JP2012249126A - Coherent receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption significantly when compared with the digital coherent system, by reproducing the local light emission stably and simply over a wide wavelength range.SOLUTION: The coherent receiver comprises: an optical amplifier 1 which amplifies the input signal light; an optical demultiplexer 2 which demultiplexes the signal light amplified by the optical amplifier 1 into two; a local emission reproducer 3 which reproduces the local emission from one signal light demultiplexed by the optical demultiplexer 2; an optical multiplexer 4 which multiplexes the other signal light demultiplexed by the optical demultiplexer 2 and the local emission output from the local emission reproducer 3; and an optical receiver 5 which performs photoelectric conversion of the light output from the optical multiplexer 4. The local emission reproducer 3 consists of an optical frequency multiplexer 6 which outputs the second harmonic having twice the frequency of one signal light demultiplexed by the optical demultiplexer 2, and an optical frequency divider 7 which outputs the local emission while dividing the frequency of the second harmonic by 2.

Description

  The present invention relates to an optical receiver that can be used for optical communication and the like.

  As a detection method used in coherent optical communication, homodyne detection using local light emission and delayed detection using a delay interferometer are used. Although delayed detection does not require local light emission, the reception sensitivity is inferior by 3 dB compared to homodyne detection. On the other hand, with homodyne detection, it is difficult to reproduce local light, and at present, a digital coherent method that demodulates a data signal by calculating a signal at high speed after photoelectric conversion to estimate the local light frequency is mainly used. (Refer nonpatent literature 1).

Kazuo Kikuchi, “Latest Trends and Prospects of Coherent Optical Communication Technology”, Optoelectronics Technology Promotion Association, Optnews, Vol. 3, No. 4,2009

  However, the digital coherent method has a problem that a very large electric power is required for the calculation. On the other hand, before the digital coherent method was proposed, a method of reproducing local light by synchronization of light injection into a laser was proposed. However, in this method, local light is reproduced stably and easily in a wide wavelength range. It was difficult.

  The present invention has been made in order to solve the above-described problems, and can reproduce local light emission stably and easily in a wide wavelength range, and can significantly reduce power consumption compared with a digital coherent method. An object is to provide a receiver.

  The present invention relates to an optical demultiplexer that demultiplexes an input signal light into two in a coherent receiver that demodulates a signal from input signal light whose modulation format is binary phase modulation, and is demultiplexed by the optical demultiplexer. A local light regenerator that regenerates local light from one signal light, and an optical multiplexer that combines the other signal light demultiplexed by the optical demultiplexer and the local light output from the local light regenerator And a photoreceiver that photoelectrically converts the light output from the optical multiplexer, and the local light regenerator has a frequency that is twice that of one of the signal lights demultiplexed by the optical demultiplexer. An optical frequency multiplier that outputs a second harmonic and an optical frequency divider that divides the second harmonic output from the optical frequency multiplier by two and outputs the local light. It is characterized by this.

Further, in the configuration example of the coherent receiver according to the present invention, the phase difference between the other signal light demultiplexed by the optical demultiplexer and the local light output from the local light regenerator is further adjusted. The phase shifter is provided.
In the configuration example of the coherent receiver of the present invention, the local light regenerator further includes an output light of the optical frequency multiplier between the optical frequency multiplier and the optical frequency divider. A high-pass filter that transmits only the second-order harmonics is provided.
In the configuration example of the coherent receiver according to the present invention, the optical demultiplexer and the optical multiplexer are optical fiber couplers, respectively, and the optical frequency multiplier is a second harmonic generation element using PPLN. In addition, the optical frequency divider is a 1 / 2-order frequency dividing element using PPLN.

  The present invention also provides a polarization demultiplexer that separates input signal light into TE polarization and TM polarization in a coherent receiver that demodulates a signal from input signal light whose polarization format is polarization multiplexed quaternary phase modulation. The first optical demultiplexer that demultiplexes the TM polarized signal light output from the polarization demultiplexer into two, and the TE polarized signal light output from the polarization demultiplexer. A polarization rotator for converting into TM polarized signal light, a second optical demultiplexer for splitting the TM polarized signal light output from the polarization rotator into two, and the first First and second local light regenerators that are connected in series in two stages after the optical demultiplexer and reproduce local light from one signal light demultiplexed by the first optical demultiplexer; A second stage is connected in series after the second optical demultiplexer, and regenerates local light from one signal light demultiplexed by the second optical demultiplexer. The first local light regenerator, the other signal light demultiplexed by the first optical demultiplexer, and the local light output from the second local light regenerator are combined. An optical multiplexer; a second optical multiplexer that combines the other signal light demultiplexed by the second optical demultiplexer and the local light output from the fourth local light regenerator; A first light receiver that photoelectrically converts light output from the first optical multiplexer; and a second light receiver that photoelectrically converts light output from the second optical multiplexer; The regenerator divides the second harmonic output from the optical frequency multiplier that outputs a second harmonic having a frequency twice that of the input signal light by 1/2. And an output optical frequency divider.

In addition, one configuration example of the coherent receiver according to the present invention further includes the other signal light demultiplexed by the first optical demultiplexer and the local light output from the second local light regenerator. Between the first phase shifter that adjusts the phase difference between the signal light, the other signal light demultiplexed by the second optical demultiplexer, and the local light output from the fourth local light regenerator And a second phase shifter for adjusting the phase difference.
Further, in one configuration example of the coherent receiver of the present invention, each local light regenerator further includes the light output from the optical frequency multiplier between the optical frequency multiplier and the optical frequency divider. A high-pass filter that transmits only the second harmonic is provided.
In the configuration example of the coherent receiver of the present invention, the first and second optical demultiplexers and the first and second optical multiplexers are optical fiber couplers, respectively, and the optical frequency multiplier The device is a second harmonic generation element by PPLN, and the optical frequency divider is a 1/2 second frequency generation element by PPLN.

  According to the present invention, an optical demultiplexer, a local light regenerator, an optical multiplexer, and a light receiver are provided, and the local light regenerator includes an optical frequency multiplier and an optical frequency divider. As a result, local light can be reproduced stably and easily in a wide wavelength range, and there is no need to perform arithmetic processing as in the conventional digital coherent method, so the power consumption is greatly reduced compared to the digital coherent method. be able to. In the present invention, there may be dispersion compensation when the dispersion is large, or computation processing after photoelectric conversion to separate the polarization multiplexed signal, but the processing speed is low because there is no need to perform carrier estimation. The power consumption can be greatly reduced compared to the conventional digital coherent method.

  In the present invention, the polarization demultiplexer, the first and second optical demultiplexers, the polarization rotation element, the first, second, third, and fourth local light regenerators, By providing the first and second optical multiplexers and the first and second optical receivers, and by forming each local light regenerator from an optical frequency multiplier and an optical frequency divider, in a wide wavelength range The local light can be reproduced stably and easily, and the power consumption can be greatly suppressed as compared with the digital coherent method. In the present invention, there may be dispersion compensation when the dispersion is large, or computation processing after photoelectric conversion to separate the polarization multiplexed signal, but the processing speed is low because there is no need to perform carrier estimation. The power consumption can be greatly reduced compared to the conventional digital coherent method.

It is a block diagram which shows the structure of the coherent receiver which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the coherent receiver which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the coherent receiver which concerns on the 3rd Embodiment of this invention.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a coherent receiver according to the first embodiment of the present invention.
The coherent receiver according to the present embodiment includes an optical amplifier 1, an optical demultiplexer 2, a local light regenerator 3, an optical multiplexer 4, and a light receiver 5. The local light regenerator 3 includes at least a pair of optical frequency multipliers 6 and an optical frequency divider 7.

Hereinafter, the operation of the coherent receiver according to the present embodiment will be described. The optical amplifier 1 amplifies input signal light. The optical demultiplexer 2 demultiplexes the signal light amplified by the optical amplifier 1 into two.
The optical frequency multiplier 6 outputs signal light (second harmonic) having a frequency twice that of one signal light demultiplexed by the optical demultiplexer 2. When binary phase modulation is considered as the modulation format of the input signal light, in the second harmonic generated by the optical frequency multiplier 6, the binary phase becomes the same phase, and the modulation component is removed.

  The optical frequency divider 7 divides the second harmonic output from the optical frequency multiplier 6 by ½. As a result, the frequency of the light output from the optical frequency divider 7 becomes half the frequency of the second harmonic, so that the light whose phase is not modulated at the same frequency as the input signal light, that is, local light is emitted. Played.

The optical multiplexer 4 combines the other signal light demultiplexed by the optical demultiplexer 2 and the local light output from the optical frequency divider 7. As a result, interference between the signal light and the local light occurs.
The light receiver 5 such as a photodiode photoelectrically converts the light output from the optical multiplexer 4 and outputs an electrical signal. Thus, homodyne detection for demodulating a signal using local light is performed.

  In this embodiment, local light can be reproduced stably and easily in a wide wavelength range, and it is not necessary to perform arithmetic processing as in the conventional digital coherent method. Can be suppressed.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a configuration of a coherent receiver according to the second exemplary embodiment of the present invention. This embodiment shows a specific example of the first embodiment, and shows an example in which binary phase modulation is used as the modulation format of the input signal light.

  The coherent receiver of this embodiment includes an erbium-doped fiber amplifier (EDFA) 10 that is an optical amplifier, an optical fiber coupler 11 that is an optical demultiplexer, a local light regenerator 12, and a phase shifter. 13, an optical fiber coupler 14 that is an optical multiplexer, and a light receiver 15. The local light regenerator 12 includes a second harmonic generation element (Second Harmonic Generation: SHG) 16 that is an optical frequency multiplier, a high-pass filter 17, and a 1/2 order frequency generation that is an optical frequency divider. It consists of the element 18. As the second harmonic generation element 16, a second harmonic generation element using a periodically poled lithium niobate crystal (Periodically Poled Lithium Niobate: PPLN) is used. Is used.

The EDFA 10 amplifies input signal light. The optical fiber coupler 11 demultiplexes the signal light amplified by the EDFA 10 into two.
The second harmonic generation element 16 outputs signal light (second harmonic) having a frequency twice that of one of the signal lights demultiplexed by the optical fiber coupler 11.

The high-pass transmission filter 17 transmits only the second harmonic in the output light of the second harmonic generation element 16. Thereby, the phase noise of local light can be reduced and the frequency purity can be increased.
The 1/2 order frequency dividing element 18 divides the second harmonic output from the high-pass transmission filter 17 into 1/2 and reproduces local light.

  In order to fix the level for each sign of the intensity modulation signal output from the light receiver 15, the phase shifter 13 outputs from the other signal light demultiplexed by the optical fiber coupler 11 and the half-order frequency division generation element 18. The phase difference between the generated local light and the local light is adjusted. Specifically, the phase shifter 13 delays the signal light from the optical fiber coupler 11 by the delay time of the local light regenerator 12.

The optical fiber coupler 14 combines the signal light output from the phase shifter 13 and the local light output from the 1 / 2-order frequency division generating element 18.
The light receiver 15 photoelectrically converts the light output from the optical fiber coupler 14 and outputs an electrical signal. Thus, in the present embodiment, the effects described in the first embodiment can be obtained in an example in which binary phase modulation is used as the modulation format.

  Although not shown, in this embodiment, the polarization of the signal light entering the local light regenerator 12 is set to TM (Transverse Magnetic) polarization by using a polarization controller in advance.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 3 is a block diagram showing a configuration of a coherent receiver according to the third embodiment of the present invention. This embodiment shows an example different from the first embodiment, and shows an example in which polarization multiplexed quaternary phase modulation is used as the modulation format of the input signal light.

  The coherent receiver of the present embodiment includes an EDFA 20 that is an optical amplifier, a polarization beam splitter (PBS) 21, an optical fiber coupler 22, a polarization rotation element 23, and an optical fiber coupler 24. Two local light regenerators 25 and 26 connected in series, a phase shifter 27, an optical fiber coupler 28, a light receiver 29, two local light regenerators 30 and 31 connected in series, and a phase A shifter 32, an optical fiber coupler 33, and a light receiver 34 are included. The configuration of each local light regenerator 25, 26, 30, 31 is the same as that of the local light regenerator 12 of the second embodiment.

The EDFA 20 amplifies input signal light. In order to separate polarization multiplexing, the polarization demultiplexer 21 separates the signal light amplified by the EDFA 20 into TE (Transverse Electric) polarization and TM polarization.
The optical fiber coupler 22 demultiplexes the TM polarized signal light output from the polarization demultiplexer 21 into two. The polarization rotation element 23 converts the TE polarized signal light output from the polarization demultiplexer 21 into TM polarized signal light. The optical fiber coupler 24 demultiplexes the TM polarized signal light output from the polarization rotation element 23 into two.

  The operation of each local light regenerator 25, 26, 30, 31 is the same as that of the local light regenerator 12 of the second embodiment. In the present embodiment, since the modulation format is quaternary phase modulation, two-stage local light regenerators connected in series are used for local light reproduction. The local light regenerators 25 and 26 regenerate local light from one signal light demultiplexed by the optical fiber coupler 22. Similarly, the local light regenerators 30 and 31 regenerate local light from one signal light demultiplexed by the optical fiber coupler 24.

The phase shifter 27 adjusts the phase difference between the other signal light demultiplexed by the optical fiber coupler 22 and the local light output from the local light regenerator 26. Specifically, the phase shifter 27 delays the signal light from the optical fiber coupler 22 by the time that is the sum of the delay time of the local light regenerator 25 and the delay time of the local light regenerator 26.
The optical fiber coupler 28 combines the signal light output from the phase shifter 27 and the local light output from the local light regenerator 26. The light receiver 29 photoelectrically converts the light output from the optical fiber coupler 28 and outputs an electrical signal. Thereby, the TM polarization component can be demodulated.

The phase shifter 32 adjusts the phase difference between the other signal light demultiplexed by the optical fiber coupler 24 and the local light output from the local light regenerator 31. Specifically, the phase shifter 32 delays the signal light from the optical fiber coupler 24 by a time corresponding to the sum of the delay time of the local light regenerator 30 and the delay time of the local light regenerator 31.
The optical fiber coupler 33 combines the signal light output from the phase shifter 32 and the local light output from the local light regenerator 31. The light receiver 34 photoelectrically converts the light output from the optical fiber coupler 33 and outputs an electrical signal. Thereby, the TE polarization component can be demodulated.

  Thus, in the present embodiment, the effects described in the first embodiment can be obtained in an example in which polarization multiplexed quaternary phase modulation is used as the modulation format.

  The present invention can be applied to a coherent receiver that demodulates a signal using local light.

  DESCRIPTION OF SYMBOLS 1 ... Optical amplifier, 2 ... Optical demultiplexer, 3, 12, 25, 26, 30, 31 ... Local light emission regenerator, 4 ... Optical multiplexer, 5, 15, 29, 34 ... Light receiver, 6 ... Optical frequency Multiplier, 7 ... Optical frequency divider, 10, 20 ... Erbium-doped fiber amplifier, 11, 14, 22, 24, 28, 33 ... Optical fiber coupler, 13, 27, 32 ... Phase shifter, 16 ... Second harmonic Wave generating element, 17... High-pass filter, 18... 1/2 order frequency generating element, 21... Polarization splitter, 23.

Claims (8)

In a coherent receiver that demodulates a signal from input signal light whose modulation format is binary phase modulation,
An optical demultiplexer that demultiplexes the input signal light into two;
A local light regenerator that reproduces local light from one signal light demultiplexed by the optical demultiplexer;
An optical multiplexer for multiplexing the other signal light demultiplexed by the optical demultiplexer and the local light output from the local light regenerator;
A light receiver that photoelectrically converts the light output from the optical multiplexer,
The local light regenerator includes an optical frequency multiplier that outputs a second-order harmonic having a frequency twice that of one of the signal lights demultiplexed by the optical demultiplexer, and 2 output from the optical frequency multiplier. A coherent receiver comprising: an optical frequency divider that divides a second harmonic by half and outputs the local light. The coherent receiver of claim 1.
The coherent receiver further includes a phase shifter that adjusts a phase difference between the other signal light demultiplexed by the optical demultiplexer and the local light output from the local light regenerator. The coherent receiver according to claim 1 or 2,
The local light regenerator further includes a high-pass filter between the optical frequency multiplier and the optical frequency divider for transmitting only the second harmonic of the output light of the optical frequency multiplier. A coherent receiver comprising: The coherent receiver according to any one of claims 1 to 3,
Each of the optical demultiplexer and the optical multiplexer is an optical fiber coupler,
The optical frequency multiplier is a second harmonic generation element by PPLN,
The coherent receiver is characterized in that the optical frequency divider is a 1/2 order frequency generation element using PPLN. In a coherent receiver that demodulates a signal from input signal light whose modulation format is polarization multiplexed quaternary phase modulation,
A polarization demultiplexer that separates input signal light into TE polarization and TM polarization;
A first optical demultiplexer that demultiplexes the TM polarized signal light output from the polarization demultiplexer into two;
A polarization rotator for converting TE polarized signal light output from the polarization demultiplexer into TM polarized signal light;
A second optical demultiplexer that demultiplexes the TM polarized signal light output from the polarization rotation element into two;
First and second local light regenerators connected in series in two stages after the first optical demultiplexer and reproducing local light from one signal light demultiplexed by the first optical demultiplexer When,
Third and fourth local light regenerators connected in series in two stages after the second optical demultiplexer and reproducing local light from one signal light demultiplexed by the second optical demultiplexer When,
A first optical multiplexer that multiplexes the other signal light demultiplexed by the first optical demultiplexer and the local light output from the second local light regenerator;
A second optical multiplexer that combines the other signal light demultiplexed by the second optical demultiplexer and the local light output from the fourth local light regenerator;
A first light receiver that photoelectrically converts light output from the first optical multiplexer;
A second light receiver that photoelectrically converts light output from the second optical multiplexer,
Each local light regenerator outputs an optical frequency multiplier that outputs a second harmonic of twice the frequency of the input signal light, and divides the second harmonic output from the optical frequency multiplier by half. A coherent receiver comprising: an optical frequency divider that outputs the signal; The coherent receiver of claim 5, wherein
A first phase shifter that adjusts a phase difference between the other signal light demultiplexed by the first optical demultiplexer and the local light output from the second local light regenerator;
A second phase shifter that adjusts a phase difference between the other signal light demultiplexed by the second optical demultiplexer and the local light output from the fourth local light regenerator; A coherent receiver. The coherent receiver according to claim 5 or 6,
Each local light regenerator further includes a high-pass filter between the optical frequency multiplier and the optical frequency divider that transmits only the second harmonic of the output light of the optical frequency multiplier. A coherent receiver. The coherent receiver according to any one of claims 5 to 7,
The first and second optical demultiplexers and the first and second optical multiplexers are optical fiber couplers, respectively.
The optical frequency multiplier is a second harmonic generation element by PPLN,
The coherent receiver is characterized in that the optical frequency divider is a 1/2 order frequency generation element using PPLN.

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