Abstract
We review work on self-homodyne detection (SHD) for optical communication systems. SHD uses a transmitted pilot-tone (PT), originating from the transmitter laser, to exploit phase noise cancellation at a coherent receiver and to enable transmitter linewidth tolerance and potential energy savings. We give an overview of SHD performance, outlining the key contributors to the optical signal-to-noise ratio penalty compared to equivalent intradyne systems, and summarize the advantages, differences and similarities between schemes using polarization-division multiplexed PTs (PDM-SHD) and those using space-division multiplexed PTs (SDM-SHD). For PDM-SHD, we review the extensive work on the transmission of advanced modulation formats and techniques to minimize the trade-off with spectral efficiency, as well as recent work on digital SHD, where the SHD receiver is combined with an polarization-diversity ID front-end receiver to provide both polarization and modulation format alignment. We then focus on SDM-SHD systems, describing experimental results using multi-core fibers (MCFs) with up to 19 cores, including high capacity transmission with broad-linewidth lasers and experiments incorporating SDM-SHD in networking. Additionally, we discuss the requirement for polarization tracking of the PTs at the receiver and path length alignment and review some variants of SHD before outlining the future challenges of self-homodyne optical transmission and gaps in current knowledge.
Highlights
Self-homodyne detection (SHD) by using a transmitted pilot-tone (PT) as the local oscillator (LO)for coherent reception has long been proposed and investigated as a useful technique to minimize the impact of laser phase noise in optical communication systems [1,2,3]
The work summarized in this paper shows that self-homodyne detection has been well studied in optical transmission links for point-to-point communication in optical fiber systems with clear advantages and disadvantages
The spectral efficiency cost is more severe for a polarization multiplexed pilot-tone (PT), where it is typically 50%, reducing to 33% using spectral interleaving techniques
Summary
Self-homodyne detection (SHD) by using a transmitted pilot-tone (PT) as the local oscillator (LO). The laser phase noise cancellation property of SHD systems arises from having the signal and LO originating from the same laser and preserving their coherence throughout the optical transmission path This can relax requirements for narrow linewidth lasers [4,5,6,7], when using phase-noise-sensitive, spectrally efficient, high-order modulation formats [8,9,10] or orthogonal frequency division multiplexing (OFDM) [11]. Since it is only possible to modulate a single polarization with data signals, the SE of PDM-SHD systems can be reduced by up to 50% compared to PDM transmission using intradyne detection (ID), techniques, such as spectral interleaving of the PT and signal, may be used to improve the SE [14,15] For this reason, SHD has recently been applied to space-division multiplexing (SDM) systems and to multi-core fiber (MCF) technology [16,17,18].
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