersion compensation of the output signal of the fifth means.

  The coherent reception process and the compensation process performed after digital signal conversion enable an optical transmission system in which the number of optical components used compared to the prior art is reduced and errors are suppressed. In particular, it is advantageous for a system using polarization multiplexing by performing polarization mode dispersion compensation after digital conversion.

  The best mode for carrying out the present invention will be described in detail below with reference to the drawings. In the following, a system using two subcarriers will be described, but it is naturally possible to use three or more subcarriers.

  FIG. 1 is a block diagram of an optical transmitter used in the optical transmission system of the present invention. According to FIG. 1, the optical transmission apparatus includes a laser diode 81, a Mach-Zehnder modulator 82, a duplexer 83, DQPSK modulators 84 and 85, and a multiplexer 86.

  The laser diode 81 generates continuous light having a predetermined wavelength, the Mach-Zehnder modulator 82 generates a signal including two subcarriers by phase-modulating the continuous light, and the duplexer 83 outputs the output of the Mach-Zehnder modulator 2. Each subcarrier is extracted from the optical signal and output to DQPSK modulators 84 and 85, respectively. The DQPSK modulators 84 and 85 respectively DQPSK-modulate and output the input subcarriers, and the multiplexer 86 multiplexes and outputs the optical signals from the DQPSK modulators 84 and 85.

  For example, if the modulation rate at the DQPSK modulators 84 and 85 is 25 Gbaud, a transmission rate of 100 Gb / s can be obtained.

  FIG. 2 is a block diagram of the optical receiver according to the first embodiment of the present invention. According to FIG. 2, the optical receiver includes a laser diode 1 and a receiver 2, and the receiver 2 includes a 90-degree hybrid 20, photoelectric converters (PD) 31 and 32, and an analog-digital converter. (ADC) 41 and 42, a compensation circuit 50, a Fourier transformer (FFT) 60, and a compensation circuit 70 are provided. In addition, this embodiment can be used when the band of the photoelectric converters 31 and 32 can process the frequency band of the received optical signal, that is, the band including all subcarriers.

  The receiving unit 2 performs coherent reception of an optical signal from the optical transmission device by local light from the laser diode 1. Specifically, the 90-degree hybrid 2 inputs local light and an optical signal from an optical transmission device, and outputs an in-phase (I) and quadrature (Q) optical signal. The photoelectric converters 31 and 32 convert in-phase and quadrature optical signals into electrical signals, respectively, and the analog-digital converters 41 and 42 convert in-phase and quadrature signals from analog signals into digital signals, respectively.

  The compensation circuit 50 is an FIR filter that compensates the digitized in-phase and quadrature signals for chromatic dispersion and the like applied in the optical transmission line, and the Fourier transformer 60 applies the signal after dispersion compensation to the Fourier transform. The signal after conversion and Fourier transform is compensated and decoded by the compensation circuit 70 as necessary. The compensation circuit 70 compensates for a signal by using, for example, a training signal or by using a Blind Optimization Algorithm. The compensation circuit 70 can also compensate for polarization mode dispersion (PMD: Polarization Mode Dispersion), so that signal degradation when using polarization division multiplexing (PDM) can be efficiently suppressed.

  FIG. 3 is a block diagram of an optical receiver according to the second embodiment of the present invention. According to FIG. 3, the optical receiver includes a laser diode 1, a Mach-Zehnder modulator 3, a duplexer 4, and a receiving unit 2 corresponding to each subcarrier. The functional block of the receiving unit 2 is the same as that shown in FIG. In this embodiment, the Mach-Zehnder modulator 3 phase-modulates continuous light generated by the laser diode 1 and generates a signal including the same number of local lights as the receiver 2, as in the optical transmission device shown in FIG. The demultiplexer 4 demultiplexes an optical signal including a plurality of local lights each having a different frequency, which is output from the Mach-Zehnder modulator 3, and outputs each local light to the receiving unit 2. The receiving unit 2 The same processing as described in the first embodiment is performed on the sub-carrier.

  The frequency of local light received by each receiver 2 is the subcarrier frequency to be processed by the receiver 2 of the optical signal output from the 90-degree hybrid 20 of the receiver 2. The electric signal for phase modulating the continuous light output from the laser diode 1 in the Mach-Zehnder modulator 3 is designed so that the frequency of each local light emission satisfies the above conditions.

  As described above, the coherent reception process and the compensation process performed by the compensation circuits 50 and 70 after the digital signal conversion enable an optical transmission system in which the number of optical components used and the occurrence of errors are suppressed compared to the prior art. . In particular, it is advantageous for a system using a PDM by the compensation processing in the compensation circuit 70.

  2 or 3, that is, a configuration in which a plurality of receiving units 2 that process a plurality of subcarriers are provided may be employed.

It is a block diagram of an optical transmitter. It is a block diagram of the optical receiver in 1st Embodiment of this invention. It is a block diagram of the optical receiver in 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,81 Laser diode 2 Receiving part 3,82 Mach-Zehnder modulator 4,83 Demultiplexer 20 90 degree hybrid 31,32 Photoelectric converter 41,42 Analog-digital converter 50,70 Compensation circuit 60 Fourier transformer 84,85 DQPSK modulator 86 multiplexer

Claims (3)

An apparatus for receiving a transmission optical signal including a plurality of subcarriers from an optical transmission apparatus,
A laser diode for generating local light;
Receiving means;
With
The receiving means includes
First means for coherently receiving a transmission optical signal using local light and outputting in-phase and quadrature optical signals;
Second means for converting the optical signal output by the first means into an electrical signal and outputting the electrical signal;
Third means for converting the output of the second means into a digital signal;
A fourth means for performing dispersion compensation on the in-phase and quadrature signals after digital conversion;
A fifth means for performing Fourier transform processing of the in-phase and quadrature signals after dispersion compensation;
A receiving device. A plurality of receiving means;
Means for generating local light to be input to each receiving means from the continuous light output from the laser diode;
The apparatus of claim 1. The receiving means further includes sixth means for performing polarization mode dispersion compensation of the output signal of the fifth means.
The apparatus according to claim 1 or 2.

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