JP2002204210A - Device and method for optical reception - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give the same constitution to a plurality of optical receivers of a WDM system and to provide an optical receiver which automatically adjusts the optimum threshold. SOLUTION: The optical receiver 10 is equipped with an optical coupler 101 which branches an optical signal, an optical amplifier 102 and a photoelectric converting circuit 103 which inputs the branched lights respectively, a discriminative regeneration part 109 on the output side of the optical amplifier 102, a low-pass filter 104 on the output side of the photoelectric conversion part 103, a phase difference detecting circuit 105 which detects the phase difference between its output signal and the output signal of a monitoring receiver, and a threshold adjusting circuit 110 which controls the threshold of the discriminative regeneration part 109 according to its output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver, and more particularly to an optical receiver having an automatic threshold adjusting circuit for automatically adjusting a threshold in an optical communication system using an optical fiber and an optical receiving method.

[0002]

2. Description of the Related Art Optical communication using optical fibers is rapidly replacing conventional telecommunications in fields such as subscriber telephones, data communication, and LANs (local area networks) due to their large communication capacity and excellent noise immunity. Spreading.

The prior art in such a technical field is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2000-236298, "Automatic dispersion compensation circuit and optical transmission system using the same,"
"Method and Apparatus for Controlling Chromatic Dispersion and Method of Detecting Dispersion Amount" in JP-A-68657, "Fiberoptic Dispersion Method and Apparatus" in JP-A-62-134535, and "Automatic Method and Apparatus" in JP-A-10-163962. And the like.

[0004] D-WDM (Dense Wavelength Divisio)
n Multiplexing) system, 30 to 100
Optical signals of different wavelengths are input to the optical receiver with different degradations (or reception errors or the like).
On the other hand, it is preferable that all receivers are basically realized by the same configuration and adjustment. However, in the related art, since adjustment is performed using a signal of a specific (or fundamental) wavelength, when a signal of another wavelength is received, there is a case where deterioration is greater than that of a signal of the fundamental wavelength.

[0005]

For example, in backbone optical communication, a 1.3 μm zero-dispersion fiber is used for a transmission line.
Approximately 18 ps / nm / km when transmitting optical signals in the 1.5 μm band
Is known to have a variance of Due to the deterioration of the optical signal due to the influence of the dispersion, the optical signal may not be transmitted and received correctly in long-distance transmission. In particular, in the case of D-WDM, 30 to 100 or more optical signals are transmitted collectively at intervals of 1 nm or less, so that the wavelengths of the transmitted optical signals are diversified. Therefore, the degree of deterioration of each optical signal affected by dispersion differs depending on the transmission distance or the wavelength. Even if the dispersion of the transmission line is compensated so as to be 0 with reference to a certain wavelength, the dispersion remains at other wavelengths by the wavelength difference from the reference optical signal. Depending on the degree of deterioration of the optical waveform caused by this, there is a problem that deterioration occurs in the discriminating / reproducing unit of the receiver and a signal cannot be transmitted correctly.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve or mitigate the above-mentioned problems, and to control the threshold value of the discrimination / reproduction unit in accordance with the degree of deterioration due to chromatic dispersion, thereby preventing the reception deterioration from occurring. The purpose is to provide a receiving method.

[0007]

SUMMARY OF THE INVENTION An optical receiver according to the present invention comprises: an optical transmission section including a plurality of optical transmitters each using light of a different wavelength and a monitoring optical transmitter; What is claimed is: 1. An optical receiver for a WDM system, comprising: a transmission unit including a WDM coupler; and an optical reception unit including a plurality of optical receivers and a monitoring optical receiver, wherein the optical receiver splits an optical signal received via the WDM coupler. A coupler, an optical amplifier that amplifies one of the lights split by the optical coupler, an identification reproducing unit connected to an output side of the optical amplifier, and converts the other light split by the optical amplifier into an electric signal. An optical-to-electrical conversion circuit, a low-pass filter connected to the output side of the optical-to-electrical conversion circuit, and a phase difference detector for detecting a phase difference between an output signal of the low-pass filter and an output signal of the above-mentioned monitoring optical receiver. Times When provided with a threshold adjustment circuit that controls the threshold of the reproducing unit receives the output of the phase difference detecting circuit.

According to a preferred embodiment of the optical receiver of the present invention, a plurality of optical receivers used in the WDM system have the same configuration. A light receiving unit and an equalizing amplifier are provided between the optical amplifier and the identification reproducing unit. An identification reproduction circuit using a PLL is used as the identification reproduction unit. The optical signal to be transmitted is 1.5
The transmission line is a 1.3 μm band zero dispersion fiber.

Further, in the optical receiving method of the present invention, an optical transmitting unit including a plurality of optical transmitters using different wavelengths of light and a supervisory control optical transmitter, and the optical transmitting unit are disposed at both ends of an optical fiber transmission line. W having a transmission unit including a WDM coupler and an optical reception unit including a plurality of optical receivers and a monitoring optical receiver
In an optical receiving method of a DM system, an optical signal received via a WDM coupler is branched by an optical coupler, one of the branched lights is amplified, and then discriminated and reproduced, and the other light branched by the optical coupler is separated. The signal is converted into an electric signal and passed through a low-pass filter, and the threshold value of the identification reproduction is controlled based on the phase difference between the output signal of the low-pass filter and the output signal of the monitoring optical receiver.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of a preferred embodiment of an optical receiver and an optical receiving method according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a system configuration diagram of an optical transmission system to which an optical receiver and an optical receiving method according to the present invention can be applied. This optical transmission system includes an optical transmission unit, an optical transmission unit, and an optical reception unit. The optical transmitter includes a plurality of optical transmitters 1 and 2, a supervisory control optical transmitter 3, and a low-frequency superimposing circuit 4. The optical transmission unit is a WDM coupler 5,
The transmission path (optical fiber) 6 and the WDM coupler 7 are included. Further, the optical receiving unit includes a plurality of optical receivers 10 and 20.
And a monitoring optical receiver 30.

The optical transmission system shown in FIG. 1 will be described as a WDM system having a first optical signal wave for monitoring and control and a second signal wave for an optical main signal. Note that this is merely an example of the present invention, and the present invention has no limitation on the number of wavelengths. The optical transmitter 1 of the optical transmitter transmits an optical main signal of, for example, 1.552 μm. The optical transmitter 2 transmits an optical main signal of, for example, 1.600 μm. The supervisory control optical transmitter 3 transmits an optical signal of, for example, 1.520 μm. The low-frequency superimposing circuit 4 superimposes a low-frequency pulse signal for monitoring and control on the optical main signals of the optical transmitters 1 and 2, respectively. Further, as shown in FIG. 1, optical transmitters 1 and 2 include an optical amplifier (amplifier) 1.
a, 2a, and amplifies each optical main signal and the optical signal for monitoring and control. And the WDM coupler 5 of the optical transmission unit is
The optical wavelengths from the optical transmitters 1 and 2 and the supervisory control optical transmitter 3 are combined.

The transmitted optical signal is propagated on a transmission line 6 (80 km in this example) using an optical fiber. Then, the light is branched by the WDM coupler 7 and the optical receiver 1
0, 20, and 30 are input.

FIG. 2 is a block diagram showing the configuration of the first embodiment of the optical receiver (eg, optical receiver 10) according to the present invention shown in FIG. The optical receivers 10 and 20 have the same configuration. Further, the monitoring optical receiver 30 includes:
The same applies to the optical coupler 101, the optical-to-electrical conversion circuit 103 for performing optical-to-electrical conversion, and the low-pass filter 104 for extracting a low-frequency signal therefrom, for monitoring control signals. When the number of optical wavelengths is increased, the optical receivers 10, 20
Etc. also increase.

The optical receiver 10 includes an optical coupler 101, an optical amplifier 102, an optical-electrical conversion circuit 103, a low-pass filter 104, a phase difference detection circuit 105, a light receiving section 106, an equalizing amplification section 107, and a CLK (clock) filter. 108, an identification reproducing unit 109 and a threshold adjustment circuit 110. Here, the optical coupler 101 splits the input optical signal. The optical-electrical conversion circuit 103 includes the optical coupler 1
01 is subjected to optical-electrical conversion of the optical signal split by 01. The low-pass filter 104 extracts a superposed low-frequency signal from the signal converted into an electric signal by the optical-electrical conversion circuit 103. The phase difference detection circuit 105 includes the low-pass filter 10
4 is compared with the phase detected by the receiver 30.

Next, the operation of the optical receiver according to the present invention will be described with reference to FIGS. Here, the configuration of the WDM system of the monitoring control optical signal, the first optical signal wave, and the second optical signal wave will be described. An optical transmitter 1 for transmitting an optical main signal of 1.550 μm, an optical transmitter 2 for transmitting an optical main signal of 1.600 μm, and 1.520 μ for monitoring and control
The low-frequency superimposing circuit 4 superimposing the synchronized low-frequency pulse signal is superimposed on the supervisory control optical transmitter 3 transmitting the m optical signal. These optical main signals pass through the optical amplifiers 1a and 2a, and the optical signals for monitoring and control are directly input to the WDM coupler 5. The phase relationship between the respective optical signals on which the low-frequency signal is superimposed is shown in FIG. The transmitted optical signal propagates through 80 km of the transmission line 6 using an optical fiber. And WDM
The phase relationship after being branched by the coupler 7 is as shown by A 'under the influence of the dispersion of the transmission path.

The optical signals input to the optical receivers 10 and 20 are compared with 1.520 μm, which is a reference, respectively.
This produces a phase difference of 8 nsec (nanoseconds) and 46 nsec. This phase difference is a value sufficient to be detected by a normal phase difference detection circuit. In the receiver 10, the input light is split by the optical coupler 101. One branched by the optical coupler 101 is amplified by the optical amplifier 102 as a main signal and input to the light receiving unit 106. From here, the equalization amplification section 107 performs equalization amplification and CLK extraction with the CLK filter 108, and inputs the same to the identification reproduction section 109. Optical coupler 101
The other optical signal branched by is converted into an electric signal by an optical-electrical conversion circuit 103 that performs optical-electrical conversion, and a low-frequency signal superimposed by a low-pass filter 104 is extracted. Here, the detected phase is the same as the detected optical receiver 3.
The phase of the 0 signal is compared with the phase difference detection circuit 105.

FIG. 3 is an explanatory diagram simply showing the relationship between the variance and the optimum identification level. 3A shows a case where the variance is 0, FIG. 3B shows a case where the variance is small, and FIG. 3C shows a case where the variance is large. Generally, in waveform deterioration due to dispersion, as is apparent from FIGS. 3A to 3C, the optimum value of identification tends to approach the “0” side. Therefore, based on the value indicated by the phase difference detection circuit 105, the threshold adjustment circuit 110 adjusts the voltage of the identification reproduction unit 109. Thereby, it is possible to always maintain the optimum discrimination level even when an optical signal of any wavelength is used.

Next, FIG. 4 shows a configuration diagram of a second embodiment of the optical receiver according to the present invention. In the optical receiver 10 ', the same reference numerals are used for the components corresponding to the components of the optical receiver 10 shown in FIG. 3 for convenience. The optical receiver 10 'includes an optical coupler 101, an optical amplifier 102, an optical-electrical conversion circuit 103, a low-pass filter 104, a phase difference detection circuit 105, a light receiving unit 106, and a PLL (Phase
It is composed of an identification reproduction circuit 120 using a locked loop. In another embodiment, the main signal portion is
Instead of the equalization amplification and identification reproduction circuit using clock extraction using a filter, the identification reproduction circuit 120 uses a PLL instead.

The configuration and operation of the preferred embodiment of the optical receiver and the optical receiving method according to the present invention have been described above in detail. However, such embodiments are merely exemplary of the present invention,
It should be noted that the present invention is not limited in any way. It will be readily apparent to those skilled in the art that various modifications can be made in accordance with the particular application without departing from the spirit of the invention.

[0021]

As will be understood from the above description, according to the optical receiver and the optical receiving method of the present invention, the following remarkable practical effects can be obtained. That is, even when the transmission path is switched and the amount of dispersion changes, the threshold value of the identification reproducing unit can be automatically adjusted to the optimum value. Therefore, it is not necessary to individually adjust the threshold according to the reception wavelength.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a WDM system to which an optical receiver and an optical receiving method according to the present invention can be applied.

FIG. 2 shows a first embodiment of the optical receiver according to the invention shown in FIG.
FIG. 2 is a block diagram illustrating a configuration of the embodiment.

FIG. 3 is an operation explanatory diagram of the optical receiver shown in FIG. 2;

FIG. 4 is a block diagram showing a configuration of a second embodiment of the optical receiver according to the present invention.

[Explanation of symbols]

 1, 2 optical transmitter 3 supervisory control optical transmitter 4 low frequency superposition circuit 5, 7 WDM coupler 6 transmission line (optical fiber) 10, 20 optical receiver 30 supervisory optical receiver 101 optical coupler 102 optical amplifier 103 light -Electric conversion circuit 104 Low-pass filter 105 Phase difference detection circuit 106 Light receiving unit 107 Equalization amplification unit 109 Identification reproduction unit 110 Threshold adjustment circuit 120 Identification reproduction circuit using PLL

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04J 14/00 14/02

Claims (6)

[Claims] An optical transmitter including a plurality of optical transmitters each using light of a different wavelength and an optical transmitter for supervisory control;
An optical receiver of a WDM system including a transmission unit including a WDM coupler disposed at both ends of an optical fiber transmission line and an optical reception unit including a plurality of optical receivers and a monitoring optical receiver. An optical coupler that splits an optical signal to be received by the optical amplifier, an optical amplifier that amplifies one of the lights split by the coupler, an identification reproducing unit connected to an output side of the optical amplifier, and an optical coupler that is split by the optical coupler. An optical-electrical conversion circuit for converting the other light into an electric signal, a low-pass filter connected to the output side of the optical-electrical conversion circuit, and an output signal of the low-pass filter and an output signal of the monitoring optical receiver. An optical receiver, comprising: a phase difference detection circuit that detects a phase difference; and a threshold adjustment circuit that receives an output of the phase difference detection circuit as an input and controls a threshold of the identification reproducing unit. 2. The apparatus according to claim 1, wherein the plurality of optical receivers used in the WDM system have the same configuration.
An optical receiver according to claim 1. 3. The optical receiver according to claim 1, further comprising a light receiving unit and an equalizing amplifier between said optical amplifier and said reproducing unit. 4. A phase-locked loop (PLL) as said discrimination reproducing section.
3. The optical receiver according to claim 1, wherein an identification reproduction circuit using an ocked loop is used. 5. An optical signal to be transmitted having a band of 1.5 μm,
5. The optical receiver according to claim 1, wherein a 1.3 μm band zero dispersion fiber is used for the transmission line. 6. An optical transmission unit including a plurality of optical transmitters each using light of a different wavelength and an optical transmitter for supervisory control,
In an optical receiving method of a WDM system having a transmitting unit including a WDM coupler disposed at both ends of an optical fiber transmission line and an optical receiving unit including a plurality of optical receivers and a monitoring optical receiver, The optical signal to be received is split by an optical coupler, one of the split lights is amplified, and then discriminated and reproduced. The other light split by the optical coupler is converted into an electric signal and passed through a low-pass filter. An optical receiving method, comprising: controlling a threshold value of the identification and reproduction based on a phase difference between an output signal of a filter and an output signal of a monitoring optical receiver.