Jiayuan He

Block-wise phase switching for double-sideband direct detected optical OFDM signals.

We propose phase switching for either main-carrier or subcarriers of two consecutive signal blocks to achieve fading-free double-sideband direct-detection (DD). In our demonstration, 40-Gb/s DD-OOFDM is successfully received over 80-km SSMF with single polarization and single detector.

Signal-carrier interleaved optical OFDM for direct detection optical communication

We propose signal-carrier interleaved (SCI) optical OFDM for direct detected transmission systems. Such a scheme can be considered as a variation of self-coherent detection where the carrier and signal are supplied at the transmitter and extracted at the receiver for coherent-like detection. This provides high OSNR sensitivity while maintaining very low carrier-to-signal power ratio (CSR). Our experiment results show that with 0 dB CSR, 43.2 Gb/s 16 QAM OFDM signal can be successfully delivered over 80 km standard single mode fiber (SSMF) with 24 dB OSNR requirements at 7% FEC limit.

Characterization of dynamic evolution of channel matrix in two-mode fibers

We employ coherent detection and digital signal processing to characterize dynamic evolution of channel matrix in two-mode fibers. Experimental results reveal that the evolution frequency of channel matrix can reach as fast as 4 kHz.

Characterization and Analysis of Few-Mode Fiber Channel Dynamics

We employ coherent detection and digital signal processing (DSP) to characterize the dynamic evolution of channel matrix in two-mode fibers (TMFs). We develop novel DSP algorithms to compute channel evolution frequency. We measure a few different fiber spools in the lab and find that the evolution frequency of TMF channel matrix can reach as fast as 25 kHz, and the channel of TMF evolves faster than that of single mode fiber.

Equalization of two-mode fiber based MIMO signals with larger receiver sets.

We demonstrate channel equalization of two-mode fiber based MIMO system using more receivers than transmitters. Specifically, the equalization performances are compared among three methods including zero-forcing (ZF), minimum-mean-square-error (MMSE), and successive-interference-cancellation (SIC).

Hybrid Modulated Multiband Coherent Optical OFDM for Low-Complexity Phase Noise Compensation

In this paper, we propose and demonstrate effective laser phase noise compensation for coherent optical orthogonal frequency-division multiplexing (OFDM) systems that have long OFDM symbols. The phase noise compensation is achieved via hybrid modulated multiband optical OFDM, aided by the digital filter bank technique. For this, one of the multiple subbands is modulated as discrete Fourier transform spread OFDM. Our experimental results show that laser phase noise up to 1 MHz can be compensated for 114.8-Gb/s 16-QAM signals with 480-km standard single mode fiber transmission.

Fiber Nonlinearity Impact on Direct-Detection Block-Wise Phase Switched Systems

We carry out comprehensive analysis on the fiber nonlinearity impact on the block-wise phase switching (BPS) direct detection (DD) systems. We find that the degenerate four-wave mixing components produced by the interaction between the main carrier and the subcarriers are intrinsically compensated through the direct detection process. For a 100-Gb/s BPS-DD system over 80-km standard single-mode-fiber link, the optimum launch power is found to be 5 dBm, and the optimum carrier-to-signal power ratio is 12 dB. For a single-channel BPS-DD system, the fiber nonlinearity impairment is reduced when low-dispersion fiber is used. However, for a multi-channel BPS-DD system, the nonlinearity noise induced by the crosstalk among the channels is enhanced when the chromatic dispersion of the fiber link decreases.

Demonstration of Direct Detected Optical OFDM Signals via Block-Wise Phase Switching

In this paper, we propose and demonstrate phase switching for either main carrier or subcarriers of two consecutive signal blocks to achieve fading-free double-sideband direct-detection. The proposed approach has twice of the electrical spectral efficiency (SE) of offset OFDM, and the same electrical SE as single-side band OFDM. We perform numerical simulation and verify the system robustness against polarization mode dispersion and laser phase noise. Our experimental results show that 40-Gb/s direct-detection OOFDM can be successfully delivered over 80-km SSMF with single polarization and single detector.

Training Symbol Assisted Signal-to-Signal Beat Noise Cancellation for Direct Detected Optical OFDM Systems

We propose an algorithm for signal-to-signal-beat-noise (SSBN) cancellation in direct detection optical OFDM systems. Experimental results show that by using our proposed algorithm, the OSNR sensitivity can be improved by more than 8 dB.