WO2009049364A1 - Method and apparatus for improving reception of optical signals - Google Patents
Method and apparatus for improving reception of optical signals Download PDFInfo
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- WO2009049364A1 WO2009049364A1 PCT/AU2008/001526 AU2008001526W WO2009049364A1 WO 2009049364 A1 WO2009049364 A1 WO 2009049364A1 AU 2008001526 W AU2008001526 W AU 2008001526W WO 2009049364 A1 WO2009049364 A1 WO 2009049364A1
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- Prior art keywords
- optical
- carrier
- power
- signal
- sideband
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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
- H04B10/60—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 optical signals transmitted along with a corresponding optical carrier.
- the invention may have particular benefits when employed in conjunction with subcarrier multiplexed optical signals, including orthogonal frequency division multiplexed (OFDM) signals, and/or in combination with optical single sideband (OSSB) and related transmission and modulation techniques.
- OFDM orthogonal frequency division multiplexed
- OSSB optical single sideband
- the invention is not limited to systems employing such techniques.
- Optical transmission in which an information signal is modulated onto an optical carrier
- 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, using one or more optical carriers, or wavelengths, over each fibre.
- the maximum distance over which data may be transmitted in single-mode optical fibres before some form of regeneration is required is substantially limited by dispersion and nonlinear processes.
- the impact of chromatic dispersion increases rapidly as the bit rate of optical data channels is increased.
- Methods and apparatus capable of compensating chromatic dispersion, as well as other processes such as polarisation mode dispersion (PMD) and optical nonlinearities are thus of vital importance in the deployment of modern communications systems.
- the invention provides a method of receiving digital information transmitted via an optical signal over an optical channel, the optical signal including an optical carrier and at least one information-bearing optical sideband in an optical frequency domain, wherein transmitted optical power of the optical signal is distributed between the optical carrier and the optical sideband, the method including the steps of: processing the optical signal received from the optical channel to increase received power in the optical carrier relative to power in the optical sideband; detecting the processed optical signal to produce a corresponding electrical signal; and processing the electrical signal to recover the digital information.
- the present inventor has determined, through analysis and computer simulations, that optical processing of the received signal to boost carrier power relative to sideband power, prior to detection and electronic processing, can result in improved signal-to-noise ratio (SNR) in the detected electrical signal, and a corresponding improvement in the accuracy and reliability of information recovery.
- SNR signal-to-noise ratio
- optical processing which boosts the optical carrier power relative to the sideband power is able to reduce the effect of certain types of noise and/or distortion present in the detected electrical signal in such a way that a net improvement in SNR may be achieved, despite attenuation of the optical signal which may occur in the optical processing step.
- the use of an optical signal including substantially only a single information-bearing optical sideband is particularly preferred in order, for example, to facilitate processing such as dispersion compensation within the electrical domain, such as is disclosed in international application publication no. WO 2007/041799, which is hereby incorporated herein in its entirety by reference.
- the step of processing the optical signal includes passing the signal through one or more optical filters, wherein an optical attenuation applied to the optical carrier is less than a corresponding optical attenuation applied to the optical sideband. While this approach results in an overall reduction in the detected signal power, and/or an increase in optical noise if a compensating optical amplifier is employed, it is nonetheless surprisingly possible to achieve an overall improvement in SNR.
- a suitable optical filter includes at least a first attenuation band corresponding with a frequency range including the optical carrier, and a second attenuation band corresponding with a frequency range including the optical sideband, wherein the filter attenuation in the second frequency range is greater than the filter attenuation in the first frequency range.
- the filter includes a transition band between the first and second attenuation bands.
- improvements may be achieved, in accordance with the inventive principles, even for relatively modest differences in attenuation between the first and second attenuation bands, such that practical realisations of the required optical filters are readily achievable using available components and technologies.
- the step of processing the optical signal may include amplifying the optical signal to increase optical power available in the detecting step.
- amplifying the optical signal may be used to compensate for attenuation occurring during transmission through the optical channel, and/or in the filters used to boost the optical carrier power relative to the sideband power, such amplification also inevitably results in the addition of optical noise, such as amplified spontaneous emission (ASE) noise, to the optical signal. Nonetheless, as noted previously, the present invention surprisingly enables an overall improvement in SNR of the detected signal to be achieved.
- ASE amplified spontaneous emission
- the information-bearing optical sideband corresponds with a transmitted time-bearing signal generated from a series of transmitted data blocks, each of which includes a plurality of transmitted data symbols corresponding with one or more bits of the digital information
- the step of processing the detected electrical signal then preferably includes: generating a series of received data blocks from the electrical signal; and performing a frequency domain equalisation of received data symbols included in each of said received data blocks, thereby to recover the transmitted data symbols.
- the processing of the electrical signal is performed in accordance with an orthogonal frequency division multiplexing (OFDM) method.
- OFDM orthogonal frequency division multiplexing
- a ratio between power in the optical carrier and power in the optical sideband of the transmitted optical signal is between about 0.5 and about 2.0.
- the power in the optical carrier and the power in the optical sideband of the transmitted optical signal may be approximately equal.
- the power in the optical carrier of the transmitted optical signal may be less than a corresponding power in the optical sideband.
- a reduction in power of the carrier in the transmitted optical signal makes available a greater proportion of the power budget for use by the information-bearing optical sideband, thereby potentially enabling transmission over greater distances and/or with reduced distortion due to nonlinear effects.
- the optical carrier may then be boosted at the receiving end, relative to the optical sideband, in order to improve the SNR of the detected signal.
- power in the optical carrier is greater than a corresponding power in the optical sideband.
- a ratio between the optical carrier power and the optical sideband power at detection may be at least 5 dB.
- further improvements in SNR of the detected electrical signal may be realised if the ratio between the optical carrier power and the optical sideband power is at least 10 dB.
- the optical filters and/or other components required to achieve greater ratios in practice may be more costly and/or technically difficult to realise.
- the most substantial benefits of the present invention are able to be achieved with relative modest ratios between carrier power and sideband power.
- the invention provides an apparatus for receiving digital information transmitted via an optical signal over an optical channel, the optical signal including an optical carrier and at least one information-bearing optical sideband in an optical frequency domain, wherein transmitted optical power of the optical signal is distributed between the optical carrier and the optical sideband
- the apparatus includes: at least one optical filter arrangement having an input port arranged to receive the optical signal, and an output port, the filter arrangement being configured such that a ratio of power in the optical carrier relative to power in the optical sideband is increased at the output port relative to a corresponding ratio at the input port; a detector arranged to receive the optical signal output from the optical filter arrangement to produce a corresponding electrical signal; and an electronic processor configured to recover the digital information.
- the optical filter arrangement is characterised in that it includes at least a first attenuation band corresponding with a frequency range including the optical carrier, and a second attenuation band corresponding with a frequency range including the optical sideband, wherein the attenuation in the second band is greater than the attenuation in the first band.
- the apparatus may further include one or more optical amplifiers disposed prior to the input port of the optical filter, and/or between the output port of the optical filter and the detector, in order to increase detected optical signal power.
- the information-bearing optical sideband preferably corresponds with a transmitted time-bearing signal generated from a series of transmitted data blocks, each of which includes a plurality of transmitted data symbols corresponding with one or more bits of the digital information
- the electronic processor preferably includes: means for generating a series of received data blocks from a time-varying electrical signal output from the detector; and an equaliser arranged to perform a frequency domain equalisation of received data symbols included in each of said received data blocks, thereby to recover the transmitted data symbols.
- the electronic processor is configured to recover the digital information in accordance with an OFDM method.
- Figure 1 illustrates schematically a system for communicating digital information over an optical channel, incorporating a receiver according to an embodiment of the present invention
- Figure 2 is a schematic diagram illustrating the various signal, noise and distortion components generated at the receiver of Figure 1 ;
- Figure 3 is a graph of simulation results comparing performance of prior art direct detection and coherent detection receivers
- Figure 4 is a schematic illustration of the operation of a boost filter according to an embodiment of the invention
- Figure 5 is a graph of simulation results illustrating performance improvements achieved in accordance with embodiments of the present invention
- Figure 6 is a graph of simulation results illustrating a potential for reduction in a frequency guard band achieved in accordance with embodiment of the present invention
- Figure 7 is a graph of simulation results illustrating further performance improvements achieved in accordance with embodiments of the invention employing carrier suppression at the transmitting end;
- Figure 8 is a graph of simulation results illustrating improvements in nonlinearity compensation achieved in accordance with embodiments of the invention.
- FIG. 1 there is shown schematically a system 100 for communicating digital information over an optical channel.
- the exemplary system 100 includes a transmitter 102 for generating an optical signal bearing digital information, which is input via the data channels 104.
- the exemplary transmitter 102 operates generally to generate an optical signal including an optical carrier and substantially only a single information-bearing optical sideband in an optical frequency domain.
- the information-bearing optical sideband corresponds with a transmitted time-bearing signal generated from a series of transmitted data blocks, each of which includes a plurality of transmitted data symbols corresponding with one or more bits of the digital information input via data channels 104.
- the transmitter 102 operates in accordance with an OFDM method, substantially in the manner described in international application publication no. WO 2007/041799.
- a signal processing block 106 generates a time-varying OFDM signal 108.
- a laser source 110 is modulated with the OFDM signal 108, using optical modulator 112.
- an optical filter 114 is configured to at least substantially suppress one optical frequency sideband of the intensity modulated signal output from the optical modulator 112.
- the output of optical filter 114 thus includes substantially only a single information-varying optical sideband in the optical frequency domain, corresponding with the time- varying electrical signal 108.
- optical channel 116 which may consist, for example, of a number of spans of single-mode optical fibre and a corresponding series of optical power amplifiers.
- optical channel 116 at the receiving end of the optical channel there is provided a first optical power amplifier 118, a "boost" filter 120 (the operation of which is described in greater detail below with reference to Figure 4) a second optical amplifier 122, and an ASE filter 124 for rejecting out-of-band optical noise generated in the optical amplifiers.
- optical amplifiers 118 and/or 122 may be optional, depending upon the power of the signal at the output of the optical channel 116.
- the ASE filter 124 is similarly optional, and the functions of the boost filter 120 and ASE filter 124 may, in appropriate circumstances, be combined into a single component.
- a receiver 126 includes an optical detector, in the form of photodiode 128, and an electronic processor 130. Signal recovery, processing and equalisation in the processor 130 are performed substantially in accordance with the methods described in international application publication no. WO 2007/041799.
- the processor 130 includes digital and/or analog electronic components for generating a series of received data blocks from the time-varying electrical signal output by photodiode 128.
- An equaliser 132 is arranged to perform a frequency domain equalisation of received data symbols includes in each of the received data blocks, so as to recover data symbols transmitted by the transmitter 102.
- the recovered digital information is output on data channels 134.
- the boost filter 120 is an exemplary device configured to process the optical signal received from the optical channel 116 in order to increase received power in the optical carrier relative to power in the optical sideband.
- the boost filter 120 it will be advantageous to provide a more-detailed discussion of the various signal, noise, interference and distortion products generated in the electrical signal output from the photo diode 128.
- Figure 2 is a schematic diagram 200 illustrating the various signal, noise, interference and distortion components generated in the detector 128 of the receiver 126 of the exemplary transmission system 100. More particularly, Figure 2 illustrates the received optical spectrum 202, which is output from the optical channel 116.
- the optical spectrum 202 includes optical carrier 204, information- bearing optical sideband 206, upper sideband ASE noise component 208, and lower sideband ASE noise component 210.
- the information-bearing subcarriers 206 occupy a bandwidth B sc , which are separated from the optical carrier 204 by a frequency guard band of width B gap .
- ASE noise occurring in portions of the optical spectrum 202 not occupied by the optical carrier 204 and information-bearing subcarriers 206 may be filtered out, however in practice this is generally not technically feasible. Instead, a band of ASE noise, having a bandwidth BN, will generally be passed by a noise filter, eg ASE filter 124.
- the optical field represented by spectrum 202 is incident upon the photodiode 128, which results in the generation of a corresponding baseband electrical signal at the input to the processor 130.
- the various spectral contributions to the overall electrical signal are further illustrated in Figure 2 as described following.
- the desired received electrical OFDM signal having a bandwidth B S c, is generated by mixing between the optical carrier and information-bearing subcarriers, 214, to generate the electrical signal spectrum 216.
- the remaining components illustrated in Figure 2 represent unwanted, but unavoidable, noise, interference or distortion components.
- the subcarriers 218 also mix amongst themselves to produce a band of unwanted mixing products 220. These occupy a bandwidth of B sc at baseband. If the frequency guard band B gap is greater than or equal to B sc , then all of these unwanted mixing products lie at frequencies below the desired electrical subcarrier frequencies, as illustrated in Figure 2.
- the optical carrier and ASE noise components 222 mix to produce baseband electrical noise components 224. These may be considered to consist of a "real noise” component, corresponding with the unavoidable ASE noise falling within the optical bandwidth of the information-bearing subcarriers 206, as well as “image noise” components, lying within the unused sideband, but which are not rejected by the ASE filter 124.
- the information-bearing subcarriers also combine with the ASE noise components, as illustrated in the spectrum 226, to produce additional electrical noise spectral components 228. Finally, ASE noise components 230 intermix to produce corresponding electrical noise components 232.
- the diagram 200 illustrates an important insight of the present inventor, which is that only the desired signal spectrum 216, and the spectrum 224 resulting from mixing between the carrier and ASE noise components, are dependent upon the power of the optical carrier 204. Increasing the optical carrier power relative to the other optical spectral components will therefore increase only the power of the desired electrical signal, and the noise contribution 224, while having no impact on the magnitude of the other noise, interference and distortion components 220, 228, 232. There is accordingly a potential benefit, in respect of the received electrical SNR, in manipulating the power in the optical carrier 204 relative to the power in the information-bearing subcarriers 206.
- ASS B 1n OSNR.B m where P SU b ca rriers is the total signal power at the photodiode integrated over the subcarrier sideband, PoDcamer is the power at the photodiode of any transmitted carrier (zero for a coherent system) and P AS E is the ASE power in both polarizations integrated over the OSNR measurement bandwidth, B m .
- the detected electrical signal power of a single subcarrier is related to the optical power in a single subcarrier, PSC.RF, by:
- Psc, R F 2. ⁇ Ji 2 fR L )P S cP c ⁇ rner (2)
- P C amer is the carrier power at the photodiode provided from the transmitter in a DD system, or from the local oscillator in a coherent system
- R is the photodiode responsivity
- RL is the load resistance
- Equation (4) gives a SNR up to 9-dB poorer than a coherent image-rejection receiver according to Equation (5).
- Equation (5) may be modified for a coherent system without image rejection, by multiplying by kcar-
- Figure 3 is a graph 300 of simulation results comparing, in detail, the performance of prior art direct detection and coherent detection receivers.
- the X-axis 302 of the graph 300 represents the bandwidth of the ASC filter 124.
- the Y-axis 304 is the corresponding electrical SNR, measured after detection by the photodiode 128.
- the simulations corresponded with the exemplary system diagram 100, and were performed using the commercially-available simulation software package VPItransmissionMaker, Version 7.1.
- the ASE was represented as Gaussian white noise, filtered with a brickwall optical filter. This was added to an optical OFDM signal using 4-QAM modulation, with 1024 bits per OFDM symbol (512 subcarriers).
- the OFDM waveform was modulated onto an optical carrier using a Mach Zender-type modulator, biased such that the output optical field was proportional to the input OFDM electrical voltage.
- the resulting bandwidth of the subcarrier spectrum was 5 GHz.
- a frequency guard band B gap of 5 GHz was provided between the optical carrier and the information- bearing subcarriers.
- the optical signal-to-noise ratio (OSNR) is defined in the conventional manner, as the mean optical signal power (including carrier) divided by the total ASE noise in both polarisations falling within a 12.5 GHz bandwidth.
- the electrical SNR (or, equivalently, Q value) is defined in a conventional manner as the square of the mean distance of the detected sample values to the appropriate decision thresholds, divided by the variance in the corresponding components of the QAM signal. Under this definition, an SNR of 9.8 dB gives a bit error ratio (BER) of 1 (T 3 .
- Illustrated in the graph 300 are simulation results for a polarisation diverse balanced coherent receiver with 7dB OSNR (306), and direct detection receivers with OSNRs of 7, 10, and 13 dB (308,310,312).
- the electrical SNR is 5 dB worse than for an ideal coherent receiver when the optical filter bandwidth is 10 GHz.
- practical cost-effective direct detection systems necessarily utilise wider bandwidth optical filters. As the simulation results show, this results in additional SNR degradation due to the mechanisms 224, 228 and 232 illustrated in Figure 2.
- the electrical SNR achieved using a conventional direct detection system may be more than 9 dB less than the corresponding SNR achievable using a coherent detection system, for the same OSNR.
- the direct detection receiver requires an improvement in input OSNR of around 6 dB or greater, in order to achieve performance comparable with that of the corresponding coherent detection system.
- FIG. 4 illustrates schematically a characteristic 400 of a suitable boost filter 120.
- the characteristic 400 shows an optical carrier 402, and corresponding information-bearing sideband 404.
- An appropriate optical filter characteristic includes a first attenuation band 406 corresponding with a frequency range than includes the optical carrier 402, and a second attenuation band 408 corresponding with a frequency range than includes the information-bearing optical sideband 404.
- the attenuation in the first band 406 is lower than the attenuation in the second band 408, such that the power in the optical carrier 402 at the output of the filter is increased relative to the corresponding output power in the optical sideband 404.
- a transition band 410 exists between the first attenuation band 406 and the second attenuation band 408, and it will be appreciated that the difficulty of designing and implementing a suitable boost filter will depend substantially upon the required characteristics of the first and second attenuation bands 406, 408, and the transition 410 therebetween.
- a ratio between the attenuation bands 406, 408 of as little as 5 dB may provide a useful improvement in receiver performance, and this degree of filter discrimination, given a transition band (B gap ) on the order of a few gigahertz, is readily achievable using existing optical filter technology.
- Figure 5 shows a graph 500 of simulation results illustrating performance improvements achieved using boost filters providing ratios of 5 dB, 10 dB and 20 dB between the attenuation applied to the optical carrier and the information-bearing optical sideband.
- the optical power in the carrier is equal to the total optical power in the sideband prior to processing by the optical boost filter 120.
- the curve 502 represents the electrical SNR (or Q factor) as a function of OSNR of the received optical signal.
- the curves 504, 506 and 508 represent the corresponding electrical SNR for relative carrier boost of 5 dB, 10 dB and 20 dB respectively. Substantial improvements in electrical SNR are achieved even with only 5 dB of carrier boost.
- a 2.4 dB improvement is obtained with a relatively modest 10 dB of carrier boost. This may be increased to around 2.8 dB of improvement, using 20 dB carrier boost. This is within 3.4 dB of a corresponding coherent system, but is implemented using a far simpler, and cheaper, direct detection receiver.
- carrier boost increases the power of the desired electrical signal 216, without a corresponding increase in power of the unwanted subcarrier mixing products 220.
- a further potential advantage of embodiments of the present invention is therefore that the frequency guard band B gap may potentially be reduced in order to improve spectral efficiency of transmission. Reduction of B gap below the subcarrier bandwidth B SG results in overlap between low frequency information-bearing subcarriers and higher frequency mixing products.
- carrier boost increases the corresponding signal-to-interference ratio.
- Figure 6 is a graph 600 which illustrates the corresponding improvements achieved using carrier boost when the frequency guard band is reduced to 2.5 GHz, in the case of a signal having a subcarrier bandwidth of 5 GHz.
- the curve 602 represents detected electrical SNR as a function of received OSNR without carrier boost, while the curves 604, 606, 608 correspond with carrier boost of 5 dB, 10 dB and 20 dB respectively.
- the electrical SNR is reduced from 7.8 dB to 6.2 dB as a result of the reduced frequency guard band.
- FIG. 7 is a graph 700 of simulation results illustrating the effect of combining carrier suppression at the transmitter with carrier boost at the receiver, in accordance with embodiments of the present invention. More particularly, the graph 700 illustrates electrical SNR following detection in the receiver as a function of the level of carrier suppression applied at the transmitter.
- the curve 702 represents the case in which no carrier boost is applied (Ze a conventional direct detection receiver), while the curves 704, 706 correspond with 10 dB and 20 dB of carrier boost respectively.
- a reduction in power of the carrier in the transmitted optical signal makes available a greater proportion of the power budget for use by the information- bearing optical sideband, thereby potentially enabling transmission over greater distances and/or with reduced distortion due to nonlinear effects.
- a reduction in distortion will result, for example, from a reduction in the total optical power due to carrier suppression, as well as a reduction in nonlinear mixing products generated between the carrier and the information-bearing sideband. Accordingly, for systems operated close to a nonlinear limit, this approach may enable the more effective use of nonlinearity compensation, such as that described in international application publication no. WO 2008/074085, which is hereby incorporated herein in its entirety by reference, to provide additional improvements in system capacity and/or reach.
- the benefits of reducing the power of the carrier in the transmitted optical signal are illustrated by the further simulation results shown in the graph 800 of Figure 8.
- the x-axis of the graph 800 is the Q-factor of the received electrical signal, which has been calculated as a function of the effective precompensation length L eff , expressed in km/span, applied in the transmitter (further details of the nonlinear precompensation techniques employed are disclosed in international application publication no. WO 2008/074085).
- the simulated system includes a 4000 kilometre link of fibre having a dispersion of 2 ps/nm/km, consisting of individual spans of 80 kilometres with fibre attenuation of 0.2 dB/km.
- Optical amplifiers are incorporated at the input of each span, to boost the optical power back to -3 dBm, however amplifier noise was artificially excluded in the simulations to enable a study of the nonlinear effects in isolation.
- one of two levels of carrier suppression was employed at the transmitter, in combination with one of four levels of carrier boost at the receiver.
- the carrier boost was achieved using a 1 GHz band-pass optical filter with a variable stop band attenuation.
- a set of simulations was performed for an ideal coherent system, for the purposes of comparison.
- the curve 802 in graph 800 represents the signal quality as a function of effective precompensation length for the ideal coherent system.
- the further curves 804, 806, 808, 810, 812 represent electrical signal quality as a function of effective precompensation length for five different direct-detection systems, employing different combinations of carrier suppression at the transmitter, and carrier boost at the receiver.
- the curve 804 represents a system with 5 dB of transmitter carrier suppression and 15 dB of receiver carrier boost.
- the curve 806 corresponds with 0 dB of transmitter carrier suppression and 10 dB of receiver carrier boost.
- the curve 808 corresponds with 0 dB of transmitter carrier suppression and 5 dB of receiver carrier boost.
- the curve 810 corresponds with 5 dB of transmitter carrier suppression and 5 dB of receiver carrier boost.
- the curve 812 corresponds with 0 dB of a transmitter carrier suppression and 0 dB of receiver carrier boost (Ze a "standard" single sideband, direct-detection, system). In all cases, carrier suppression at the transmitter is relative to a carrier power level that is equal to the total sideband power level.
- an ideal coherent system represented by the curve 802 is able to achieve the best maximum received signal quality, when an optimum level of nonlinear precompensation is applied.
- the reason for the better performance of the direct detection system in under-compensated cases is that the optical carrier accumulates the same phase modulation as the subcarriers during propagation through the optical fibre transmission link, such that nonlinear-induced phase errors are partially cancelled upon detection.
- optimal precompensation when optimal precompensation is applied the "walk-off' between the optical carrier and the subcarriers, due to fibre dispersion, ultimately limits the maximum received signal quality that can be achieved by way of nonlinear precompensation.
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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EP08800159A EP2220795A1 (en) | 2007-10-15 | 2008-10-15 | Method and apparatus for improving reception of optical signals |
US12/682,147 US8233799B2 (en) | 2007-10-15 | 2008-10-15 | Method and apparatus for improving reception of optical signals |
AU2008314499A AU2008314499A1 (en) | 2007-10-15 | 2008-10-15 | Method and apparatus for improving reception of optical signals |
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AU2007905646A AU2007905646A0 (en) | 2007-10-15 | Method and Apparatus for Improving Reception of Optical Signals | |
AU2007905646 | 2007-10-15 |
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EP (1) | EP2220795A1 (en) |
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WO2011151913A1 (en) * | 2010-06-03 | 2011-12-08 | 株式会社日立製作所 | Optical communication system, optical receiver, optical transponder, wavelength multiplexing optical communication system, wavelength multiplexing receiving device, and wavelength multiplexing optical transponder |
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JP5621530B2 (en) * | 2010-11-12 | 2014-11-12 | 富士通株式会社 | Receiver, optical spectrum shaping method, and optical communication system |
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WO2011113097A3 (en) * | 2010-03-19 | 2012-01-12 | Ofidium Pty Ltd | Method and apparatus for fiber non-linearity mitigation |
US9762323B2 (en) | 2010-03-19 | 2017-09-12 | Ofidium Pty. Ltd. | Method and apparatus for fiber non-linearity mitigation |
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EP2220795A1 (en) | 2010-08-25 |
US8233799B2 (en) | 2012-07-31 |
AU2008314499A1 (en) | 2009-04-23 |
US20110013914A1 (en) | 2011-01-20 |
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