WO2015176527A1 - 正交多载波光源及pdm-qpsk信号发射装置 - Google Patents

正交多载波光源及pdm-qpsk信号发射装置 Download PDF

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WO2015176527A1
WO2015176527A1 PCT/CN2014/093989 CN2014093989W WO2015176527A1 WO 2015176527 A1 WO2015176527 A1 WO 2015176527A1 CN 2014093989 W CN2014093989 W CN 2014093989W WO 2015176527 A1 WO2015176527 A1 WO 2015176527A1
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optical
signal
frequency signal
radio frequency
input
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PCT/CN2014/093989
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English (en)
French (fr)
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迟楠
余建军
苏婕
黄新刚
马壮
张佩华
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复旦大学
中兴通讯股份有限公司
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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]

Definitions

  • the present invention relates to the field of coherent communication, and in particular to an orthogonal multi-carrier light source and a polarization demultiplexing quadrature phase shift keying (PDM-QPSK) signal transmitting apparatus.
  • PDM-QPSK polarization demultiplexing quadrature phase shift keying
  • orthogonal multi-carrier generation techniques In the field of optical communication, a wide range of frequency-locked and power-flat orthogonal multi-carrier generation techniques are available, which can be used for microwave photonics, all-optical signal processing, optical arbitrary waveform generation, and wavelength division multiplexing (WDM) ultra-wideband. Light source, etc. Especially when multi-carrier is used as WDM coherent ultra-wideband light source, orthogonal multi-carrier generation technology is considered as a key enabling technology for future Tbit/s optical communication.
  • the main technical solutions in the orthogonal multi-carrier generation technology include: (1) cascading scheme based on phase modulator (PM) and intensity modulator (IM); (2) phase-based modulator and its multiplier-driven Cascading scheme; (3) I/Q modulator-based generation scheme; (4) phase modulation-based loop multi-carrier generation scheme; (5) generation scheme based on combination of IQ modulator and frequency shift loop (RFS) Wait. All of the above solutions can produce orthogonal multi-carriers with adjustable wavelength, frequency locking and power flatness, but have the disadvantage of high insertion loss and high cost.
  • a multi-carrier generation scheme based on direct modulation distributed feedback laser (DML) and phase modulator cascade is proposed, which can effectively overcome the high cost of the above five schemes and has a simple structure.
  • DML direct modulation distributed feedback laser
  • the subcarriers generated by this scheme have a relatively wide linewidth (about 25 MHz), and thus can only be used to modulate the intensity modulated optical signal, and differently for modulating the PDM-QPSK modulated signal.
  • Embodiments of the present invention provide an orthogonal multi-carrier light source and a PDM-QPSK signal transmitting apparatus to at least solve the problem of high insertion loss and high cost existing in generating PDM-QPSK modulated signals in the related art.
  • an orthogonal multi-carrier light source comprising: an electroabsorption modulation laser, a phase modulator, a sinusoidal RF signal source, a power divider, a phase shifter, a first electric power amplifier, and a second An electric power amplifier, wherein: the sinusoidal radio frequency signal source is configured to output a sinusoidal radio frequency signal of a predetermined signal frequency to the power divider; the power divider is configured to divide the input sinusoidal radio frequency signal into a left sine a radio frequency signal and a right sinusoidal radio frequency signal, the left sinusoidal radio frequency signal is input to the electric power amplifier, and the right sinusoidal radio frequency signal is input to the phase shifter; the first electric power amplifier is set to be The left sinusoidal radio frequency signal is subjected to power amplification, and the power amplified left sinusoidal radio frequency signal is input to the electroabsorption modulation laser; and the phase shifter is configured to adjust the right sinusoidal radio frequency signal Activating the right sinusoidal RF signal with the
  • the method further includes: a frequency multiplier connected between the phase shifter and the second electric power amplifier, configured to implement the second frequency of the right sinusoidal RF signal output by the phase shifter And inputting the right sinusoidal radio frequency signal after 2 times frequency to the second electric power amplifier.
  • a frequency multiplier connected between the phase shifter and the second electric power amplifier, configured to implement the second frequency of the right sinusoidal RF signal output by the phase shifter And inputting the right sinusoidal radio frequency signal after 2 times frequency to the second electric power amplifier.
  • the electroabsorption modulation laser comprises: a distributed feedback laser configured to output an optical signal; and an electroabsorption modulator configured to be driven by the left sinusoidal radio frequency signal output by the first electric power amplifier
  • the optical signal output by the distributed feedback laser is optically modulated to output a modulated optical signal.
  • the operating current of the distributed feedback laser is greater than a threshold current of the distributed feedback laser.
  • the bias voltage of the electroabsorption modulator is within a linear modulation region of the electroabsorption modulator.
  • the electroabsorption modulation laser further includes: a semiconductor optical amplifier configured to perform input compensation on the optical signal output by the electroabsorption modulator to compensate for insertion loss of the electroabsorption modulator, and output compensation After the light signal.
  • a semiconductor optical amplifier configured to perform input compensation on the optical signal output by the electroabsorption modulator to compensate for insertion loss of the electroabsorption modulator, and output compensation After the light signal.
  • the line width of the electroabsorption modulation laser is 1.9 MHz.
  • the phase modulator is further configured to increase the number of orthogonal subcarriers generated by increasing the amplitude of the radio frequency signal driving the phase modulator.
  • the electroabsorption modulation laser is further arranged to flatten the amplitude of the generated subcarriers by adjusting the amplitude of the radio frequency signal driving the electroabsorption modulation laser.
  • a polarization multiplexing quadrature phase modulation PDM-QPSK signal transmitting apparatus comprising: a sequential connected orthogonal multi-carrier light source, a photo subcarrier selection module, and a PDM-QPSK optical signal.
  • the orthogonal multi-carrier light source is the orthogonal multi-carrier light source
  • the photo subcarrier selection module comprises: an optical add/drop multiplexer, configured to divide the multi-carrier output of the orthogonal carrier light source Inputting an odd-numbered multi-carrier or even-path multi-carrier to a tunable optical filter
  • the tunable optical filter is configured to adjust the bandwidth and wavelength of the tunable optical filter to The carrier is filtered to obtain a desired optical carrier
  • the PDM-QPSK optical signal transmitting module includes: an I/Q modulator, and the phase difference between the upper and lower arms is ⁇ /2, and is set to be outputted in the photo subcarrier selection module.
  • the optical QPSK signal is generated and outputted by the optical carrier; the polarization multiplexer is configured to divide the optical QPSK signal output by the I/Q modulator into two branches, and delay one of the optical signals, One optical signal power equalization, and then the two optical signals are combined, the polarization multiplexed analog signal, generating an optical PDM-QPSK signal, the PDM-QPSK signal is transmitted over the optical fiber link.
  • the optical add/drop multiplexer has a frequency of 12.5/25-GHz.
  • the polarization multiplexer comprises: a polarization maintaining optical coupler, an optical delay line, an optical attenuator and a polarization combiner, wherein the polarization maintaining optical coupler is configured to input the QPSK
  • the optical signal is divided into two branches, one of which is input to the optical delay line and the other of which is input to the optical attenuator;
  • the optical delay line is set to generate 150 symbols by inputting an input QPSK optical signal Length delay, inputting the delayed QPSK optical signal to the polarization combiner;
  • the optical attenuator is configured to adjust the power of the QPSK optical signal of the , to realize the power of the QPSK optical signal for the two branches Equalization, inputting the adjusted QPSK optical signal to the polarization combiner;
  • the polarization combiner is configured to combine the input two optical signals, and polarization multiplexing of the analog signals to generate the PDM -QPSK signal.
  • an orthogonal multi-carrier light source based on an electro-absorption modulated laser (EML) and a phase modulator (PM) is used, which can not only generate a certain number of subcarriers with good flatness, but also effectively overcome DML and In the PM cascading scheme, insufficient line width of the subcarrier is generated, so that coherent light reception can be performed on the high speed PDM-QPSK modulated signal.
  • EML electro-absorption modulated laser
  • PM phase modulator
  • FIG. 1 is a schematic structural diagram of an orthogonal multi-carrier light source according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram of a spectrum of an output of an orthogonal multi-carrier light source in accordance with an embodiment of the present invention
  • 3A is a schematic structural diagram of a PDM-QPSK signal transmitting apparatus according to an embodiment of the present invention.
  • 3B is a schematic structural diagram of a PDM-QPSK signal coherent light receiving system according to an embodiment of the present invention.
  • FIG. 4 is a schematic structural diagram of a photo subcarrier selection module according to an embodiment of the present invention.
  • FIG. 5 is a spectrum diagram of an odd-numbered multi-carrier output by an optical add/drop multiplexer of a photonic carrier selection module used in an embodiment of the present invention
  • FIG. 6 is a spectrum diagram of a required photon carrier output by a polarization-maintaining tunable optical filter of a photonic carrier selection module used in an embodiment of the present invention
  • FIG. 7 is a schematic structural diagram of a PDM-QPSK optical signal transmitting module according to an embodiment of the present invention.
  • FIG. 8 is a schematic structural diagram of a homodyne coherent light detecting module according to an embodiment of the present invention.
  • an orthogonal multi-carrier light source is provided.
  • the orthogonal multi-carrier light source mainly includes: an electroabsorption modulation laser (EML), a phase modulator (PM), and a sinusoidal radio frequency.
  • EML electroabsorption modulation laser
  • PM phase modulator
  • PS phase shifter
  • EA electrical power amplifiers
  • the sinusoidal radio frequency signal source is configured to output a sinusoidal radio frequency signal of a predetermined signal frequency (eg, 12.5 GHz) to the power divider.
  • the power splitter is configured to split the input sinusoidal RF signal into left and right paths, input the left channel signal to the first electrical power amplifier (EA), and input the right channel signal to the phase shifter.
  • the first electric power amplifier performs power amplification on the left sinusoidal RF signal output by the power splitter, and inputs the power amplified signal as the radio frequency drive signal into the electroabsorption modulated laser (EML).
  • EML electroabsorption modulated laser
  • the main function of the electric power amplifier is to perform power amplification on the left sinusoidal radio frequency signal.
  • the phase shifter adjusts the right sinusoidal radio frequency signal to synchronize the right sinusoidal radio frequency signal with the left sinusoidal radio frequency signal, and outputs the adjusted right sinusoidal radio frequency signal.
  • the second electric power amplifier is configured to perform power amplification on the right sinusoidal radio frequency signal adjusted by the phase shifter, and input the power amplified the right sinusoidal radio frequency signal to the phase modulator.
  • An electroabsorption modulated laser is arranged to generate an optical signal driven by said left sinusoidal radio frequency signal output by a first electrical power amplifier and to input said generated optical signal to said phase modulator.
  • the phase modulator is configured to modulate the input optical signal under the driving of the right sinusoidal radio frequency signal output by the second electrical power amplifier to generate a frequency-locked and orthogonal multi-carrier.
  • the orthogonal multi-carrier light source may further include a double frequency multiplier connected between the phase shifter and the second electric power amplifier, right.
  • the sinusoidal radio frequency signal first passes through the phase shifter, then realizes 2 times frequency of the signal frequency through the 2 frequency multiplier, and finally is power amplified by the second electric amplifier and then input to the phase modulator as a radio frequency driving signal.
  • the primary function of the 2 frequency multiplier is to achieve a 2 octave of the right sinusoidal RF signal.
  • the phase modulator Since the phase modulator has a relatively large modulation bandwidth, in the present embodiment, the phase modulator is driven by a higher 2 frequency RF signal, and a lower single frequency RF signal is used to drive the phase. An electroabsorption modulated laser is described. Performing a 2x operation on the RF signal driving the phase modulator helps to further increase the number of subcarriers generated.
  • the electroabsorption modulation laser may be composed of a distributed feedback (DFB) laser and an electroabsorption modulator (EAM), optionally,
  • the line width of the EML is only 1.9 MHz (far less than the line width of DML of 25 MHz).
  • the operating current of the distributed feedback laser needs to be greater than a threshold current of the distributed feedback laser, and the operating current of the electroabsorption modulation laser is provided by a direct current power source (DC); the optical signal output by the distributed feedback laser is injected into the one way
  • the RF signal driven electroabsorption modulator and the bias voltage of the electroabsorption modulator are required to be within the linear modulation region of the electroabsorption modulator.
  • the bias voltage of the electroabsorption modulator will widen the optimal operating range of the electroabsorption modulated laser over a linear modulation range.
  • the bias voltage of the electroabsorption modulator is too high, the average power of the output signal of the electroabsorption modulation laser will be less than -10 dBm due to the introduction of a large insertion loss.
  • An integrated semiconductor optical amplifier (SOA) can be considered to compensate for the insertion loss of the modulator.
  • the modulation factor of the electroabsorption modulation laser is defined as follows: the ratio of the amplitude of the radio frequency signal driving the electroabsorption modulation laser to the bias voltage of the electroabsorption modulator.
  • the electro-absorption modulated laser output optical signal is further input to the phase modulator driven by another 2 frequency-doubled radio frequency signal to generate a frequency-locked and orthogonal multi-carrier, multi-carrier.
  • the frequency spacing between them is 12.5 GHz.
  • the modulation factor of the phase modulator is defined as follows: the ratio of the amplitude of the RF signal driving the phase modulator to the half-wave voltage of the phase modulator. Under the premise that the half-wave voltage is constant, increasing the amplitude of the RF signal driving the phase modulator can effectively adjust the number of output sub-carriers. As the amplitude of the RF signal increases, the number of generated subcarriers will increase.
  • the amplitude of the RF signal driving the electro-absorption modulation laser and the phase modulator should be reasonably adjusted to generate as many multi-carriers as possible with good power flatness.
  • the phase modulator is further arranged to increase the number of orthogonal subcarriers generated by increasing the amplitude of the radio frequency signal driving the phase modulator.
  • the electroabsorption modulation laser is further arranged to flatten the amplitude of the generated subcarriers by adjusting the amplitude of the radio frequency signal driving the electroabsorption modulation laser.
  • an orthogonal multi-carrier light source including an electroabsorption modulation laser, a phase modulator, a sinusoidal RF signal source, a power divider, a phase shifter, a 2 frequency multiplier, and an electric amplifier
  • an orthogonal multi-carrier light source including an electroabsorption modulation laser, a phase modulator, a sinusoidal RF signal source, a power divider, a phase shifter, a 2 frequency multiplier, and an electric amplifier
  • the sinusoidal RF signal source outputs a sinusoidal RF signal having a signal frequency of 12.5 GHz to the power divider.
  • the power divider divides the above radio frequency signals into two paths: one of the single frequency radio frequency signals is power amplified by the electric amplifier to drive the electroabsorption modulation laser; the other path first passes through the phase shifter. Then, the 2 times frequency of the signal frequency is realized by the 2 frequency multiplier, and finally the 2 ⁇ frequency frequency radio frequency signal is power amplified by the electric amplifier to drive the phase modulator.
  • the phase shifter used in the above second branch mainly serves to synchronize the two RF signals.
  • the electroabsorption modulation laser is composed of a distributed feedback laser and an electroabsorption modulator.
  • a DC power supply provides operating current to the distributed feedback laser.
  • the operating current needs to be greater than the threshold current of the laser.
  • the optical signal output by the distributed feedback laser is input to the electroabsorption modulator driven by a single frequency RF signal and the bias voltage of the electroabsorption modulator is within a linear modulation region of the device.
  • the optical signal output by the electroabsorption modulator is further input to a polarization-maintained erbium-doped fiber amplifier to compensate for the modulation loss introduced by the electro-absorption modulator.
  • the power amplified optical signal output by the polarization-maintaining erbium-doped fiber amplifier is further input to the phase modulator driven by another 2 frequency-frequency RF signal to generate a frequency-locked and orthogonal multi-carrier, and an output signal thereof
  • the electrical domain expression is as follows:
  • R1 is the modulation coefficient of the electroabsorption modulation laser, which is defined as follows: the ratio of the amplitude of the RF signal of the electroabsorption modulated laser to the bias voltage of the electroabsorption modulator;
  • R2 is the modulation factor of the phase modulator, which is defined as follows: driving phase modulation The ratio of the RF signal amplitude of the device to the half-wave voltage of the phase modulator.
  • the electric amplifiers of the two branches as shown in FIG. 1 can be separately adjusted to achieve reasonable adjustment of the amplitude of the single-frequency RF signal for driving the electroabsorption modulated laser and the frequency of the second-frequency RF signal driving the phase modulator.
  • the above orthogonal multi-carrier light source based on EML and PM cascade can finally output 25 frequency-locked orthogonal multi-carriers with sub-power difference of less than 5dB at the output of the phase modulator, and the sub-carriers The frequency interval between them is 12.5 GHz.
  • the orthogonal multi-carrier light source may further provide an optical amplifier (PM-EDFA) between the EML and the PM cascade to amplify the optical signal.
  • PM-EDFA optical amplifier
  • a PDM-QPSK signal transmitting apparatus is also provided.
  • FIG. 3A is a schematic structural diagram of a PDM-QPSK signal transmitting apparatus according to an embodiment of the present invention.
  • the apparatus mainly includes: a sequential connected orthogonal multi-carrier light source, a photon carrier selection module, and a PDM-QPSK optical signal transmission. Module.
  • the transmitting apparatus provided by the embodiment of the present invention generates multiple carriers by using an orthogonal multi-carrier light source based on EML and PM cascade, and generates a high-speed PDM-QPSK modulated signal by using a PDM-QPSK optical signal generating module.
  • the orthogonal multi-carrier light source is the orthogonal multi-carrier light source as shown in FIG. 1 provided in the embodiment of the present invention. For details, refer to the above description, and details are not described herein again.
  • the photo subcarrier selection module may include an optical add/drop multiplexer (IL) and a tunable optical filter (PM-TOF).
  • the photonic carrier selection module is composed of an optical add/drop multiplexer (IL) consisting of a 12.5/25-GHz and a polarization-maintained tunable optical filter (PM-TOF).
  • the optical add/drop multiplexer is configured to divide the multi-carrier outputted by the orthogonal carrier light source into two parts, and input odd-numbered multi-carrier or even-path multi-carrier into the tunable optical filter; the tunable optical filter And arranging to filter the input multi-carrier to obtain a desired optical carrier by adjusting the bandwidth and wavelength of the tunable optical filter.
  • the multi-carrier output by the orthogonal multi-carrier light source based on the EML and the PM cascade is first divided into two parts by the optical add/drop multiplexer, and the frequency interval between the odd-numbered or even-numbered multi-carriers. This will increase to 25 GHz.
  • the odd or even path multi-carrier output from the optical add/drop multiplexer is then input to the polarization-preserving tunable optical filter, and the required optical carrier is filtered out by adjusting the bandwidth and wavelength of the tunable optical filter.
  • the tunable optical filter can be a polarization-maintaining doped fiber amplifier.
  • the orthogonal multi-carrier input generated by the orthogonal multi-carrier light source is divided into two parts of the parity.
  • the optical add/drop multiplexer device parameter is 12.5/25-GHz in order to match the RF signal source frequency of 12.5 GHz.
  • Intersection uses alternatives to other add/drop multiplexer device parameters that enable optimal separation of optical multicarrier signals.
  • the frequency spacing between the odd or even path multiple carriers will thus increase to 25 GHz.
  • the odd-numbered multi-carrier spectrum of the output of the optical add-drop multiplexer is as shown in FIG.
  • the odd-numbered multi-carrier is then input to the polarization-preserving tunable optical filter.
  • the bandwidth and wavelength of the tunable optical filter should be consistent with the desired optical carrier.
  • the tunable optical filter also simultaneously performs filtering of the ASE noise of the polarization-maintaining doped fiber amplifier used to compensate the modulation loss of the electroabsorption modulator for the orthogonal multi-carrier light source.
  • a plurality of center-frequency band-pass filters may be used to filter the corresponding optical carrier, but the tunable optical filter may simplify the system structure on the one hand, and adjust the center frequency of the filter on the other hand. The aspect is also more flexible and convenient.
  • a spectrum of the desired photon carrier output of the polarization-preserving tunable optical filter is shown in FIG.
  • the photon carrier output of the polarization-maintaining tunable optical filter is further amplified by a polarization-maintaining doped fiber amplifier, and the PDM-QPSK optical signal transmitting module is used as an optical carrier signal to realize QPSK optical signal modulation.
  • the PDM-QPSK optical signal transmitting module may include an I/O modulator and a polarization multiplexer.
  • the I/O modulator has a phase difference of ⁇ /2 between the upper and lower arms, and is configured to drive an optical carrier output by the photo subcarrier selection module to generate an optical QPSK signal; and a polarization multiplexer configured to modulate the I/O
  • the optical QPSK signal output by the device is divided into two branches, one of which is delayed, the other optical signal is power balanced, then the two optical signals are combined, and the polarization of the analog signal is multiplexed to generate PDM-QPSK light. And transmitting, by the PDM-QPSK optical signal, to the homodyne coherent light detecting module via a fiber link.
  • the PDM-QPSK optical signal transmitting module is composed of an I/Q modulator and a polarization multiplexer.
  • the I/Q modulator consists of two parallel Mach-Zehnder modulators (MZM), and the Mach-Zehnder modulators are both biased at a null point and driven to full-wave.
  • the phase difference between the upper and lower arms of the I/Q modulator is controlled to be ⁇ /2.
  • the optical carrier filtered by the photo subcarrier selection module is driven to generate an optical QPSK signal for a 28G baud electrical binary signal via the I/Q modulator, and the electrical binary signal is generated by a pattern generator (PPG).
  • PPG pattern generator
  • the polarization multiplexer consists of a polarization maintaining optical coupler (PM-OC), a length of optical delay line (DL), an optical attenuator and a polarization combiner (PBC).
  • the polarization maintaining optocoupler first splits the input optical QPSK signal into two branches, wherein one signal is simulated by the optical delay line to generate a delay of 150 symbol lengths, and the other path is implemented by the optical attenuator Balance of branch optical signal power. Finally, the two optical signals are combined by the polarization combiner, and the polarization multiplexing of the analog signals is performed to generate the PDM-QPSK signal.
  • an optical carrier signal and a 28G baud electrical binary signal are input to an I/Q modulator for optical modulation, and a QPSK modulated optical signal is output.
  • the electrical binary signal consists of a pseudo-random binary sequence of length 223-1 and is generated by a pattern transmitter.
  • the I/Q modulator consists of two parallel parallel Mach-Zehnder modulators and there is a ⁇ /2 phase difference, the Mach-Zehnder modulators are each biased at a null point and driven to a full wave.
  • the arrangement enables optimal phase modulation of zero ⁇ , ⁇ phase hopping.
  • the polarization multiplexer is formed by a polarization maintaining optical coupler, a length of optical delay line, an optical attenuator and a polarization combiner.
  • the polarization maintaining optical coupler first inputs the QPSK modulated optical signal into two branches.
  • one of the signals is simulated by the optical delay line to generate a delay of 150 symbol lengths, and the other path is implemented by the optical attenuator. Equalization of the power of the optical signals of the two branches.
  • the two optical signals are combined by the polarization combiner to simulate polarization multiplexing of the signals.
  • the integrated optical polarization multiplexer module is directly used, but the analog optical signal polarization multiplexing module has an advantage on the one hand in terms of the cost of the experimental device, and on the other hand, it can be directly Optical delay line The festival is more flexible and convenient.
  • the generated 112-Gb/s optical PDM-QPSK signal is then transmitted to the receiving end via the fiber optic link.
  • a PDM-QPSK signal coherent light receiving system is further provided according to an embodiment of the present invention.
  • FIG. 3B is a schematic structural diagram of a PDM-QPSK signal coherent light receiving system according to an embodiment of the present invention.
  • the system includes a receiving device and the above PDM-QPSK signal transmitting device.
  • the receiving device uses the homodyne coherent light detecting module to realize coherent detection and data recovery of the local oscillator and the signal optical signal.
  • the 112-Gb/s optical PDM-QPSK signal generated by the transmitting device is then transmitted to the receiving device via a fiber optic link consisting of 80 km of standard single mode fiber-28 (SMF-28).
  • SMF-28 standard single mode fiber-28
  • the homodyne coherent light detecting module of the receiving device may include: a polarization diversity plus phase diversity optical coherent detecting module and a digital signal processing unit.
  • the polarization diversity plus phase diversity optical coherent detection module comprises an external cavity laser, two polarization beam splitters, two 90° optical mixers, four photodiodes, and four high speed analog to digital converters, wherein
  • the external cavity laser is arranged to act as a local oscillator and the received PDM-QPSK optical signal respectively passes through one of the polarization beam splitters, the polarization beam splitter and the PDM-QPSK optical signal Separating into two orthogonal polarization optical signals, and inputting the local oscillator light of the same polarization state together with the PDM-QPSK optical signal into one of the 90° optical mixers;
  • the 90° optical mixer It is configured to generate a phase shift of 0°, 90°, 180°, and 270° of the input optical signal, and perform a beat frequency with the PDM-QPSK
  • the homodyne coherent light detecting module is composed of a polarization diversity plus phase diversity optical coherent detecting module and a digital signal processing (DSP) unit.
  • the polarization diversity plus phase diversity optical coherent detection module comprises an external cavity laser (ECL), two polarization beam splitters (PBS), two 90° optical mixers, four photodiodes (PD) and four high speeds.
  • ECL external cavity laser
  • PBS polarization beam splitters
  • PD photodiodes
  • AEC Analog to digital converter
  • the external cavity laser acts as a local oscillator light source (LO) and the received signal light transmitted through the fiber optic link is separated into two orthogonal polarization states by one of the polarization beam splitters;
  • the local oscillator light of the same polarization state and the signal light are input together into one of the 90° optical mixers, and the main function of the 90° optical mixer is to generate 0°, 90°, 180°, 270 of the local oscillator light.
  • the phase shift of ° then coheres with the signal light for coherent detection; then the four coherent probe optical signals output by the two 90° optical mixers (X polarization direction in-phase component, quadrature component; Y polarization direction in phase)
  • the components and the quadrature components are respectively input into the four photodiodes for balance detection, and the four photocurrents are output and then input into four high-speed analog-to-digital converters for Nyqusit sampling to be converted into sampling signals.
  • Digital signal The main function of the unit is to perform data recovery on the sampled signals obtained by high-speed analog-to-digital conversion sampling, including: signal retiming, dispersion compensation, constant modulus algorithm equalization, carrier recovery, differential decoding, and bit error rate calculation.
  • the PDM-QPSK optical signal output by the transmitting device is first transmitted via the 80km standard single mode fiber 28 as the received signal light into the polarization diversity plus phase diversity optical coherent detection module.
  • the polarization diversity plus phase diversity optical coherent detection module comprises an external cavity laser, two polarization beam splitters, two 90° optical mixers, four photodiodes and four high speed analog to digital converters.
  • the input received signal light and the local oscillator light are separated by two polarization polarization beams respectively through one of the polarization beam splitters, and the local oscillator light source is realized by the external cavity laser.
  • the local oscillator light and the signal light having the same polarization state are input into the 90° optical mixer together, and the main function of the 90° optical mixer is to generate 0°, 90°, and 180° of the local oscillator light.
  • the phase shift of 270° is then coherently detected with the signal light.
  • the four photocurrents are respectively input to the four high-speed analog-to-digital converters for Nyqusit sampling to be converted into sampled electrical signals.
  • the frequency between the local oscillator source and the originating optical carrier is It is difficult to maintain complete agreement and the linewidth of the local oscillator source will introduce a corresponding phase offset.
  • the frequency and phase of the sampled electrical signal will be disturbed by the local oscillator frequency and phase.
  • there are other signal impairments such as channel sampling mismatch at the transceiver end and channel static damage due to fiber dispersion and polarization mode dispersion effects during coherent detection.
  • the digital signal processing unit needs to be introduced to separately estimate and compensate for the above loss, thereby completing recovery recovery and recovery of the original transmitted signal.
  • the digital signal processing unit includes: signal retiming, dispersion compensation, constant modulus algorithm equalization, carrier recovery, differential decoding, and bit error rate calculation.
  • the signal retiming is mainly used to solve the clock misalignment caused by the mismatch of the ADC sampling clock.
  • the dispersion compensation and the constant mode algorithm equalization are mainly used to eliminate the damage caused by the fiber dispersion and the polarization mode dispersion.
  • the carrier recovery is mainly used to eliminate the signal. The effect of the phase offset on the signal, and finally the differentially decoded signal constellation is differentially decoded and restored to a 0-1 bit sequence and the overall performance of the system is evaluated by the bit error rate calculation.
  • the above system provided by the embodiment of the present invention can effectively output the subcarriers by using the orthogonal multi-carrier light source based on the EML and the PM cascade, so that the line width of the transmitting end can be controlled at 1.9 MHz, thereby ensuring the optical carrier.
  • the product of the line width and the symbol duration satisfies the condition (product of less than 1 ⁇ 10-4) capable of implementing the coherent reception of the 28G baud high-speed PDM-QPSK signal, making the implementation of Embodiment 3 possible.
  • an orthogonal multi-carrier light source based on EML and PM cascade is proposed, and the multi-carrier light source is applied to a PDM-QPSK modulated signal transmitting device and Coherent light detection system.
  • the orthogonal multi-carrier light source can not only generate a certain number of sub-carriers with good flatness, but also effectively overcome the shortage of the generated sub-carrier line width in the DML and PM cascading scheme, so that the high-speed PDM-QPSK modulated signal is performed. Coherent light reception is possible.
  • the orthogonal multi-carrier light source proposed by the invention has the characteristics of small volume, low power consumption and easy integration, and thus has broad application prospects in practical systems.
  • modules or steps of the present invention described above can be implemented by a general-purpose computing device that can be centralized on a single computing device or distributed across a network of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device such that they may be stored in the storage device by the computing device and, in some cases, may be different from the order herein.
  • the steps shown or described are performed, or they are separately fabricated into individual integrated circuit modules, or a plurality of modules or steps thereof are fabricated as a single integrated circuit module.
  • the invention is not limited to any specific combination of hardware and software.
  • an orthogonal multi-carrier light source and a PDM-QPSK signal transmitting apparatus have the following beneficial effects: positively using a cascade based on an electroabsorption modulated laser (EML) and a phase modulator (PM) Multi-carrier light source can not only generate a certain number of sub-carriers with good flatness, but also effectively overcome the shortcomings of generating sub-carrier line widths in DML and PM cascade schemes, so that high-speed PDM-QPSK modulated signals can be coherent Light reception.
  • EML electroabsorption modulated laser
  • PM phase modulator

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Abstract

本发明公开了一种正交多载波光源及PDM-QPSK信号发射装置。其中，所述正交多载波光源包括：正弦射频信号源，设置为输出预定信号频率的正弦射频信号至功率分配器；功率分配器，设置为将输入的正弦射频信号分为左路正弦射频信号和右路正弦射频信号；第一电功率放大器，设置为对左路正弦射频信号进行功率放大；相移器，设置为对右路正弦射频信号进行调整；第二电功率放大器，设置为对经相移器调整后的右路正弦射频信号进行功率放大；电吸收调制激光器，设置为在第一电功率放大器输出的左路正弦射频信号的驱动下产生光信号；相位调制器，设置为在第二电功率放大器输出的右路正弦射频信号的驱动下，对输入的光信号进行调制，产生频率锁定且正交的多载波。

Description

正交多载波光源及PDM-QPSK信号发射装置 技术领域
本发明涉及相干通信领域，具体而言，涉及一种正交多载波光源及偏振复用正交相位调制(Polarization division multiplexed quadrature phase shift keying，PDM-QPSK)信号发射装置。
背景技术
在光通信领域中，广泛的应用频率锁定且功率平坦的正交多载波产生技术，该技术能够用于微波光子学、全光信号处理、光任意波形发生以及波分复用(WDM)超宽带光源等。特别是在多载波作为WDM相干超宽带光源时，正交多载波产生技术被认为是未来Tbit/s光通信的一项关键的使能技术。
目前在正交多载波产生技术方面的主要技术方案包括：(1)基于相位调制器(PM)和强度调制器(IM)的级联方案；(2)基于相位调制器及其倍频驱动的级联方案；(3)基于I/Q调制器的产生方案；(4)基于相位调制的环路多载波产生方案；(5)基于IQ调制器与频移环路(RFS)结合的产生方案等。以上方案均能产生波长可调、频率锁定且功率平坦的正交多载波，但却具有高插入损耗与高成本的不足。
在相关技术中，还提出了一类基于直接调制分布反馈激光器(DML)和相位调制器级联的多载波产生方案，该方案虽能有效克服以上五种方案成本高的不足并且具有结构简单的特点，但该方案生成的子载波具有相对较宽的线宽(约25MHz)，因而只能用于调制强度调制光信号，不同用于调制PDM-QPSK调制信号。
然而，与直接探测强度调制信号相比，相干探测PDM-QPSK调制信号具有更高的频谱效率且应用也日趋广泛。因而针对能应用于PDM-QPSK调制信号相干光探测系统中的正交多载波产生技术尤为重要。
针对相关技术中在产生PDM-QPSK调制信号时存在的高插入损耗与高成本的问题，目前尚未提出有效的解决方案。
发明内容
本发明实施例提供了一种正交多载波光源及PDM-QPSK信号发射装置，以至少解决相关技术中在产生PDM-QPSK调制信号时存在的高插入损耗与高成本的问题。
根据本发明的一个实施例，提供了一种正交多载波光源，包括：电吸收调制激光器,相位调制器，正弦射频信号源，功率分配器，相移器，第一电功率放大器，以及第二电功率放大器，其中；所述正弦射频信号源，设置为输出预定信号频率的正弦射频信号至所述功率分配器；所述功率分配器，设置为将输入的所述正弦射频信号分为左路正弦射频信号和右路正弦射频信号，将所述左路正弦射频信号输入到所述电功率放大器，将所述右路正弦射频信号输入到所述相移器；所述第一电功率放大器，设置为对所述左路正弦射频信号进行功率放大，将功率放大后的所述左路正弦射频信号输入到所述电吸收调制激光器；所述相移器，设置为对所述右路正弦射频信号进行调整，以使所述右路正弦射频信号同所述左路正弦射频信号同步，并输出调整后的所述右路正弦射频信号；所述第二电功率放大器，设置为对经所述相移器调整后的所述右路正弦射频信号进行功率放大，将功率放大后的所述右路正弦射频信号输入到所述相位调制器；所述电吸收调制激光器，设置为在所述第一电功率放大器输出的所述左路正弦射频信号的驱动下产生光信号，并将产生的所述光信号输入到所述相位调制器；所述相位调制器，设置为在所述第二电功率放大器输出的所述右路正弦射频信号的驱动下，对输入的所述光信号进行调制，产生频率锁定且正交的多载波。
可选地，还包括：2倍频器，连接在所述相移器和所述第二电功率放大器之间，设置为实现所述相移器输出的所述右路正弦射频信号的2倍频，将2倍频后的所述右路正弦射频信号输入到所述第二电功率放大器。
可选地，所述电吸收调制激光器包括：分布反馈激光器，设置为输出光信号；电吸收调制器，设置为在所述第一电功率放大器输出的所述左路正弦射频信号的驱动下，对所述分布反馈激光器输出的所述光信号进行光调制，输出调制后的光信号。
可选地，所述分布反馈激光器的工作电流大于所述分布反馈激光器的阈值电流。
可选地，所述电吸收调制器的偏置电压在所述电吸收调制器的线性调制区域内。
可选地，所述电吸收调制激光器还包括：半导体光放大器，设置为对所述电吸收调制器输出的所述光信号进行进入补偿，以补偿所述电吸收调制器的插入损耗，输出补偿后的光信号。
可选地，所述电吸收调制激光器的线宽为1.9MHz。
可选地，所述相位调制器还设置为通过增大驱动所述相位调制器的射频信号幅度增加生成的正交子载波数目。
可选地，所述电吸收调制激光器还设置为通过调节驱动所述电吸收调制激光器的射频信号幅度使生成的子载波的幅度平坦。
根据本发明的另一个实施例，还提供了一种偏振复用正交相位调制PDM-QPSK信号发射装置，包括：顺序连接的正交多载波光源、光子载波选择模块、以及PDM-QPSK光信号发射模块；其中，所述正交多载波光源为上述的正交多载波光源；所述光子载波选择模块包括：光分插复用器，设置为将所述正交载波光源输出的多载波分为奇偶两部分，将奇数路多载波或偶数路多载波输入到可调谐光滤波器；所述可调谐光滤波器，设置为通过调节所述可调谐光滤波器的带宽与波长，对输入多载波进行滤波以得到所需的光载波；所述PDM-QPSK光信号发射模块，包括：I/Q调制器，上下两臂的相位差为π/2，设置为在所述光子载波选择模块输出的光载波驱动下，产生并输出光QPSK信号；偏振复用器，设置为将I/Q调制器输出的光QPSK信号分为两个分支，对其中一路光信号进行延迟，对另一路光信号进行功率均衡，然后将两路光信号进行合并，模拟信号的偏振复用，生成PDM-QPSK光信号，将所述PDM-QPSK光信号经光纤链路发射。
可选地，所述光分插复用器为频率为12.5/25-GHz。
可选地，所述偏振复用器包括：一个偏振保持光耦合器、一段光延迟线、一个光衰减器和一个偏振合束器，其中，所述偏振保持光耦合器设置为将输入的QPSK光信号分为两个分支，其中一路信号输入至所述光延迟线，另一路则输入至所述光衰减器；所述光延迟线，设置为通过模拟对输入的QPSK光信号产生150个符号长度的延迟，将延迟后的QPSK光信号输入至所述偏振合束器；所述光衰减器，设置为对僌的QPSK光信号的功率进行调整，实现对两支路所述QPSK光信号功率的均衡，将调整后的QPSK光信号输入至所述偏振合束器；所述偏振合束器，设置为对输入的两路光信号通过进行合并，模拟信号的偏振复用，生成所述PDM-QPSK信号。
通过本发明实施例，采用基于电吸收调制激光器(EML)与相位调制器(PM)级联的正交多载波光源，不仅能够生成一定数目且平坦度良好的子载波，还有效克服了DML与PM级联方案中生成子载波线宽过大的不足，从而可以对高速PDM-QPSK调制信号进行相干光接收。
附图说明
此处所说明的附图用来提供对本发明的进一步理解，构成本申请的一部分，本发明的示意性实施例及其说明用于解释本发明，并不构成对本发明的不当限定。在附图中：
图1为根据本发明实施例的正交多载波光源的结构示意图；
图2为根据本发明实施例正交多载波光源输出的光谱的示意图；
图3A为根据本发明实施例的PDM-QPSK信号发射装置的结构示意图；
图3B为根据本发明实施例的PDM-QPSK信号相干光接收系统的结构示意图；
图4为根据本发明实施例的光子载波选择模块的结构示意图；
图5为本发明实施例中采用的光子载波选择模块的光分插复用器输出的奇数路多载波的光谱图；
图6为本发明实施例中采用的光子载波选择模块偏振保持可调谐光滤波器输出的所需光子载波的光谱图；
图7为根据本发明实施例中的PDM-QPSK光信号发射模块的结构示意图；
图8为根据本发明实施例的零差相干光探测模块的结构示意图。
具体实施方式
下文中将参考附图并结合实施例来详细说明本发明。需要说明的是，在不冲突的情况下，本申请中的实施例及实施例中的特征可以相互组合。
根据本发明实施例，提供了一种正交多载波光源。
图1为根据本发明实施例的正交多载波光源的结构示意图，如图1所示，该正交多载波光源主要包括：电吸收调制激光器(EML)、相位调制器(PM)、正弦射频信号源、功率分配器、相移器(PS)、以及2个电功率放大器(EA)。
其中，所述正弦射频信号源设置为向所述功率分配器输出预定信号频率(例如，12.5GHz)的正弦射频信号。所述功率分配器设置为将输入的正弦射频信号分为左右两路，将左路信号输入到第一个电功率放大器(EA)，右路信号输入至所述相移器。 第一个电功率放大器，对功率分配器输出的左路正弦射频信号进行功率放大，将功率放大后的信号作为射频驱动信号输入所述电吸收调制激光器(EML)。在本发明实施例中，该电功率放大器的主要作用是左路正弦射频信号进行功率放大，因此，通过合理调节经电功率放大器输出的左路射频信号幅度可以产生合适的子载波数目及平坦度。所述相移器对所述右路正弦射频信号进行调整，以使所述右路正弦射频信号同所述左路正弦射频信号同步，并输出调整后的所述右路正弦射频信号。第二个电功率放大器，设置为对经所述相移器调整后的所述右路正弦射频信号进行功率放大，将功率放大后的所述右路正弦射频信号输入到所述相位调制器。电吸收调制激光器，设置为在第一个电功率放大器输出的所述左路正弦射频信号的驱动下产生光信号，并将产生的所述光信号输入到所述相位调制器。所述相位调制器，设置为在第二个电功率放大器输出的所述右路正弦射频信号的驱动下，对输入的所述光信号进行调制，产生频率锁定且正交的多载波。
在本发明实施例的一个可选实施方式中，如图1所示，正交多载波光源还可以包括2倍频器，连接在所述相移器和第二个电功率放大器之间，右路正弦射频信号首先经过所述相移器，接着经过所述2倍频器实现信号频率的2倍频，最后经过第二个电放大器进行功率放大后作为射频驱动信号输入所述相位调制器。在该可选实施方案中，2倍频器的主要作用是实现对右路正弦射频信号的2倍频。由于所述相位调制器具有相对较大的调制带宽，因此，在本实施例中，采用较高的2倍频射频信号驱动所述相位调制器，同时采用较低的单倍频射频信号驱动所述电吸收调制激光器。对驱动相位调制器的射频信号进行2倍频操作，有助于进一步增加产生子载波的数目。
在本发明实施例的一个可选实施方式中，如图1所示，所述电吸收调制激光器可以由一个分布反馈(DFB)激光器和一个电吸收调制器(EAM)集成组成，可选地，所述EML的线宽仅为1.9MHz(远小于DML的线宽25MHz)。可选地，所述分布反馈激光器的工作电流需大于分布反馈激光器的阈值电流，电吸收调制激光器工作电流由一个直流电源(DC)提供；所述分布反馈激光器输出的光信号注入所述由一路射频信号驱动的电吸收调制器且所述电吸收调制器的偏置电压需在电吸收调制器的线性调制区域内。在线性调制范围内，提高所述电吸收调制器的偏置电压将扩大电吸收调制激光器的最佳工作区域范围。然而当电吸收调制器的偏置电压过高时，由于引入了较大的插入损耗，电吸收调制激光器输出信号的平均功率将小于-10dBm。此时可考虑采用一个集成的半导体光放大器(SOA)用以补偿调制器的插入损耗。可选地，所述电吸收调制激光器的调制系数如下定义：驱动电吸收调制激光器的射频信号幅度与电吸收调制器偏置电压之比。在偏置电压一定的前提下，提高驱动电吸收调制激光器的射频信号幅度能有效地实现对输出子载波功率平坦度的调节。随着射频信号幅度的增加， 生成子载波的功率差将随之减少，也即功率平坦度将随之改善；然而生成子载波的数目将保持不变。
在本发明实施例的可选实施方式中，所述电吸收调制激光器输出光信号进一步输入所述由另一路2倍频射频信号驱动的相位调制器产生频率锁定且正交的多载波，多载波间的频率间隔由为12.5GHz。可选地，所述相位调制器的调制系数如下定义：驱动相位调制器的射频信号幅度与相位调制器半波电压之比。在半波电压一定的前提下，提高驱动相位调制器的射频信号幅度能有效地实现对输出子载波数目的调节。随着射频信号幅度的增加，生成子载波的数目将随之增加。因此，在实际应用中，应对驱动电吸收调制激光器和相位调制器的射频信号幅度进行合理调节，以产生尽可能多且功率平坦性良好的多载波。因此，可选地，所述相位调制器还设置为通过增大驱动所述相位调制器的射频信号幅度增加生成的正交子载波数目。所述电吸收调制激光器还设置为通过调节驱动所述电吸收调制激光器的射频信号幅度使生成的子载波的幅度平坦。
下面将结合附图1，以包括电吸收调制激光器、相位调制器、正弦射频信号源、功率分配器、相移器、2倍频器以及电放大器的正交多载波光源为例，对本发明可选实施例提供的技术方案中的多载波生成进行详细阐述。
首先，所述正弦射频信号源向所述功率分配器输出信号频率为12.5GHz的正弦射频信号。
其次，所述功率分配器将以上射频信号分为两路：其中一路单倍频射频信号经过所述电放大器进行功率放大后驱动所述电吸收调制激光器；另一路首先经过所述相移器，接着经过所述2倍频器实现信号频率的2倍频，最后该2倍频射频信号经过所述电放大器进行功率放大后驱动所述相位调制器。
上述第二条支路所采用的相移器主要作用是实现两路射频信号的同步。
所述电吸收调制激光器由一个分布反馈激光器和一个电吸收调制器集成组成。一个直流电源提供为所述分布反馈激光器提供工作电流。优选地，该工作电流需大于激光器的阈值电流。
再次，所述分布反馈激光器输出的光信号输入所述由一路单倍频射频信号驱动的电吸收调制器进行光调制且所述电吸收调制器的偏置电压需在器件的线性调制区域内。
接着，所述电吸收调制器输出的光信号进一步输入一个偏振保持的掺铒光纤放大器用以补偿由所述电吸收调制器引入的调制损耗。
随后，所述偏振保持的掺铒光纤放大器输出的经功率放大的光信号进一步输入所述由另一路2倍频射频信号驱动的相位调制器，产生频率锁定且正交的多载波，其输出信号的电域表达式如下：
Figure PCTCN2014093989-appb-000001
其中，R1是电吸收调制激光器调制系数，具体如下定义：驱动电吸收调制激光器的射频信号幅度与电吸收调制器偏置电压之比；R2为相位调制器调制系数，具体如下定义：驱动相位调制器的射频信号幅度与相位调制器半波电压之比。通过分析上式可知，式1中的第二，三项不仅实现了对输出多载波的功率平坦，还引入了新频率分量，使得相邻子载波间的频率间隔由实际驱动相位调制器的2倍频信号频率减半为单倍频信号频率。
在实际应用中，可分别调节如附图1所示两个支路的电放大器，实现对驱动电吸收调制激光器的单倍频射频信号和驱动相位调制器的2倍频射频信号幅度的合理调节。实验证明，如附图2所示，以上基于EML与PM级联的正交多载波光源在相位调制器输出端最终能输出25条且功率差异小于5dB的频率锁定正交多载波，且子载波间的频率间隔为12.5GHz。
可选地，如图1所示，该正交多载波光源还可以在EML与PM级联之间设置一个光放大器(PM-EDFA)，对光信号进行放大。
根据本发明实施例，还提供了一种PDM-QPSK信号发射装置。
图3A为根据本发明实施例的PDM-QPSK信号发射装置的结构示意图，如图3A所示，该装置主要包括：顺序连接的正交多载波光源、光子载波选择模块、PDM-QPSK光信号发射模块。
本发明实施例提供的发射装置采用基于EML与PM级联的正交多载波光源产生多载波，采用PDM-QPSK光信号生成模块生成高速PDM-QPSK调制信号
下面分别对上述各个模块进行说明。
正交多载波光源为本发实施例提供的如图1所示的正交多载波光源，具体参见上述描述，在此不再赘述。
所述光子载波选择模块，可以包括光分插复用器(IL)和可调谐光滤波器(PM-TOF)。可选地，如图4所示，光子载波选择模块由一个光分插复用器(IL)由一个12.5/25-GHz和一个偏振保持的可调谐光滤波器(PM-TOF)组成。光分插复用器，设置为将所述正交载波光源输出的多载波分为奇偶两部分，将奇数路多载波或偶数路多载波输入到可调谐光滤波器；所述可调谐光滤波器，设置为通过调节所述可调谐光滤波器的带宽与波长，对输入多载波进行滤波以得到所需的光载波。在本发明实施例中，由基于EML与PM级联的正交多载波光源输出的多载波首先经过所述光分插复用器分为奇偶两部分，奇数或偶数路多载波间的频率间隔将由此增加到25GHz。接着将所述光分插复用器输出的奇数或偶数路多载波输入所述偏振保持可调谐光滤波器，通过调节所述可调谐光滤波器的带宽与波长滤出所需应光载波。
可选地，可调谐光滤波器可以为一个偏振保持的掺饵光纤放大器。
在本发明实施例中，正交多载波光源产生的正交多载波输入所述光分插复用器分为奇偶两部分。可选地，为了和射频信号源频率12.5GHz相匹配，所述光分插复用器器件参数为12.5/25-GHz。相交采用其它分插复用器器件参数的备选方案，该参数设定能实现对光多载波信号的最优分离。所述的奇数或偶数路多载波间的频率间隔将由此增加到25GHz。所述光分插复用器输出的奇数路多载波光谱图如附图5所示。接着将所述奇数路多载波输入所述偏振保持可调谐光滤波器。可选地，所述可调谐光滤波器的带宽与波长应与所需应光载波相一致。此处，所述可调谐光滤波器还同时实现了对上述正交多载波光源采用的用以补偿电吸收调制器调制损耗的偏振保持掺饵光纤放大器ASE噪声的滤除。可选地，可以采用若干个中心频率已定的带通滤波器实现对相应光载波的滤波，但采用所述可调谐光滤波器一方面可简化系统结构，另一方面在滤波器中心频率调节方面也更灵活便捷。所述偏振保持可调谐光滤波器输出的所需光子载波的光谱图如附图6所示。最后将偏振保持可调谐光滤波器输出的光子载波再通过一个偏振保持掺饵光纤放大器进行功率放大，输入PDM-QPSK光信号发射模块作为光载波信号实现QPSK光信号调制。
所述PDM-QPSK光信号发射模块可以包括I/O调制器和偏振复用器。I/O调制器，上下两臂的相位差为π/2，设置为对所述光子载波选择模块输出的光载波进行驱动，产生光QPSK信号；偏振复用器，设置为将I/O调制器输出的光QPSK信号分为两个分支，对其中一路光信号进行延迟，对另一路光信号进行功率均衡，然后将两路光信号进行合并，模拟信号的偏振复用，生成PDM-QPSK光信号，将所述PDM-QPSK光信号经光纤链路传输到所述零差相干光探测模块。
可选地，如图7所示，所述PDM-QPSK光信号发射模块由一个I/Q调制器和一个偏振复用器组成。所述I/Q调制器由两个并行的马赫增德尔调制器(MZM)组成，且所述马赫增德尔调制器均偏置在空点且被驱动于全波。所述I/Q调制器上下两臂的相位差控制在π/2。由所述光子载波选择模块滤出的光载波经由上述I/Q调制器为一路28G波特电二进制信号驱动产生光QPSK信号，并且所述电二进制信号产生于一个码型发生器(PPG)。所述偏振复用器由一个偏振保持光耦合器(PM-OC)，一段光延迟线(DL)，一个光衰减器和一个偏振合束器(PBC)组成。所述偏振保持光耦合器首先将输入的光QPSK信号分为两个分支，其中一路信号经过所述光延迟线模拟产生150个符号长度的延迟，另一路则经过所述光衰减器实现对两支路光信号功率的均衡。最后将两路光信号通过所述偏振合束器进行合并，模拟信号的偏振复用，生成所述PDM-QPSK信号。
在本实施例中，一路光载波信号和一路28G波特电二进制信号一同输入I/Q调制器进行光调制，输出QPSK调制光信号。所述电二进制信号由长度为223-1的伪随机二进制序列组成并通过一个码型发射器产生。优选地，所述I/Q调制器由上下两个并行的马赫增德尔调制器组成且存在π/2相位差，所述马赫增德尔调制器均偏置在空点且被驱动于全波。与其它马赫增德尔调制器参数设置方案相比，所述设置能实现最优的零啁啾，π相位跳变的相位调制。
接着将I/Q调制器输出的QPSK调制光信号输入偏振复用器，产生PDM-QPSK信号，将所述PDM-QPSK光信号经光纤链路发射。所述偏振复用器由一个偏振保持光耦合器，一段光延迟线，一个光衰减器和一个偏振合束器成。所述偏振保持光耦合器首先输入QPSK调制光信号分为两个分支，优选地，其中一路信号经过所述光延迟线模拟产生150个符号长度的延迟，另一路则经过所述光衰减器实现对两支路光信号功率的均衡。最后将两路光信号通过所述偏振合束器进行合并，模拟信号的偏振复用。此处存在一种备选方案，即直接采用集成的光偏振复用器模块，但所述模拟光信号偏振复用模块一方面在实验器件的成本上较具优势，另一方面因可直接对光延迟线进行调 节故更为灵活便捷。生成的112-Gb/s光PDM-QPSK信号接着经由光纤链路发射到接收端。
根据本发明实施例，根据本发明实施例，还提供了一种PDM-QPSK信号相干光接收系统。
图3B为根据本发明实施例的PDM-QPSK信号相干光接收系统的结构示意图，如图3B所示，该系统包括接收装置及上述的PDM-QPSK信号发射装置。如图3B所示，接收装置采用零差相干光探测模块实现本振光与信号光信号的相干探测与数据恢复。发射装置生成的112-Gb/s光PDM-QPSK信号接着经由光纤链路传输到接收装置，其中所述光纤链路由80km标准单模光纤-28(SMF-28)组成。
可选地，接收装置的零差相干光探测模块可以包括：偏振分集加相位分集光相干探测模块和数字信号处理单元。其中，偏振分集加相位分集光相干探测模块包括一个外腔激光器、两个偏振分束器、两个90°光混频器、四个光电二极管、以及四个高速模数转换器，其中，所述外腔激光器设置为充当本振光与接收到的所述PDM-QPSK光信号分别经过一个所述偏振分束器，该偏振分束器将所述本振光和所述PDM-QPSK光信号分离为两个正交的偏振态光信号，将相同偏振态的所述本振光和所述PDM-QPSK光信号一同输入一个所述90°光混频器；所述90°光混频器设置为将输入的光信号产生0°、90°、180°、270°的相移后与所述PDM-QPSK光信号进行拍频，实现相干探测后输出；所述光电二极管，设置为对两个所述90°光混频器输出的四路相干探测光信号进行平衡探测，将输出四路光电流分别输入到四个所述高速模数转换器；所述调整模数转换器，设置为对输入的光电流进行Nyqusit采样转化为采样信号。所述数字信号处理单元分别对各个所述高速模数转换采样所得的采样信号进行数据恢复。
可选地，如图8所示，所述零差相干光探测模块由一个偏振分集加相位分集光相干探测模块和一个数字信号处理(DSP)单元组成。所述偏振分集加相位分集光相干探测模块包括一个外腔激光器(ECL)，两个偏振分束器(PBS)，两个90°光混频器，四个光电二极管(PD)以及四个高速模数转换器(AEC)组成。其中，所述外腔激光器充当本振光源(LO)的作用与接收到的经所述光纤链路传输的信号光分别经过一个所述偏振分束器分离为两个正交的偏振态；接着将相同偏振态的本振光和信号光一同输入一个所述90°光混频器，所述90°光混频器的主要功能是使本振光产生0°、90°、180°、270°的相移然后与信号光进行拍频实现相干探测；随后将两个所述90°光混频器输出的四路相干探测光信号(X偏振方向同相分量、正交分量；Y偏振方向同相分量、正交分量)分别输入四个所述光电二极管进行平衡探测，输出四路光电流再分别输入四个高速模数转换器进行Nyqusit采样转化为采样信号。所述数字信号处 理单元的主要功能是实现对经高速模数转换采样所得的采样信号进行数据恢复，包括：信号重定时，色散补偿，恒模算法均衡，载波恢复，差分解码和误码率计算。
在该可选实施方式中，首先发射装置输出的PDM-QPSK光信号经由80km标准单模光纤-28传输作为接收信号光输入所述偏振分集加相位分集光相干探测模块。所述偏振分集加相位分集光相干探测模块包括一个外腔激光器，两个偏振分束器，两个90°光混频器，四个光电二极管以及四个高速模数转换器组成。
其次将输入的接收信号光与本振光分别经过一个所述偏振分束器实现两个正交的偏振态的分离，所述本振光源由所述外腔激光器实现。
接着将具有相同偏振态的本振光和信号光一同输入一个所述90°光混频器，所述90°光混频器的主要功能是使本振光产生0°、90°、180°、270°的相移然后与信号光进行拍频实现相干探测。
随后将两个所述90°光混频器输出的四路相干探测光信号(X偏振方向同相分量、正交分量；Y偏振方向同相分量、正交分量)分别输入四个所述光电二极管进行平衡探测，输出四路光电流。
最后再将所述四路光电流分别输入四个所述高速模数转换器进行Nyqusit采样转化为采样电信号。
虽然通过上述偏振分集加相位分集光相干探测能将接收信号光域中携带的幅度和相位信息完整地保留到光电转换后的采样电信号中，但由于本振光源与发端光载波之间的频率难以保持完全一致且本振光源的线宽将引入相应的相位偏移，采样电信号的频率及相位将受到本振光频率及相位的扰动。此外，相干探测过程中还存在收发端采样时钟不匹配以及由于光纤色散造成的信道静态损伤以及偏振模色散效应等其它信号损伤。因此，需引入所述数字信号处理单元针对以上损耗分别进行估计与补偿，进而完成对原始发射信号的恢复再生与恢复。如附图7所示，优选地，所述数字信号处理单元包括：信号重定时，色散补偿，恒模算法均衡，载波恢复，差分解码和误码率计算。其中信号重定时主要用于解决ADC采样时钟不匹配造成的时钟未对准问题，色散补偿和恒模算法均衡主要用于消除光纤色散与偏振模色散对信号造成的损伤，载波恢复主要用于消除相位偏移对信号的影响，最后对正确恢复的信号星座图进行差分解码恢复成0-1比特序列并通过误码率计算评估系统的总体性能。
本发明实施例提供的上述系统，由于采用基于EML与PM级联的正交多载波光源能够有效地将输出子载波，从而可以将发射端的线宽控制在1.9MHz，因而保证光载波 线宽与符号持续时间的乘积满足能够实施28G波特高速PDM-QPSK信号相干接收的条件(乘积小于1×10-4)，使得实施方案3的落实成为可能。
从以上的描述中，可以看出，本发明实施例中，提出了一种基于EML与PM级联的正交多载波光源，并将该多载波光源应用于一个PDM-QPSK调制信号发射装置及相干光探测系统。通过该正交多载波光源不仅能够生成一定数目且平坦度良好的子载波，还有效克服了DML与PM级联方案中生成子载波线宽过大的不足，使得对高速PDM-QPSK调制信号进行相干光接收成为可能。此外本发明提出的所述正交多载波光源还具有小体积，低功耗及易集成的特点，因而在实际系统的具有广阔的应用前景。
显然，本领域的技术人员应该明白，上述的本发明的各模块或各步骤可以用通用的计算装置来实现，它们可以集中在单个的计算装置上，或者分布在多个计算装置所组成的网络上，可选地，它们可以用计算装置可执行的程序代码来实现，从而，可以将它们存储在存储装置中由计算装置来执行，并且在某些情况下，可以以不同于此处的顺序执行所示出或描述的步骤，或者将它们分别制作成各个集成电路模块，或者将它们中的多个模块或步骤制作成单个集成电路模块来实现。这样，本发明不限制于任何特定的硬件和软件结合。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。
工业实用性
如上所述，本发明实施例提供的一种正交多载波光源及PDM-QPSK信号发射装置，具有以下有益效果：采用基于电吸收调制激光器(EML)与相位调制器(PM)级联的正交多载波光源，不仅能够生成一定数目且平坦度良好的子载波，还有效克服了DML与PM级联方案中生成子载波线宽过大的不足，从而可以对高速PDM-QPSK调制信号进行相干光接收。

Claims (13)

  1. 一种正交多载波光源，包括：电吸收调制激光器,相位调制器，正弦射频信号源，功率分配器，相移器，第一电功率放大器，以及第二电功率放大器，其中，
    所述正弦射频信号源，设置为输出预定信号频率的正弦射频信号至所述功率分配器；
    所述功率分配器，设置为将输入的所述正弦射频信号分为左路正弦射频信号和右路正弦射频信号，将所述左路正弦射频信号输入到所述电功率放大器，将所述右路正弦射频信号输入到所述相移器；
    所述第一电功率放大器，设置为对所述左路正弦射频信号进行功率放大，将功率放大后的所述左路正弦射频信号输入到所述电吸收调制激光器；
    所述相移器，设置为对所述右路正弦射频信号进行调整，以使所述右路正弦射频信号同所述左路正弦射频信号同步，并输出调整后的所述右路正弦射频信号；
    所述第二电功率放大器，设置为对经所述相移器调整后的所述右路正弦射频信号进行功率放大，将功率放大后的所述右路正弦射频信号输入到所述相位调制器；
    所述电吸收调制激光器，设置为在所述第一电功率放大器输出的所述左路正弦射频信号的驱动下产生光信号，并将产生的所述光信号输入到所述相位调制器；
    所述相位调制器，设置为在所述第二电功率放大器输出的所述右路正弦射频信号的驱动下，对输入的所述光信号进行调制，产生频率锁定且正交的多载波。
  2. 根据权利要求1所述的正交多载波光源，其中，还包括：2倍频器，连接在所述相移器和所述第二电功率放大器之间，设置为实现所述相移器输出的所述右路正弦射频信号的2倍频，将2倍频后的所述右路正弦射频信号输入到所述第二电功率放大器。
  3. 根据权利要求1所述的正交多载波光源，其中，所述电吸收调制激光器包括：
    分布反馈激光器，设置为输出光信号；
    电吸收调制器，设置为在所述第一电功率放大器输出的所述左路正弦射频信号的驱动下，对所述分布反馈激光器输出的所述光信号进行光调制，输出调制后的光信号。
  4. 根据权利要求3所述的正交多载波光源，其中，所述分布反馈激光器的工作电流大于所述分布反馈激光器的阈值电流。
  5. 根据权利要求3所述的正交多载波光源，其中，所述电吸收调制器的偏置电压在所述电吸收调制器的线性调制区域内。
  6. 根据权利要求3所述的正交多载波光源，其中，所述电吸收调制激光器还包括：半导体光放大器，设置为对所述电吸收调制器输出的所述光信号进行进入补偿，以补偿所述电吸收调制器的插入损耗，输出补偿后的光信号。
  7. 根据权利要求1至6中任一项所述的正交多载波光源，其中，所述电吸收调制激光器的线宽为1.9MHz。
  8. 根据权利要求1至6中任一项所述的正交多载波光源，其中，所述相位调制器还设置为通过增大驱动所述相位调制器的射频信号幅度增加生成的正交子载波数目。
  9. 根据权利要求1至6中任一项所述的正交多载波光源，其中，所述电吸收调制激光器还设置为通过调节驱动所述电吸收调制激光器的射频信号幅度使生成的子载波的幅度平坦。
  10. 一种偏振复用正交相位调制PDM-QPSK信号发射装置，包括：顺序连接的正交多载波光源、光子载波选择模块、以及PDM-QPSK光信号发射模块；其中，
    所述正交多载波光源为权利要求1至9中任一项所述的正交多载波光源；
    所述光子载波选择模块包括：
    光分插复用器，设置为将所述正交载波光源输出的多载波分为奇偶两部分，将奇数路多载波或偶数路多载波输入到可调谐光滤波器；
    所述可调谐光滤波器，设置为通过调节所述可调谐光滤波器的带宽与波长，对输入多载波进行滤波以得到所需的光载波；
    所述PDM-QPSK光信号发射模块，包括：
    I/Q调制器，上下两臂的相位差为π/2，设置为在所述光子载波选择模块输出的光载波驱动下，产生并输出光QPSK信号；
    偏振复用器，设置为将I/Q调制器输出的光QPSK信号分为两个分支，对其中一路光信号进行延迟，对另一路光信号进行功率均衡，然后将两路光信号进行合并，模拟信号的偏振复用，生成最终用于发射的PDM-QPSK光信号
  11. 根据权利要求10所述的装置，其中，所述光分插复用器为频率为12.5/25-GHz。
  12. 根据权利要求10所述的装置，其中，所述偏振复用器包括：
    一个偏振保持光耦合器、一段光延迟线、一个光衰减器和一个偏振合束器，其中，所述偏振保持光耦合器设置为将输入的QPSK光信号分为两个分支，其中一路信号输入至所述光延迟线，另一路则输入至所述光衰减器；
    所述光延迟线，设置为通过模拟对输入的QPSK光信号产生150个符号长度的延迟，将延迟后的QPSK光信号输入至所述偏振合束器；
    所述光衰减器，设置为对僌的QPSK光信号的功率进行调整，实现对两支路所述QPSK光信号功率的均衡，将调整后的QPSK光信号输入至所述偏振合束器；
    所述偏振合束器，设置为对输入的两路光信号通过进行合并，模拟信号的偏振复用，生成所述PDM-QPSK信号。
  13. 一种偏振复用正交相位调制PDM-QPSK信号相干光接收系统，包括：接收装置和权利要求10至12中任一项所述的发射装置，其中，所述接收装置设置为接收所述发射装置发送的PDM-QPSK信号。
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