Shumin Zou

A Novel Return-to-Zero FSK Format for 40-Gb/s Transmission System Applications

In this paper, we present the generation, the detection and the performance evaluation of a novel return-to-zero frequency shift keying (RZ-FSK) format for 40 Gb/s transmission. Non-return-to-zero (NRZ) FSK signal is generated by using two continues-wave (CW) lasers, one Mach-Zehnder modulator (MZM) and one Mach-Zehnder delay interferometer (MZDI). A RZ-FSK signal is successfully generated by cascading a dual-arm MZM, which is driven by a sinusoidal voltage at half of the bit rate. The demodulation can be simply achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection. By numerical simulation, two types of frequency modulation schemes using MZM or PM, and impact of the frequency tone spacing (FTS) of the generated FSK signal are discussed. The proposed scheme shows that the novel frequency modulation format offers a few transmission advantages comparing with than that of the other traditional modulation formats, such as RZ and differential phase-shift keying (DPSK), under varying dispersion management. The performance analysis of RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is introduced. We experimentally demonstrate, transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal, clearly validating the feasibility of all optical signal processing of high-speed RZ-FSK signal. Moreover, we investigate the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF), under the post-compensation management scheme. Since the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying), it can be employed in the context of the combined modulation format to decrease the data rate or enhance the symbol rate. It can also be utilized in the orthogonal label-switching as the modulation format for the payload or the label.

A novel OFDM-CPM modulation scheme and its application in WDM-PON

A novel scheme to generate, transmit, and receive an optical orthogonal frequency division multiplexing (OFDM) continuous phase modulation (CPM) signal, which is combining minimum shift keying (MSK) coding with OFDM optical modulation, for downlink application in a 4×2.5-Gb/s wavelength division multiplexing (WDM) passive optical access network, is proposed and experimentally validated. We also realize wavelength remodulation for carrying upstream on-off keying (OOK) data to reduce the cost budget at the optical network unit. The experimental results show that the power penalties for the downlink and the uplink data after transmission over 25-km SMF-28 fiber are 0.1 dB and smaller than 0.4 dB, respectively.

A novel WDM-PON structure using the orthogonal FSK/ASK re-modulation scheme

A WDM PON(wavelength-division-multiplexed passive optical network) structure using 40Gb/s FSK signal for downstream transmission and 10Gb/s orthogonal FSK/ASK re-modulated signal for upstream transmission is demonstrated. Simulations show that the PON system can transmit for more than 20km, which is a promising candidate for future high-speed access network.

Study of IQ imbalance effect in direct-detection optical OFDM systems

In-phase/quadrature-phase (IQ) imbalance can result in severe performance degradation in optical direct-detection orthogonal-frequency-division-multiplexing (DD-OFDM) systems. We build two optical back-to-back DD-OFDM systems, which implement double-sideband (DSB) and single-sideband (SSB) modulation, respectively. The tolerance to IQ imbalance of these two systems is analyzed and compared using error vector magnitude (EVM) and symbol error rate (SER). We find that, in the back-to-back case, the DSB system has stronger robustness to IQ imbalance than the SSB System. We further build two optical DD-OFDM systems each with 40-km transmission, which respectively implement DSB and SSB transmission. Similarly, we analyze and compare the tolerance to IQ imbalance of these two systems in terms of EVM and SER. We find that, however, in the case of 40-km transmission, the SSB system has stronger robustness to IQ imbalance than the DSB system. As a result, we conclude that, in the case of transmission, SSB modulation can enhance the tolerance to IQ imbalance of DD-OFDM systems.

Investigation on the Generation of coherent optical multi-carriers using cascaded phase modulators

A simple and cost-effective technique to generate coherent optical multi-carriers by using cascaded phase modulators is proposed and investigated. A detailed theoretical analysis is presented. The phase and amplitude relation of RF signals on two concatenated phase modulators are investigated. Simulation results are in good agreement with the theoretical analysis, and the experimental performance of 22 subcarriers with amplitude difference of 5dB shows that this scheme is a promising technique for the coming Tb/s optical communication.

Frequency estimation for optical coherent MSK system

We propose algorithm to compensate frequency offset in optical coherent MSK system with little computation requirement. Simulations are performed to demonstrate the algorithm and its performance is excellent.

Slow-light optical buffers based on a ring resonator and an OFDM transmitter

We propose a novel scheme to realize large group delay in a single ring resonator with an OFDM transmitter. The fundamental trade-off between transmission bandwidth and delay can be addressed with this new buffer.

Optical homodyne receiver utilizing image rejection in FSK/ASK re-modulation WDM-PON

Optical frequency shift keying (FSK) homodyne detection utilizing image rejection in FSK/amplitude shift keying (ASK) re-modulation wavelength-division-multiplexed passive optical network (WDM-PON) is proposed and demonstrated. Image rejection is adopted to achieve better performance. We show the result in back-to-back and 40-km distance respectively and apparent improvement is obtained in the latter situation by using image rejection. Several factors which affect the image rejection receiver are analyzed in order to find out the optimum parameters. Result shows that the presented scheme is suitable for super long reach access network, especially for future metro access network.

A Novel OFDM-PON Architecture Using Single-Side-Band OFDM for Down Stream and Sub-carrier Multiplexed ASK for Up Stream

We propose and experimentally demonstrate a novel architecture for OFDM-PON system. The down link is based on single side band OFDM modulation while the up link makes use of the carrier information retained in another side band to intensity modulate the data. The downstream transmission will be demonstrated experimentally to exceed 10Gb/s using 4-QAM while the upstream transmission will exceed 2.5-Gb/s using ASK modulation and Time Division Multiple Access (TDMA). This architecture can perfectly overcome the Rayleigh scattering effect. It has been proved the transmission for both directions can reach 10km without bit error. And if the scattering effect is considered, the power penalty will be less than 0.8dB for downlink and 1.8dB for uplink.