Phase Suppression in Coherent Optical Communications – High Speed
Signal Processing
KTH Contact:
Acreo Contact:
Ben Slimane (Slimane@kth.se)
Gunnar Jacobsen (Gunnar.Jacobsen@acreo.se)
Background:
The explosive growth of data traffic has transformed the landscape of modern optical
telecommunication networks. In order to reach the total system capacity in the Tb/s
range, multi-level modulation such as MPSK, MQAM, and optical orthogonal
frequency division multiplexing (OOFDM) with MPSK or MQAM modulation on each
multiplexed optical frequency are needed. Coherent multilevel modulation schemes
are now becoming the next generation systems for high capacity (up to 10 Tb/s)
communication on a single transmission wavelength, and 100 Tb/s on a single
transmission fiber [1-5]. However, such modulation formats are quite sensitive where
even minor imperfections in the coherence performance of transmitter and receiver
(local oscillator) laser sources become a strong limiting factor.
New generation coherent systems are unique in the use of high speed digital signal
processing (DSP) in transmitters and/or receivers that can be utilized to mitigate the
influence of system impairments. The impairments can occur in both optical domain,
such as fiber chromatic and polarization dispersion, added spontaneous emission
noise from in-line optical amplifiers, fiber nonlinearities; and electric domain, like
imperfections in drive electronics and in external modulators (phase and amplitude),
phase noise in the transmitter and local oscillator including equalization enhanced
phase noise due to the use of DSP, etc.
In fact, coherent detection offers the advantage of access to optical electric field
amplitude and phase in the electronic domain at the receiver. This allows fast
recovery of linear channel transfer functions. Thus, DSP can be used to eliminate the
influence of chromatic and polarization mode dispersion in the optical fiber, to adjust
signal polarization imbalance at the receiver, to extract a reference carrier phase [3,
4], and to - at least in principle - eliminate the influence of fiber nonlinearities [5].
Problem Definition:
The aim of this thesis work is to investigate the phase noise influence for a number of
multi-level modulation methods and its impact on coherent optical communications.
The objective is to investigate if the laser phase noise influence can be directly
compensated by suitable DSP techniques which are adopted from the equivalent
radio frequency counterparts [6-7]. The student should understand how the phase
noise statistics are modified by the use of DSP in the radio world and which further
considerations are needed to transfer the radio principles into the optical
transmission world, where the systems operate at much higher frequencies.
References
1. J. Yu et al., ``Generation, Transmission and Coherent Detection of 11.2 Tb/s
(112x100Gb/s) Single Source Optical OFDM Super channel,’’ Proceedings
OFC2011, post deadline paper PDPA6
2. T. Richter et al., ``Single Wavelength Channel 10.2 Tb/s TDM Data Capacity
using 16QAM and coherent detection,’’ Proceedings OFC2011, post deadline
paper PDPA9
3. T. Xu, G. Jacobsen, S. Popov, J. Li, E. Vanin, K. Wang, A. T. Friberg and Y.
Zhang, ``Chromatic dispersion compensation in coherent transmission
system using digital filters,’’ Opt. Express 18, 16243-16257 (2010). [8]
4. M. G. Taylor, ``Phase estimation methods for optical coherent detection using
digital signal processing,’’ J. Lightwave Technol. 17, 901-914 (2009).
5. D. S. Ly-Gagnon, S. Tsukamoto, K. Katoh, and K. Kikuchi, ``Coherent
detection of optical quadrature phase-shift keying signals with carrier phase
estimation,’’ J. Lightwave Technol. 24, 12-21 (2006).
6. P. Pedrosa et al., ``Bayesian approach for the estimation of phase noise in scfde schemes,’’ IEEE Globecom 2011, pp. 1-5, 2012
7. K. Sathananthan, R.M.A.P. Rajatheva, and S. Ben Slimane, ``Cancellation
technique to reduce inter-carrier interference in OFDM,’’ IEE Electronics
Letters, Vol. 36, No. 25, pp. 2078-2079, December 2000.