Ying Qiu

Seamless Sub-Band Wavelength Conversion of Tb/s-Class CO-OFDM Superchannels

We experimentally demonstrate a sub-band wavelength conversion scheme based on four-wave mixing in high-nonlinear fiber for multiple Tb/s-class superchannel coherent optical orthogonal frequency-division multiplexing networks. Combined with the wavelength selective switches in reconfigurable optical add/drop multiplexers, the overlapped spectra are efficiently relocated and almost seamlessly formed into a new superchannel with very little spectral efficiency degradation.

Ultra-High 230-bit/s/Hz Spectral Efficiency using OFDM/OQAM 64-QAM Signals over Pol-Muxed 22 Orbital Angular Momentum (OAM) Modes

We demonstrate the multiplexing/demultiplexing of pol-muxed 22 orbital angular momentum (OAM) modes. Using 17.9-Gbit/s OFDM/OQAM 64-QAM signals over pol-muxed 22 OAM modes (44 channels in total), we achieve an ultra-high spectral efficiency of 230 bit/s/Hz.

All-optical wavelength conversion for mode division multiplexed superchannels

We report in this work the first all-optical wavelength conversion (AOWC) of a mode division multiplexed (MDM) superchannel consisting of 2N modes by dividing the superchannel into N single-mode (SM) tributaries, wavelength converting N SM signals using well developed SM-AOWC techniques, and finally combining the N SM tributaries back to an MDM superchannel at the converted wavelength, inspired by the idea of using SM filtering techniques to filter multimode signals in astronomy. The conversions between multimode and SM are realized by 3D laser-writing photonic lanterns and SM-AOWCs are realized based on polarization insensitive four wave mixing (FWM) configuration in N semiconductor optical amplifiers (SOAs). As a proof of concept demonstration, the conversion of a 6-mode MDM superchannel with each mode modulated with orthogonal frequency division multiplexed (OFDM) quadrature phase-shift keying (QPSK)/16 quadrature amplitude modulation (QAM) signals is demonstrated in this work, indicating that the scheme is transparent to data format, polarization and compatible with multi-carrier signals. Data integrity of the converted superchannel has been verified by using coherent detection and digital signal processing (DSP). Bit error rates (BERs) below the forward error correction (FEC) hard limit (3.8 × 10-3) have been obtained for QPSK modulation at a net bitrate of 104.2 Gbit/s and BERs below the soft decision FEC threshold (1.98 × 10-2) have been achieved for 16-QAM format, giving a total aggregate bit rate of 185.8 Gbit/s when taking 20% coding overhead into account. Add and drop functionalities that usually come along with wavelength conversion in flexible network nodes have also been demonstrated. The working conditions of the SOAs, especially the pump and signal power levels, are critical for the quality of the converted signal and have been thoroughly discussed. The impact of imbalanced FWM conversion efficiency among different SM tributaries has also been analyzed. This work illustrates a promising way to perform all-optical signal processing for MDM superchannels.

Silicon micro-ring tunable laser for coherent optical communication

A compact external cavity tunable laser based on a silicon hybrid micro-ring resonator is demonstrated. A theoretical model is also employed for design and analysis of the wavelength tuning performance of the device. In this model, the gain section of the device is simulated by a conventional multimode rate equation model, whereas all rest passive sections are modeled by the frequency domain method. Experimental results have shown that the output power of this device can reach 29 mW, with a linewidth less than 150 kHz. The tuning range is more than 17 nm in C-band with 60 dB side-mode-suppression-ratio (SMSR). This device shows a comparable performance with the commercial narrow linewidth laser as the source in coherent transmission systems.

Mode-selective wavelength conversion of OFDM-QPSK signals in a multimode silicon waveguide

We experimentally demonstrate on-chip mode-selective wavelength conversions based on the degenerate four-wave mixing (FWM) nonlinear effect in a few-mode silicon waveguide. A multimode waveguide with tapered directional coupler based mode (de)multiplexers is designed and fabricated. Using signals with advanced modulation formats all-optical wavelength conversions of 102.6-Gb/s OFDM-QPSK signals are verified. Experimental results show that only small optical signal-to-noise ratio (OSNR) penalties are observed after wavelength conversion of both modes, which are less than 2 dB for OFDM-QPSK at 7% forward error correction (FEC) threshold.

Independent component analysis based channel equalization for 6 × 6 MIMO-OFDM transmission over few-mode fiber

We propose and experimentally demonstrate two independent component analysis (ICA) based channel equalizers (CEs) for 6 × 6 MIMO-OFDM transmission over few-mode fiber. Compared with the conventional channel equalizer based on training symbols (TSs-CE), the proposed two ICA-based channel equalizers (ICA-CE-I and ICA-CE-II) can achieve comparable performances, while requiring much less training symbols. Consequently, the overheads for channel equalization can be substantially reduced from 13.7% to 0.4% and 2.6%, respectively. Meanwhile, we also experimentally investigate the convergence speed of the proposed ICA-based CEs.

Experimental demonstration of few-mode fiber transmission with self-homodyne coherent detection

We experimentally demonstrate a self-homodyne transmission system over 10-km few-mode fiber by transmitting pilot tone and signal in different modes simultaneously. A data rate of 156 Gb/s for 16-QAM and 234 Gb/s for 64-QAM self-homodyne detection few-mode fiber transmission system is experimentally demonstrated by transmitting pilot tone and data signal at individual modes. No frequency offset and phase noise compensation is required in the digital signal processing at the receiver side when optical delay line is used at the transmitter side. The study of effects of inter-modal crosstalk indicate that LP01 and LP11 modes are preferred to transmit pilot tone and signal, respectively.

Dual-Channel AND Logic Gate Based on Four-Wave Mixing in a Multimode Silicon Waveguide

We experimentally demonstrate on-chip dual-channel all-optical AND logic operations based on four-wave mixing (FWM) for on-off keying (OOK) signals in a multimode silicon waveguide. A two-mode (de)multiplexing circuit consisting of tapered directional coupler-based (de)multiplexers and a multimode waveguide is designed and fabricated for this application. Experimental results show open eye-diagrams and confirm the logic operations with moderate power penalties for both modes.

Ultra-long Distance Distributed Optical Fiber Vibration Sensing System

Based on bi-directional amplification in the fiber sensing link, an ultra-long distance distributed optical fiber vibration sensing system is proposed and experimentally demonstrated.

SSBI-Free 100Gb/s Direct Detection Based on Fused-Type Mode-Selective Fiber Coupler

We propose and demonstrate a novel approach to achieve 100-Gb/s direct detection in two-mode fiber transmission based on fused-type mode-selective fiber coupler. The signal-to-signal beating noise can be eliminated based on the proposed scheme without requirement of guard band.