WO2015136877A1 - Émetteur optique, système de communication optique l'utilisant et procédé de communication optique - Google Patents

Émetteur optique, système de communication optique l'utilisant et procédé de communication optique Download PDF

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Publication number
WO2015136877A1
WO2015136877A1 PCT/JP2015/001047 JP2015001047W WO2015136877A1 WO 2015136877 A1 WO2015136877 A1 WO 2015136877A1 JP 2015001047 W JP2015001047 W JP 2015001047W WO 2015136877 A1 WO2015136877 A1 WO 2015136877A1
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optical
signal
data signal
modulator
optical modulator
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PCT/JP2015/001047
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English (en)
Japanese (ja)
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栄実 野口
安部　淳一
加藤　友章
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日本電気株式会社
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/58—Compensation for non-linear transmitter output
    • H04B10/588—Compensation for non-linear transmitter output in external modulation systems

Definitions

  • the present invention relates to an optical transmitter, an optical communication system and an optical transmission method using the same, and more particularly to an optical transmitter including a Mach-Zehnder optical modulator, an optical communication system and an optical transmission method using the optical transmitter.
  • waveform distortion compensation such as chromatic dispersion compensation can be compensated by digital signal processing (DSP) on the transmission side or reception side.
  • DSP digital signal processing
  • An optical communication device applied to digital coherent optical communication is disclosed in, for example, Patent Documents 1-3.
  • FIG. 10 shows a block diagram of a general digital optical transmitter applied to digital coherent optical communication.
  • a D / A (digital to analog) converter for performing multi-level modulation such as QPSK (quadture phase shift keying) modulation or QAM (quadture amplitude modulation) modulation, pre-equalization, and the like.
  • QPSK quadrature phase shift keying
  • QAM quadrature amplitude modulation
  • Such a digital optical transmitter generally uses an MZ optical modulator in which an optical waveguide type optical phase modulator is incorporated in an optical waveguide type Mach-Zehnder (MZ) interferometer.
  • the MZ optical modulator can perform various optical modulations such as intensity modulation and phase modulation by adjusting the applied voltage and the configuration of the interferometer.
  • JP 2009-171634 A International Publication No. 2012/108421 JP 2004-70130 A JP 2011-247926 A
  • An object of the present invention is to provide an optical transmitter that can be suitably maintained and maintain system performance, an optical communication system using the same, and an optical transmission method.
  • an optical transmitter branches an optical output means for outputting an optical signal based on given wavelength information, and the optical signal into a first optical signal and a second optical signal.
  • a DC offset amount for compensating for the distortion characteristics of the branching means and the second optical modulator is calculated, a first data signal including the calculated DC offset amount is output to the first optical modulator, and the first A data signal output means for calculating a DC offset amount for compensating distortion characteristics of the optical modulator, and outputting a second data signal including the calculated DC offset amount to the second optical modulator; and the first light
  • an optical communication system is characterized in that the above-mentioned digital optical transmitter is arranged and gives predetermined wavelength information to the optical transmitter.
  • an optical transmission method is an optical transmission method using a first modulator and a second modulator, and outputs an optical signal based on given wavelength information.
  • the output optical signal is branched into two to output a first optical signal and a second optical signal, a DC offset amount for compensating for distortion characteristics of the second optical modulator is calculated, and the calculated DC
  • a first data signal including an offset amount is output to the first optical modulator, a DC offset amount for compensating for distortion characteristics of the first optical modulator is calculated, and a first DC signal including the calculated DC offset amount is calculated.
  • Two data signals are output to the second optical modulator, and the first modulator modulates the first optical signal with the first data signal and outputs a first modulated signal;
  • the second optical signal is converted into the second data signal.
  • Output the second modulated signal by modulating Te outputs the transmission signal by combining the first modulated signal and second modulated signal said output.
  • the quality of the output transmission signal is suitably maintained by simple control with a small load. Performance can be maintained.
  • FIG. 1 is a block configuration diagram of an optical transmitter 10 according to a first embodiment.
  • FIG. 1 is a block configuration diagram of a digital optical transmitter 100 according to a first embodiment.
  • FIG. It is a block block diagram of the digital optical transmitter 200 which concerns on 2nd Embodiment.
  • It is a block block diagram of the front signal processing part 213 which concerns on 2nd Embodiment.
  • It is an example of the block diagram of the optical modulator 203 for I channels which concerns on 2nd Embodiment.
  • FIG. 10 is a diagram for explaining the characteristics of optical signals E + and E ⁇ output from an upper phase modulator 401 and a lower phase modulator 402 according to the second embodiment.
  • FIG. 10 is a diagram illustrating an example of output constellations from an I-channel optical modulator 203 and a Q-channel optical modulator 204 in the second embodiment. It is a diagram showing an error component .DELTA.a Q of the optical signal output from the I-channel light modulator 203 according to the second embodiment. Is a diagram showing an error component .DELTA.a Q 'after the correction of the optical signal output from the I-channel light modulator 203 according to the second embodiment.
  • It is a block block diagram of the digital optical transmitter 800 which concerns on 3rd Embodiment.
  • It is a block block diagram of the digital optical transmitter 900 which concerns on 4th Embodiment.
  • It is a block block diagram of a general digital optical transceiver.
  • FIG. 1A shows a block configuration diagram of the optical transmitter according to the present embodiment.
  • the optical transmitter 10 includes an optical output means 20, a branching means 30, a data signal output means 40, a first optical modulator 51, a second optical modulator 52, and a coupling means 60.
  • the light output means 20 generates and outputs an optical signal having a predetermined wavelength based on the given wavelength information.
  • a wavelength variable light source can be applied as the light output means 20, for example.
  • the branching unit 30 branches the optical signal output from the optical output unit 20 and sends one optical signal (first optical signal) to the first optical modulator 51 and the other optical signal (second optical signal). Are output to the second optical modulator 52 respectively.
  • the data signal output means 40 calculates a DC (direct current) offset amount for compensating for distortion characteristics of the second optical modulator 52, which will be described later, and outputs a first data signal including the calculated DC offset amount as the first data signal. Output to the optical modulator. Further, the data signal output means 40 calculates a DC offset amount for compensating for distortion characteristics of the first optical modulator 51, which will be described later, and converts the second data signal including the calculated DC offset amount to the second optical modulation. To the device 52.
  • the first data input signal, the second data input signal, and the wavelength information are given to the data signal output means 40 according to the present embodiment.
  • the data signal output means 40 responds to the distortion characteristics of the first and second optical modulators 51 and 52 corresponding to the wavelength of the optical signal output from the optical output means 20 based on the given wavelength information.
  • the DC offset amount is calculated.
  • the data signal output means 40 adds a DC offset amount for compensating the distortion characteristic of the second optical modulator 52 to the first data input signal, and the first data signal is added to the first optical modulator 51. Output to. Further, the data signal output means 40 adds a DC offset amount for compensating the distortion characteristics of the first optical modulator 51 to the second data input signal, and the second data signal is added to the second optical modulator 52. Output to.
  • the first data input signal and the second data input signal correspond to the information signal in the claims.
  • the first optical modulator 51 modulates the first optical signal input from the branching means 30 with the first data signal input from the data signal output means 40, and outputs the first modulated signal.
  • the second optical modulator 52 modulates the second optical signal input from the branching unit 30 with the second data signal input from the data signal output unit 40, and outputs a second modulated signal.
  • the coupling means 60 combines the first modulated signal input from the first optical modulator 51 and the second modulated signal input from the second optical modulator 52, and outputs a transmission signal.
  • the combining unit 60 outputs, for example, an I / Q (in-phase / quadture) transmission signal represented by QAM modulation.
  • the second data signal for driving the second optical modulator 52 corresponds to the distortion characteristic of the first optical modulator 51 corresponding to the wavelength of the optical signal output from the optical output means 20.
  • a DC offset amount is added in advance.
  • the data signal for driving the first optical modulator 51 has a DC offset amount corresponding to the distortion characteristic of the second optical modulator 52 corresponding to the wavelength of the optical signal output from the optical output means 20 in advance. It has been added.
  • the data signal output means 40 is, for example, as waveform distortion peculiar to the first and second optical modulators 51 and 52. Then, a DC offset amount corresponding to the waveform distortion caused by the extinction ratio is calculated. That is, the data signal output means 40 adds the DC offset amount for canceling the extinction ratio of the second optical modulator 52 corresponding to the wavelength information to the first data input signal to generate the first data signal.
  • the first optical modulator 51 is driven by the first data signal.
  • the data signal output means 40 adds a DC offset amount for canceling the extinction ratio of the first optical modulator 51 corresponding to the wavelength information to the second data input signal to generate a second data signal.
  • the second optical modulator 52 is driven by the second data signal.
  • the extinction ratio represents the ratio between the maximum value and the minimum value of the optical intensity of the output optical signal when the MZ optical modulator is driven by intensity modulation.
  • the minimum value of the light intensity can be made zero, so the extinction ratio is ⁇ .
  • the branching ratio of the multiplexer / demultiplexer constituting the MZ interferometer is not an ideal ratio of 50:50. The strength is not completely zero.
  • the extinction ratio shows a finite value. That is, by adding a DC offset amount corresponding to the wavelength to the first and second data input signals, the extinction ratio in the first and second optical modulators 51 and 52 can be canceled with high accuracy.
  • FIG. 1B shows a block diagram of the digital optical transmitter in this case.
  • the digital optical transmitter 100 includes an encoding unit 107, DC addition units 108-1 and 108-2, a DC offset amount calculation unit 109, and an optical modulator 106.
  • the optical modulator 106 includes a wavelength tunable light source 101, an optical branching unit 102, a first MZ optical modulator 103, a second MZ optical modulator 104, and an optical coupling unit 105.
  • DC adder 108-1 When there are a plurality of units having the same function, the reference numerals are assigned with -1, -2, etc. to distinguish them. Unless there is a particular need to distinguish, for example, “DC adder 108-1”, “DC adder 108-2” and the like are described as “DC adder 108”.
  • the encoding unit 107 receives two systems of data signals DI (I channel signal) and DQ (Q channel signal). The encoding unit 107 encodes the input data signals DI and DQ in accordance with the modulation method to generate the first data signals DI1 (I channel signal) and DQ1 (Q channel signal), and the DC adding unit 108- 1 and 108-2, respectively.
  • the DC offset amount calculation unit 109 calculates an optimal DC offset amount according to the input wavelength information, and outputs it to the DC addition unit 108. Specifically, the DC offset amount calculation unit 109 calculates a DC offset amount for canceling the extinction ratio of the second MZ optical modulator 104 corresponding to the wavelength information, and outputs the DC offset amount to the DC addition unit 108-1. . Further, the DC offset amount calculation unit 109 calculates a DC offset amount for canceling the extinction ratio of the first MZ optical modulator 103 corresponding to the wavelength information, and outputs the DC offset amount to the DC addition unit 108-2.
  • the DC adder 108-1 adds the input DC offset amount to the input first data signal DI1, and outputs the second data signal DI2 (I channel signal) to the optical modulator 106.
  • the DC adder 108-2 adds the input DC offset amount to the input first data signal DQ1, and outputs the second data signal DQ2 (Q channel signal) to the optical modulator 106. .
  • the wavelength tunable light source 101 is provided with wavelength information of an optical carrier signal used (or assigned) by an optical communication system using the digital optical transmitter 100, so that an optical signal having a desired wavelength is obtained. Is output. Note that the same wavelength information is input to the DC offset amount calculation unit 109 described above.
  • the optical signal of the carrier wave output from the wavelength tunable light source 101 is transmitted to the optical branching unit 102. Note that it is desirable to use continuous light as the optical signal of the carrier wave.
  • the optical branching unit 102 branches the optical signal of the carrier wave input from the wavelength tunable light source 101 and outputs one to the first MZ optical modulator 103 and the other to the second MZ optical modulator 104.
  • the first MZ optical modulator 103 converts one optical signal input from the optical branching unit 102 into an optical phase based on the second data signal DI2 (I channel signal) input from the DC adding unit 108-1. Modulate and output a first modulated signal.
  • the second MZ optical modulator 104 converts the other optical signal input from the optical branching unit 102 into an optical phase based on the second data signal DQ2 (Q channel signal) input from the DC adding unit 108-2. Modulate and output a second modulated signal.
  • the first modulation signal is an I-ch (in-phase channel) optical signal
  • the second modulation signal is a Q-ch (quadture channel) optical signal.
  • the optical coupling unit 105 converts the first modulation signal input from the first MZ optical modulator 103 and the second modulation signal input from the second MZ optical modulator 104 into a predetermined phase difference ⁇ ( ⁇ is, for example, In the case of I / Q modulation, ⁇ / 2) is added and combined to output a transmission signal.
  • the DC offset amount calculation unit 109 calculates a DC offset amount for canceling the extinction ratio of the second MZ optical modulator 104 according to the wavelength information. It is added in advance to the second data signal DI2 for driving the first MZ optical modulator 103. Similarly, a DC offset amount for canceling the extinction ratio of the first MZ optical modulator 103 according to the wavelength information is added in advance to the second data signal DQ2 for driving the second MZ optical modulator 104.
  • the DC offset amount calculation unit 109 separates the influence of the extinction ratio of the first MZ light modulator 103 from the influence of the extinction ratio of the second MZ light modulator 104, and compensates them independently.
  • the DC offset amount to be calculated may be calculated.
  • the calculation load of the DC offset amount calculation unit 109 increases. Without distortion, the distortion characteristics cancel each other when the outputs from the first and second MZ optical modulators 103 and 104 are coupled through the optical coupling unit 105. As a result, the waveform distortion applied in the first and second MZ optical modulators 103 and 104 is easily compensated, and a transmission signal whose quality is suitably maintained is output from the digital optical transmitter 100.
  • FIG. 2 shows a block diagram of the optical transceiver according to the present embodiment.
  • the digital optical transmitter 200 includes an encoding unit 210, a pre-equalization signal generation unit 211, addition units 212-1, 212-2, a front signal processing unit 213, a DC offset amount calculation unit 214, and an optical modulation.
  • the optical modulation unit 209 includes D / A converters (DAC: digital to analog converters) 207-1 and 207-2, driver amplifiers 208-1 and 208-2, a light source 201, and an MZ type I / Q optical modulator. 206.
  • the MZ type I / Q optical modulator 206 includes an I channel optical modulator 203, a Q channel optical modulator 204, and a ⁇ / 2 phase shifter 205.
  • the encoding unit 210 receives two systems of data signals DI (I channel signal) and DQ (Q channel signal). The encoding unit 210 performs encoding according to the modulation method on the input data signals DI and DQ, respectively, and pre-equalizes the first data signals DI1 (I channel signal) and DQ1 (Q channel signal). It outputs to the signal generation part 211.
  • the pre-equalization signal generation unit 211 performs, for example, filter processing for equalizing the characteristics in the optical transmission path on the input first data signals DI1 and DQ1, as necessary.
  • Data signals DI1 ′ and DQ1 ′ are output to the DC adders 212-1 and 212-2.
  • the DC offset amount calculation unit 214 calculates a DC offset amount for canceling the waveform distortion due to the extinction ratio of the MZ type I / Q optical modulator 206 based on the given wavelength information, and outputs the DC offset amount to the DC addition unit 212. .
  • the DC offset amount calculation unit 214 determines whether the I-channel optical modulator 203 and the Q-channel optical modulator 204 at the wavelength of continuous light output from the light source 201, which will be described later, based on the given wavelength information. A DC offset amount for canceling each extinction ratio characteristic is calculated.
  • the DC adder 212-1 adds the input DC offset amount to the input first ′ data signal DI 1 ′, and outputs the second data signal DI 2 (I channel signal) to the front signal processor 213. .
  • the DC adding unit 212-2 adds the input DC offset amount to the input first ′ data signal DQ1 ′, and outputs the second data signal DQ2 (Q channel signal) to the front signal processing unit 213. .
  • the front signal processing unit 213 performs nonlinearity of front end devices such as the DAC 207, the driver amplifier 208, the I-channel optical modulator 203, and the Q-channel optical modulator 204 with respect to the input second data signals DI2 and DQ2. Correction for linearizing the characteristic and correction for the frequency characteristic are performed.
  • the front signal processing unit 213 outputs the corrected second data signals DI2 and DQ2 to the optical modulation unit 209 as third data signals DI3 (I channel signal) and DQ3 (Q channel signal).
  • the front signal processing unit 213 will be described in detail. An example of a block diagram of the front signal processing unit 213 is shown in FIG.
  • the front signal processing unit 213 in FIG. 3 includes linearizers 301-1 and 301-2 and band compensation filters 302-1 and 302-2.
  • the linearizer 301-1 converts the input second data signal DI2 into a data string for linearizing the nonlinear characteristic of the I-channel optical modulator 203, and outputs the data string to the band compensation filter 302-1.
  • the band compensation filter 302-1 corrects the input data string so as to optimize the frequency characteristics of the I-channel optical modulator 203, and outputs it to the optical modulation unit 209 as the third data signal DI3.
  • the linearizer 301-2 converts the input second data signal DQ2 into a data string for linearizing the nonlinear characteristic of the Q-channel optical modulator 204, and outputs the data string to the band compensation filter 302-2. Output.
  • the band compensation filter 302-2 corrects the input data string so as to optimize the frequency characteristics of the Q-channel optical modulator 204, and outputs the data string to the optical modulation unit 209 as the third data signal DQ3.
  • the digital optical transmitter 200 can improve the yield of used parts, and can reduce the cost.
  • the front signal processing unit 213 further includes a linear filter such as a FIR (finite impulse response) / IIR (infinite impulse response) filter, a nonlinear filter, a signal processing unit such as a clipping process, or the like. Multiple combinations can be provided.
  • a linear filter such as a FIR (finite impulse response) / IIR (infinite impulse response) filter
  • a nonlinear filter such as a clipping process, or the like.
  • the front signal processing unit 213 may be arranged before the pre-equalization signal generation unit 211 or at both the front and rear stages. I can do it.
  • non-linear characteristic is the saturation characteristic of the DAC 207 and the driver amplifier 208.
  • Another example is a non-linear characteristic resulting from the change in the intensity of the output signal with respect to the drive applied voltage V mod of the I-channel optical modulator 203 or the Q-channel optical modulator 204 being a sine wave characteristic. It is done.
  • the sine wave characteristic is a characteristic in which the intensity change of the output signal is proportional to sin (kV mod ) or cos (kV mod ) (k is a constant).
  • the third data signals DI3 (I channel signal) and DQ3 (Q channel signal) input to the optical modulation unit 209 are proportional to the digital signal amplitudes of the third data signals DI3 and DQ3 in the DACs 207-1 and 207-2. Are converted to analog signals and output to the driver amplifiers 208-1 and 208-2, respectively.
  • the driver amplifiers 208-1 and 208-2 amplify the electrical amplitude of the input analog signal to an appropriate amplitude, and use the I-channel optical modulator 203 and the Q channel of the MZ type I / Q optical modulator 206 as drive signals. To the optical modulator 204 for output. The same wavelength information is also input to the DC offset amount calculation unit 214 described above.
  • the light source 201 is provided with wavelength information from the outside, for example, and outputs an optical signal of continuous light corresponding to the wavelength information to the MZ type I / Q optical modulator 206.
  • the MZ type I / Q optical modulator 206 branches the optical signal input from the light source 201 into two optical signals passing through the I channel optical waveguide and the Q channel optical waveguide along the optical waveguide.
  • One of the branched optical signals passes through the I-channel optical modulator 203, and the other optical signal passes through the Q-channel optical modulator 204 and the ⁇ / 2 phase shifter 205.
  • optical phase modulation is performed according to the electrical signals input from the driver amplifiers 208-1 and 208-2.
  • the phase of the optical signal that has passed through the Q-channel optical modulator 204 changes by ⁇ / 2 in the ⁇ / 2 phase shifter 205.
  • the optical signal that has passed through the I-channel optical modulator 203 and the optical signal that has passed through the Q-channel optical modulator 204 and the ⁇ / 2 phase shifter 205 are combined by a Y-coupled optical waveguide and transmitted. Is output as
  • the DC offset amount calculation unit 214 includes the I-channel optical modulator 203 and the Q-channel optical modulator at the wavelength of continuous light output from the light source 201. A DC offset amount for canceling each extinction ratio characteristic of 204 is calculated. Then, the I-channel optical modulator 203 and the Q-channel optical modulator 204 are driven by a data signal to which a DC offset amount is given in advance. As a result, the waveform distortion due to the extinction ratio of the MZ type I / Q optical modulator 206 is compensated, and a transmission signal whose quality is suitably maintained is output.
  • FIG. 4 An example of the configuration of the I-channel optical modulator 203 constituting the MZ type I / Q optical modulator 206 is shown in FIG.
  • an MZ optical modulator composed of an upper phase modulator 401 and a lower phase modulator 402 can be applied as the I-channel optical modulator 203.
  • the Q-channel optical modulator 204 can be configured in the same manner.
  • the optical signal exp (i ⁇ t) (i: imaginary unit, ⁇ : angular frequency of the optical signal) input to the I-channel optical modulator 203 is branched into two optical signals, one to the upper phase modulator 401 and the other Is directed to the lower phase modulator 402.
  • the electric field strength of the optical signal input to the upper phase modulator 401 is given by A + exp (i ⁇ t)
  • the electric field strength of the optical signal input to the lower phase modulator 402 is given by A ⁇ exp (i ⁇ t).
  • the phase rotation amount given by the upper phase modulator 401 is given by exp (i ⁇ V / 2V ⁇ ), and the phase rotation amount given by the lower phase modulator 402 is given by exp ( ⁇ i ⁇ V / 2V ⁇ ).
  • V is a driving voltage for driving the upper phase modulator 401 and a lower phase modulator 402
  • the V [pi is the applied voltage phase rotation amount becomes [pi.
  • FIG. 5A shows E + and E ⁇ when A + ⁇ A ⁇
  • the black line represents E +
  • the gray line represents E ⁇
  • FIG. 5B shows E out for each extinction ratio of the upper phase modulator 401 and the lower phase modulator 402.
  • each of I and Q A constellation when a 4-bit (16 tone) precision data string is input has the form shown in FIG.
  • the output constellations from the I-channel optical modulator 203 and the Q-channel optical modulator 204 are distorted in a bow shape.
  • FIG. 7A shows a conceptual diagram of waveform distortion (corresponding to the error shown in FIG. 5B) when the extinction ratio is not ideal ( ⁇ ).
  • ⁇ the distortion amount ⁇ a Q to the Q channel component included in the output from the I channel optical modulator 203 when the data string a I is input as a signal for driving the I channel optical modulator 203 is shown. Illustrated. Since the Q-channel optical modulator 204 also operates according to the same principle, only the I-channel optical modulator 203 will be described.
  • the DC offset amount calculation unit 214 acquires a DC offset amount for canceling ErrQ from the given wavelength information, and uses the acquired DC offset amount as a DC addition unit 212-2 (Q channel side). Is added in advance to the drive signal of the Q-channel optical modulator 204. Thereby, by combining at the optical coupling part of the MZ type I / Q optical modulator 206, it is possible to compensate for an error of the Q channel component in the optical modulator output.
  • FIG. 7B shows the error ⁇ a Q ′ after compensating for the Q channel component error.
  • the configuration of the present embodiment can reduce the increase in the carrier signal component due to the extinction ratio, and reduce the degradation of the signal S / N due to the increase in the carrier signal component due to the extinction ratio compared with the same transmission power. it can. Therefore, an effect of reducing the deterioration of transmission characteristics can be obtained.
  • the DC offset amount calculation unit 214 calculates an appropriate DC offset amount based on the applied wavelength information. For example, for each wavelength, the extinction ratio of the optical modulator or an appropriate DC offset amount to compensate for it is measured in advance and recorded in a LUT (Look-Up Table). Based on the LUT, an appropriate DC offset amount may be extracted and set. Alternatively, if the relationship between the wavelength information and the extinction ratio is known, it may be calculated. Furthermore, a more accurate DC offset amount may be calculated by combining the LUT and the interpolation operation, and the method is not limited to these.
  • the quality of the output transmission signal is suitably maintained, and the system Performance can be maintained.
  • FIG. 8 shows a block diagram of the optical transceiver according to the present embodiment.
  • the digital optical transmitter 800 according to this embodiment is configured by adding a signal quality monitor 801 and a waveform distortion amount detection unit 802 to the digital optical transmitter 200 of FIG. 2 described in the second embodiment.
  • the same components as those of the digital optical transmitter 200 of FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.
  • the signal quality monitor 801 monitors the transmission signal output from the light modulation unit 209 and outputs monitor information to the waveform distortion amount detection unit 802.
  • a suitable monitor such as a waveform monitor, a spectrum monitor, an error rate monitor, a constellation monitor, or a power monitor is selected according to the transmission signal and the type of distortion to be generated.
  • the waveform distortion amount detection unit 802 detects the waveform distortion amount based on the input monitor information, and outputs the detected waveform distortion amount to the DC offset amount calculation unit 214.
  • the DC offset amount calculation unit 214 has been adjusted (feedback controlled) so that the waveform distortion input from the waveform distortion amount detection unit 802 is minimized.
  • D) Output the DC offset amount to the DC adder 212.
  • the signal quality of the transmission signal output from the digital optical transmitter 800 deteriorates due to the waveform distortion caused by the extinction ratio that varies with time. Even in this case, the influence can be reduced adaptively.
  • the initial value of the waveform distortion amount is preset in advance, and when a certain amount of waveform distortion occurs due to long-term fluctuation due to secular change or the like, the DC offset amount calculation unit 214
  • the setting can also be updated based on the waveform distortion input from the waveform distortion amount detection unit 802. In this case, the signal quality of the transmission signal can be easily maintained without performing complicated control.
  • FIG. 9 shows a block diagram of the optical transceiver according to the present embodiment.
  • a digital optical transmitter 900 according to this embodiment includes an I channel signal quality monitor 901-1 and a Q channel signal quality monitor 901-2 in addition to the digital optical transmitter 200 of FIG. 2 described in the second embodiment. Prepare.
  • the I channel signal quality monitor 901-1 and the Q channel signal quality monitor 901-2 are characteristics of optical signals output from the I channel optical modulator 203 and the Q channel optical modulator 204, such as a waveform monitor and a spectrum analyzer. A monitor that can preferably acquire the is selected. Specifically, in the I channel signal quality monitor 901-1 and the Q channel signal quality monitor 901-2, some of the optical signals output from the I channel optical modulator 203 and the Q channel optical modulator 204 are stored. Input and monitor various characteristics of the input optical signal.
  • the DC offset amount calculation unit 214 includes an I channel calculation unit 902-1 and a Q channel side calculation unit 902-2. Then, the characteristics of the optical signal acquired by the I channel signal quality monitor 901-1 are sent to the Q channel calculation unit 902-2, and the characteristics of the optical signal acquired by the Q channel signal quality monitor 901-2 are sent to the I channel calculation unit 902. Feedback to -1.
  • the influence of the extinction ratio in the I-channel optical modulator 203 is compensated by adjusting the DC offset amount on the Q channel side, and the influence of the extinction ratio in the Q-channel optical modulator 204 is compensated. Is compensated by adjusting the DC offset amount on the I channel side. Accordingly, as shown in FIG. 9, the characteristics of the I-channel optical modulator 203 and the Q-channel optical modulator 204 are monitored and fed back to the calculation unit 902 on the other side. Even when the waveform distortion is given by the extinction ratio in the state where the characteristics of the Q-channel optical modulator 204 are temporally varied independently, the influence can be reduced more directly and adaptively. it can.
  • the function of the waveform distortion amount detection unit 802 in FIG. 8 that detects the distortion amount from the signal quality monitor information shown in the third embodiment is the same as the I channel calculation unit. This is performed in 902-1 and the Q channel calculation unit 902-2.
  • the digital optical transmitter according to the above-described embodiment can simply add a DC offset even when a multi-level modulation signal such as QAM or a pre-equalization signal using a complicated transmission waveform is used.
  • waveform distortion caused by the extinction ratio of the MZ optical modulator to be used can be corrected, and deterioration of communication quality can be suppressed.
  • waveform distortion due to the extinction ratio but also waveform distortion caused by characteristics of the driver and the like are taken into account by taking into account the offset of an electric device such as a driver amplifier when calculating the DC offset amount. Can compensate.
  • the present invention can be applied not only to communication networks for cores and metros but also to all communication networks using light. Furthermore, the invention of the present application is not limited to the above-described embodiment, and any design change or the like within a range not departing from the gist of the invention is included in the invention. Moreover, although a part or all of said embodiment can be described also as the following additional remarks, it is not restricted to the following.
  • Optical output means for outputting an optical signal based on given wavelength information; Branching means for branching the optical signal into a first optical signal and a second optical signal; Based on the given wavelength information, a DC offset amount corresponding to each distortion of the first optical modulator and the second optical modulator is calculated, and the calculated DC offset amount is added to each of the two data signals.
  • Data signal output means for outputting the first data signal and the second data signal;
  • a first optical modulator that modulates the first optical signal with the first data signal and outputs a first modulated signal;
  • a second optical modulator that modulates the second optical signal with the second data signal and outputs a second modulated signal;
  • Coupling means for combining the first modulated signal and the second modulated signal to output a transmission signal;
  • An optical transmitter An optical transmitter.
  • the data output means includes By adding a DC offset amount that cancels distortion of the second optical modulator at the wavelength of the optical signal output from the optical output means, to the data signal for modulating the first optical signal, the first data Generate a signal, By adding to the data signal for modulating the second optical signal a DC offset amount that cancels the distortion of the first optical modulator at the wavelength of the optical signal output from the optical output means, the second data Generate signal,
  • the optical transmitter according to appendix 1.
  • Appendix 3 And further comprising monitor means for extracting waveform distortion from the transmission signal output from the combining means, The data signal output means calculates the DC offset amount based on the given wavelength information and the extracted waveform distortion.
  • the optical transmitter according to appendix 1 or 2.
  • the data signal output means includes a table in which DC offset amounts of the first optical modulator and the second optical modulator are registered for each wavelength, and the DC offset amount corresponding to the given wavelength information is The optical transmitter according to any one of appendices 1 to 4, which is extracted from a table.
  • the first optical modulator is an I-channel optical modulator;
  • the second optical modulator is a Q-channel optical modulator;
  • a ⁇ / 2 phase shifter disposed between the second optical modulator and the coupling means;
  • the branching means and the coupling means are each constituted by a Y-branched optical waveguide.
  • the optical transmitter according to any one of appendices 1 to 5.
  • [Appendix 7] Encoding means for encoding and outputting two transmission signals according to a modulation method; Pre-equalization means for outputting the two data signals by giving inverse characteristics of transmission path characteristics to the two encoded transmission signals;
  • the first data modulator and the second data signal are subjected to a process for linearizing a nonlinear characteristic of a front-end device and a process for correcting a frequency characteristic to the first data signal and the second data signal output from the data signal output unit.
  • Front signal processing means for outputting to each optical modulator,
  • Appendix 8 An optical communication system in which the optical transmitter according to any one of appendices 1 to 7 is arranged.
  • the first modulator the first optical signal is modulated with the first data signal to output a first modulated signal
  • the second optical signal is modulated with the second data signal to output a second modulated signal
  • Combining the output first modulated signal and second modulated signal to output a transmission signal Optical transmission method.
  • the first data signal is generated by adding a DC offset amount that cancels the distortion of the second optical modulator at the wavelength of the output optical signal to the data signal for modulating the first optical signal.
  • the second data signal is generated by adding a DC offset amount that cancels the distortion of the first optical modulator at the wavelength of the output optical signal to the data signal for modulating the second optical signal.
  • the present invention can be widely applied to an optical transmitter that multiplexes and transmits optical signals modulated by two optical modulators and an optical communication system in which the optical transmitter is arranged.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Nonlinear Science (AREA)
  • Optical Communication System (AREA)

Abstract

De manière à maintenir convenablement la qualité d'un signal d'émission et à maintenir les performances d'un système au moyen d'une commande simple avec une faible charge, même lorsqu'une distorsion de forme d'onde est subie en raison de la caractéristique d'un modulateur optique, un émetteur optique selon la présente invention est équipé : d'un moyen de dérivation qui délivre en sortie un premier signal optique et un second signal optique ayant une longueur d'onde prescrite ; d'un moyen de sortie de signal de données qui délivre à un premier modulateur optique un premier signal de données qui compense la caractéristique de distorsion d'un second modulateur optique, et délivre au second modulateur optique un second signal de données qui compense la caractéristique de distorsion du premier modulateur optique ; des modulateurs optiques, qui modulent un signal optique au moyen des signaux de données ; et d'un moyen de couplage qui couple les signaux modulés et délivre en sortie un signal d'émission.
PCT/JP2015/001047 2014-03-10 2015-02-27 Émetteur optique, système de communication optique l'utilisant et procédé de communication optique WO2015136877A1 (fr)

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Publication number Priority date Publication date Assignee Title
JP2017079459A (ja) * 2015-10-19 2017-04-27 日本電信電話株式会社 コヒーレント光受信装置
WO2017069086A1 (fr) * 2015-10-19 2017-04-27 日本電信電話株式会社 Dispositif de réception de lumière cohérente
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