Chunning Hou

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 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.

10Gbit/s MSK modulation for radio-over-fiber system

In this paper, We propose a single sideband RoF system based on MSK modulation. One sideband of terahertz wave undergoes the single sideband MSK modulation while the terahertz wave is obtained via carrier-suppression double sideband modulation. The BER performance achieves 1×10−9 and the sensitivity of the receiver is −17.8dBm with a data rate of 5Gb/s after 40km transmission.

FSK/ASK re-modulation WDM-PON with image rejection receiver

We propose FSK/ASK re-modulation WDM-PON with coherent receiver. Apparent BER improvement is obtained by utilizing FSK image rejection receiver, especially for long distance transmission. Parameters in image rejection receiver which affect the system performance are analyzed. Results show that the presented scheme is promising in super long reach access network.

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.

The improvement of transmission properties for multi-mode fiber based on launching optical field shaping and feedback equalization

Recently, as the continual development of services and needs, people have a higher expectation on the optical communication system especially the passive optical network (PON). Deciding which kind of fiber to be the optimal media for PON is becoming a critical problem. This paper analyzed the feasibility for the applying of multimode fiber (MMF) in the future long haul, high bit-rate, and large capacity PON, and summarized the strengths and weakness of MMF. Then, initiating from the waveguide theory in the weakly guiding fiber and neglecting the intra-modal dispersion as well as nonlinearity, we built a simple model for multimode fiber, based on which we made analysis, research and comparison through simulation experiments on some performance improving techniques of MMF: offset launching, mode size changing, ring launching and feedback equalization. The simulation results demonstrated that the combination of field shaping and feedback equalization can obviously improve the transmission properties of MMF, because of which, the 10Gbit/s data can travel in the MMF for more than 1km.

Sideband characteristic analysis of millimeter wave generation based on Optical Carrier Suppression

Abstract In this paper, we analyze the sideband performance of millimeter-wave (mm-wave) generated by the optical carrier suppression (OCS) method. Through adjusting the direct current (DC) bias of the Mach-Zehnder modulator (MZM), we study the output optical signal powers at different orders bands, and the DC bias tolerance while the value of the carrier suppression ratio is not lower than 10 dB. The separated right sideband is modulated by 5 Gbit/s data, and then combined with the left sideband. The generated millimeter wave optical signal is transmitted over 20 km standard single mode fiber (SMF), and the received power penalty is only 0.28 dB.

Modulation format transformation from return-to-zero ASK To frequency shift keying at 40 Gb/s base rate based on nonlinear polarization rotation

We propose and experimentally validate a novel approach of high-speed format transformation from RZ-ASK to FSK at 40Gb/s and 100km SMF transmission link for the transferred signal utilizing cross polarization modulation in an SOA.