Dual Polarization Full-Field Signal Waveform Reconstruction Using Intensity Only Measurements for Coherent Communications

• Published in: Journal of lightwave technology Vol. 38; no. 9; pp. 2587 - 2597
• Main Authors: Chen, Haoshuo, Fontaine, Nicolas K., Gene, Joan M., Ryf, Roland, Neilson, David T., Raybon, Gregory
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Bit error rate; Coherence; Coherent communication; Computer simulation; Continuous radiation; Digital signal processing; Dispersion; Dual polarization (waves); Equalization; Measurement techniques; Noise levels; Optical communication; Optical noise; Optical receivers; Phase measurement; Phase retrieval; Phase shift keying; polarization division multiplexing; Polarization mode dispersion; Signal detection; Signal processing; Signal to noise ratio; Waveforms
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2020.2978052

Conventional optical coherent receivers capture the full electrical field, including amplitude and phase, of a signal waveform by measuring its interference against a stable continuous-wave local oscillator (LO). In optical coherent communications, powerful digital signal processing (DSP) techniques operating on the full electrical field can effectively undo transmission impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD). Simpler direct detection techniques do not have access to the full electrical field and therefore lack the ability to compensate for these impairments. We present a full-field measurement technique using only direct detection that does not require any beating with a strong carrier LO. Rather, phase retrieval algorithms based on alternating projections that makes use of dispersive elements are discussed, allowing to recover the optical phase from intensity-only measurements. In this demonstration, the phase retrieval algorithm is a modified Gerchberg-Saxton (GS) algorithm that achieves a simulated optical signal-to-noise ratio (OSNR) penalty of less than 4 dB compared to theory at a bit-error rate of 2<inline-formula><tex-math notation="LaTeX">\;\times 10^{-2}</tex-math></inline-formula>. Based on the proposed phase retrieval scheme, we experimentally demonstrate signal detection and subsequent standard 2 × 2 multiple-input-multiple-output (MIMO) equalization of a polarization-multiplexed 30-Gbaud QPSK transmitted over a 520-km standard single-mode fiber (SMF) span.