WO2008040053A1 - Single sideband orthogonal frequency division multiplexed optical fibre transmission - Google Patents
Single sideband orthogonal frequency division multiplexed optical fibre transmission Download PDFInfo
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- WO2008040053A1 WO2008040053A1 PCT/AU2007/001465 AU2007001465W WO2008040053A1 WO 2008040053 A1 WO2008040053 A1 WO 2008040053A1 AU 2007001465 W AU2007001465 W AU 2007001465W WO 2008040053 A1 WO2008040053 A1 WO 2008040053A1
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- qam
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- modulator
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Classifications
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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
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
- H04B10/505—Laser transmitters using external 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
- H04B10/5165—Carrier suppressed; Single sideband; Double sideband or vestigial
-
- 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
Definitions
- the present invention relates to data transmission over an optical fibre or optical network, and in particular relates to transmission of data using orthogonal frequency division multiplexing (OFDM) and single sideband (SSB) transmission.
- OFDM orthogonal frequency division multiplexing
- SSB single sideband
- FCD Optical fibre chromatic dispersion
- FCD arises due to the variation in refractive index of an optical fibre medium for differing wavelengths of optical transmissions, such that a signal component having a first wavelength propagates at a velocity which is different to the velocity of a signal component having a second wavelength.
- FCD leads to pulse spreading, which constrains the bandwidth distance product (BPD) for a given optical medium, and is thus a limiting factor upon the data rate and/or optical link distance.
- BPD bandwidth distance product
- PMD polarisation mode dispersion
- FCD and PMD present a major problem in multi-gigabit fibre transmission.
- DCF dispersion compensated fibre
- O-SSB optically created single sideband
- OF-VSB optically created vestigial sideband
- proposed solutions include the use of optical filters or the phasing of optical modulators, provision of electrical dispersion compensation (EDC), use of a linear feed forward equaliser (FFE), use of nonlinear decision feed back (DFE) and maximum likelihood sequence equalisation (MLSE).
- EDC electrical dispersion compensation
- FFE linear feed forward equaliser
- DFE nonlinear decision feed back
- MBE maximum likelihood sequence equalisation
- Orthogonal frequency division multiplexed optical transmissions offer another prospect to improve the BPD, and involve the use of many RF sub-carriers with low bit-rates to transmit a high bit rate signal, in a similar manner to wireless OFDM systems.
- Such solutions tend to be complex as they require up-conversion to an orthogonal microwave carrier for each OFDM sub-carrier before optical transmission, and corresponding down-conversion at the receiver before FFT processing.
- the present invention provides a method of data transmission over an optical medium, the method comprising: performing signal processing upon data to be transmitted, to generate two baseband broadband orthogonal frequency division multiplexed 90 degree feed signals; and driving a quadrature dual optical modulator with the two 90 degree feed signals, wherein the signal processing is performed such that the two generated 90 degree feed signals cause an output of the modulator to be single sideband.
- the present invention provides a transmitter for data transmission over an optical medium, the transmitter comprising: a signal processor for performing signal processing upon data to be transmitted, to generate two baseband broadband orthogonal frequency division multiplexed 90 degree feed signals; and a quadrature dual optical modulator configured to be driven by the two 90 degree feed signals, wherein the signal processor is configured to generate the two 90 degree feed signals in a manner which causes an output of the modulator to be single sideband.
- the present invention provides a solution in which FCD will affect only the phase of the OFDM sub-carriers, which may thus be corrected by a training sequence.
- the present invention positions the single sideband immediately adjacent to the optical carrier frequency, in contrast to proposals utilising a RF sub-carrier which position the sidebands in a range away from the optical carrier frequency, for example in the range between 5 GHz and 10 GHz away from the optical carrier frequency.
- a RF sub-carrier which position the sidebands in a range away from the optical carrier frequency, for example in the range between 5 GHz and 10 GHz away from the optical carrier frequency.
- the signal processing comprises QAM modulation of the data to be transmitted, to N QAM symbols.
- the signal processing comprises parallel processing along two processing arms to generate each feed signal.
- the 90 degree phase shift between the drive signals is imposed upon the N QAM symbols of one of the processing arms, before OFDM processing in that arm.
- the parallel processing in each processing arm preferably comprises reverse complex conjugate addition of the N QAM symbols, to 2N symbols.
- the 2N symbols are preferably processed by an inverse fast Fourier transform (IFFT).
- IFFT inverse fast Fourier transform
- Such embodiments are particularly advantageous in avoiding the need for a Hubert transformer, or similar block such as a FIR filter or other DSP filter to effect the 90 degree phase difference in the drive signals.
- a Hubert transformer, or similar block such as a FIR filter or other DSP filter to effect the 90 degree phase difference in the drive signals.
- To implement baseband OFDM with low frequency sidebands would require a very large number of filter taps, and thus the present embodiment provides for particularly efficient implementations which may permit application in very high data rate environments.
- Real processing of the IFFT output is preferably utilised. Cyclic prefixing is preferably applied to each 2N block, although inter-block guard bands may additionally or alternatively be utilised.
- the feed signal from each processing arm is preferably produced in analogue form by way of up sampling, interpolation and digital to analogue (D/A) conversion. Such interpolation preferably comprises post-IFFT packing.
- the modulator is preferably a dual electrode Mach Zehnder modulator biased for SSB generation.
- the present invention provides a receiver for receiving SSB OFDM transmissions, the receiver comprising: a channel phase correctional device for correcting a phase of the channel as a whole under the control of a channel phase shift bias value; a sub-carrier group divider for dividing the channel into a plurality of sub-carrier groups; and for each sub-carrier group, a group phase correctional device for correcting the phase of the sub-carrier group under the control of a group phase shift bias value.
- the receiver may utilise a training sequence to correct phase drift in each group.
- Figure Ia is a schematic of an optical transmission system for transmitting baseband SSB OFDM optical data signals
- Figure Ib is a more detailed schematic of the transmitter-side of the schematic of Figure Ia, illustrating the generation of the two 90 degree baseband drive signals
- Figure 2a is a generalised schematic
- Figure 2b is a detailed schematic, of a system used in a computer simulation of a first embodiment of the present invention for 10 Gb/s rate and having a zero length of optical fibre between transmitter and receiver
- Figure 2c illustrates the transmitted SSB spectrum of the system of Figure 2b
- Figure 2d illustrates the received QAM constellation in the system of Figure 2b
- Figures 3a and 3b illustrate bit sequence insertion and extraction points and a constellation rotation input of the schematic of Figures 2a and 2b, respectively
- Figure 3c illustrates a transmitted pseudo-random bit sequence
- Figure 3d illustrates the received pseudo-random bit sequence
- Figure 3e illustrates the post-rotation QAM constellation
- Figure 4a is a detail of
- Figure 5a illustrates the received channel QAM constellation for all 128 sub- carriers after transmission over 400 km of fibre
- Figure 5b illustrates the received QAM constellation for sub-carriers 1 to 11 of the channel
- Figure 5c illustrates the received QAM constellation for sub-carriers 101 to 111 of the channel
- Figure 6a illustrates the received channel QAM constellation for all 128 sub- carriers after transmission over 1000 km of fibre
- Figure 6b illustrates the received QAM constellation for sub-carriers 1 to 11 of the channel
- Figure 6c illustrates the received QAM constellation for sub-carriers 101 to 111 of the channel.
- Figure 1 is a schematic of an optical transmission system 100 for transmitting baseband SSB OFDM optical data signals.
- System 100 takes as an input a pseudo-random bit sequence 110 which is passed to a QAM modulator 120 for conversion to blocks of N QAM symbols.
- the N symbols are in turn passed to a baseband OFDM processor 130, adapted to generate two feed signals 132 and 134.
- An optical source in the form of laser 140 is modulated by a dual Mach Zehnder modulator 142, the modulator being biased such that the I and Q feed signals used as inputs produce a SSB output of the modulator.
- the baseband feed signals 132 and 134 generated by the processor 130 are used to drive the dual Mach Zehnder modulator 142.
- the modulated optical signal is then transmitted over a length of fibre to a receiver, where it is detected by a PIN receiver 150, A/D converted by A/D converter 160, and processed by FFT 170.
- Processor 180 performs 2N to N processing, and demodulator 190 performs QAM demodulation to recover data bits.
- OFDM processor 130 generates feed signals 132 and 134 in such a manner that the transmitted optical signal is a SSB OFDM optical signal.
- processor 130 uses reverse complex conjugate addition, IFFT, cyclic prefix, dual 90 degree processing, and interpolation and D/A conversion, which in a sense can be considered as a Hubert transform.
- the digital processing 130 makes it possible to achieve constant 90 degree phase difference between the two driving arms 132, 134 of the dual MZ modulator 142.
- Baseband real processing is used in the Inverse Fast
- IFFT Fourier transform
- the first processing arm in Figure Ib includes the following processing steps: reverse complex conjugate addition 1312; IFFT 1314; cyclic prefixing 1316 and interpolation and D/A conversion 1318.
- the second arm includes an initial digital phase shifter 1320 which performs R to P conversion to effect 90 degree rotation of the QAM symbols in the second arm.
- the second arm then includes the same processing steps as the first arm, namely: reverse complex conjugate addition 1322; IFFT 1324; cyclic prefixing 1326 and interpolation and D/A conversion 1328.
- all processing within the first arm includes the following processing steps: reverse complex conjugate addition 1312; IFFT 1314; cyclic prefixing 1316 and interpolation and D/A conversion 1318.
- the second arm includes an initial digital phase shifter 1320 which performs R to P conversion to effect 90 degree rotation of the QAM symbols in the second arm.
- the second arm then includes the same processing steps as the first arm, namely: reverse complex conjugate addition 1322; IFFT 1324;
- CMOS 130 occurs at baseband, and the present embodiment thus does not require any intermediate RF frequency stage.
- the present embodiment exploits the recognition that the necessary phasing of the OFDM sidebands will then arise through the subsequent IFFT processing.
- a 90 degree rotation is a simple CMOS processing operation, and in real time parallel processing this technique will be substantially faster than the alternative of including an FIR or HR Hubert transform stage.
- the broadband requirements of SSB OFDM demand a high number of taps in such filters, further hampering processing speeds.
- the present embodiment is particularly suitable for OFDM over optical SSB with direct detection, as in such applications it is desirable to transmit the optical carrier for direct detection in a simple low cost optical system.
- Figure 2a is a generalised schematic
- Figure 2b is a detailed schematic, of a system used in a computer simulation of a first embodiment of the present invention for 10 Gb/s data rate and having a zero length of optical fibre between transmitter and receiver.
- Parallel processing paths 200a and 200b are utilised in order to generate the two feed signals for Mach Zehnder modulator 210.
- a 90 degree phase shift is applied at 202b at the start of path 200b to provide the 90 degree processing.
- Figure 2c illustrates the SSB spectrum of the signal transmitted at 220 in the system of Figure 2b.
- the signal spectrum is SSB, and notably the SSB spectrum is achieved by appropriate signal processing without need for optical filtering to convert DSB to SSB.
- the signal spectrum is immediately adjacent to the carrier frequency which allows close spacing of multiple such channels and thus permits high spectral efficiency.
- Figure 2d illustrates the QAM constellation received at 230 in the system of Figure 2b. As can be seen there exists tight grouping of the points of the 4-QAM constellation, albeit with 45 degrees of rotation from expected constellation point positions.
- Figure 3 a is another representation of the schematic of Figure 2a
- Figure 3b is another representation of the schematic of Figure 2b, illustrating bit sequence insertion point 310 and bit sequence extraction point 330, and a constellation rotation input 320.
- Figures 3a to 3e relate to an embodiment in which the transmitter and receiver are back to back with zero length of optical fibre between them.
- Figure 3c illustrates a transmitted pseudo-random bit sequence inserted at 310
- Figure 3d illustrates the received pseudo-random bit sequence extracted from 330, showing proper bit sequence recovery.
- Constellation rotation input 320 allows a phase shift bias value to be applied to the receiver in order to rotate the received QAM constellation from the received position, such as that shown in Figure 2d, to the expected 4-QAM point positions.
- Figure 3e illustrates the post-rotation QAM constellation, illustrating the phase shift of 135 degrees achieved by a phase shift bias value of (1.57/2 + 1.57) applied at 320.
- the phase shift bias point 320 thus provides a very simple means for phase adjustment of the received channel for rotation of the constellation back to the expected QAM positions.
- Figure 4a is a detail of the schematic of Figures 2a and 3a
- Figure 4b is a detail of the schematic of Figures 2b and 3b
- Figures 4a and 4b illustrate in the receiver a channel constellation rotation input 410, sub-carrier group constellation rotation inputs 420, and signal outputs 430.
- Channel constellation rotation input 410 rotates the entire received constellation in the same manner as noted in the preceding with respect to Figures 3e and 2d.
- Figure 4c illustrates the received channel QAM constellation for all 128 sub-carriers output at 430a, after transmission over a 40 km length of fibre, and after correctional channel rotation provided by phase shift bias 410.
- each point in the QAM constellation has undergone spreading over the 40 km optical link, for example due to FCD and/or PMD.
- transmission of a SSB signal in accordance with the present invention ensures that such spreading manifests only as rotation in the QAM plane.
- Figure 4d illustrates that the received QAM constellation points at 430b for sub-carriers 1 to 11 of the channel are closely grouped and undergo little or no constellation rotation.
- Figure 4e illustrates that the received QAM constellation points at 430c for sub-carriers 101 to 111 of the channel suffer a greater amount of spreading than sub-carriers 1-11, and further that, when phase shift bias 420b is inactive, the QAM constellation points for sub-carriers 101-111 undergo a notable amount of constellation rotation.
- the present invention recognises that sub-carriers in such a baseband SSB OFDM transmission can be dealt with in groups.
- the present embodiment thus provides sub- carrier group constellation rotation inputs 420, each of which can be individually adjusted to rotate that group's QAM constellation points by a desired angle.
- Figure 4f illustrates the effect of activation of phase shift bias 420b upon the output at 430c, showing that the sub-carrier QAM constellation of sub-carriers 101-111 of the channel can be rotated as a group to be located substantially at the ideal 4-QAM points.
- Applying suitable phase shift biases to each sub-carrier group thus allows the spreading evident in Figure 4c to be accounted for and for the data to be accurately recovered by QAM demodulation.
- baseband modulation further causes constellation rotation to be roughly progressive or incremental from one sub-carrier to the next, and thus from one sub- carrier group to the next, such that a deterministic derivation of appropriate phase shift biases 420 may be obtained, rather than requiring feedback phase shift bias control for all groups.
- Figure 5a illustrates the received channel QAM constellation for all 128 sub-carriers output at 430b after transmission over 400 km of fibre.
- Figure 5b illustrates the received QAM constellation at 430b for sub-carriers 1 to 11 of the channel.
- Figure 5c illustrates the received QAM constellation at 430c for sub-carriers 101 to 111 of the channel, with phase shift bias 420b inactive. While the QAM points for carriers 101 to 111 have undergone substantial rotation in the I/Q plane this can be corrected by appropriate control of phase shift bias 420b.
- sub-carriers 101-111 remain adequately grouped together that QAM demodulation can be performed to accurately recover the original data.
- the present simulations thus suggest that the present invention has promise in applications having optical links of 400 km.
- Figure 6a illustrates the received channel QAM constellation for all 128 sub-carriers output at 430b after transmission over 1000 km of fibre. Visual inspection of Fig 6a reveals substantial spreading of the QAM points of the overall channel.
- Figure 6b illustrates the received QAM constellation at 430b for sub-carriers 1 to 11 of the channel. Clearly, it would be possible to QAM demodulate sub-carriers 1 to 11 from such compact QAM point clusters.
- Figure 6c illustrates the received QAM constellation at 430c for sub-carriers 101 to 111 of the channel, with phase shift bias 420b inactive. While the QAM points for carriers 101 to 111 have undergone substantial rotation in the I/Q plane this can be corrected by appropriate control of phase shift bias 420b.
- sub- carriers 101-1 1 1 can still be seen to be grouped together so that QAM demodulation can be performed to accurately recover the original data.
- the present simulations thus suggest that the present invention has promise in applications having optical links of 1000 km.
- the present embodiment of the invention thus illustrates that it is possible to modify the baseband silicon processor generating the baseband OFDM sub-carriers, and in effect realise a broadband Hubert transform for directly driving a dual Mach-Zehnder
- the present embodiment directly generates, electrically, a
- the close spacing of OFDM sub-carriers to the optical carrier in this invention means that even for transmission distances greater than 1000 km low order OFDM sidebands may need no electrical dispersion compensation at the receiver and higher order OFDM sidebands may be electrically compensated simply using block channel phase compensation techniques (and not necessarily individual channel compensation).
- the present invention recognises that a key objective of system vendors and network providers is transmission of 10 Gbit/s and 40 GBit/s optical signals over standard single mode (SSM) optical fibre, without dispersion compensated fibre (DCF), and in the presence of polarisation mode dispersion (PMD).
- SSM standard single mode
- DCF dispersion compensated fibre
- PMD polarisation mode dispersion
- the present embodiment provides baseband OFDM over optical SSB and may present a valuable tool in achieving this objective. Further, the present embodiment may be appropriate for use in optically- switched networks where either small electrical phase compensation is required or rapid electrical adaptive compensation is necessary as signals are switched dynamically.
- Sub-carrier groupings can be chosen to include a number of channels appropriate to the application in question. For example a large number of sub-carriers may be grouped together for correctional rotation by phase shift bias 420 in applications where the constellation rotation is sufficiently similar for sub-carriers throughout that grouping. Alternatively, sub-carriers may be phase shift biased in small groups, or even on a one- by-one basis by a larger number of phase shift biases 420, in applications such as long- haul where constellation rotation causes excessive spreading of the constellation of adjacent sub-carriers.
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Priority Applications (1)
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AU2007304876A AU2007304876B2 (en) | 2006-10-03 | 2007-10-03 | Single sideband orthogonal frequency division multiplexed optical fibre transmission |
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AU2006905457 | 2006-10-03 | ||
AU2006905457A AU2006905457A0 (en) | 2006-10-03 | Single Sideband Orthogonal Frequency Division Multiplexed Optical Fibre Transmission |
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Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN101860507A (en) * | 2009-04-09 | 2010-10-13 | 财团法人工业技术研究院 | Receiving method of optical orthogonal frequency-division multitask signal and receiver thereof |
CN102307069A (en) * | 2011-09-15 | 2012-01-04 | 中兴通讯股份有限公司 | System and method for compensating OFMD (orthogonal frequency division multiplexing) signal dispersion |
CN102664860A (en) * | 2012-05-22 | 2012-09-12 | 哈尔滨工业大学 | Method and device for modulating and demodulating single side band multi-carrier transmission signal |
CN103091935A (en) * | 2012-12-28 | 2013-05-08 | 南京航空航天大学 | Light single side band (SSB) modulation method and device |
CN104363047A (en) * | 2014-10-09 | 2015-02-18 | 中国科学院半导体研究所 | Light vector network analyzer system based on double-channel Mach-Zehnder modulator |
CN106487451A (en) * | 2016-11-11 | 2017-03-08 | 中国科学院半导体研究所 | Microwave photon phase changer and method |
WO2017070949A1 (en) * | 2015-10-30 | 2017-05-04 | 华为技术有限公司 | Signal processing device and method in optical communication systems |
CN110361107A (en) * | 2019-05-31 | 2019-10-22 | 上海波汇软件有限公司 | A kind of distributed temperature detection system and method based on iir digital filter |
JP2021057845A (en) * | 2019-10-01 | 2021-04-08 | Kddi株式会社 | Optical modulator and optical transmission device |
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US20050113045A1 (en) * | 2003-11-21 | 2005-05-26 | John Santhoff | Bridged ultra-wideband communication method and apparatus |
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2007
- 2007-10-03 WO PCT/AU2007/001465 patent/WO2008040053A1/en active Application Filing
- 2007-10-03 AU AU2007304876A patent/AU2007304876B2/en not_active Ceased
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US20020030877A1 (en) * | 2000-03-07 | 2002-03-14 | Winston Way | Method and apparatus for interleaved optical single sideband modulation |
US20060140643A1 (en) * | 2000-03-07 | 2006-06-29 | Opvista, Inc., A California Corporation | Method and apparatus for interleaved optical single sideband modulation |
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Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN101860507A (en) * | 2009-04-09 | 2010-10-13 | 财团法人工业技术研究院 | Receiving method of optical orthogonal frequency-division multitask signal and receiver thereof |
CN102307069A (en) * | 2011-09-15 | 2012-01-04 | 中兴通讯股份有限公司 | System and method for compensating OFMD (orthogonal frequency division multiplexing) signal dispersion |
CN102307069B (en) * | 2011-09-15 | 2016-09-28 | 中兴通讯股份有限公司 | A kind of system and method for ofdm signal dispersion compensation |
CN102664860A (en) * | 2012-05-22 | 2012-09-12 | 哈尔滨工业大学 | Method and device for modulating and demodulating single side band multi-carrier transmission signal |
CN103091935A (en) * | 2012-12-28 | 2013-05-08 | 南京航空航天大学 | Light single side band (SSB) modulation method and device |
CN103091935B (en) * | 2012-12-28 | 2015-01-14 | 南京航空航天大学 | Light single side band (SSB) modulation method and device |
CN104363047A (en) * | 2014-10-09 | 2015-02-18 | 中国科学院半导体研究所 | Light vector network analyzer system based on double-channel Mach-Zehnder modulator |
WO2017070949A1 (en) * | 2015-10-30 | 2017-05-04 | 华为技术有限公司 | Signal processing device and method in optical communication systems |
CN106487451A (en) * | 2016-11-11 | 2017-03-08 | 中国科学院半导体研究所 | Microwave photon phase changer and method |
CN110361107A (en) * | 2019-05-31 | 2019-10-22 | 上海波汇软件有限公司 | A kind of distributed temperature detection system and method based on iir digital filter |
JP2021057845A (en) * | 2019-10-01 | 2021-04-08 | Kddi株式会社 | Optical modulator and optical transmission device |
JP7164504B2 (en) | 2019-10-01 | 2022-11-01 | Kddi株式会社 | Optical modulator and optical transmitter |
Also Published As
Publication number | Publication date |
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AU2007304876B2 (en) | 2012-05-24 |
AU2007304876A1 (en) | 2008-04-10 |
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