Wang Yuncai

Supercontinuum Generation with Output Power of 1.7 W Pumped by a Picosecond Laser Pulse

By using a photonic crystal fiber, a supercontinuum source with output power up to 1.7W, pumped by a passively mode-locked diode-pumped Nd:YVO4 picosecond laser is obtained. A spectral width of the supercontinuum is 1700 nm (500–2200 nm) with the 5 dB spectral width approximately 1000 nm (1200–2200 nm). This high power wide band supercontinuum source meets the demand of many applications such as optical coherence tomography, frequency metrology and wavelength-division-multiplexing systems. The evolution of the supercontinuum with the increasing pump power is presented and analyzed.

Improving performance of optical fibre chaotic communication by dispersion compensation techniques

This paper numerically investigates the effects of dispersion on optical fibre chaotic communication, and proposes a dispersion compensation scheme to improve the performance of optical fibre chaotic communication system. The obtained results show that the transmitter—receiver synchronization progressively degrades and the signal-to-noise ratio of the recovered message deteriorates as the fibre length increases due to the dispersion accumulation. Two segments of 2.5-km dispersion-compensating fibres are symmetrically placed at both ends of a segment of 245-km nonzero dispersion-shifted fibre with low dispersion in one compensation period. The numerical results show that the signal-to-noise ratio of the extracted 1 GHz sinusoidal message is improved from —2.92dB to 15.38 dB by this dispersion compensation for the transmission distance of 500 km.

Multiple-Pulse Operation in Passively Mode-Locked Fibre Laser with Positive Dispersion Cavity

We report the observation of rectangular shape spectrum in passively mode-locked fibre laser with positive dispersion cavity. The spectrum is broad and flat, and 3 dB bandwidth can be up to 17.61 nm. Multiple-pulse operation is observed in our laser system. The spectrum width, pulse energy, pulse width and peak power of the mode-locked laser output change with the appearance of multiple-pulse operation.

Extraction of periodic signals in chaotic secure communication using Duffing oscillators

This paper presents a novel approach to extract the periodic signals masked by a chaotic carrier. It verifies that the driven Duffing oscillator is immune to the chaotic carrier and sensitive to certain periodic signals. A preliminary detection scenario illustrates that the frequency and amplitude of the hidden sine wave signal can be extracted from the chaotic carrier by numerical simulation. The obtained results indicate that the hidden messages in chaotic secure communication can be eavesdropped utilizing Duffing oscillators.

Control of period-one oscillation for all-optical clock division and clock recovery by optical pulse injection driven semiconductor laser

The period-one oscillation produced by an external optical pulse injection driven semiconductor laser is applied to clock recovery and frequency division. By adjusting the repetition rate or injection power of the external injection optical pulses to lock the different harmonic frequencies of the period-one state, the clock recovery and the frequency division (the second and third frequency divisions) are achieved experimentally. In addition, in frequency locking ranges of 2 GHz and 1.9 GHz, the second and third frequency divisions are obtained with the phase noise lower than -100 dBc/Hz, respectively. Our experimental results are consistent well with the numerical simulations.

Period Doubling in a Fabry–Perot Laser Diode Subject to Optical Pulse Injection

Experimental study and numerical simulations of the period doubling of injected optical pulses in Fabry–Perot laser diodes are presented. In our experiments, the period doubling is achieved within a wide input frequency range and the period doubling of the injected optical pulses with 6.32 GHz repetition rate is investigated in detail. The obtained experimental results indicate that period doubling occurs at an appropriate injected optical power level when the bias current of the Fabry–Perot laser diode is located in lower ranges. Moreover, the experimental observed features have been numerically demonstrated by using a coupled rate-equation model. Numerical simulations are consistent with the experimental results.

Pulse-Width Jitter Measurement for Laser Diode Pulses

Theoretical analysis and experimental measurement of pulse-width jitter of diode laser pulses are presented. The expression of pulse power spectra with all amplitude jitter, timing jitter and pulse-width jitter is deduced. The power spectra with and without pulse-width jitter are numerically simulated. The simulation results indicate that the pulse-width jitter will contribute considerably noise to the pulse power spectrum while the product of pulse width and angular frequency is larger than 1. The experimental measurement of pulse-width jitter of a gain-switched Fabry–Perot laser diode with 2.4 GHz repetition rate is also reported. In comparison of the noise power spectra of the first, fourth and seventh harmonics of the pulse repetition rate, 2.3 ps pulse-width jitter is obtained.

Spread spectrum communication based on hardware encryption

The scheme of 1 Gbit/s random sequence generated by chaotic laser as spreading code is proposed. Theoretical analysis indicates that the pseudo random sequence exhibited periodic behavior is eliminated by the random sequence and the capability of spreading code is enlarged. Meanwhile, the communication security can be improved by variable spreading code. The corresponding spread spectrum system is numerically simulated by Simulink software and the results demonstrate that the greater the used spreading gain, the lower the obtained error rate will be when the information speed is constant, which is consistent with the theoretical results. The anti-jamming ability of the spread spectrum system is strengthened and the security is enhanced compared with those of the traditional spreading system.

Chaotic ultra-wideband microwave signal generation utilizing an optical injection chaotic laser diode

The ideal ultra-wideband (UWB) microwave pulses that fully comply with the indoor spectrum mask governed by Federal Communications Commission(FCC Indoor Mask)are generated by using continuous-wave optical injection to a chaotic laser diode. We firstly simulate and demonstrate the photonic generation of the chaotic UWB signal according to the rate equations of laser diode with optical feedback and injection. The simulations display that the -10 dB bandwidth of UWB signal increases with the increases of optical injection strength, frequency detuning, linewidth enhancement factor and with the decrease of bias current of the slave laser, and the UWB signal central frequency changes in a range from 5 to 8 GHz. We further experimentally obtain tunable chaotic UWB microwave signals with a rate up to 500 Mbit/s by tuning optical injection strength when the other parameters are fixed. The experimental results are in accordance with the theoretical analyses.

Experimental Investigation of Chaos Synchronization in DFB Diode Lasers with Unsymmetrical Scheme

We experimentally generate high dimension chaotic waveforms with smooth spectrum using a distributed feedback (DFB) semiconductor laser with unidirectional fibre ring long-cavity feedback, and implement the stable chaos synchronization when the chaotic light is injected into a solitary DFB laser diode. The synchronization quality is investigated by time-domain and frequency-domain analysis separately. The frequency-domain analysis indicates that the synchronization has higher quality in the high frequency band. The influences of the injection strength and the frequency detuning on the synchronization are measured. Our experimental results show that the robust synchronization can be maintained with the optical frequency detuning from -UGHz to 40 GHz.