JP4176659B2 - Automatic dispersion compensator - Google Patents

Description

  The present invention relates to an automatic dispersion compensator suitable for use in a wavelength division multiplexing optical transmission system.

A wavelength division multiplexing optical transmission system multiplexes and transmits optical signals of a plurality of wavelengths on one optical fiber. In such a system, it is essential to maintain more uniform and stable transmission quality in a wide band while multiplexing more wavelengths in order to improve transmission capacity. One factor that limits transmission quality is the chromatic dispersion of optical fibers, and how to compensate for this chromatic dispersion is an important issue. Conventionally, as a technique for compensating for chromatic dispersion, for example, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, in order to measure dispersion, light of a plurality of wavelengths is separately modulated and transmitted. A technique for compensating for dispersion according to a propagation delay difference between wavelengths measured on the receiving side is known.
Akihide Sano et al, “Adaptive Dispersion Equalization by Monitoring Relative Phase Shift Between Spacing-Fixed WDM Signals”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.19, NO.3, pp.336-344 (2001) Toshiya Matsuda, Takeshi Kawasaki, Akihide Sano, Tomoyoshi Kataoka, “Variable dispersion compensation experiment using 40 Gbit / s multiplexed transmission equipment”, IEICE Communication Society Conference (September 2003)

By the way, when the above prior art is applied to a wavelength multiplexing system, in order to measure the propagation delay between two wavelengths, two modulators are provided on the transmission side and two O / Es (optical / electrical) are provided on the reception side. In addition, it is necessary to install a converter, and an accurate compensation dispersion amount including a sign cannot be measured with only two wavelengths. Therefore, in order to measure the accurate compensation dispersion amount including the code, there arises a problem that the apparatus configuration becomes complicated.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an automatic dispersion compensator capable of accurately compensating for dispersion including a sign with a simple configuration.

In order to achieve the above object, according to the first aspect of the present invention, there are provided first and second light sources that respectively output light having first and second wavelengths having wavelength recirculation, and the first and second light sources. a coupler for coupling light from, a modulator for modulating the sinusoidal signal combined beam by the coupler, and the light of the light and a second wavelength of the first wavelength that has passed through the modulator A delay unit for providing a delay between the optical unit , a wavelength circulatory transmission characteristic, and an optical multiplexer that multiplexes the light passing through the delay unit and another client signal and outputs the multiplexed signal to an optical fiber, a variable dispersion compensator for compensating the dispersion of the light passing through the optical fiber has a wavelength cyclic frequency in transmission characteristic, and a light and said another client signal passing through the variable dispersion compensator demultiplexed, demultiplexing The light that has passed through the delay means enters An optical demultiplexer for output from the port corresponding to the port of the optical multiplexer that is, an optical / electrical converter for converting the light output from the corresponding port of the optical demultiplexer into electrical signals, determine the dispersion compensation amount corresponding to the spectral intensity at the modulation frequency of the output Ru electrical signal from the optical / electrical converter, the dispersion value to control the dispersion value of the variable dispersion compensator according to the dispersion compensation amount determined control Means.

  The invention according to claim 2 that is dependent on claim 1 is characterized in that the delay means is a dispersion compensating fiber.

  According to a third aspect of the present invention, which is dependent on the first aspect, a modulated signal output for directly outputting a sine wave signal for modulating each output light of the first and second light sources to the first and second light sources. Means are provided in place of the modulator, and a dispersion compensating fiber is used as the delay means.

  The invention according to claim 4 that is dependent on claim 1 is characterized in that the delay means is a fiber Bragg grating.

  In the invention according to claim 5, which is dependent on claim 1, a modulation signal output for directly inputting a sine wave signal for modulating each output light of the first light source and the second light source to the first light source and the second light source. Means are provided in place of the modulator, and a fiber Bragg grating is used as the delay means.

  In the invention according to claim 6 that is dependent on claim 1, a sine wave signal that modulates each output light of the first and second light sources passes through a delay circuit that delays the modulation signal, and the first Modulation signal output means for outputting to the second light source a signal that is output to the light source and does not pass through the delay circuit is used as the delay means.

In the seventh aspect of the present invention, the first and second light sources that output light of the first and second wavelengths having wavelength reciprocity , the signal that oscillates at the first frequency, and the second frequency, respectively. A mixer for combining the oscillating signal and outputting it to the light source of the first wavelength, a signal for oscillating at the first frequency and a signal oscillating at the third frequency, and a light source of the second wavelength A mixer that outputs light from the first and second light sources, a modulator that modulates light combined by the coupler with a sine wave signal, and the modulator that has passed through the modulator Delay means for providing a delay between the light of the first wavelength and the light of the second wavelength, and the transmission characteristic having a wavelength circulatory property, the light passing through the delay means and another client signal are multiplexed. Passed through the optical fiber and an optical multiplexer that outputs to the optical fiber A variable dispersion compensator for compensating the dispersion having a wavelength cyclic frequency in the transmission characteristic, the variable dispersion compensator and the light passing through the and said another client signal demultiplexed, demultiplexing light, wherein An optical demultiplexer that is output from a port corresponding to the port of the optical multiplexer to which light that has passed through the delay means is input , and light that converts the light output from the corresponding port of the demultiplexer into an electrical signal / Electric converter, filter means for extracting first, second and third modulation frequency components from the electric signal output from the optical / electric converter, and the first extracted by the filter means Dispersion value control means for obtaining a dispersion compensation amount corresponding to the spectrum intensity at the modulation frequency, and controlling the dispersion value of the variable dispersion compensator according to the obtained dispersion compensation amount; and the second value extracted by the filter means. Modulation frequency Characterized by comprising a light source control means for controlling the output of said first and second light sources so that the signal strength of the signal strength third modulation frequency equal.

  In the invention according to claim 8, which is dependent on claim 7, the filter means extracts first, second and third modulation frequency components from the electric signal output from the optical / electrical converter, respectively. The light source control means includes a second modulation frequency signal and a third modulation frequency signal output from the second and third band pass filters, respectively. And switching means for switching the signal of the second modulation frequency and the signal of the third modulation frequency to measure the intensity, and the first signal so that the two signal intensities are equal to each other. And controlling the output of the second light source.

  In the invention according to claim 9, which is dependent on claim 7, the filter means extracts first, second and third modulation frequency components from the electrical signal output from the optical / electrical converter, respectively. The light source control means includes a second modulation frequency signal and a third modulation frequency signal output from the second and third band pass filters, respectively. And the outputs of the first and second light sources are controlled so that the two signal intensities are equal.

  In the invention according to claim 10, which is dependent on claim 7, the filter means extracts first, second and third modulation frequency components from the electrical signal output from the optical / electrical converter, respectively. The light source control means includes a second modulation frequency signal and a third modulation frequency signal output from the second and third band pass filters, respectively. The output of the second light source is controlled so that the difference between them becomes zero.

  The invention according to claim 11 that depends on claim 7 is characterized in that a dispersion compensating fiber is used as the delay means.

  The invention according to claim 12 that depends on claim 7 is characterized in that a fiber Bragg grating is used as the delay means.

  In a thirteenth aspect dependent on the seventh aspect, the sine wave signal for modulating the output light of the first and second light sources passes through the delay circuit for delaying the modulation signal, and the first Modulation signal output means for outputting a signal that is output to the light source and does not pass through the delay circuit to the second light source is used as the delay means.

  In the invention according to claim 14 dependent on either claim 1 or claim 7, a light source that oscillates at the first and third wavelengths is provided instead of the first light source, and the first and And measuring means for measuring the dispersion value of the optical fiber from the difference in delay of the light of the second wavelength and the difference of delay of the light in the second and third wavelengths.

  According to the first aspect of the present invention, the transmission side adds a delay to the modulated first and second wavelengths of light and then multiplexes and outputs the multiplexed light to the optical fiber. On the receiving side, a tunable dispersion compensator is provided to compensate for the dispersion of the light that has passed through the optical fiber. Since the corresponding dispersion compensation amount is obtained and the dispersion value of the tunable dispersion compensator is controlled in accordance with the obtained dispersion compensation amount, the dispersion compensation can be accurately performed with a simple configuration.

  In addition, according to the first aspect of the present invention, since the wavelength reciprocity of the transmittance characteristics of the optical multiplexer and the optical demultiplexer is used, dispersion compensation can be achieved with a simpler configuration than the conventional one, and transmission It is also possible to detect a failure on the receiving side on the receiving side. In addition, since the configuration of the apparatus can be simplified, there is an advantage that it can be very easily mounted on a high-density wavelength-weighted apparatus.

  According to the seventh aspect of the present invention, after the light that has passed through the tunable dispersion compensator is converted into an electric signal, the first, second, and third modulation frequency components are extracted from the converted electric signal, A dispersion compensation amount corresponding to the extracted spectrum intensity at the first modulation frequency is obtained, the dispersion value of the variable dispersion compensator is controlled in accordance with the obtained dispersion compensation amount, and the extracted signal at the second modulation frequency Since the outputs of the first and second light sources are controlled so that the intensity and the signal intensity of the third modulation frequency are equal, dispersion compensation including a sign is possible with a simple configuration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A. First Embodiment FIG. 1 is a block diagram showing a configuration of an automatic dispersion compensator 100 according to a first embodiment of the present invention. The automatic dispersion compensation device 100 includes a light source 11, a modulator 12, a dispersion compensation fiber (DCF) 13, an optical multiplexing unit 14, an optical fiber 15, a variable dispersion compensator 16, an optical demultiplexing unit 17, an optical / electrical converter 18, It comprises a spectrum intensity measuring device 19 and a control unit 20. The light source 11 is composed of a laser diode (LD) or the like, and emits a _first wavelength λ ₁ and a second wavelength λ _{N + 1} . The modulator 12 modulates the optical signal having the first wavelength λ _{1 and} the optical signal having the second wavelength λ _{N + 1} output from the light source 11 with a sine wave. The dispersion compensating fiber (DCF) 13 gives a predetermined delay to the modulated optical signal. The optical multiplexing unit 14 multiplexes and outputs two optical signals input via the dispersion compensating fiber (DCF) 13.

  The optical fiber 15 transmits the multiplexed output from the optical multiplexing unit 14 to the reception side. The tunable dispersion compensator 16 variably controls the dispersion value of the transmission line (optical fiber 15) in accordance with an instruction from the control unit 20. The optical demultiplexing unit 17 demultiplexes the multiplexed optical signal input via the tunable dispersion compensator 16. The optical / electrical converter 18 converts the optical signal demultiplexed by the optical demultiplexing unit 17 into an electric signal and outputs it. The spectrum intensity measuring device 19 performs spectrum analysis on the electrical signal output from the optical / electrical converter 18 and measures the RF power at the modulation frequency of the modulator 12. The control unit 20 instructs the tunable dispersion compensator 16 to specify a dispersion value corresponding to the RF power measured by the spectrum intensity measuring device 19.

In the automatic dispersion compensator 100 having the above-described configuration, the optical multiplexing unit 14 and the optical demultiplexing unit 17 are used as an optical multiplexing / demultiplexing unit having a wavelength circulation property in transmission characteristics. Therefore, both the optical signal of the _first wavelength λ _{1 and} the optical signal of the second wavelength λ _{N + 1} can be transmitted through the same port of the optical multiplexer 14 and are modulated by the sine wave signal by the same modulator 12. And then multiplexed. Further, in the process of transmitting through the dispersion compensating fiber (DCF) 13, a delay difference occurs between the optical signal of the _first wavelength λ _{1 and} the optical signal of the second wavelength λ _{N + 1} due to the chromatic dispersion characteristics. The optical signal of the _first wavelength λ _{1 and} the optical signal of the second wavelength λ _{N + 1} transmitted through the optical fiber 15 are output again to the same port by the optical demultiplexing unit 17, and then subjected to optical / electrical conversion. It is converted into an electric signal by the device 18.

  The spectrum intensity measuring device 19 performs spectrum analysis on the electrical signal output from the optical / electrical converter 18 and measures the RF power at the modulation frequency of the modulator 12. In order to obtain an unknown dispersion value from the RF power, it is necessary to obtain a correspondence relationship between the dispersion value and the RF power in advance. A method for obtaining the dispersion value from the RF power of the two-wavelength signal will be described with reference to FIG.

FIG. 2 is a diagram for explaining the principle of the dispersion value monitoring method. When the optical signals of the two wavelengths λ ₁ and λ ₂ are output from the same port of the optical demultiplexing unit 17, the electrical signal output from the optical / electrical converter 18 is the optical signal of the two wavelengths λ ₁ and λ ₂ . The signal level changes depending on how they overlap. For example, if the optical signal is amplitude-modulated at the modulation frequency fm and has two wavelengths λ ₁ and λ ₂ with a phase difference of 0, the power spectrum of the modulation frequency fm becomes maximum as shown in (1) in FIG. If the phase difference is π (reverse phase), the power spectrum of the modulation frequency fm becomes zero as shown in (3) of FIG. Thus, the power spectrum of the electrical signal output from the optical / electrical converter 18 reflects the phase difference between the optical signals of the two wavelengths λ ₁ and λ ₂ .

Therefore, if the RF power at the modulation frequency fm is known, the phase difference between the two wavelengths λ ₁ and λ ₂ , that is, the dispersion is known. The dispersion here refers to an average value of dispersion at two wavelengths λ ₁ and λ ₂ . The modulation frequency fm is set according to the dispersion fluctuation amount of the transmission line to be monitored. When amplitude modulation is performed with a sine wave, as is clear from the example illustrated in FIG. 3A, the RF power changes in a sine wave shape with respect to the dispersion fluctuation amount of the optical fiber. The phase difference Δφ after fiber transmission is given by the following equation.

Here, fm is the modulation frequency, D is the dispersion of the transmission line, L is the fiber length, and Δλ is the wavelength interval of two wavelengths, and the dispersion slope is not considered here. In the automatic dispersion compensator 100 configured as shown in FIG. 1, the optical signal having the first wavelength λ _{1 and} the optical signal having the second wavelength λ _{N + 1} are modulated by the same modulator 12. The phase difference is zero. The modulated dispersion compensating fiber (DCF) 13 gives an appropriate phase difference in advance between optical signals of two wavelengths on the transmission side. As a result, if the dispersion fluctuation amount is measured in the dispersion monitoring range shown in FIG. 3A, that is, the region in which the RF power fluctuation can be linearly approximated, an accurate code including a sign can be obtained as in the example shown in FIG. It becomes possible to measure the dispersion fluctuation amount. Specifically, the dispersion value of the transmission line (optical fiber 15) is changed by the variable dispersion compensator 16, and the corresponding RF power is measured by the spectrum intensity measuring device 19. If the correspondence between the dispersion fluctuation amount and the RF power is acquired in advance in this way, an accurate dispersion fluctuation amount including a sign corresponding to the measured RF power can be obtained.

Note that the automatic dispersion compensator 100 according to the present embodiment is not limited to the configuration illustrated in FIG. 1 and can be variously modified. For example, as in the modification shown in FIG. 4, the light source 11 (LD) that emits the first wavelength λ ₁ and the second wavelength λ _{N + 1} may be directly modulated. Further, as in the modification shown in FIGS. 5 and 6, a configuration using a Bragg fiber grating FBG may be used instead of the dispersion compensating fiber (DCF) 13. Furthermore, as in the modification shown in FIG. 7, a phase difference is provided between the first wavelength λ ₁ and the second wavelength λ _{N + 1} by providing a delay circuit on the modulator side and performing direct modulation. A mode of giving is also possible.

B. Second Embodiment FIG. 8 is a block diagram showing a configuration of an automatic dispersion compensator 200 according to a second embodiment of the present invention. The automatic dispersion compensation apparatus 200 includes a light source 11, a delay unit 30, an optical multiplexing unit 14, an optical fiber 15, a variable dispersion compensator 16, an optical demultiplexing unit 17, an optical / electrical converter 18, a spectral intensity measuring device 19, and a control unit. 20, a coupler 31, bandpass filters 32 to 34, and a current control unit 35. In FIG. 8, the same reference numerals are given to the same components as those in the first embodiment (see FIG. 1) described above, and the description thereof is omitted.

One laser diode LD constituting the light source 11 is directly modulated by modulation frequency components f ₁ and f ₁ -2f ₂ mixed by a mixer, and the other laser diode LD is modulated frequency component f ₁ mixed by a mixer. , F ₁ -2f ₃ . Accordingly, the light source 11 has an optical signal having the first wavelength λ ₁ having the modulation frequency components f ₁ and f ₁ -2f ₂ and a second wavelength λ _{N + 1} having the modulation frequency components f ₁ and f ₁ -2f _3. The optical signal is generated. The delay unit 30 includes any one of a dispersion compensating fiber (DCF), a Bragg fiber grating FBG, and a delay electric circuit, and an optical signal having a _first wavelength λ ₁ and a second wavelength λ _{N + 1} generated by the light source 11. The optical signal is delayed and output. The optical multiplexing unit 14 and the optical demultiplexing unit 17 are used as an optical multiplexing / demultiplexing unit having a wavelength circulation property in transmission characteristics. Therefore, both the optical signal having the first wavelength λ _{1 and} the optical signal having the second wavelength λ _{N + 1} are multiplexed through the same port of the optical multiplexing unit 14. Further, in the process of transmitting the delay unit 30, a delay difference occurs between the optical signal of the _first wavelength λ _{1 and} the optical signal of the second wavelength λ _{N + 1} due to the chromatic dispersion characteristics. The optical signal of the _first wavelength λ _{1 and} the optical signal of the second wavelength λ _{N + 1} transmitted through the optical fiber 15 are output again to the same port by the optical demultiplexing unit 17, and then subjected to optical / electrical conversion. It is converted into an electric signal by the device 18.

The electrical signal output from the optical / electrical converter 18 is supplied to the bandpass filter 32 (BPF (1)) and the bandpass filters 33 to 34 (BPF (2) to BPF (3)) via the coupler 31. The The band pass filter 32 extracts the modulation frequency component f ₁ . The band pass filter 33 extracts the modulation frequency component f ₁ -2f ₂ . The band pass filter 34 extracts the modulation frequency component f ₁ -2f ₃ . The band pass filters 33 to 34 are selected by the selector SEL. The selector SEL selects one of the bandpass filters 33 and 34 according to a switching signal generated by the current control unit 35, for example.

The modulation frequency component f ₁ output from the bandpass filter 32 is measured by the spectrum intensity measuring device 19 as in the first embodiment, and the control unit 20 responds to the output (measured value) of the spectrum intensity measuring device 19. The dispersion compensation amount is estimated and the variable dispersion compensator 16 is controlled. As shown in FIG. 2, the RF power changes depending on how the two-wavelength modulation signals are overlapped. Therefore, when the balance of the intensity of the two-wavelength signals is lost, the RF power changes due to effects other than the delay and correct dispersion is achieved. The value cannot be measured.

Therefore, in this embodiment, the current control unit 35 determines the intensity of the modulation frequency component f ₁ -2f ₂ extracted by the band pass filter 33 and the modulation frequency component f ₁ -2f ₃ extracted by the band pass filter 34. In comparison, the injection current of the laser diode LD constituting the light source 11 is controlled so as to equalize the intensity of both components. As a result, optical intensity compensation is performed to maintain the proper intensity of the optical signal having the first wavelength λ _{1 and} the optical signal having the second wavelength λ _{N + 1} . Therefore, under such light intensity compensation, an accurate dispersion fluctuation amount including a sign corresponding to the measured RF power can be obtained based on the correspondence relationship between the dispersion fluctuation amount and the RF power acquired in advance.

The automatic dispersion compensator 200 according to the present embodiment is not limited to the configuration shown in FIG. 8 and can be variously modified. For example, as in the modification shown in FIG. 9, a coupler SEL is used instead of the selector SEL. By using C, the intensity of the modulation frequency component f ₁ -2f ₂ and the intensity of the modulation frequency component f ₁ -2f ₃ may be simultaneously monitored while compensating for the light intensity. Further, for example, as in the modification shown in FIG. 10, a differential circuit DEF is provided, and an intensity difference between the modulation frequency component f ₁ -2f ₂ and the modulation frequency component f ₁ -2f ₃ is measured. It is good also as an aspect which compensates light intensity so that it may become fixed. Further, similarly to the modification of the first embodiment (see FIG. 7), in the automatic dispersion compensator 200 according to the present embodiment, the first wavelength λ _{1 is} obtained by providing a delay circuit on the modulator side and performing direct modulation. A mode in which a phase difference is given between the second wavelength λ _{N + 1} and the second wavelength λ _{N + 1} is also possible.

C. Third Embodiment FIG. 11 is a block diagram showing a configuration of an automatic dispersion compensator 300 according to a third embodiment of the present invention. The automatic dispersion compensation device 300 includes a light source 11, a delay unit 30, an optical multiplexing unit 14, an optical fiber 15, a variable dispersion compensator 16, an optical demultiplexing unit 17, an optical / electrical converter 18, a spectral intensity measuring device 19, and a control unit. 20, a coupler 31, a band pass filter 32, a current control unit 35, and a monitor unit 40. In FIG. 11, the same reference numerals are given to components common to the automatic dispersion compensator 200 according to the second embodiment described above, and description thereof is omitted.
The automatic dispersion compensator 300 according to the third embodiment is different from the automatic dispersion compensator 200 according to the second embodiment described above in that the light source 11 has wavelengths λ ₁ , λ _{N + 1} , λ _{2N + 1} , λ _{1−. It is} to output _N at the same time. In addition, the optical multiplexing unit 14 and the optical demultiplexing unit 17 are used as an optical multiplexing / demultiplexing unit having a wavelength circulation property in transmission characteristics. Accordingly, the optical signals of wavelengths λ ₁ , λ _{N + 1} , λ _{2N + 1} , and λ _1-N are all multiplexed through the same port of the optical multiplexing unit 14.

In the process of transmitting the delay unit 30, a delay difference occurs in each of the optical signals having wavelengths λ ₁ , λ _{N + 1} , λ _{2N + 1} , and λ _1-N due to chromatic dispersion characteristics. The optical signals of wavelengths λ ₁ , λ _{N + 1} , λ _{2N + 1} , and λ _1-N transmitted through the optical fiber 15 are output to the same port again by the optical demultiplexing unit 17 and then optical / electrical It is converted into an electric signal by the converter 18. An electrical signal output from the optical / electrical converter 18 is supplied to the band pass filter 32 via the coupler 31 and also to the monitor unit 40. The modulation frequency component f ₁ output from the bandpass filter 32 is measured by the spectrum intensity measuring device 19 as in the first embodiment, and the control unit 20 responds to the output (measured value) of the spectrum intensity measuring device 19. The dispersion compensation amount is estimated and the variable dispersion compensator 16 is controlled.

In the present embodiment, the monitor unit 40 measures the initial dispersion value in the optical fiber 15 from the delay difference between the wavelengths λ ₁ and λ _{N + 1} and the delay difference between the wavelengths λ _{N + 1} and λ _{2N + 1.} . In accordance with the initial dispersion value measured by the monitor unit 40, light intensity compensation is performed in which the current control unit 35 controls the injection current of the light source 11 that generates the optical signal having the wavelength λ _1-N . Therefore, under such light intensity compensation, an accurate dispersion fluctuation amount including a sign corresponding to the measured RF power can be obtained based on the correspondence relationship between the dispersion fluctuation amount and the RF power acquired in advance.

The principle by which the monitor unit 40 measures the initial dispersion value from the delay difference between the wavelengths λ ₁ and λ _{N + 1} and the delay difference between the wavelengths λ _{N + 1} and λ _{2N + 1} will be described with reference to FIG. To do. FIG. 12 is a diagram showing the wavelength dependence of the group velocity delay of the optical fiber 15. The arrival time τ of the optical signal propagating through the optical fiber 15 is given by the following equation.

In this [Expression 2], D (λ) and D ′ (λ) are dispersion and dispersion slope, respectively. L represents the fiber length, and λ ₀ represents the zero dispersion wavelength. Assuming that the delay difference between wavelengths λ ₁ and λ _{N + 1} is Δτ ₁ , and the delay difference between wavelengths λ _{N + 1} and λ _{2N + 1} is Δτ ₂ , the above equation 2 is used as follows: I can write.

Here, the wavelength intervals of λ _1-N , λ ₁ , λ _{N + 1} , and λ _{2N + 1} are constant. If this wavelength interval is Δλ, Δλ = λ _{N + 1} −λ ₁ = λ _{2N Since + 1} −λ _{N + 1} = λ ₁ −λ _1−N , when the above [Equation 3] is rewritten and transformed using Δλ, it is expressed as follows.

Here, D ″ is the average value of the dispersion values at λ ₁ and λ _{2N + 1.} Assuming that the influence of dispersion by the dispersion slope is small, the second term on the right side of the above equation can be ignored. As a result, the dispersion can be obtained from the delay difference change amount, and similarly, the initial dispersion value of the optical fiber 15 is obtained by obtaining the delay difference change amount between the wavelengths λ _1-N , λ ₁ , and λ _{N + 1.} Thus, in this embodiment, the light source 11 that oscillates at a plurality of wavelengths passing through the same AWG port is used as the light source for dispersion monitoring, and the monitor unit 40 provided on the receiving side has the wavelengths λ ₁ , λ _The configuration is characterized in that the initial dispersion value is measured from the delay difference between _{N + 1} and the delay difference between the wavelengths λ _{N + 1} and λ _{2N + 1} . Applied to the dispersion compensator 100 or the automatic dispersion compensator 200 according to the second embodiment. Of course it is also possible.

It is a block diagram which shows the structure of 1st Embodiment by this invention. It is a figure for demonstrating the principle of a dispersion value monitoring system. It is a figure for demonstrating the correspondence of a dispersion | variation variation | change_quantity and RF power. It is a block diagram which shows the structure of the modification of 1st Embodiment. It is a block diagram which shows the structure of the modification of 1st Embodiment. It is a block diagram which shows the structure of the modification of 1st Embodiment. It is a block diagram which shows the structure of the modification of 1st Embodiment. It is a block diagram which shows the structure of 2nd Embodiment by this invention. It is a block diagram which shows the structure of the modification of 2nd Embodiment. It is a block diagram which shows the structure of the modification of 1st Embodiment. It is a block diagram which shows the structure of 3rd Embodiment by this invention. It is a figure for demonstrating the principle which measures an initial dispersion value from the delay difference between wavelength (lambda) ₁ , (lambda) _{N + 1,} and the delay difference between wavelength (lambda) _{N + 1} , (lambda) _{2N + 1} .

Explanation of symbols

11 Light source 12 Modulator 13 Dispersion compensation fiber (DCF)
DESCRIPTION OF SYMBOLS 14 Optical multiplexing part 15 Optical fiber 16 Variable dispersion compensator 17 Optical demultiplexing part 18 Optical / electrical converter 19 Spectral intensity measuring device 20 Control part

Claims (13)

First and second light sources that respectively output light of first and second wavelengths having wavelength recirculation ,
A coupler for combining lights from the first and second light sources;
A modulator that modulates the light combined by the coupler with a sine wave signal;
Delay means for imparting a delay between the light of the first wavelength and the light of the second wavelength that has passed through the modulator;
An optical multiplexer having a wavelength circulatory transmission characteristic, and multiplexing the light passing through the delay means and another client signal and outputting the multiplexed signal to an optical fiber;
A variable dispersion compensator that compensates for dispersion of light that has passed through the optical fiber;
The transmission characteristic has wavelength recursion , demultiplexes the light that has passed through the tunable dispersion compensator and the other client signal, and the demultiplexed light is input with the light that has passed through the delay means An optical demultiplexer that outputs from a port corresponding to the optical multiplexer port ;
An optical / electrical converter for converting the light output from the corresponding port of the optical demultiplexer into electrical signals,
Determine the dispersion compensation amount corresponding to the spectral intensity at the modulation frequency of the output Ru electrical signal from the optical / electrical converter, the dispersion value to control the dispersion value of the variable dispersion compensator according to the dispersion compensation amount determined control And an automatic dispersion compensator.   The automatic dispersion compensator according to claim 1, wherein the delay unit is a dispersion compensating fiber.   A modulation signal output means for directly outputting a sine wave signal for modulating each output light of the first and second light sources to the first and second light sources is provided in place of the modulator, and distributed as the delay means. 2. The automatic dispersion compensator according to claim 1, wherein a compensation fiber is used.   The automatic dispersion compensator according to claim 1, wherein the delay unit is a fiber Bragg grating.   Modulation signal output means for directly inputting a sine wave signal for modulating each output light of the first and second light sources to the first and second light sources is provided instead of the modulator, and a fiber as the delay means. The automatic dispersion compensator according to claim 1, wherein a Bragg grating is used.   A sine wave signal that modulates each output light of the first and second light sources is output to the first light source through a delay circuit that gives a delay to the modulated signal, and a signal that does not pass through the delay circuit is second. 2. The automatic dispersion compensator according to claim 1, wherein modulation signal output means for outputting to the light source is used as the delay means. First and second light sources that respectively output light of first and second wavelengths having wavelength recirculation ,
A mixer that combines a signal that oscillates at a first frequency and a signal that oscillates at a second frequency, and outputs the resultant signal to a light source having a first wavelength;
A mixer for combining a signal oscillating at a first frequency and a signal oscillating at a third frequency and outputting the resultant signal to a light source of a second wavelength;
A coupler for combining lights from the first and second light sources;
A modulator that modulates the light combined by the coupler with a sine wave signal;
Delay means for providing a delay between the light of the first wavelength and the light of the second wavelength that has passed through the modulator;
An optical multiplexer having a wavelength circulatory transmission characteristic, and multiplexing the light passing through the delay means and another client signal and outputting the multiplexed signal to an optical fiber;
A variable dispersion compensator that compensates for dispersion of light that has passed through the optical fiber;
The transmission characteristic has wavelength recursion , demultiplexes the light that has passed through the tunable dispersion compensator and the other client signal, and the demultiplexed light is input with the light that has passed through the delay means An optical demultiplexer that outputs from a port corresponding to the optical multiplexer port ;
An optical / electrical converter that converts light output from the corresponding port of the duplexer into an electrical signal;
Filter means for extracting first, second and third modulation frequency components from the electrical signal output by the optical / electrical converter;
Dispersion value control means for obtaining a dispersion compensation amount corresponding to the spectrum intensity at the first modulation frequency extracted by the filter means, and controlling a dispersion value of the variable dispersion compensator according to the obtained dispersion compensation amount; ,
Light source control means for controlling the outputs of the first and second light sources so that the signal intensity of the second modulation frequency and the signal intensity of the third modulation frequency extracted by the filter means are equal. An automatic dispersion compensator characterized by comprising: The filter means includes first, second, and third bandpass filters that respectively extract first, second, and third modulation frequency components from the electrical signal output by the optical / electrical converter,
The light source control means includes switching means for switching between the second modulation frequency signal and the third modulation frequency signal output from the second and third bandpass filters, respectively. Switching the signal of the second modulation frequency and the signal of the third modulation frequency to measure the intensity, and controlling the outputs of the first and second light sources so that the two signal intensities are equal. 8. The automatic dispersion compensator according to claim 7, wherein The filter means includes first, second, and third bandpass filters that respectively extract first, second, and third modulation frequency components from the electrical signal output by the optical / electrical converter,
The light source control means compares the signal of the second modulation frequency and the signal of the third modulation frequency output from the second and third band pass filters, respectively, so that the two signal intensities are equal. 8. The automatic dispersion compensator according to claim 7, wherein outputs of the first and second light sources are controlled. The filter means includes first, second, and third bandpass filters that respectively extract first, second, and third modulation frequency components from the electrical signal output by the optical / electrical converter,
The light source control means is configured such that the difference between the second modulation frequency signal and the third modulation frequency signal respectively output from the second and third band pass filters is zero. 8. The automatic dispersion compensator according to claim 7, wherein the output of the light source is controlled.   8. The automatic dispersion compensating apparatus according to claim 7, wherein a dispersion compensating fiber is used as the delay means.   8. The automatic dispersion compensator according to claim 7, wherein a fiber Bragg grating is used as the delay means.   A sine wave signal that modulates the output light of the first and second light sources is output to the first light source through a delay circuit that gives a delay to the modulated signal, and a signal that does not pass through the delay circuit is second 8. The automatic dispersion compensator according to claim 7, wherein modulation signal output means for outputting to a light source is used as the delay means.

Images