Search

We propose a ditherless bias control algorithm, which uses relative detection and neural network to predict bias state. Experimental results show the precision is 1.5% and 0.3% of 2V π for bias IQ and P.

Chromatic dispersion appears to be a major performance limiting problem in optical intensity modulation direct detection (IM/DD) transmission systems, especially for a double-sideband (DSB) signal. We propose a complexity-reduced look-up-table based maximum likelihood sequence estimation (LUT-MLSE) for DSB C-band IM/DD transmission based on pre-decision-assisted trellis compression and a path-decision-assisted Viterbi algorithm. To further compress the size of the LUT and reduce the length of the training sequence, we proposed a finite impulse response (FIR) and LUT hybrid channel model for the LUT-MLSE. For PAM-6 and PAM-4, the proposed methods can compress the size of the LUT into 1/6 and 1/4, and reduce the number of multipliers by 98.1% and 86.6% with slight performance degradation. We successfully demonstrate a 20-km 100-Gb/s PAM-6 and a 30-km 80-Gb/s PAM-4 C-band transmission over dispersion-uncompensated links.

This paper experimentally demonstrates a real-time bidirectional communication system of 16-ary pulse position modulation over a free space optical transmission. This system can guarantee error-free transmission when the received optical power is higher than -38dBm.

Chromatic dispersion, which introduces pattern-dependent inter-symbol interference (ISI), appears to be a long-standing performance limiting problem in optical intensity modulation direct detection (IM/DD) transmission systems. In this paper, we propose a multiplier-free maximum likelihood sequence estimation (MLSE) equalizer for C-band double-sideband IM/DD transmission. It models the IM/DD channel with dispersion-induced ISI and Gaussian noise. A look-up table is applied to record ISI for transition probability calculation and the Viterbi algorithm for decision sequence acquisition. Specifically, to reduce the number of multipliers, a refined construction of Viterbi algorithm based on tentative path decisions is adopted, which compresses the complexity of branch metric calculation to less than 1/4 for PAM-4 format. Moreover, approximation calculation is employed to realize multiplier-free hardware implementation, which greatly reduces the hardware consumption. The proposed MLSE equalizer offers superior performance and lower complexity over conventional equalizers. In the experimental verification, we experimentally demonstrate a C-band 56-Gb/s double-sideband 4-level pulse amplitude modulation (PAM-4) IM/DD transmission over 40-km standard single mode fiber exploiting the proposed refined MLSE without any optical amplifier, filter or dispersion managed modules at the receiver end, achieving a bit-error-ratio of 2.65×10−4, which is 2.28 orders of magnitude lower than the scheme using Volterra nonlinear equalizer.

Baud rate clock recovery scheme that supports high order modulation formats is an essential part in digital signal processing for current short reach transmission. In this paper, we propose an improved multiplier-free Mueller-Müller timing error detector (MMTED) sampling at baud rate, which shows excellent performance with low complexity. Using the sign operation, the multiplier is eliminated. The further use of error signal to substitute the original data helps to reduce the jitter of the clock. 25 GBaud PAM-4/8 and 50 GBaud PAM-4 transmission are carried out to evaluate the TED performance. Compared to the sign MMTED, more than 12 dB timing jitter improvement is realized.

We apply a multi-layer perceptron as the timing error detector for PPM signal clock recovery. Simulation results show that the proposed MLP-based CDR method can improve the accuracy of phase detection with large sampling frequency offset over 1200 ppm. © 2020 The Author(s)

We propose a novel 100Gbps transceiver scheme for medium reach application. A simulation of 112-Gbps block-wise 16-QAM signal transmission is conducted over 240-km SSMF using a single-end PD with a great cost reduction.