Interpolators for digital coherent receivers

Abstract:
Interpolation filters are used in digital clock retiming as well as variable delay filters for aligning signals. In-phase and quadrature (IQ) misalignment in particular can result in serious performance degradation of coherent optical systems. The impact is more severe for higher order modulation formats and in narrow band systems. In this paper, we analyse the performance of several finite impulse response (FIR) interpolation filters for different quadrature amplitude modulation (QAM) formats. It was observed that for higher order modulation formats, long interpolation filters are needed, which in-turn will increase the overall system cost and complexity.