Performance comparison of singly-polarized and polarisation-multiplexed coherent transmission at 10 Gbauds under linear impairments

Which is the most power-efficient modulation format in optical links?

“…It is possible to directly implement C 2 in a conventional (see e.g. [2]) optical transmitter for DP-QPSK, although it would require three modulation levels (−2, 0, 2). However, we will consider also a few other representations of the C 2 format, that might give rise to simpler transmitter structures.…”

“…The recent interest in coherent optical transmission technologies has resulted in a remarkable progress, such as demonstration of transmission at 10 Gbaud with 4 bits/symbol using offline [1,2] and online [3] post-processing of the data. The modulation format used in [1][2][3] is referred to as dual-polarization quaternary phase-shift keying (DP-QPSK), which is a 16level format that can be seen as independent binary phase-shift keying (BPSK) modulation in the four quadratures of the optical field.…”

Multidimensional Optimized Optical Modulation Formats

“…These clusters, which are also included in figure 2.2, are unpublished and not as well optimized as those on [28]. 2 With "exact known values" we mean, like for most other sphere packing problems, that they are found from extensive numerical optimization. No formal proofs of optimality are known.…”

“…The development of advanced digital signal processing (DSP) to enable intradyne coherent optical receivers [1][2][3] caused a paradigm shift within optical communications, and there is little doubt that the future of optical transport will be coherent. Coherent receivers ideally map the optical signal to the electrical domain, which enables a lot of novel advanced communication algorithms to be implemented in optical links, e.g., digital equalization and advanced modulation.…”

“…As optical transmission systems had traditionally used rudimentary modulation (typically on-off-keying (OOK) or differential phase-shift-keying (DPSK), [9]), the coherent receivers meant great opportunity to study novel modulation formats, tailored for the emerging coherent optical links. The first such format used was the polarization-multiplexed quadrature shift keying (PM-QPSK) [2,3], which in its simplest form is binary phase shift keying (BPSK) in all four quadratures in parallel. As coding and modulation are key building blocks in the design of any communication link, it is a natural first approach to separate them and study the performance of each block separately.…”