Single DPLL Joint Carrier Phase Compensation for Few-Mode Fiber Transmission

Abstract

A carrier phase estimation and compensation algorithm using a digital phase locked loop is proposed which exploits the common-mode impairment from the shared local oscillator at the receiver side in a few-mode fiber transmission system. We verify that the proposed algorithm is more tolerant to phasemismatches than earlier work. The carrier phase estimation (CPE) scheme is evaluated for a 3 × 112 Gbit/s dual polarization quadrature phase shift keying mode division multiplexed transmission over 80 km including an in-line multimode erbium doped fiber amplifier. The digital signal processing computational complexity is reduced in comparison to a traditional CPE stage. In addition, the proposed scheme is shown to perform similarly with respect to the 3.8 × 10 −3 forward error correcting limit optical signal to noise ratio tolerance of the traditional CPE scheme.

Advanced coding techniques for few mode transmission systems

“…Space-time coding was applied to improve the FMF transmission quality indicating better performance than single mode fiber at back-to-back. An OSNR gain of 3.2, 4.1, 4.9, and 6.8 dB at the hard-decision forward error correcting limit with respect to single mode fiber back-to-back performance is shown for QPSK, 8,16, and 32 QAM, respectively. In addition, the transmission of 4D symbols over few-mode fiber (of 41.7 km) has been further detailed in this paper.…”

“…The weight matrix of the FDE is heuristically updated using the least mean squares (LMS) algorithm during convergence and decisiondirected least mean squares (DD-LMS) during data transmission. To compensate the frequency offset between the transmitter laser and LO, one carrier phase estimation (CPE) block per polarization output channel in the form of a digital phase locked loop is used [16]. After this stage, the constellations are demapped, and the bit error rate (BER) is measured.…”

“…Note that the performance with respect to theory for 32-SP-QAM is not as good as the performance of 128-SP-QAM. This issue may be caused by the carrier recovery algorithm, which requires more constellation points to perform optimally [16,24]. The difference in performance is also the case in single mode fiber transmission, as shown in [24].…”

“…In tandem with technological improvements in mode multiplexers (fiber-based and integrated [10,11]) and recent research in fibers for SDM [7,12], there are ongoing developments in digital-to-analogue converters (DACs) in the transmitter [13], and coherent reception techniques at the receiver [14], where the development of digital signal processing (DSP) algorithms is key [15,16]. Further developments in transmitter DSP presents the opportunity to investigate novel coding at the symbol level to generate advanced modulation formats.…”

“…The OSNR tolerance gain is achieved through exploiting the spatial diversity few-mode-fibers offer. With respect to a conventional single-mode back-to-back transmission, an OSNR gain of upto 3.2, 4.1, 4.9, and 6.8 dB at the hard-decision forward error correcting (HD-FEC) limit is shown for DP-QPSK, 8,16, and 32 DP-QAM, respectively. Further in this work, the progress made in FMF transmission systems is combined with the progress in 4D digital modulation formats.…”