WO2016145493A1 - Procédé et système d'émission optique multiplexée par répartition en polarisation - Google Patents

Procédé et système d'émission optique multiplexée par répartition en polarisation Download PDF

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Publication number
WO2016145493A1
WO2016145493A1 PCT/AU2016/050192 AU2016050192W WO2016145493A1 WO 2016145493 A1 WO2016145493 A1 WO 2016145493A1 AU 2016050192 W AU2016050192 W AU 2016050192W WO 2016145493 A1 WO2016145493 A1 WO 2016145493A1
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WO
WIPO (PCT)
Prior art keywords
complex
optical
polarisation
symbol sets
symbol
Prior art date
Application number
PCT/AU2016/050192
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English (en)
Inventor
Chen Zhu
Arthur Lowery
William Peter Corcoran
Leimeng ZHUANG
Original Assignee
Monash University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2015900977A external-priority patent/AU2015900977A0/en
Application filed by Monash University filed Critical Monash University
Publication of WO2016145493A1 publication Critical patent/WO2016145493A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/06—Polarisation multiplex systems
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2572—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to forms of polarisation-dependent distortion other than PMD
    • 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
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5053—Laser transmitters using external modulation using a parallel, i.e. shunt, combination of modulators
    • 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
    • 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]
    • H04B10/5561—Digital phase modulation
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers

Definitions

  • the present invention relates generally to optical communications, and more particularly to a method and apparatus for improving the quality of reception of polarisation division multiplexed (PDM) optical signals in the presence of polarisation-dependent loss (PDL).
  • PDM polarisation division multiplexed
  • Optical transmission in which an information signal is modulated onto an optical carrier, is widely employed in modern communications systems.
  • wide area communications networks employ long-haul transmission links using single-mode optical fibres for the transmission of digital information at very high bit-rates (e.g. up to and beyond 100 Gb/s per wavelength), using one or more optical carriers, or wavelengths, over each fibre.
  • bit-rates e.g. up to and beyond 100 Gb/s per wavelength
  • Polarisation division multiplexing in which different information is transmitted on each of two orthogonal polarisation states, is employed in high bit-rate systems to double the transmission capacity of each channel.
  • PDL causes non-orthogonality and amplified spontaneous emission (ASE) depolarisation of PDM signals.
  • the non-orthogonality can be equalised by an adaptive PMD equaliser.
  • depolarised ASE noise degrades the optical signal-to-noise ratio (OSNR) of the lossy polarisation state, and errors in the received signal in the lossy state dominate the overall system performance.
  • OSNR optical signal-to-noise ratio
  • the invention provides a method of transmitting digital information over an optical channel comprising:
  • the method implements a pairwise coding of transmitted symbols across the two polarisation states.
  • the invention is based on the novel insight that PDL may be viewed as a form of 'polarisation-selective fading', analogous to frequency-dependent fading in wireless RF systems.
  • pairwise coding does not involve any additional overhead and therefore does not impact on payload data rate, and requires only a few extra computations per symbol, because only pairs of symbols are processed together.
  • a complementary aspect of the invention provides a method of recovering digital information modulated onto first and second polarisation states of an optical carrier and transmitted over an optical channel, the method comprising:
  • the invention provides an optical transmitter comprising:
  • a digital processor configured to:
  • DAC digital-to-analog conversion
  • an optical carrier source having first and second polarisation states, coupled to first and second modulation units, the first modulation unit being configured to modulate in-phase (I) and quadrature (Q) components of the first polarisation state of the optical source with the first and third electrical signals, respectively, and the second modulation unit being configured to modulate in- phase (I) and quadrature (Q) components of the second polarisation state with the second and fourth electrical signals, respectively.
  • the invention provides an optical receiver, configured to recover digital information modulated onto first and second polarisation states of an optical carrier and transmitted over an optical channel, the receiver comprising a digital processor configured to:
  • OSNR optical signal-to-noise ratio
  • FIG. 1 is a schematic diagram of an optical transmission system embodying the invention
  • Figure 2 is a schematic diagram of a proof-of-concept experimental demonstration corresponding with the system of Figure 1 ;
  • Figure 3 shows a spectrum of first and second polarisation states of the optical signal generated in the demonstration system of Figure 2;
  • Figure 4 is a graph of OSNR penalty as a function of PDL
  • Figure 5 is a graph of received signal quality factor for each channel of a wavelength division multiplexed (WDM) signal generated in the demonstration system of Figure 2;
  • Figure 6 shows exemplary constellation diagrams of a received signal, generated within the demonstration system of Figure 2.
  • FIG. 1 there is shown schematically a system 100 for
  • a transmitter 101 receives input digital information bits 102 which are selectively divided via a 1-2 demultiplexer 104.
  • the resulting bit sequences are input to corresponding mapping units 106, 108.
  • Each mapping unit 106, 108 maps groups of input bits to corresponding complex-valued symbols.
  • a number of different symbol mappings may be employed by embodiments of the invention, including, without limitation, quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) mappings. Different mappings, and/or different numbers of levels, may be selected depending upon the available signal-to-noise ratio, and the number of bits to be encoded within each mapped symbol.
  • QPSK quadrature phase shift keying
  • QAM quadrature amplitude modulation
  • ⁇ represents the ratio between the OSNR in the 'good' polarisation state to the OSNR in the 'bad' polarisation state. This rotation angle is designed to minimise the bit error rate (BER) for a given OSNR difference between the two polarisation states.
  • BER bit error rate
  • Interleaving is performed following angle rotation.
  • the real parts of the rotated symbol values are input to digital-to-analog converters (DACs) 1 14, 1 16, while the imaginary parts are input to DACs 1 16, 120.
  • the outputs of DACs 1 14, 1 16 comprise the in-phase (I) and quadrature (Q) components to be modulated onto a first polarisation state of the transmitted signal, while the outputs of DACs 1 18, 120 comprise I and Q components of a signal to be modulated onto a second polarisation state of the transmitted signal.
  • a PDM optical signal source comprises an optical carrier source 122, a polarisation beam splitter 124, and a pair of l/Q (complex) modulators 126, 128.
  • the I and Q components output from DACs 1 14, 1 16 are input to modulator 126, thereby modulating the first polarisation state of the optical carrier source 122.
  • the outputs of DACs 1 18, 120 are input to modulator 128, thereby modulating the second polarisation state of the optical carrier 122.
  • the modulated polarisation states are recombined in polarisation beam splitter 130, to produce the PDM optical signal which is transmitted through an optically-amplified transmission link 132.
  • the system 100 further comprises a receiver 133 which is configured to recover the transmitted information bits 102.
  • the transmitted PDM signal is detected, for example using a dual-polarisation coherent detector 134.
  • the detector 134 may comprise, for example, a local oscillator laser source, a pair of optical hybrid circuits, and four pairs of balanced detectors, resulting in the detection of in-phase and quadrature components of the signals transmitted on the two polarisation states.
  • the detected in-phase and quadrature components of the first polarisation state are input to analog-to-digital converters (ADCs) 136, 138, while the corresponding I and Q components of the second polarisation state are input to ADCs 140, 142. This results in four corresponding sequences of digitised samples, which are subject to front-end processing 144 within a digital signal processing (DSP) unit.
  • DSP digital signal processing
  • the front-end DSP processes include front-end correction, clock recovery, channel impairment compensation and carrier recovery.
  • the outputs from the front-end processing comprise a pair of equalised complex-valued sample sequences, i.e. real and imaginary parts corresponding with the I and Q components of the two received polarisation states respectively.
  • the equalised symbol values corresponding with the first polarisation state are input to OSNR estimation and scaling block 146, while the equalised symbol values corresponding with the second polarisation state are input to OSNR estimation and scaling block 148.
  • OSNR estimation and scaling block 146 the equalised symbol values corresponding with the second polarisation state are input to OSNR estimation and scaling block 148.
  • the corresponding OSNR is estimated, for example using the statistical moments method as described by C Zhu et al, 'Statistical Moments Based OSNR
  • the equalised symbols are then rescaled differently, according to the estimated OSNR of each polarisation.
  • the equalised symbols are multiplied by the square root of the estimated OSNR.
  • the OSNR varies as a result of the stochastic nature of PDL, and therefore the OSNR estimation and rescaling should be updated periodically, in accordance with the associated state-of-polarisation rotation rate. Typically, a few thousand updates per second (i.e. kHz update rate) should be sufficient for transmission fibre having fast state-of-polarisation rotation.
  • the outputs of OSNR estimation and scaling blocks 146, 148 comprise real and imaginary parts of the corresponding rescaled and equalised symbols.
  • the interleaving and data recovery are performed by inputting the real parts of the rescaled symbols to maximum likelihood detector (MLD) block 150, while the imaginary parts are input to MLD block 152.
  • MLD maximum likelihood detector
  • C k is the constellation alphabet (i.e. [1 +j, 1 -j, -1 +j, -1-j] for QPSK modulation) and D k are the rotated and rescaled symbol values.
  • the resulting decisions represent information bits that are recombined in multiplexer 154 in order to recover the output bit sequence 156.
  • a bit error rate (BER) may be determined by comparing the recovered output bits 156 with the original transmitted input bits 102.
  • the presently disclosed embodiments of the invention are implemented substantially via digital signal processing. Such processing is performed both in the transmitter 101 and in the receiver 133.
  • the various signal processing blocks shown in the exemplary embodiment 100 represent conceptual processing functions, which may be implemented, in practice, in a variety of different ways, as will be apparent to persons skilled in the art of signal processing.
  • the digital processing may be implemented in software executing on a suitable central processing unit (e.g. a DSP device), or as a custom, or semi- custom, hardware unit, such as an application-specific integrated circuit (ASIC), or programmable hardware, such as a field programmable gate array (FPGA).
  • a suitable central processing unit e.g. a DSP device
  • ASIC application-specific integrated circuit
  • FPGA field programmable gate array
  • FIG. 2 is a schematic diagram showing the configuration 200 of a proof-of-concept experimental demonstration corresponding with the exemplary system of Figure 1 .
  • Eight external cavity lasers (ECLs) 202 having a 50 GHz carrier spacing, are multiplexed with an 8x1 polarisation-maintaining (PM) coupler 204.
  • the carrier waves are amplified using a polarisation-maintaining erbium- doped fibre amplifier (PM-EDFA) 206.
  • An arbitrary waveform generator (AWG) 208 is used to generate baseband signals at 10 GSa/s, with either conventional PDM-QPSK, or polarisation pairwise coding QPSK (PPC-QPSK) embodying the invention.
  • a pair of electrical amplifiers 210 is used to amplify the I and Q components of the signal generated by the AWG 208, which are then used to drive an optical l/Q modulator 212.
  • the resulting modulated signals are amplified using a further PM-EDFA 214.
  • a PDM emulator 216 is used to delay the ⁇ polarisation state of the optical signal with respect to the 'X' polarisation state.
  • the delay was equivalent to 195 symbols, enabling the single AWG 208 to be used to generate dual-polarisation signals. This is illustrated schematically by the blocks 228, which show that the desired PDM signals, suitable for decoding at the receiver, occupy alternate 195 symbol blocks.
  • the resulting optical signal is divided into its two polarisation states by polarisation beam splitter (PBS) 218.
  • a frequency/channel-dependent PDL is generated using a Finisar WaveShaper (WS) 220, while a variable attenuator 222 is used to match the insertion loss of WS 220.
  • the two polarisation states are recombined in PBC 224.
  • the resulting PDL-emulated signal is passed through a 50 GHz interleaver 226, and a further optical amplifier 230, before entering a recirculating loop 232.
  • the recirculating loop 232 comprises two acousto-optic modulator (AOM) switches, 640 km of standard single-mode fibre, consisting of six 80 km spans and associated optical amplifiers, a gain-flattening WS, and a polarisation scrambler.
  • AOM acousto-optic modulator
  • an ASE source 234 is used to add optical noise, e.g. to control the OSNR for single-channel back-to-back measurements.
  • a further WS 236 is used to select the desired channel for coherent detection.
  • the detection is performed by receiver 238, which generates four outputs (i.e. I and Q components of each of the X and Y polarisation states) which are sampled and digitised by a real-time oscilloscope 240.
  • the resulting signals can be processed offline, in accordance with conventional PDM-QPSK processing techniques, or according to PPC-QPSK techniques embodying the invention.
  • Figure 3 shows a graph 300, comprising the spectrum of X and Y polarisation states of the WDM optical signal generated and transmitted into the recirculating loop 232 of the system 200 shown in Figure 2.
  • the spectrum 300 shows wavelength on the horizontal axis 302, and corresponding power on the vertical axis 304.
  • the higher-quality (Y) polarisation state is shown by the trace 306, while the lower-quality (X) polarisation state is shown by the trace 308.
  • Figure 4 shows a graph 400 of OSNR penalty as a function of PDL.
  • PDL in dB
  • OSNR penalty for a BER of 10 ⁇ 3 is shown on the vertical axis 404.
  • the BER is based on averaging across the two polarisation states. The measurements were performed for a single channel operating in back-to-back mode, i.e. without recirculation in the loop 232, and with added ASE generated by the source 234.
  • the PDM-QPSK experimental results closely match the simulation results for worst case PDL, with a 3.5 dB OSNR penalty occurring for a PDL value of 7 dB.
  • a PPC-QPSK signal, embodying the invention and using a ⁇ /4 rotation angle outperforms the PDM-QPSK signal significantly, show it just over 1 dB OSNR penalty with 7 dB PDL.
  • differences between the ⁇ /4 rotation angle and optimum angle, for PDL less than 7 dB are not significant. This demonstrates that a fixed rotation angle can be used for all cases, thereby avoiding the need to feed back OSNR estimates from the receiver to the transmitter.
  • FIG. 5 shows a graph 500 of received signal quality factor for each of the eight WDM channels transmitted using the experimental configuration 200.
  • the horizontal axis 502 shows channel index, while the vertical axis 504 shows quality factor, defined as:
  • Figure 6 shows exemplary constellation diagrams 600 of a received signal embodying the invention. These constellation diagrams are, respectively: received signal in the X polarisation after equalisation (602); received signal in the Y polarisation after equalisation (604); the received signal in the X polarisation after rescaling (606); the received signal in the Y polarisation after rescaling (608); and the received signals following de-interleaving (610, 612).
  • embodiments of the invention employ polarisation pairwise coding for PDM coherent optical signals, improving transmission performance in the presence of PDL.
  • the principles of rotating the original information symbols and interleaving the real and imaginary components between two polarisation states are employed.
  • the detected X and Y polarisation signals are rescaled according to respective OSNRs, and de-interleaved.
  • the overall decoded signals extracted from the two polarisation states have similarly low error rates, and the overall performance is always superior to that of conventionally (non-pairwise-coded) PDM signals, which are dominated by high error rates in the poor quality polarisation state.
  • An experimental proof-of-concept demonstration establishes that greatly enhanced overall system performance can be achieved, over a wide range of PDL, without any coding overhead, for single channel and WDM transmission systems.
  • mapping methods other than QPSK may be employed, such as QAM, or other multi-level mapping techniques.
  • QAM quadrature mapping technique

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

Abstract

L'invention concerne un procédé d'émission d'informations numériques sur un canal optique (132), comprenant l'étape consistant à faire correspondre (106, 108) des bits d'informations numériques d'entrée à des premier et deuxième ensembles de symboles à valeurs complexes. Une rotation complexe (110, 112) est appliquée à chaque symbole des premier et deuxième ensembles de symboles à valeurs complexes. Des composantes en phase (I) et en quadrature (Q) d'un premier état de polarisation d'une porteuse optique (122) sont modulées respectivement avec les parties réelles des premier et deuxième ensembles de symboles à valeurs complexes, tandis que des composantes en phase (I) et en quadrature (Q) d'un deuxième état de polarisation de la porteuse optique sont modulées respectivement avec les parties imaginaires des premier et deuxième ensembles de symboles à valeurs complexes.
PCT/AU2016/050192 2015-03-18 2016-03-18 Procédé et système d'émission optique multiplexée par répartition en polarisation WO2016145493A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2015900977A AU2015900977A0 (en) 2015-03-18 Method and system for polarisation division multiplexed optical transmission
AU2015900977 2015-03-18

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023021260A1 (fr) * 2021-08-20 2023-02-23 Mimopt Technology Méthode de codage iq pour système de communication wdm sur fibre optique
WO2023187299A1 (fr) * 2022-04-01 2023-10-05 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication wdm sur fibre optique
WO2023187300A1 (fr) * 2022-04-01 2023-10-05 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication sdm sur fibre optique

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KR20110139931A (ko) * 2010-06-24 2011-12-30 충북대학교 산학협력단 가시광 송신 장치, 가시광 수신 장치 및 이를 포함하는 가시광 통신 시스템
US20130034193A1 (en) * 2010-10-16 2013-02-07 Zte Corporation method and device for demodulating complex carriers
US20130034174A1 (en) * 2010-10-16 2013-02-07 Zte Corporation Method, device and system for complex carrier modulation
WO2013039968A1 (fr) * 2011-09-16 2013-03-21 Alcatel Lucent Amélioration de performance à travers des variantes optiques

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Publication number Priority date Publication date Assignee Title
KR20100065034A (ko) * 2008-12-05 2010-06-15 한국전자통신연구원 다중 반송파를 이용한 가시광 무선통신 시스템 및 그 방법
KR20110139931A (ko) * 2010-06-24 2011-12-30 충북대학교 산학협력단 가시광 송신 장치, 가시광 수신 장치 및 이를 포함하는 가시광 통신 시스템
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WO2013039968A1 (fr) * 2011-09-16 2013-03-21 Alcatel Lucent Amélioration de performance à travers des variantes optiques

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023021260A1 (fr) * 2021-08-20 2023-02-23 Mimopt Technology Méthode de codage iq pour système de communication wdm sur fibre optique
FR3126274A1 (fr) * 2021-08-20 2023-02-24 Mimopt Technology Méthode de codage iq pour système de communication wdm sur fibre optique
WO2023187299A1 (fr) * 2022-04-01 2023-10-05 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication wdm sur fibre optique
WO2023187300A1 (fr) * 2022-04-01 2023-10-05 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication sdm sur fibre optique
FR3134267A1 (fr) * 2022-04-01 2023-10-06 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication sdm sur fibre optique
FR3134266A1 (fr) * 2022-04-01 2023-10-06 Mimopt Technology Méthode et dispositif de codage iq dense pour système de communication wdm sur fibre optique

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