Analysis of underwater wireless optical communication system performance.

Because the underwater channel environment is complicated, it is difficult to do an actual experiment in the ocean to analyze the performance of underwater wireless optical communication (UWOC) systems. In this study, the spot-expansion characteristics and time-domain broadening characteristics of underwater wireless optical signals are simulated and analyzed by a Monte Carlo statistical method. Thus, what we believe is an improved underwater channel transmission-attenuation model and time-domain broadening model based on UWOC are proposed, so the transmission distance characteristics of the UWOC system are obtained by combining the system parameters, and the transmission-rate characteristics can be analyzed by using the Shannon-Hartley theorem. The results show that the transmission distance is linear with the receiver sensitivity, and the transmission rate decays exponentially with the transmission distance and is limited by the receiver sensitivity in the UWOC system.

The effects of five-order nonlinear on the dynamics of dark solitons in optical fiber.

We study the influence of five-order nonlinear on the dynamic of dark soliton. Starting from the cubic-quintic nonlinear Schrodinger equation with the quadratic phase chirp term, by using a similarity transformation technique, we give the exact solution of dark soliton and calculate the precise expressions of dark soliton's width, amplitude, wave central position, and wave velocity which can describe the dynamic behavior of soliton's evolution. From two different kinds of quadratic phase chirps, we mainly analyze the effect on dark soliton's dynamics which different fiver-order nonlinear term generates. The results show the following two points with quintic nonlinearities coefficient increasing: (1) if the coefficients of the quadratic phase chirp term relate to the propagation distance, the solitary wave displays a periodic change and the soliton's width increases, while its amplitude and wave velocity reduce. (2) If the coefficients of the quadratic phase chirp term do not depend on propagation distance, the wave function only emerges in a fixed area. The soliton's width increases, while its amplitude and the wave velocity reduce.

Reduction of fast carrier-envelope phase jitter in femtosecond laser amplifiers.

The phase noise of the f-to-2f interferometer used for stabilizing the carrier-envelope phase of a femtosecond laser oscillator was studied by adding a He-Ne laser beam co-propagating with the short pulse laser beam. The noise was reduced to ~60 mrad by stabilizing the optical path length difference of the interferometer. This suppressed the fast jitter of the carrier-envelope phase of the amplified laser pulses from 79 to 48 mrad.

Time-resolved investigation of low-density plasma channels produced by a kilohertz femtosecond laser in air.

By employing pump-probe back longitudinal diffractometry, the electron density and decay dynamics of a weak plasma channel created by a 1-KHz fs laser in air has been investigated. With ultrashort laser pulses of 50 fs and low energy of 0.6 mJ, we observe weak plasma channels with a length approximately 2 cm in air. An analytical reconstruction method of electron density has been analyzed, which is sensitive to the phase shift and channel size. The electron density in the weak plasma channel is extracted to be about 4 x 10(16) cm(-3). The diameters of the plasma channel and the filament are about 50 and 150 microm, respectively, and the measurable electron density can be extended to less than 10(15) cm(-3). Moreover, a different time-frequency technique called linearly chirped longitudinal diffractometry is proposed to time-resolved investigate ultrafast ionization dynamics of laser-irradiated gas, laser interaction with cluster beam, etc.