JP3380755B2 - Automatic chromatic dispersion equalizing optical transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system of an optical transmission system in which a linear repeater and a regenerator are arranged at a predetermined interval between a transmitter and a receiver connected via a transmission optical fiber. The present invention relates to an automatic chromatic dispersion equalization optical transmission system that automatically equalizes the total chromatic dispersion amount in a regenerative repeater section for each linear repeater section.

[0002]

2. Description of the Related Art In recent years, development of optical technology and integration technology,
Due to the progress of high-speed electric circuit technology, the speed of optical transmission systems has been increased, and up to now, a transmission experiment with a transmission speed of 40 Gbit / s per channel due to multiplexing of electric stages has been reported (reference: M. Yoneyama). et al., "A 40-Gbit / s Optica
l Repeater Circuits using InAlAs / InGaAs HEMT Digit
al IC Chip Set ", IEEE MTT-S Digest, WE1D-2,199
7). In a practical system, an ultrahigh-speed optical transmission system having a transmission capacity of 10 Gbit / s is operated as a backbone network (reference: K. Hagimoto et al., "M
ulti-Gigabit-per-second Optical Transmission Syste
ms ", IOOC'95, WC1-1, 1995).

In the future, the development of high-speed broadband communication services is expected due to the opticalization of subscriber systems and the development of multimedia services. In order to provide such communication services economically and efficiently, further speedup is required.
For that purpose, it is an important issue to overcome the limitation of the transmission distance due to the wavelength dispersion of the optical fiber.

Here, chromatic dispersion will be described. Chromatic dispersion is a phenomenon in which different wavelength components forming an optical pulse propagate at different speeds due to the wavelength dependence of the refractive index, which causes waveform distortion after transmission and greatly limits the transmission speed and transmission distance. In the following description, chromatic dispersion will be simply referred to as “dispersion”.

The relationship between the bit rate B and the allowable dispersion amount D is
The signal light wavelength is λ, the speed of light is c, the optical fiber loss is α, the Kerr constant is n ₂ , the effective core area is Seff, the regenerative repeater distance is L, the linear repeater distance is Za, and the transmission output of each linear repeater is P.
out,

[0006]

[Equation 1] (Reference: A. Naka et al., "In-Line Ampli
fier Transmission Distance Determined by Self-Phas
e Modulation and Group-Velocity Dispertion ", J.Ligh
twave Technol., vol.12, no.2, p.280, 1994).

As shown in the equation (1), the allowable dispersion amount D decreases in proportion to the square of the bit rate B, and further decreases in proportion to the square of the regeneration relay distance L. Therefore, the automatic dispersion equalization technology, which automatically measures and equalizes the dispersion characteristic for each transmission line when the system is introduced, is being considered as a useful method in a high-speed optical transmission system.

As a conventional automatic dispersion equalization technique, there is an "automatic equalization system" described in, for example, Japanese Patent Laid-Open No. 9-326755. In this system, by providing a means for automatically equalizing the dispersion in the regenerative repeater section in the transmitter / receiver, it is possible to reduce the design cost and personnel cost required for dispersion compensation. This makes it possible to avoid costly over-specification, which is the worst-case design.

[0009]

By the way, in the automatic dispersion equalization technique described in the above publication, the dispersion amount of the regeneration relay section is collectively determined according to the average dispersion amount of the regeneration relay section which is the transmission path between the transmission and the reception. Equalize. On the other hand, in order to increase the speed, it is necessary to increase the output of the transmission power in order to secure the conventional SN ratio. However, increasing the output power of the transmission power increases the influence of the dispersion and the nonlinear optical effect, and limits the regeneration relay distance at which collective dispersion equalization is possible. Further, in the conventional technique, linear relay becomes difficult as the speed increases. Therefore, it is necessary to introduce a regenerative repeater for each conventional linear repeater section, which causes a significant increase in cost.

The present invention automatically performs dispersion equalization for each linear repeater section, and further optimizes the identification voltage, the phase of the data signal and the clock in the receiving section of the linear repeater to realize high-speed optical An object of the present invention is to provide an automatic wavelength dispersion equalization optical transmission system that enables a long distance of a regenerative repeater section of the transmission system.

[0011]

An automatic wavelength dispersion equalization optical transmission system according to claims 1 to 3 is arranged at a predetermined interval between a transmitter and a receiver connected via an optical fiber for transmission. Equipped with variable dispersion equalizer in linear repeater and regenerative repeater, chromatic dispersion equalization in linear repeater section is performed by linear repeater, and chromatic dispersion equalization in regenerative repeater section is performed by receiver of receiver and regenerator. It is a configuration for performing.

In the automatic chromatic dispersion equalization optical transmission system according to claims 4 to 9 , the modulation frequency component of the alternating chirp signal light transmitted as the test signal light with respect to the dispersion amount set in the variable dispersion equalizer of the linear repeater. Minimum strength ( claims
4 ), the ratio of the modulation frequency component intensity of the alternating chirp signal light to the direct current component intensity is minimized ( claim 5 ), and the modulation frequency component intensity of the phase modulation signal light transmitted as the test signal light due to the PM-AM conversion effect. Is minimized ( claim 6 ), P
The ratio of the modulation frequency component intensity to the DC component intensity due to the M-AM conversion effect is minimized ( claim 7 ), the clock component intensity of the data signal is maximized ( claim 8 ), and the position of the test signal light of two wavelengths is increased. Control is performed so that the phase difference is minimized ( claim 9 ).

In the automatic wavelength dispersion equalization optical transmission system of claims 10 to 12 , the code error rate of the received signal is minimized with respect to the amount of dispersion set in the variable dispersion equalizer of the receiver of the receiver or the regenerator. ( Claim 10 ), the Q value of the received signal becomes maximum ( Claim 11 ), and the clock component strength of the received signal becomes maximum ( Claim 12 ).

According to a thirteenth aspect of the automatic wavelength dispersion equalization optical transmission system of the present invention, the receiving section of the receiving device or the regenerator is arranged so that the code error rate of the received signal is minimized or the Q value of the received signal is maximized. Control the dispersion amount set in the variable dispersion equalizer and the clock phase of the discrimination circuit.

The automatic chromatic dispersion such Kahikari transmission system according to claim 14, bit error rate of the received signal is minimized, or as Q values of the received signal is maximized, the reception unit of the reception device or regenerator It controls the amount of dispersion set in the variable dispersion equalizer and the identification voltage of the identification circuit.

In the automatic chromatic dispersion equalization optical transmission system according to claim 15 , the dispersion amount set in the variable dispersion equalizer of the receiving section of the receiving device or the regenerator is maximized so that the clock component strength of the received signal is maximized. Further, the clock phase of the discriminating circuit of the receiving unit of the receiving device or the regenerative repeater is controlled so that the code error rate of the receiving signal is minimized or the Q value of the receiving signal is maximized.

The automatic chromatic dispersion such Kahikari transmission system according to claim 16, the amount of dispersion clock component intensity is set in the variable dispersion equalizer of the receiving portion of the receiver or regenerator so as to maximize the received signal Further, the discrimination voltage of the discrimination circuit of the reception device or the reception section of the regenerative repeater is controlled so that the code error rate of the reception signal is minimized or the Q value of the reception signal is maximized.

In the automatic chromatic dispersion equalization optical transmission system according to claim 17 , a control line is wired between the transmitter and the receiver, and the transmitter, the linear repeater, the receiving section of the regenerator and the receiver are provided. Each has a control signal transmission / reception circuit, and transmits / receives a test signal and data signal transmission switching and other control signals accompanying the start and end of automatic chromatic dispersion equalization.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION (Basic Structure: Claims 1 to 3 ) FIG. 1 shows the basic structure of an automatic wavelength dispersion equalization optical transmission system of the present invention. In the figure, an automatic wavelength dispersion equalization optical transmission system according to the present invention includes a linear repeater 20 and a regenerative repeater at a predetermined interval between a transmitter 10 and a receiver 30 connected via a transmission optical fiber 1. This is a configuration in which vessels are arranged. The transmitting device 10 and the receiving device 30 can be replaced with the transmitting unit and the receiving unit of the regenerator, respectively. A feature of the present invention is that the linear repeater 20 performs chromatic dispersion equalization in the linear repeater section, and the receiving device (reception unit of the regenerative repeater) 30 performs chromatic dispersion equalization in the regenerative repeater section.

In the figure, in an automatic wavelength dispersion equalization optical transmission system of the present invention, a linear repeater 20 is provided at a predetermined interval between a transmission device 10 and a reception device 30 connected via a transmission optical fiber 1. And a regenerator is arranged. The transmitting device 10 and the receiving device 30 can be replaced with the transmitting unit and the receiving unit of the regenerator, respectively. A feature of the present invention is that the linear repeater 20 performs chromatic dispersion equalization in the linear repeater section, and the receiving device (reception unit of the regenerative repeater) 30 performs chromatic dispersion equalization in the regenerative repeater section.

The transmission device (transmission unit of the regenerator) 10 comprises:
Measurement that switches between test signal and data signal for dispersion equalization
A data transmission switching circuit 11, an optical modulation circuit 12 for generating a data signal light modulated with a data signal at the time of data transmission, and a test signal light modulated with a test signal at the time of dispersion equalization, and an optical amplifier 13. Prepare The data signal light and the test signal light output from the transmitter (transmitter of the regenerator) 10 are sent to the transmission optical fiber 1.

The linear repeater 20 includes a variable dispersion equalizer 21 for performing dispersion equalization by changing the amount of dispersion, an optical branching device 22, and
The optical amplifier 23 and the control circuit 2 for controlling the amount of dispersion set in the variable dispersion equalizer 21 according to the chromatic dispersion in the linear repeater section.
4 and.

The receiving device (reception unit of regenerative repeater) 30 is
An optical amplifier 31, a variable dispersion equalizer 32 that performs dispersion equalization by changing the amount of dispersion, an opto-electric converter (O / E) 33,
The equalization amplifier 34, the clock extraction circuit 35, the identification circuit 36, and the control circuit 37 that controls the amount of dispersion set in the variable dispersion equalizer 32 according to the chromatic dispersion in the regenerative repeater section are provided.

For the optical amplifiers 13, 23 and 31, for example, erbium-doped optical fiber amplifiers are used. O / E3
For example, a PIN photodiode is used for 3.
For the clock extraction circuit 35, for example, a combination of a differentiation circuit, a full-wave rectification circuit, and a dielectric resonator filter is used. For the identification circuit 36, for example, InP HEMT is used.

The variable dispersion equalizers 21 and 32 are realized by, for example, a configuration in which dispersion fibers having different dispersion amounts (lengths) are switched using an optical switch. As other configurations of the variable dispersion equalizers 21 and 32, a plurality of fiber gratings may be switched by an optical switch, temperature or tension may be applied to the chirped grating,
The dispersion amount may be changed by changing the temperature of the PLC.

FIG. 2 shows an example of the equalization procedure of the automatic wavelength dispersion equalization transmission system of the present invention. Here, three linear repeaters 20-1, 20-2, 20- are provided between the transmitting device (the transmitting unit of the regenerative repeater) 10 and the receiving device (the receiving unit of the regenerative repeater) 30, that is, in the regenerative repeating section. 3 shows an example in which 3 is arranged.

In the first stage, the first linear repeater 20-1 performs dispersion equalization on the first linear repeater section. Here, as the variable dispersion equalizer 21 of the linear repeater, for example, the dispersion amount (length)
When the configuration is such that different dispersion fibers are switched using an optical switch, the amount of dispersion to be set becomes a discrete value, and the dispersion in the linear relay section cannot be completely equalized to zero dispersion. A residual dispersion value results. Therefore, in the second stage, the residual equalization value of the first linear relay section and the second linear relay section are collectively subjected to dispersion equalization. At the third stage, residual equalization values up to the second linear relay section and the third linear relay section are collectively subjected to dispersion equalization. In the fourth stage, the receiving apparatus (reception unit of the regenerative repeater) 30 performs the dispersion equalization of the regenerative repeater section including the residual dispersion value up to the third linear repeater section and the fourth linear repeater section.

By such a procedure, the accumulation of residual dispersion values generated in each linear repeater is suppressed, the dispersion value of each linear relay section is controlled to the minimum value, and the regenerative relay section is equalized to the optimum dispersion value. Therefore, it is possible to make the regeneration relay interval longer.

When the amount of dispersion set in the variable dispersion equalizer 21 has a discrete value, the number of set values is selected so as to satisfy the required equalization accuracy and be minimized. It In addition, the variable dispersion and the like are optimized by optimizing the equalization range and equalization accuracy of the variable repeater equalizers of the linear repeater 20 and the receiving device (reception unit of the regenerative repeater) 30 according to the dispersion tolerance of the system. The constituent parts of the chemical converter can be simplified, and the cost can be reduced.

(First Embodiment: Claims 4 to 12 ) In the description of this embodiment, there are 6 examples ( claims 4 to 9 ) as a configuration example of chromatic dispersion equalization in a linear repeater, and wavelengths in a regenerative repeater. Three examples of configuration of dispersion equalization ( claims 10 to 1)
2 ) are shown individually, but they are combinations (18 examples) for an automatic wavelength dispersion equalization optical transmission system.

(Configuration Example of Linear Repeater) FIG. 3 shows a first configuration example in which chromatic dispersion equalization is performed by the linear repeater ( claim 4 ). In the figure, a transmitter (transmitter of a regenerator) 10 includes a measurement / data transmission switching circuit 11,
A light source 121, a modulator 122, which constitutes the light modulation circuit 12,
A bias voltage setting circuit 123 and an optical amplifier 13 are provided. The linear repeater 20 includes a variable dispersion equalizer 21, an optical branching device 22, an optical amplifier 23, an opto-electric converter (O / E) 241, a modulation frequency component intensity measuring circuit 242, which constitutes a control circuit 24. And a dispersion amount control circuit 243.

The feature of this configuration example is that the transmission device (transmission unit of regenerative repeater) 10 outputs, as the test signal light, an alternating chirp signal light in which the sign of the chirp parameter changes for each pulse, and the linear repeater 20 The intensity of the modulation frequency component is measured, and the variable dispersion equalizer 21 is set so that the intensity is minimized.
Is to control the amount of dispersion.

Here, a method of generating the alternating chirp signal light will be described. FIG. 15 shows the static characteristic of the extinction ratio of the modulator 122 and the relationship between the input signal and the output optical signal. Modulator 122
For example, a Mach-Zehnder type LN modulator is used. The bias voltage setting circuit 123 monitors the output light power of the modulator 122 (FIG. 3 is omitted), and the insertion loss of the bias voltage of the modulator 122 is maximum (output light power is minimum).
Set the voltage to It is also possible to superimpose a minute intensity modulation component on the bias voltage and set the bias voltage so that the intensity of this modulation component is minimized. At this time, the input signal voltage and the output optical signal power are expressed as an even function relationship.

When a test signal is applied to the modulator 122 via the measurement / data transmission switching circuit 11, it has a frequency component doubled to the input modulation frequency and the sign of the chirp parameter changes for each pulse. Alternating chirp signal light is output. In this alternating chirp signal light, pulses having the same chirp are affected by the same dispersion with respect to the change in the dispersion amount of the transmission path, and thus the input modulation frequency component intensity changes with the change in the dispersion amount. FIG. 16 shows the result of measurement of the intensity change of the 20 GHz component with respect to the change of the dispersion amount using the 40 GHz alternating chirp signal light.

The alternating chirp signal light transmitted through the transmission optical fiber is input to the variable dispersion equalizer 21. The optical signal equalized with the predetermined dispersion amount by the variable dispersion equalizer 21 is output to the next stage via the optical branching device 22 and the optical amplifier 23, and a part of the optical signal is branched to the O / E 241. Modulation frequency component strength measuring circuit 24 converted into an electric signal
2 and the intensity of the modulation frequency component is measured. The dispersion amount control circuit 243 controls the dispersion amount set in the variable dispersion equalizer 21 so that the measured intensity becomes minimum, and equalizes the dispersion in the linear relay section. The modulation frequency component intensity measuring circuit 242 can be realized by, for example, a configuration of a filter for extracting an input modulation frequency component, a diode, a low pass filter, and an ammeter.

In the prior art, in order to measure the dispersion value of the linear relay section, it is necessary to measure the dispersion value using a dispersion measuring instrument or the like, and there has been a problem that the apparatus is large-scaled and complicated. However, in this method, it is possible to obtain the information corresponding to the change in the dispersion amount of the transmission line from the intensity of the input modulation frequency component with a simple configuration. That is, the dispersion value at which the input modulation frequency component intensity of the alternating chirp signal light becomes the minimum value becomes zero dispersion, and equalization is performed by setting the dispersion amount of the variable dispersion equalizer 21 so that this intensity becomes the minimum value. be able to.

As described above, in this configuration example, the test signal light (alternating chirp signal light) can be easily generated, and the linear repeater can be used to monitor the intensity of the modulation frequency component and control the dispersion amount. It is possible to easily perform the variance equalization of the sections. As a result, it becomes possible to extend the regeneration relay interval. In the transmission device (transmission unit of the linear repeater) 10, the modulation amplitude of the test signal can be made equal to the modulation amplitude at the time of data transmission, and a fixed pattern of 1 and 0 of the data signal is used as the test signal. As a result, the measurement / data transmission switching circuit 11 can be omitted.

FIG. 4 shows a second configuration example in which chromatic dispersion equalization is performed by a linear repeater ( claim 5 ). In the figure, a transmission device (transmission unit of the regenerator) 10 is the same as that of the first configuration example of FIG. The linear repeater 20 includes a variable dispersion equalizer 21 and
An optical branching device 22, an optical amplifier 23, an opto-electric converter (O / E) 241, a modulation frequency component intensity measuring circuit 242, a DC component intensity measuring circuit 244, and a dispersion amount control circuit 243, which constitute a control circuit 24, are provided. Prepare

The feature of this configuration example is that the transmission device (transmission unit of the regenerator) 10 outputs an alternating chirp signal light as a test signal light, and the linear repeater 20 measures the modulation frequency component strength and DC component strength thereof. However, the dispersion amount of the variable dispersion equalizer 21 is controlled so that the intensity ratio is minimized.
By monitoring and standardizing the DC component intensity of the alternating chirp signal light with this configuration, it is possible to cope with the fluctuation of the input light power. Note that the vertical axis of FIG. 16 is the standardization of the modulation frequency component intensity with this DC component intensity.

A third configuration example in which chromatic dispersion equalization is performed by a linear repeater will be described ( claim 6 ). The features of this configuration example are:
In a configuration similar to that of FIG. 3, the transmission device (transmission unit of the regenerator) outputs the phase modulation signal light as the test signal light, and the linear repeater 20 performs the phase modulation on the dispersion of the transmission line.
The intensity of the modulation frequency component due to the intensity modulation conversion effect (PM-AM conversion effect) is measured, and the dispersion amount of the variable dispersion equalizer 21 is controlled so that the intensity is minimized.

A phase modulator and an intensity modulator are used as the modulator 122. A data signal is input to the intensity modulator during data transmission, and a test signal is input to the phase modulator during dispersion equalization. As the phase modulator, as shown in FIG. 17, the intensity modulator may perform modulation with a bias voltage that minimizes the insertion loss of the intensity modulator and with an amplitude that does not change the loss.

The PM-AM conversion effect is an effect in which the phase-modulated signal light is converted into intensity modulation by the dispersion of the transmission line, and the intensity of the modulation frequency component changes depending on the dispersion amount. FIG. 18 shows the measurement result of the intensity change with respect to the change in dispersion amount due to the PM-AM conversion effect at the modulation frequency of 20 GHz. The horizontal axis of the figure is the wavelength of the phase modulation signal light, and the wavelength of the phase modulation signal light was changed instead of changing the dispersion amount of the transmission line. As in the case of the alternating chirp signal light, the dispersion value at which the modulation frequency component intensity of the phase modulation signal light becomes the minimum value becomes zero dispersion, and the dispersion amount of the variable dispersion equalizer 21 is set so that this intensity becomes the minimum value. By setting, it is possible to perform distributed equalization of the linear relay section.

In FIG. 3, the phase modulated signal light transmitted through the transmission optical fiber is input to the variable dispersion equalizer 21. The optical signal equalized with the predetermined dispersion amount by the variable dispersion equalizer 21 is output to the next stage via the optical branching device 22 and the optical amplifier 23, and a part of the optical signal is branched to the O / E 241. The signal is converted into an electric signal and input to the modulation frequency component strength measuring circuit 242, and the modulation frequency component strength is measured. The dispersion amount control circuit 243 controls the dispersion amount set in the variable dispersion equalizer 21 so that the measured intensity becomes minimum, and equalizes the dispersion in the linear relay section. That is, the variance value at which the intensity of the input modulation frequency component becomes the minimum value becomes zero variance, and the variable dispersion equalizer 21 is set so that the intensity becomes the minimum value.
Equalization can be performed by setting the dispersion amount of.

In this configuration example, the test signal light (phase modulated signal light) is easily generated, and the linear repeater monitors the intensity of the modulation frequency component to control the amount of dispersion, whereby the dispersion of the linear repeater section is controlled. Equalization can be easily performed. As a result, it becomes possible to extend the regeneration relay interval.

A fourth configuration example for performing chromatic dispersion equalization with a linear repeater will be described ( claim 7 ). The features of this configuration example are:
In the same configuration as in FIG. 4, the transmitter (transmitter of the regenerator) 10 outputs the phase modulation signal light as the test signal light, and the linear repeater 20 outputs the phase modulation-intensity modulation conversion effect (PM-AM) for dispersion. The modulation frequency component intensity and the direct current component intensity due to the conversion effect) are measured, and the dispersion amount of the variable dispersion equalizer 21 is controlled so that the intensity ratio becomes a minimum. By monitoring and standardizing the intensity of the DC component of the phase-modulated signal light with this configuration, it is possible to deal with fluctuations in the input light power.

FIG. 5 shows a fifth configuration example in which chromatic dispersion equalization is performed by a linear repeater ( claim 8 ). In the figure, a transmission device (transmission unit of a regenerator) 10 includes a light source 121, a modulator 122, a bias voltage setting circuit 123, and an optical amplifier 13 which form an optical modulation circuit 12. Linear repeater 20
Is a variable dispersion equalizer 21, an optical branching device 22, an optical amplifier 23, and an opto-electric converter (O / O) that constitutes a control circuit 24.
E) 241, a clock extraction circuit 245, a clock component strength measurement circuit 246, and a dispersion amount control circuit 243.
The clock extraction circuit 245 can be realized by, for example, a combination of a differentiating circuit, a full-wave rectifying circuit, and a dielectric resonator filter. The clock component strength measuring circuit 246
For example, an RF power meter can be used.

The feature of this configuration example is that the intensity of the clock extracted from the data signal is measured by the linear repeater 10 and the dispersion amount of the variable dispersion equalizer 21 is controlled so that the intensity is maximized. .

The data signal light transmitted through the transmission optical fiber is input to the variable dispersion equalizer 21. The optical signal equalized with the predetermined dispersion amount by the variable dispersion equalizer 21 is
While being output to the next stage via the optical branching device 22 and the optical amplifier 23, a part thereof is branched to the O / E 241 and converted into an electric signal, which is input to the clock extraction circuit 245 to extract the clock component, Clock component strength measuring circuit 24
At 6, the clock component strength is measured. Here, 20Gbit /
FIG. 19 shows the measurement result of the intensity change with respect to the change of the dispersion amount of the clock component extracted from the s and NRZ signals. As shown in the figure, the strength of the clock component changes with the change of the dispersion amount. The dispersion amount control circuit 243 controls the dispersion amount set in the variable dispersion equalizer 21 so that the clock component strength becomes maximum, and equalizes the dispersion in the linear relay section.

In the prior art, in order to measure the dispersion value in the linear relay section, it is necessary to measure the dispersion value using a dispersion measuring instrument or the like, which poses a problem of large scale and complicated apparatus. However, in this method, it is possible to obtain information corresponding to the change in the dispersion amount of the transmission line from the clock component strength of the data signal with a simple configuration. That is, the variance value at which the clock component intensity becomes the maximum value becomes zero variance, and equalization can be performed by setting the variance amount of the variable dispersion equalizer 21 so that the intensity becomes the maximum value.

In this configuration example, it is not necessary to switch between the data signal and the test signal, and the linear repeater monitors the intensity of the clock component of the data signal to control the amount of dispersion, thereby performing the dispersion equalization of the linear relay section. Can be done easily. As a result, it becomes possible to extend the regeneration relay interval.

FIG. 6 shows a sixth configuration example in which chromatic dispersion equalization is performed by a linear repeater ( claim 9 ). In the figure, a transmitter (transmitter of a regenerator) 10 includes a light source 121- that constitutes a measurement / data transmission switching circuit 11 and an optical modulation circuit 12.
1, 121-2, modulators 122-1 and 122-2, an optical multiplexer 14, and an optical amplifier 13. Linear repeater 2
Reference numeral 0 denotes a variable dispersion equalizer 21, an optical branching device 22, an optical amplifier 23, an optical demultiplexer 247 constituting the control circuit 24, and optoelectric converters (O / E) 241-1 and 241-2. , A phase comparison circuit 248 and a dispersion amount control circuit 243.

The feature of this configuration example is that the transmitter (transmitter of the regenerator) 10 outputs the test signal light of two wavelengths, and the linear repeater 10 measures the phase difference of the test signal light of two wavelengths. The dispersion amount of the variable dispersion equalizer 21 is controlled so that the phase difference is minimized.

The measurement / data transmission switching circuit 11 inputs the data signal to the modulator 122-1 and outputs the test signal to the modulator 1.
22-1 and 122-2. A signal output from an oscillator or a divided clock may be used as the test signal. The modulators 122-1 and 122-2 modulate the output light from the light source 121-1 having the wavelength λs and the light source 121-2 having the wavelength λm. Thereby, the test signal light of two wavelengths is generated, multiplexed by the optical multiplexer 14, and output via the optical amplifier 13. The two-wavelength test signal light is adjusted so that the phase difference up to the point where it is input to the transmission optical fiber becomes equal, or the internal phase difference is measured in advance.

The test signal light of two wavelengths transmitted through the transmission optical fiber is input to the variable dispersion equalizer 21. The optical signal equalized with the predetermined dispersion amount by the variable dispersion equalizer 21 is output to the next stage via the optical branching device 22 and the optical amplifier 23, and the optical demultiplexer 247 converts the wavelengths λs and λm. The optical signals are demultiplexed, converted into electrical signals by O / Es 241-1 and 241-2, and the phase difference is detected by the phase comparison circuit 248. In addition, instead of the optical demultiplexer 247,
An optical branching device and an optical bandpass filter may be used. A mixer can be used for the phase comparison circuit 248.

The dispersion amount control circuit 243 controls the dispersion amount set in the variable dispersion equalizer 21 so as to minimize the phase difference between the two signals, and equalizes the dispersion in the linear relay section. In the linear repeater 20 as well, adjustment is made so that the phase difference between the test signal lights of two wavelengths becomes equal, or the internal phase difference is measured in advance.

This configuration example uses test signal light of two wavelengths,
By controlling the amount of dispersion by monitoring the phase difference of each test signal light with the linear repeater, it is possible to easily perform dispersion equalization in the linear repeater section. As a result, it becomes possible to extend the regeneration relay interval.

(Configuration Example of Receiving Unit of Receiving Device or Regenerative Repeater) FIG. 7 shows a first configuration example of performing chromatic dispersion equalization in the receiving unit of the receiving device or regenerating repeater ( claim 10 ).

In the figure, a transmitter (transmitter section of a regenerator) 10 includes a measurement / data transmission switching circuit 11, a light source 121, a modulator 122, a bias voltage setting circuit 123, and an optical modulator 121. And an amplifier 13. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31.
, Variable dispersion equalizer 32, and photoelectric converter (O / E) 3
3, an equalization amplifier 34, a clock extraction circuit 35, an identification circuit 36, and an error rate detection circuit 37 as a control circuit 37.
1 and a dispersion amount control circuit 372.

The feature of this configuration example is that the code error rate of the output signal of the identification circuit 36 of the receiving apparatus (reception section of the regenerator) 30 is measured, and variable dispersion equalization is performed so that the code error rate is minimized. This is to control the dispersion amount of the device 32 (code error rate monitoring method).

The data signal light transmitted through the transmission optical fiber is transmitted through the optical amplifier 31 to the variable dispersion equalizer 32.
Entered in. The optical signal equalized by the variable dispersion equalizer 32 with a predetermined dispersion amount is converted into an electric signal by the O / E 33, amplified by the equalization amplifier 34, and then extracted by the clock extraction circuit 35.
And the identification circuit 36. Clock extraction circuit 3
The clock component extracted in 5 is supplied to the discrimination processing of the discrimination circuit 36. The error rate detection circuit 371 includes the identification circuit 36.
The bit error rate of the output signal of is measured. Dispersion amount control circuit 3
Reference numeral 72 controls the amount of dispersion set in the variable dispersion equalizer 32 so that the code error rate is minimized, and equalizes the dispersion in the regenerative repeater section. The details of the method of setting the dispersion amount of the variable dispersion equalizer 32 with respect to the code error rate will be described later.

In the conventional dispersion equalization technique, the total dispersion amount of the transmission line is controlled to be zero dispersion in the regenerative repeater section. However, due to the influence of the non-linear optical effect due to the increase in speed, it is optimum from the viewpoint of reception sensitivity. That is, the amount of dispersion does not always become zero. In this configuration example, by monitoring the bit error rate of the received signal, the regenerative relay section can be set to an optimum dispersion amount, and the regenerative relay interval can be increased.

FIG. 8 shows a second configuration example in which chromatic dispersion equalization is performed in the receiving unit of the receiving device or the regenerator ( claim 1).
1 ). In the figure, a transmitter (transmitter of a regenerator) 1
0 is the same as the first configuration example shown in FIG. 7. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31, a variable dispersion equalizer 32, an optoelectric converter (O / E) 33, an equalizing amplifier 34, a clock extracting circuit 35, and Identification circuit 3
6 and a Q value measuring circuit 373 and a dispersion amount control circuit 372 as the control circuit 37.

The feature of this configuration example is that the Q value of the output signal of the identification circuit 36 of the receiving device (reception unit of the regenerator) 30 is measured, and the variable dispersion equalizer 32 is set so that the Q value becomes maximum. Is to control the dispersion amount of (Q value monitoring method).

The data signal light transmitted through the transmission optical fiber is transmitted via the optical amplifier 31 to the variable dispersion equalizer 32.
Entered in. The optical signal equalized by the variable dispersion equalizer 32 with a predetermined dispersion amount is converted into an electric signal by the O / E 33, amplified by the equalization amplifier 34, and then extracted by the clock extraction circuit 35.
And the identification circuit 36. Clock extraction circuit 3
The clock component extracted in 5 is supplied to the discrimination processing of the discrimination circuit 36. The Q value measurement circuit 373 measures the code error rate of the output signal of the identification circuit 36, and obtains the Q value from the error rate and the identification voltage of the identification circuit 36 (Q value monitoring method by code error rate monitor). The dispersion amount control circuit 372 determines the Q
The amount of dispersion set in the variable dispersion equalizer 32 is controlled so that the value becomes maximum, and the dispersion in the regenerative repeater section is equalized.

It should be noted that although the configuration for monitoring the minimum value of the code error rate in the first configuration example of FIG. 7 requires a considerable amount of time, extrapolation of the Q value by this method enables measurement in a short time. . As a method of measuring the Q value, a method of measuring each average value and standard deviation of 0 and 1 levels using optical sampling may be used (Q value monitoring method by optical waveform monitor). Also in this configuration example, the regeneration relay section can be set to an optimum dispersion amount by monitoring the Q value of the received signal, and the regeneration relay interval can be lengthened.

FIG. 9 shows a third configuration example in which chromatic dispersion equalization is performed in the receiving section of the receiving device or the regenerator ( claim 1
2 ). In the figure, a transmitter (transmitter of a regenerator) 1
0 is the same as the first configuration example shown in FIG. 7. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31, a variable dispersion equalizer 32, an optoelectric converter (O / E) 33, an equalizing amplifier 34, a clock extracting circuit 35, and Identification circuit 3
6 and the clock component strength measuring circuit 3 as the control circuit 37.
74 and a dispersion amount control circuit 372.

The feature of this configuration example is that the strength of the clock component extracted by the clock extraction circuit 35 of the receiver (reception repeater) 30 is measured, and variable dispersion equalization is performed so that the strength is maximized. This is to control the amount of dispersion of the device 32 (clock component intensity monitor method).

The data signal light transmitted through the transmission optical fiber is transmitted through the optical amplifier 31 to the variable dispersion equalizer 32.
Entered in. The optical signal equalized by the variable dispersion equalizer 32 with a predetermined dispersion amount is converted into an electric signal by the O / E 33, amplified by the equalization amplifier 34, and then extracted by the clock extraction circuit 35.
And the identification circuit 36. Clock extraction circuit 3
The clock component extracted in 5 is supplied to the identification processing of the identification circuit 36 and the clock component strength measuring circuit 374.
And the clock component strength is measured. The dispersion amount control circuit 372 controls the dispersion amount set in the variable dispersion equalizer 32 so that the strength of the clock component becomes maximum, and equalizes the dispersion in the regeneration relay section.

Since the present method monitors the strength of the extracted clock component without measuring the code error rate, it is possible to optimize the regeneration repeating section in a shorter time than the above-mentioned code error rate monitoring method and Q value monitoring method. The amount of dispersion can be obtained. This allows
It is possible to increase the regenerative relay interval.

The above-described six configurations for performing the linear equalization of the linear relay section in the linear repeater 20 and the three configurations for performing the equalization of the distribution of the regeneration relay section in the receiving device (reception unit of the regenerative repeater) 30. The linear repeater 20 performs chromatic dispersion equalization in the linear repeater section, and the receiving device (reception unit of the regenerative repeater) 30 further performs chromatic dispersion equalization in the regenerative repeater section according to the 18 combinations of configurations. be able to.

(Second Embodiment: Claim 13 ) Due to the dispersion of the transmission path, the optimum clock phase and the phase margin of the identification circuit of the receiver of the receiver or the regenerator are changed. For this reason, in the high-speed optical transmission system, the identification sensitivity is deteriorated and the extension of the regenerative repeater interval is limited, so that it is necessary to optimize the clock phase.

FIG. 10 shows a configuration example in which a clock phase adjusting circuit is added to the receiving section of the receiving device or the regenerator.
In this configuration example, a clock phase adjusting circuit is added to the first configuration example of the receiving unit of the receiving device or the regenerator shown in FIG. 7 ( claims 10 and 13 ).

In the figure, the configuration of the transmission device (transmission unit of the regenerator) 10 is the same. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31 and a variable dispersion equalizer 32.
An opto-electrical converter (O / E) 33 and an equalizing amplifier 34.
, Clock extraction circuit 35, and clock phase adjustment circuit 3
8, an identification circuit 36, an error rate detection circuit 371 as a control circuit 37, a controller 375, and a dispersion amount control circuit 372.

The feature of this configuration example is that the code error rate of the output signal of the discriminating circuit 36 of the receiving device (reception unit of the regenerator) 30 is measured, and variable dispersion equalization is performed so that the code error rate is minimized. This is to control the dispersion amount of the device 32 and the clock phase of the identification circuit 36.

The data signal light transmitted through the transmission optical fiber is transmitted through the optical amplifier 31 to the variable dispersion equalizer 32.
Entered in. The optical signal equalized by the variable dispersion equalizer 32 with a predetermined dispersion amount is converted into an electric signal by the O / E 33, amplified by the equalization amplifier 34, and then extracted by the clock extraction circuit 35.
And the identification circuit 36. Clock extraction circuit 3
The clock component extracted in 5 is supplied to the identification processing of the identification circuit 36 via the clock phase adjustment circuit 38. The error rate detection circuit 371 measures the code error rate of the output signal of the identification circuit 36. The controller 375 controls the clock phase adjustment circuit 38 and the dispersion amount control circuit 372 to control the clock phase and the dispersion amount set in the variable dispersion equalizer 32 so as to minimize the code error rate, and Equalize the variance. The relationship between the dispersion amount setting method and the optimum clock phase setting method will be described later.

As described above, while the variable equalizer 32 is used to perform the dispersion equalization of the regenerative repeater section, the optimum clock phase that minimizes the code error rate is set to suppress the deterioration of the reception sensitivity. Therefore, it is possible to increase the regenerative relay interval.

The optimum clock phase detecting means may be a Q value monitor method in which the error rate detecting circuit 371 is replaced with a Q value measuring circuit 373. That is, the clock phase adjusting circuit 38 may be added to the second configuration example of the receiving unit of the receiving device or the regenerator shown in FIG. 8 ( claims 11, 1
3 ).

(Third Embodiment: Claim 14 ) Due to the dispersion of the transmission path, the optimum discrimination voltage and discrimination margin of the discrimination circuit of the receiving unit of the receiving device or the regenerator are changed. For this reason, in the high-speed optical transmission system, the identification sensitivity is deteriorated and the regeneration relay interval is limited to a long distance. Therefore, it is necessary to optimize the identification voltage.

FIG. 11 shows a configuration example in which an identification voltage adjusting circuit is added to the receiving section of the receiving device or the regenerative repeater. In this configuration example, an identification voltage adjusting circuit is added to the first configuration example of the receiving section of the receiving device or the regenerator shown in FIG. 7 ( claims 10 and 14 ).

In the figure, the configuration of the transmission device (transmission unit of the regenerator) 10 is the same. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31 and a variable dispersion equalizer 32.
An opto-electrical converter (O / E) 33 and an equalizing amplifier 34.
A clock extraction circuit 35, an identification circuit 36, an identification voltage adjustment circuit 39, a control circuit 37, an error rate detection circuit 371, a controller 375, and a dispersion amount control circuit 37.
2 and.

The feature of this configuration example is that the code error rate of the output signal of the identification circuit 36 of the receiver (reception repeater) 30 is measured, and variable dispersion equalization is performed so that the code error rate is minimized. This is to control the dispersion amount of the device 32 and the discrimination voltage of the discrimination circuit 36.

The data signal light transmitted through the transmission optical fiber is transmitted through the optical amplifier 31 to the variable dispersion equalizer 32.
Entered in. The optical signal equalized by the variable dispersion equalizer 32 with a predetermined dispersion amount is converted into an electric signal by the O / E 33, amplified by the equalization amplifier 34, and then extracted by the clock extraction circuit 35.
And the identification circuit 36. Clock extraction circuit 3
The clock component extracted in 5 is supplied to the discrimination processing of the discrimination circuit 36. The error rate detection circuit 371 includes the identification circuit 36.
The bit error rate of the output signal of is measured. Controller 37
5 is an identification voltage adjustment circuit 39 and a dispersion amount control circuit 37.
For 2, the discrimination voltage and the amount of dispersion set in the variable dispersion equalizer 32 are controlled so that the code error rate is minimized, and the dispersion in the regenerative repeater section is equalized. The relationship between the setting method of the dispersion amount and the setting method of the optimum discrimination voltage will be described later.

As described above, by performing the dispersion equalization of the regenerative repeater interval and setting the optimum discrimination voltage that minimizes the code error rate, the deterioration of the reception sensitivity is suppressed and the regenerative repeater interval is made longer. Can be planned.

Further, the optimum discrimination voltage detecting means may be a Q value monitor method in which the error rate detecting circuit 371 is replaced with a Q value measuring circuit 373. That is, the identification voltage adjusting circuit 39 may be added to the second configuration example of the receiving unit of the receiving device or the regenerator shown in FIG. 8 ( claims 11 and 14 ).

FIG. 12 shows a configuration example in which a clock phase adjusting circuit and a discrimination voltage adjusting circuit are added to the receiving section of the receiving device or the regenerator. In this configuration example, a clock phase adjustment circuit 38 and an identification voltage adjustment circuit 39 are added to the first configuration example of the receiving unit of the receiving device or the regenerator shown in FIG. 7, and FIGS. it is those (請
Requirement 10, 13, 14 ).

The feature of this configuration example is that the code error rate of the output signal of the identification circuit 36 of the receiving device (reception unit of the regenerator) 30 is measured, and variable dispersion equalization is performed so that the code error rate is minimized. This is for controlling the dispersion amount of the device 32, the clock phase of the discrimination circuit 36, and the discrimination voltage. Controller 37
Reference numeral 5 is a clock phase adjustment circuit 38, an identification voltage adjustment circuit 3
9 and the dispersion amount control circuit 372, the clock phase, the discrimination voltage, and the dispersion amount set in the variable dispersion equalizer 32 are controlled so as to minimize the code error rate, and the dispersion in the regenerative repeater section is equalized. .

The means for detecting the optimum clock phase and the discrimination voltage are the error rate detection circuit 371 and the Q value measurement circuit 37.
A Q value monitor method in which the Q value is replaced by 3 may be used. As described above, the clock phase adjustment circuit 38 or the identification voltage adjustment circuit 39 is provided in the configuration in which the amount of dispersion is controlled by the code error rate or the Q value of the output signal of the identification circuit 36 of the receiver (reception repeater) 30. Six configurations with at least one are possible. 10, 11, and 12 have three configurations among them.

(Fourth Embodiment: Claims 15 and 16 ) The dispersion amount set in the variable dispersion equalizer 32 has the maximum intensity of the clock component extracted by the clock extraction circuit 35, as shown in FIG. The clock phase or the discrimination voltage of the discrimination circuit 36 may be controlled so that the code error rate of the output signal of the discrimination circuit 36 is minimized or the Q value is maximized. .

FIG. 13 shows another configuration example in which a clock phase adjusting circuit and a discrimination voltage adjusting circuit are added to the receiving section of the receiving device or the regenerator. In this configuration example, a clock phase adjusting circuit 38 and an identification voltage adjusting circuit 39 are added to the third configuration example of the receiving unit of the receiving device or the regenerator shown in FIG. 9 ( claims 12, 15, 16). ).

In the figure, the configuration of the transmission device (transmission unit of the regenerator) 10 is the same. The receiving device (reception unit of the regenerator) 30 includes an optical amplifier 31 and a variable dispersion equalizer 32.
An opto-electrical converter (O / E) 33 and an equalizing amplifier 34.
, Clock extraction circuit 35, and clock phase adjustment circuit 3
8, an identification circuit 36, an identification voltage adjustment circuit 39, an error rate detection circuit 371 as a control circuit 37, a clock component strength measurement circuit 374, a controller 375, and a dispersion amount control circuit 372.

The feature of this configuration example is that the clock extraction circuit 35 is used.
The dispersion amount of the variable dispersion equalizer 32 is controlled so that the intensity of the clock component extracted in step 6 is maximized, and the discrimination circuit 36 is controlled so that the code error rate of the output signal of the discrimination circuit 36 is minimized.
Is to control the clock phase and identification voltage of the. The controller 375 controls the dispersion amount control circuit 372 so that the clock component strength measured by the clock component strength measuring circuit 374 is maximized, and causes the clock phase adjusting circuit 38 and the discrimination voltage adjusting circuit 39 to have a code error rate. The clock phase and the discrimination voltage are controlled so that

The means for detecting the optimum clock phase and the discrimination voltage includes the error rate detecting circuit 371 and the Q value measuring circuit 37.
A Q value monitor method in which the Q value is replaced by 3 may be used. In this way, at least one of the clock phase adjusting circuit 38 and the identifying voltage adjusting circuit 39 is provided in the configuration for controlling the amount of dispersion by the clock component intensity of the identifying circuit 36 of the receiving device (reception unit of the regenerator) 30. Street configurations are possible. FIG.
Is one of them.

In the automatic wavelength dispersion equalization optical transmission system of the present invention, 72 kinds of configurations are possible by combining the configurations of the linear repeater 20 and the receiving device (reception section of the regenerative repeater) 30 described above. is there. As a result, the linear repeater 20 performs chromatic dispersion equalization in the linear repeater section, the receiving device (reception section of the regenerative repeater) 30 performs chromatic dispersion equalization in the regenerative repeater section, and further, the clock phase and the identification voltage By optimizing, the regeneration relay interval can be increased.

(Fifth Embodiment: Claim 17 ) FIG. 14 shows a configuration example in which the automatic chromatic dispersion equalization optical transmission system of the present invention is provided with a control line. In this configuration example, the control line 2 is wired between the transmitter 10 and the receiver 30,
The transmission device (transmission unit of the linear repeater) 10 is provided with the control signal receiving circuit 3, and the linear repeater 20 and the reception device (reception unit of the regenerative repeater) 30 are provided with the control signal transmission / reception circuit 4, respectively. Then, transmission / reception of control signals such as transmission switching of test signals and data signals accompanying the start and end of automatic chromatic dispersion equalization are performed. A specific example of the control signal will be described in the sixth embodiment. As a result, it is possible to automatically switch between the transmission mode and the test mode and perform the measurement, and it is possible to reduce the number of personnel and the cost during the test.

(Sixth Embodiment) In this embodiment, a method of setting an optimum dispersion amount, an optimum discrimination voltage, an optimum clock phase of a receiving device (reception unit of a regenerator) and an optimizing procedure will be described. For each dispersion amount of the variable dispersion equalizer 32 of the receiving device (reception unit of regenerative repeater) 30, the bit error rate (BER) characteristic with respect to the identification voltage shown in FIG. The two discriminating voltages against the rate are recorded. After the measurement is performed for all the dispersion amounts, the map of the identification voltage with respect to the dispersion amount shown in FIG. 21 is recorded. In this map, the amount of variance that maximizes the potential difference between the identification voltages is defined as the optimal amount of variance.
The average value (intermediate value) of the two discrimination voltages is set as the optimum discrimination voltage. In the figure, the cross indicates the optimum discrimination voltage.

By using this procedure, it is possible to increase the fluctuation tolerance of the identification voltage against the dispersion fluctuation of the transmission line. Further, in the method of setting the identification voltage that minimizes the code error rate measured in the above procedure as the optimum identification voltage, it is possible to minimize the deterioration of the reception sensitivity, and it is possible to lengthen the regenerative relay interval. Become.

FIG. 22 shows the result of measuring the discrimination voltage with respect to the amount of dispersion at a specific code error rate (BER) at the time of 10 Gbit / s, NRZ signal transmission. Instead of changing the dispersion value of the transmission line, the wavelength of the signal light was changed to be equivalent. The horizontal axis of the figure shows the wavelength of the signal light, and the vertical axis shows the discrimination voltage. As shown in the figure, the potential difference between the identification voltages, which is the code error rate required for dispersion, changes. When the signal light wavelength that maximizes this potential difference is set, the deterioration of reception sensitivity can be minimized, and the effectiveness of this method was confirmed.

The same applies to the method of setting the optimum clock phase. The bit error rate (BER) characteristic with respect to the clock phase shown in FIG. 23 is measured for each dispersion amount of the variable dispersion equalizer 32 of the receiving device (reception unit of the regenerative repeater), and the required code error rate is obtained. 24 are recorded, and the map of the clock phase with respect to the dispersion amount shown in FIG. 24 is recorded. In this map, the amount of dispersion that maximizes the phase difference between the clock phases is set as the optimum amount of dispersion, and the average value (intermediate value) of the two clock phases is set as the optimum clock phase. In the figure, the mark x indicates the optimum clock phase.

By using this procedure, it is possible to increase the fluctuation tolerance of the clock phase against the dispersion fluctuation of the transmission line. In addition, the method of setting the clock phase that minimizes the code error rate measured by the above procedure as the optimum clock phase can minimize the deterioration of the reception sensitivity and can lengthen the regenerative relay interval. Become.

FIG. 25 shows an example of the dispersion equalization procedure of the automatic wavelength dispersion equalization optical transmission system of the present invention. Here, a case where an alternating chirp signal light is used as the test signal light will be described.

The transmitter (the transmitter of the regenerator) first adjusts the bias voltage of the modulator, switches the modulator input to the test signal, transmits the ACK signal, and then transmits the alternating chirp signal light.

The linear repeater enters the measurement mode when it receives the ACK signal, and performs the dispersion equalization processing of the linear repeater section when it receives the alternating chirp signal light. Then, the ACK signal is transmitted to the next-stage linear repeater, the measurement mode is terminated, and the transmission mode is entered. This process is sequentially performed by each linear repeater.
As shown in FIG. 26, the distributed equalization processing of the linear relay section is performed as follows.
The dispersion amount of the variable dispersion equalizer is changed to measure the modulation frequency component intensity of the alternating chirp signal light, and the dispersion amount that minimizes the intensity is set in the variable dispersion equalizer.

The receiving device (reception unit of the regenerator) is an AC
When the K signal is received, the alternating chirp signal light end command is transmitted to enter the measurement mode. Upon receiving the alternating chirp signal light end command, the transmitter (the transmitter of the regenerator) adjusts the bias voltage of the modulator, switches the modulator input to the data signal, and transmits the data signal light. When receiving the data signal light, the receiving device (reception unit of the regenerator) performs the setting process of the optimum dispersion amount and the optimum discrimination voltage by the code error rate monitoring method. After that, the optimum clock phase is set by the same code error rate monitoring method. Then, a test end command is transmitted to end the measurement mode and enter the transmission mode.

As shown in FIG. 27, the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase are set by changing the dispersion amount of the variable dispersion equalizer to measure the code error rate with respect to the discrimination voltage, The two discrimination voltages, which are the code error rate, are recorded. After this is performed for all the dispersion amounts, the dispersion amount that maximizes the potential difference between the two identification voltages is set as the optimal dispersion amount, and the midpoint between the two identification voltages is set as the optimal identification voltage. After that, the clock phase is changed to measure the code error rate with respect to the clock phase, and the midpoint between the two clock phases having a specific code error rate is set as the optimum clock phase.

FIG. 28 shows another procedure for setting the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase in the receiver (reception unit of the regenerator). Here, the procedure for changing the clock phase each time the dispersion amount of the variable dispersion equalizer is changed and setting the optimum clock phase for the dispersion amount will be described.

After the dispersion equalization in the linear repeater is completed, the dispersion amount of the variable dispersion equalizer of the receiver (reception section of the regenerative repeater) is set. The clock error is measured by changing the clock phase. Set the clock phase at the midpoint of the two clock phases that will result in a specific code error rate,
The code error rate with respect to the identification voltage is measured, and two identification voltages having a specific code error rate are recorded. After performing this for all dispersion amounts, the dispersion amount that maximizes the potential difference between the two identification voltages is set as the optimum dispersion amount, and the optimum clock phase measured at the set dispersion amount is set. Then, the midpoint between the two discrimination voltages is set as the optimum discrimination voltage.

Since the optimum clock phase changes with respect to the dispersion of the transmission line, the optimum dispersion amount and the optimum discrimination voltage can be accurately detected by adjusting the clock phase for each dispersion amount to be equalized. For the optimization of the discrimination voltage and the clock phase, a simple method of independently optimizing each may be used, or the two-dimensional method of scanning all points on the two-dimensional grid and the hill climbing method of the local search method may be used. You may use.

FIG. 29 shows the procedure for setting the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase in consideration of the dispersion fluctuation of the transmission line. After the dispersion equalization in the linear repeater is completed, the dispersion amount of the variable dispersion equalizer of the receiving device (reception unit of the regenerative repeater) is set. The clock error is measured by changing the clock phase. Set the clock phase at the midpoint of the two clock phases that will result in a specific code error rate,
The code error rate with respect to the discrimination voltage is measured, and a map of the discrimination voltage with respect to the dispersion amount is recorded.

At this time, among the dispersion amounts within the required conditions, the dispersion amounts within the range of the dispersion variation amount ΔD expected from the recorded dispersion amounts at both ends are excluded from the target. Further, when there are a plurality of dispersion amounts in the target, for example, the sum of the potential difference between the two identification voltages having the target dispersion amount and the potential difference between the two identification voltages having the dispersion amounts on both sides thereof becomes the maximum. Amount and optimum value. Further, among the discrimination voltages recorded at the two closest dispersion amounts separated from the optimal dispersion amount by the expected dispersion variation amount or more, the intermediate point of the combination having the smallest potential difference is set as the optimal discrimination voltage.

By using this method, it is possible to set the amount of dispersion and the identification voltage that are resistant to the dispersion fluctuation of the transmission line.

[0111]

As described above, the automatic chromatic dispersion equalization optical transmission system of the present invention performs chromatic dispersion equalization for each linear repeater section in the linear repeater, and the receiving section of the receiving device and the regenerative repeater. Finally, chromatic dispersion equalization in the regenerative repeater section can be performed. Further, by optimizing the identification voltage and the clock phase for identifying the data signal in the receiving device and the receiving section of the regenerative repeater, it is possible to increase the length of the regenerative repeater section of the high-speed optical transmission system.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an automatic wavelength dispersion equalization optical transmission system of the present invention.

FIG. 2 is a diagram showing an example of an equalization procedure of the automatic wavelength dispersion equalization optical transmission system of the present invention.

FIG. 3 is a block diagram showing a first configuration example in which chromatic dispersion equalization is performed by a linear repeater.

FIG. 4 is a block diagram showing a second configuration example in which chromatic dispersion equalization is performed by a linear repeater.

FIG. 5 is a block diagram showing a fifth configuration example in which chromatic dispersion equalization is performed by a linear repeater.

FIG. 6 is a block diagram showing a sixth configuration example in which chromatic dispersion equalization is performed by a linear repeater.

FIG. 7 is a block diagram showing a first configuration example in which chromatic dispersion equalization is performed in a receiver of a receiver or a regenerator.

FIG. 8 is a block diagram showing a second configuration example in which chromatic dispersion equalization is performed in the receiving unit of the receiving device or the regenerator.

FIG. 9 is a block diagram showing a third configuration example in which chromatic dispersion equalization is performed in the receiving unit of the receiving device or the regenerator.

FIG. 10 is a block diagram showing a configuration example in which a clock phase adjusting circuit is added to the receiving unit of the receiving device or the regenerator.

FIG. 11 is a block diagram showing a configuration example in which an identification voltage adjusting circuit is added to the receiving unit of the receiving device or the regenerator.

FIG. 12 is a block diagram showing a configuration example in which a clock phase adjusting circuit and an identification voltage adjusting circuit are added to the receiving unit of the receiving device or the regenerator.

FIG. 13 is a block diagram showing another configuration example in which a clock phase adjusting circuit and a discrimination voltage adjusting circuit are added to the receiving unit of the receiving device or the regenerator.

FIG. 14 is a configuration example in which a control line is provided in the automatic wavelength dispersion equalization optical transmission system of the present invention.

FIG. 15 is a diagram showing an example of generating alternating chirp signal light.

FIG. 16 is a diagram showing an example of measurement of modulation frequency component intensity of alternating chirp signal light with respect to dispersion.

FIG. 17 is a diagram showing an example of generation of a phase modulation signal.

FIG. 18 is a diagram showing an example of measurement of modulation frequency component strength by the PM-AM conversion effect on dispersion.

FIG. 19 is a diagram showing a measurement example of clock component strength with respect to dispersion.

FIG. 20 is a diagram showing a code error rate characteristic with respect to an identification voltage.

FIG. 21 is a diagram showing an identification voltage with respect to a specific variance of a code error rate.

FIG. 22 is a diagram showing an example of measurement of an identification voltage with respect to a specific dispersion of a code error rate.

FIG. 23 is a diagram showing a code error rate characteristic with respect to a clock phase.

FIG. 24 is a diagram showing a clock phase with respect to a specific dispersion of a code error rate.

FIG. 25 is a flowchart showing an example of a dispersion equalization procedure of the automatic wavelength dispersion equalization optical transmission system of the present invention.

FIG. 26 is a flowchart showing a distributed equalization procedure of a linear relay section.

FIG. 27 is a flowchart showing the procedure for setting the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase in the reception device (reception unit of the linear repeater).

FIG. 28 is a flowchart showing another setting processing procedure of the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase in the receiving device (reception unit of the regenerator).

FIG. 29 is a flowchart showing a procedure for setting the optimum dispersion amount, the optimum discrimination voltage, and the optimum clock phase in consideration of the dispersion fluctuation of the transmission line.

[Explanation of symbols]

1 Optical fiber for transmission 2 control lines 3 Control signal receiving circuit 4 Control signal transmission / reception circuit 10 Transmitter (transmitter of regenerator) 11 Measurement / data transmission switching circuit 12 Optical modulation circuit 121 light source 122 modulator 123 Bias voltage setting circuit 13 Optical amplifier 14 Optical multiplexer 20 linear repeater 21 Variable dispersion equalizer 22 Optical splitter 23 Optical amplifier 24 Control circuit 241 Photoelectric converter (O / E) 242 Modulation frequency component strength measurement circuit 243 Dispersion control circuit 244 DC component strength measurement circuit 245 clock extraction circuit 246 Clock component strength measurement circuit 247 Optical demultiplexer 248 Phase comparison circuit 30 Receiver (reception repeater receiver) 31 Optical amplifier 32 Variable dispersion equalizer 33 Opto-electric converter (O / E) 34 Equalization amplifier 35 Clock extraction circuit 36 Identification circuit 37 Control circuit 371 Error rate detection circuit 372 Dispersion amount control circuit 373 Q value measurement circuit 374 Clock component strength measurement circuit 375 controller 38 Clock phase adjustment circuit 39 Identification voltage adjustment circuit

Front page continuation (72) Inventor Hiroshi Miyamoto 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Mikio Yoneyama 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Date Inside the Telegraph and Telephone Corporation (72) Inventor Hiroshi Toba 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside the Nippon Telegraph and Telephone Corporation (56) Reference JP-A-9-326755 (JP, A) HEI 10-163962 (JP, A) JP-A-8-340320 (JP, A) Shoichiro Kuwahara et al., A study on a preset automatic distributed equalization system using alternating chirp signals, 1998 IEICE General Conference Proceedings of the Communications 2, Japan, The Institute of Electronics, Information and Communication Engineers, March 6, 1998, p. 587 (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 JISST file (JOIS)

Claims (17)

(57) [Claims] 1. An optical transmission system in which a linear repeater and a regenerative repeater are arranged at predetermined intervals between a transmitter and a receiver connected via a transmission optical fiber, wherein the linear repeater comprises A variable dispersion equalizer that performs dispersion equalization by changing the amount of dispersion, and a control circuit that controls the amount of dispersion set in the variable dispersion equalizer according to the chromatic dispersion in the linear relay section are provided. The receiving unit of the regenerative repeater controls a variable dispersion equalizer that performs dispersion equalization by changing the amount of dispersion, and a control that controls the amount of dispersion set in the variable dispersion equalizer according to chromatic dispersion in the regenerative repeater section. A first linear repeater in the transmission direction order within the regeneration repeater section.
A second linear repeater for equalizing chromatic dispersion in the first linear repeater section;
Equalizes the chromatic dispersion in the first and second linear repeater sections,
Type repeater (n is an integer of 2 or more) is a first to nth linear repeater section
An automatic chromatic dispersion equalization optical transmission system characterized in that it is configured to equalize chromatic dispersion between the two . 2. The automatic chromatic dispersion equalization optical transmission system according to claim 1 , wherein the control circuit of the m-th linear repeater (m is an integer of 1 to n) has wavelengths in the first to m-th linear repeater sections. An automatic chromatic dispersion equalization optical transmission system having a configuration for controlling the amount of dispersion set in a variable dispersion equalizer so that the dispersion value is minimized. 3. The automatic wavelength dispersion equalization optical transmission system according to claim 1, wherein each control circuit of the linear repeater, the receiver and the receiver of the regenerative repeater has a discrete dispersion in the variable dispersion equalizer. An automatic chromatic dispersion equalization optical transmission system, which is configured to set an amount and perform equalization processing, and the number of set values satisfies a required equalization accuracy and is minimum. 4. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the transmitter and the transmitter of the regenerator output an alternating chirp signal light in which the sign of the chirp parameter changes for each pulse. The control circuit of the linear repeater comprises a modulation frequency component intensity measuring circuit for measuring the modulation frequency component intensity of the alternating chirp signal light, and a dispersion set in the variable dispersion equalizer so that the measurement intensity is minimized. An automatic chromatic dispersion equalization optical transmission system comprising a dispersion amount control circuit for controlling the amount. 5. The automatic wavelength dispersion equalization optical transmission system according to claim 4 , wherein the control circuit of the linear repeater comprises a DC component intensity measuring circuit for measuring the DC component intensity of the alternating chirp signal light, and the dispersion amount. The control circuit is configured to control the amount of dispersion set in the variable dispersion equalizer so that the intensity ratio of the modulation frequency component and the DC component of the alternating chirp signal light is minimized. Transmission system. 6. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the transmitter and the transmitter of the regenerator have means for outputting phase-modulated or frequency-modulated test signal light. The control circuit of the repeater comprises a modulation frequency component intensity measuring circuit for measuring the modulation frequency component intensity of the test signal light and a dispersion controlling the amount of dispersion set in the variable dispersion equalizer so that the measurement intensity is minimized. An automatic wavelength dispersion equalization optical transmission system comprising a quantity control circuit. 7. The automatic chromatic dispersion equalization optical transmission system according to claim 6 , wherein the control circuit of the linear repeater measures the direct current component intensity of the phase modulated or frequency modulated test signal light. A dispersion amount control circuit is provided with a circuit, and the dispersion amount control circuit is configured to control the dispersion amount set in the variable dispersion equalizer so that the intensity ratio of the modulation frequency component and the DC component of the test signal light is minimized. Wavelength dispersion equalization optical transmission system. 8. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the control circuit of the linear repeater has a clock extraction circuit for extracting a clock component of the data signal light, and an intensity of the extracted clock component. An automatic chromatic dispersion equalization characterized by comprising a clock component intensity measuring circuit for measuring the dispersion intensity and a dispersion amount control circuit for controlling the dispersion amount set in the variable dispersion equalizer so that the measurement intensity is maximized. Optical transmission system. 9. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the transmitter and the transmitter of the regenerator have means for outputting test signal lights of two different wavelengths, and a linear repeater. The control circuit includes a phase comparison circuit that measures the phase difference between the test signal lights of the two wavelengths, and a dispersion amount control circuit that controls the dispersion amount set in the variable dispersion equalizer so as to minimize the phase difference. An automatic chromatic dispersion equalization optical transmission system characterized by comprising: 10. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the control circuit of the receiving unit of the receiving device and the regenerator is an error rate measuring circuit for measuring an error rate of a received signal, and An automatic chromatic dispersion equalization optical transmission system comprising: a dispersion amount control circuit that controls a dispersion amount set in a variable dispersion equalizer so that an error rate is minimized. 11. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the control circuit of the receiving section of the receiving device and the regenerator is a Q value measuring circuit for measuring the Q value of the received signal, and An automatic chromatic dispersion equalization optical transmission system, comprising: a dispersion amount control circuit that controls a dispersion amount set in a variable dispersion equalizer so that a Q value becomes maximum. 12. The automatic chromatic dispersion equalization optical transmission system according to claim 1, wherein the control circuit of the receiving unit of the receiving device and the regenerator is a clock component intensity measuring circuit for measuring the clock component intensity of the received signal. An automatic chromatic dispersion equalization optical transmission system comprising: a dispersion amount control circuit that controls a dispersion amount set in a variable dispersion equalizer so that the measured intensity is maximized. 13. The automatic wavelength dispersion equalization optical transmission system according to claim 10 or 11 , wherein the receiver and the receiver of the regenerator adjust the phase of the clock extracted by the clock extraction circuit. A clock phase adjustment circuit provided to the identification circuit, and a controller for controlling the clock phase adjustment circuit so that the clock phase with respect to the data signal becomes optimum according to the error rate or Q value of the received signal. Automatic wavelength dispersion equalization optical transmission system. 14. The automatic chromatic dispersion equalization optical transmission system according to claim 10 or 11 , wherein the receiving section of the receiving device and the regenerator has an identification voltage for adjusting an identification voltage of an identification circuit for identifying a data signal. An automatic chromatic dispersion comprising a voltage adjustment circuit and a controller for controlling the identification voltage adjustment circuit so that the identification voltage set in the identification circuit is optimized according to the error rate or Q value of the received signal. Equalized optical transmission system. 15. The automatic chromatic dispersion equalization optical transmission system according to claim 12 , wherein the receiving section of the receiving device and the regenerator is an error rate / Q value measuring circuit for measuring the error rate or Q value of the received signal. And a clock phase adjustment circuit that adjusts the phase of the clock extracted by the clock extraction circuit and provides it to the identification circuit, and a clock that optimizes the clock phase for the data signal according to the error rate or Q value of the received signal. An automatic wavelength dispersion equalization optical transmission system, comprising: a controller for controlling a phase adjustment circuit. 16. The automatic chromatic dispersion equalization optical transmission system according to claim 12 , wherein the receiving section of the receiving device and the regenerator is an error rate / Q value measuring circuit for measuring the error rate or Q value of the received signal. And an identification voltage adjusting circuit for adjusting an identification voltage of an identification circuit for identifying a data signal, and an error rate or a Q value of a received signal,
An automatic wavelength dispersion equalization optical transmission system comprising: a controller that controls an identification voltage adjusting circuit so that an identification voltage set in the identification circuit is optimal. 17. The automatic wavelength dispersion equalization optical transmission system according to claim 1 , wherein a control line is wired between the transmitter and the receiver, and the transmitter, the linear repeater and the regenerator are connected. Each of the receiving unit and the receiving device of the repeater is equipped with a control signal transmission / reception circuit, and is configured to transmit / receive a control signal and other control signals for transmission / reception of a test signal and a data signal accompanying the start and end of automatic chromatic dispersion equalization. Automatic wavelength dispersion equalization optical transmission system.