Deming Kong

All-Optical xor Gates for QPSK Signals Based on Four-Wave Mixing in a Semiconductor Optical Amplifier

With the development of transmission systems, all-optical networks need to adapt and process signals utilizing advanced modulation formats. One key element of all-optical networks is all-optical logic gates. Yet few research works on all-optical logic gates are focused on processing such signals. In this letter, all-optical XOR gates for optical quadrature phase-shift keying signals are proposed and demonstrated based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). Error-free performance is achieved through a 40-GBaud proof-of-concept experiment with an average power penalty of 6 dB. Cross-phase modulation (XPM) effect is found to be the key limiting factor. Given the integration ability of SOA and the format transparency of FWM process, our scheme has potential for future all-optical networks. Yet the XPM effect still needs to be mitigated to achieve better performance in future works.

All-Optical Logic Gate for XOR Operation Between 40-Gbaud QPSK Tributaries in an Ultra-Short Silicon Nanowire

We demonstrate an all-optical XOR logic gate for 40-Gbaud quadrature phase-shift keying (QPSK) tributaries in a silicon nanowire for the first time. The XOR logic operation is realized based on four-wave mixing (FWM) in the C-band. Experimental results show negligible power penalty at a bit error ratio (BER) of 10-6 compared with the back-to-back signals. The BER floor appears at BER of 10-6 for both I and Q tributaries of the logic operation, and the main reasons are the optical signal-to-noise ratio (OSNR) deterioration caused by nonlinear loss due to free carrier absorption (FCA) and two-photon absorption (TPA) and the cross-phase modulation (XPM)-induced phase impairments.

APSK Modulated CO-OFDM System With Increased Tolerance Toward Fiber Nonlinearity

An amplitude and phase-shift keying (APSK) modulated coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system is proposed, with increased tolerance toward fiber nonlinearity. Numerical simulation results, based on 30.2-Gb/s single-channel and 5×30.2-Gb/s wavelength-division-multiplexing (WDM) single-polarization CO-OFDM systems, show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, the 16 APSK modulated optical OFDM signal has a higher tolerance toward fiber nonlinearity, such as self-phase modulation and cross-phase modulation. The optimal launch power and the corresponding Q2 factor are, respectively, 2 and 0.5 dB higher than 16 QAM modulated optical OFDM signal after 640-km transmission, both in single-channel and WDM CO-OFDM systems.

320 Gb/s Nyquist OTDM received by polarization-insensitive time-domain OFT

We have demonstrated the generation of a 320 Gb/s Nyquist-OTDM signal by rectangular filtering on an RZ-OTDM signal with the filter bandwidth (320 GHz) equal to the baud rate (320 Gbaud) and the reception of such a Nyquist-OTDM signal using polarization-insensitive time-domain optical Fourier transformation (TD-OFT) followed by passive filtering. After the time-to-frequency mapping in the TD-OFT, the Nyquist-OTDM signal with its characteristic sinc-shaped time-domain trace is converted into an orthogonal frequency division multiplexing (OFDM) signal with sinc-shaped spectra for each subcarrier. The subcarrier frequency spacing of the converted OFDM signal is designed to be larger than the transform-limited case, here 10 times greater than the symbol rate of each subcarrier. Therefore, only passive filtering is needed to extract the subcarriers of the converted OFDM signal. In addition, a polarization diversity scheme is used in the four-wave mixing (FWM) based TD-OFT, and less than 0.5 dB polarization sensitivity is demonstrated in the OTDM receiver.

All-optical OFDM demultiplexing by spectral magnification and band-pass filtering

We propose a simple OFDM receiver allowing for the use of standard WDM receivers to receive spectrally advanced OFDM signals. We propose to spectrally magnify the optical-OFDM super-channels using a spectral telescope consisting of two time-lenses, which enables reduced inter-carrier-interference in subcarrier detection by simple band-pass filtering. A demonstration on an emulated 100 Gbit/s DPSK optical-OFDM channel shows improved sensitivities after 4-times spectral magnification.

Real-Time All-Optical OFDM Transmission System Based on Time-Domain Optical Fourier Transformation

We propose a novel simple all-optical OFDM transmission system based on time-domain OFT using time-lenses. A real-time 160 Gbit/s DPSK OFDM transmission with 16 decorrelated data subcarriers is successfully demonstrated over 100 km.

Ultrafast all-optical clock recovery based on phase-only linear optical filtering

We report on a novel technique for all-optical clock recovery from RZ OOK data based on phase-only filtering, significantly enhancing the recovered clock quality and energy-efficiency compared to the use of a Fabry-Perot filter.

Multi-wavelength in-band OSNR monitor based on Lyot-Sagnac interferometer

An in-band OSNR monitor based on Lyot-Sagnac interferometer is experimentally demonstrated for 4×40GBaud NRZ-QPSK WDM signal without requirement for prior knowledge of the noise-free coherence properties of the signal. OSNR from 7.5~25dB was realized.

Low overhead slipless carrier phase estimation scheme.

Two slipless schemes are compared with application to single carrier 30 Gbaud quadrature phase shift keying (QPSK) system. An equivalent linewidth model considering the phase noise induced by both the laser linewidth and fiber nonlinearity is applied in the performance analysis. The simulation results show that it is possible to mitigate cycle slip (CS) using only 0.39% pilot overhead for the proposed blind carrier phase recovery (CPR) + pilot-symbols-aided phase unwrapping (PAPU) scheme within 1 dB signal-to-noise ratio (SNR) penalty limit at the bit error ratio (BER) of 10(-3) with 4 MHz equivalent linewidth.

Multicarrier Group Detection in Receiver-Side Duobinary-Shaped WDM Superchannel Systems

Spectrally efficient multicarrier superchannel is a promising technique to address the great challenges for optical transmission systems beyond 100 G. Based on the previously reported receiver-side duobinary-shaped wavelength-division multiplexing (RS-DBS-WDM) scheme, we propose to apply the multicarrier group detection method for the RS-DBS-WDM superchannels to further improve the sampling efficiencies. The tolerance of the RS-DBS-WDM systems with three-carrier group detection to the transceiver bandwidth constraint is investigated by simulations. Proof-of-concept experiments were carried out to demonstrate the feasibility of three-carrier group detection.