Stable multiwavelength lasing is demonstrated with a novel laser, in which a semiconductor optical amplifier offers optical gain and cascaded sampled fiber gratings serve as a comb filter. Five lasing lines are obtained with a fixed wavelength spacing of 0.8 nm. Optical power fluctuations among the lasing lines are improved by adjusting reflectivity profile through the cascade of two sampled gratings.

Impacts of residual facet reflection on the performances of wavelength converters based on semiconductor optical amplifiers (SOAs) are theoretically investigated. Residual facet reflection definitely degrades the converter performance. A probe signal feedback scheme is introduced to improve the wavelength conversion characteristics. With the probe signal feedback, the wavelength conversion parameters, including extinction ratio, frequency chirping and modulation response, can be enhanced, and the facet reflection limits are relaxed due to the enhancement of carrier-photon interaction.

Noninverted wavelength conversion has been demonstrated using Fabry-Perot semiconductor optical amplifiers (FP-SOAs), and its mechanism is theoretically analyzed. The noninverted behavior is dominated by the shift of gain spectrum in the FP-SOA. Increasing the input optical power suppresses the spontaneous emission and drives the gain spectrum toward the longer wavelength side due to the enhancement of carrier-photon interaction. The performance of wavelength converters is improved owing to the resonant effect at the probe wavelength and this type of converter provides an effective approach for wavelength conversion in the future broadband networks.

Multiwavelength oscillation is demonstrated with a novel laser scheme, in which cascaded second-order nonlinearity in a periodically poled LiNbO3 (PPLN) waveguide is used to double the lasing lines. Twenty-two wavelengths approaching S- and L-bands are simultaneously achieved with a channel spacing of 1.6 nm, and the band separation is changeable. The number of wavelengths and channel spacing can be controlled by the adjustment of the tunable Fabry-Perot (FP) etalon and light polarization states in the laser cavity.

Simultaneous multiwavelength lasing is demonstrated exploiting intracavity polarization hole burning in an erbium-doped fiber laser. Experimental results indicate that polarization hole burning can be enhanced by the changes of the light polarization states and bias current of optical MQW waveguide which serves as reflector in the laser. Eleven wavelengths with 0.9 nm spacing are generated at room temperature.

Ten-channel wavelength conversion is achieved by exploiting cascaded second-order nonlinearity in periodically poled LiNbO3 waveguides. No external pump input is required in the converter and conversion efficiency is improved due to the enhancement of pump and signal interaction. Approximate 70-nm conversion bandwidth is realized under pump power less than 25mW at 1550-nm band.

Intraband crosstalk contributions in three types of WDM cross-connect topologies based on the Benes architectures are identified. The crosstalk behaviours of the WDM networks are compared and discussed. It is demonstrated that the first-order crosstalk contributions are dominated by the crosstalk from the switching elements. The network scalability is analysed in terms of fibres, wavelengths and nodes. The results show that routing different wavelengths in each switching architecture in WDM cross-connect networks is a reasonable approach to achieve perfect performance in the presence of component crosstalk.

A theoretical model of ultrashort pulse difference-frequency generation (DFG) is presented and developed with quasi-phase matching (QPM) gratings in the undepleted-pump, unamplified-signal approximation. An analytic solution to a case of ultrashort pulse pumped DFG process, including groupvelocity mismatching effects and input pulses with frequency chirp and time delay, is obtained. The influences of group-velocity mismatching effects and input signal pulse parameters on the conversion efficiency and output converted pulse characteristics are analyzed and discussed. The results indicate that the conversion efficiency is increased due to the enhancement of pump and signal interaction. The output pulse is inevitable compressed under pulsed pumping and can be compensated by introducing the initial frequency chirp and time delay.

Bandwidth and tunability enhancement of difference frequency generation (DFG)-based wavelength conversion by introducing various distributing formats of p-phase shifting domains into the quasi-phase-matching (QPM) gratings is demonstrated, and the concise expressions describing the tuning curves in these cases are obtained for the first time. The results show not only the pump and signal bandwidth can be obviously broadened and flattened, but also diverse comblike pump-wavelength tuning curves with controllable channel spacing can be achieved by introducing periodically distributed p-phase shifting domains into the QPM gratings, which would greatly improve the tunability and practibility of DFG-based wavelength converters.

With the consideration of cross-gain modulation (XGM) and probe-depletion (PD) effects, an analytical solution of four-wae mixing (FWM) between picosecond optical pulses in semiconductor optical amplifiers is developed based on our "splitting model" The results indicate that the effect of PD plays an important role in the FWM process for lower pump pulse energy and smaller pump-probe frequency detuning, while the effect of XGM dominates for the pump pulse with higher energy, a shorter pulsewidth, and a larger pump-probe frequency detuning.