Phase Noise Influence in Coherent Optical DnPSK Systems with DSP based Dispersion Compensation

Abstract

Abstract:We present a comparative study of the influence of dispersion induced phase noise for n-level PSK systems. From the analysis, we conclude that the phase noise influence for classical homodyne/heterodyne PSK systems is entirely determined by the modulation complexity (expressed in terms of constellation diagram) and the analogue demodulation format. On the other hand, the use of digital signal processing (DSP) in homodyne/intradyne systems renders a fiber length dependence originating from the generation of equalization enhanced phase noise. For future high capacity systems, high constellations must be used in order to lower the symbol rate to practically manageable speeds, and this fact puts severe requirements to the signal and local oscillator (LO) linewidths. Our results for the bit-error-rate (BER) floor caused by the phase noise influence in the case of QPSK, 16PSK and 64PSK systems outline tolerance limitations for the LO performance: 5 MHz linewidth (at 3-dB level) for 100 Gb/s QPSK; 1 MHz for 400 Gb/s QPSK; 0.1 MHz for 400 Gb/s 16PSK and 1Tb/s 64PSK systems. This defines design constrains for the phase noise impact in distributed-feed-back (DFB) or distributed-Bragg-reflector (DBR) semiconductor lasers, that would allow moving the system capacity from 100 Gb/s system capacity to 400 Gb/s in 3 years (1 Tb/s in 5 years). It is imperative at the same time to increase the analogue to digital conversion (ADC) speed such that the single quadrature symbol rate goes from today's 25 GS/s to 100 Gs/s (using two samples per symbol).

Carrier phase estimation in dispersion-unmanaged optical transmission systems

“…The estimated carrier phase in VV method for the n-level PSK optical networks is described using the equation in Ref [35,38] (13) where N VV is the block size of VV CPE algorithm.…”

“…Long-haul high-capacity optical fibre networks can be seriously deteriorated by physical impairments in the transmission systems, e.g. chromatic dispersion (CD), polarization mode dispersion, laser phase noise (PN) and fibre nonlinearities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Since the compensation and mitigation of these system impairments can be implemented in electrical domain, the combination of coherent optical detection, advanced modulation formats and digital signal processing (DSP) has become one of the most popular and promising solution for new-generation long-haul and metro optical communication networks to perform close to the limit of Shannon capacity, based on the knowledge of signal amplitude and phase [21][22][23][24][25][26][27][28][29].…”

Analysis of chromatic dispersion compensation and carrier phase recovery in long-haul optical transmission system influenced by equalization enhanced phase noise

“…Meanwhile, some experimental studies regarding EEPN have also been carried out in the QPSK transmission systems [30,31]. In addition, some approaches have also been investigated to mitigate the EEPN, by using the traditional CPR algorithms [32,33], the differential phase estimation [34], the pre-compensation of chromatic dispersion [35], the digital coherence enhancement [27], the optical reference carrier [36,37], and the partially modulated optical carrier [38,39]. Among these methods, the digital coherence enhancement can offer an effective compensation of EEPN [27], while it requires a complicated hardware implementation to measure the LO laser phase fluctuation.…”

“…Among these methods, the digital coherence enhancement can offer an effective compensation of EEPN [27], while it requires a complicated hardware implementation to measure the LO laser phase fluctuation. The impact of EEPN scales with the increment of fiber length, laser linewidth, symbol rate and modulation format, and significantly degrades the performance of the long-haul high speed coherent optical communication systems [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The conventional analysis of CD compensation and carrier phase recovery, which only takes into account the intrinsic Tx and LO lasers phase noise, is not suitable any longer for the long-haul coherent transmission system with a considerable EEPN.…”

Digital Adaptive Carrier Phase Estimation in Multi-level Phase Shift Keying Coherent Optical Communication Systems

“…With the full capture of the amplitude and the phase of optical signals, coherent optical detection and digital signal processing (DSP) allow the powerful equalization and mitigation of the communication system impairments in the electrical domain, and thus have become one of the most promising techniques for the next-generation optical fiber transmission networks . Recently, some feed-forward and feed-back carrier phase estimation (CPE) algorithms have been proposed to compensate the phase noise from the laser sources [22][23][24][25][26][27][28][29][30][31][32][33][34]. Among these reported carrier phase estimation methods, the one-tap normalized least-mean-square (LMS) algorithm has been validated for compensating the laser phase noise effectively in the high speed coherent optical transmission systems [24][25][26].…”