Hequan Wu

Low-voltage, high speed, compact silicon modulator for BPSK modulation.

A low voltage, high speed, compact silicon Mach-Zehnder Interferometer (MZI) modulator for Binary Phase Shift Keying (BPSK) modulation has been demonstrated. High modulation efficiency, VπLπ equals to 0.45V·cm, was obtained in a 1mm length device owing to a higher doping concentration and low-loss traveling-wave electrode. 25 Gb/s non-return-to-zero(NRZ)-BPSK with 6Vpp RF driving signal was achieved. Driven by a very low 3Vpp RF signal, the 10 Gb/s NRZ-BPSK was also realized benefiting from the high modulation efficiency and the low-voltage driving scheme. The power consumption for the BPSK modulation was as low as 0.118 W. These results prove that the silicon modulator is suitable for advanced communication system with low power consumption.

Experimental demonstration of a single-carrier frequency division multiple address based PON (SCFDMA-PON) architecture

We introduce a novel architecture for next generation passive optical network base on the Single-carrier Frequency Division Multiple Address (SC-FDMA) technique. Both downstream and upstream SC-FDMA transmissions are experimentally demonstrated.

Demonstration of 6.25 Gbaud advanced modulation formats with subcarrier multiplexed technique on silicon Mach-Zehnder modulator

Silicon Mach-Zehnder modulators (Si MZMs) with good linearity are designed and fabricated. 6.25 Gbaud Nyquist 16, 32 and 64-Quadrature Amplitude Modulation (QAM) optical signals were successfully generated by intensity modulation from the Si MZM, and the effective data rates are 22.61 Gb/s, 28.26 Gb/s and 33.91 Gb/s respectively. The subcarrier multiplexed technique and direct detection scheme were employed in this experiment. After 53.1 km transmission, the BERs of 16-QAM and 32-QAM are both below the 7% hard-decision forward error correction limit, while the back-to-back BER of 64-QAM is well below the 20% soft-decision forward error correction limit. These results demonstrated that the Si MZM can be used in the high-capacity low-cost short-haul intensity modulation and direct detection system.

Bidirectional 60-GHz radio-over-fiber systems with downstream OFDMA and wavelength reuse upstream SC-FDMA

We have proposed and experimentally demonstrated a 60-GHz bidirectional radio-over-fiber system with downstream orthogonal frequency division multiplexing address (OFDMA) and wavelength reuse upstream single-carrier frequency division multiple address (SC-FDMA). In the downstream, a 3-dB optical coupler is used for two-carrier injection-locking a distributed feedback (DFB) laser in order to realize the single-sideband modulation. In the upstream, the weakly modulated one of the two downstream carriers is filtered out for wavelength reuse. Transmission of 9.65-Gb/s 16-QAM downstream OFDMA on 60-GHz carrier and 5-Gb/s QPSK upstream SC-FDMA (2.5 Gb/s for each user) are both successfully demonstrated over 53-km standard single mode fiber without chromatic dispersion compensation. The crosstalk between the downstream OFDMA and the upstream SC-FDMA can be neglected.

Collision-free bandwidth-variable optical burst switching ring network

Recently, flexible bandwidth allocation has been proposed in an orthogonal frequency division multiplexing based elastic optical network, which is a promising technology for 100G and beyond optical networks. In this paper, for the first time we introduce flexible bandwidth to an optical burst switching (OBS) ring network and propose a novel bandwidth-variable OBS (BV-OBS) ring network. In the proposed BV-OBS ring network, the durations of bursts are fixed to one timeslot in the time domain, while the bandwidths are variable in the frequency domain according to the burst size. With fixed burst duration and variable bandwidth, the BV-OBS ring can achieve the state of being collision free with high bandwidth efficiency. Simulation results show that a BV-OBS ring network outperforms previous OBS rings proposed in wavelength division multiplexing networks in both network throughput and end-to-end delay.

100Gbps, 160 km IM-DD transmission of WDM Nyquist-16QAM signal based on silicon Mach-Zehnder modulator

100-Gb/s WDM Nyquist-16QAM signals (10×10Gb/s with 15GHz channel spacing) are generated by intensity modulation on silicon MZM. After 160 km SSMF transmission and direct detection, the BERs of all the ten channels are below the FEC threshold of 3.8×10-3.

30-Gbit/s OFDM intensity modulation of 1550-nm VCSEL

We experimentally demonstrate 30-Gbit/s (24.7-Gbit/s net) OFDM intensity modulation of a low-cost 1550-nm VCSEL. The optical OFDM signals transmission over 7-km G.655 SMF is also realized successfully.

Mid-infrared Ge-on-Si electro-absorption modulator

We present the first waveguide electro-absorption modulator in germanium-on-silicon material platform at 3.8 μm wavelength, based on free-carrier injection into a straight waveguide. The fabricated 1 mm long device has modulation depth of >35 dB at 7 V.

Silicon Modulators for Advanced Optical Communications

Silicon Mach-Zehnder modulators were used in IM-DD advanced optical communications. 6.25 Gbaud Nyquist-16, 32 and 64-Quadrature Amplitude Modulation optical signals were generated. 160 km transmission of 100 Gb/s WDM Nyquist-16QAM signals were also demonstrated.

Bandwidth-variable optical burst switching for ring network

In this paper, we propose bandwidth-variable OBS (BV-OBS) for elastic optical ring network which supports flexible bandwidth allocation. In BV-OBS ring network, bursts of variable sizes are scheduled in the fixed time slot but with variable bandwidths in the frequency domain.