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

Abstract

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 intensityonly measurements. In this demonstration, the phase retrieval algorithm is a modified GerchbergSaxton (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 2×10 −2 . 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.

Hybrid OFDM-Digital Filter Multiple Access PONs Utilizing Spectrally Overlapped Digital Orthogonal Filtering

“…Fig. 6 also shows that for the adopted numerical simulation parameters, for Hybrid Case-II (A) and Hybrid Case-II (B), their receiver sensitivities are -7.3dBm and -9.6dBm respectively, both of which can be further improved when use is made of some well-documented techniques such as wavelength-offset optical filtering [21] and DSP-enabled optical field reconstruction in the receiver [22].…”

Data-Aided Iterative Algorithms for Linearizing IM/DD Optical Transmission Systems

“…11. The DD-DIA is capable of reducing the SER below the 20% and 7% FEC limit within only 25 and 60 iterations, which saves more time and reduces the computational complexities compared to the "error escape" method in [13]. To explore the tolerance of DIA and DD-DIA to dispersion parameter mismatch between the real value and the estimated value, numerical simulations are conducted where the dispersion mismatch is represented by a fiber length mismatch in kilometer.…”

“…This local-optimum problem is more significant for large accumulated dispersion cases. To address such a problem, in a recently published paper [13], with the help of training symbols and a dispersion device, the G-S algorithm is used to reconstruct the complex optical signal iteratively. However, the algorithm requires an extra dispersive device and two PDs, leading to the increase in the receiver complexity.…”

“…However, the algorithm requires an extra dispersive device and two PDs, leading to the increase in the receiver complexity. In addition, to reduce the estimated errors, the algorithm reported in [13] also needs an "escape" operation that may require thousands of iterations.…”

Carrier-Assisted Phase Retrieval

“…Compared with the algorithm used in conventional PR schemes using pilot symbols [7][8][9][10][11][12], these 2 PR schemes eliminate the use of pilot symbols, leading to reduced redundancy. The NOI can be reduced to several times, and thus the computational complexity is also reduced.…”