Effect Of Initial Chirp Research Articles

Effect of initial chirp for input pulse on supercontinuum generation

The generation of supercontinuum spectrum is a very complex nonlinear process. Based on the nonlinear Schrodinger equation (NLSE), the effect of initial chirp on supercontinuum generation is numerically studied by split-step Fourier (SSF) method. The positive chirp and negative chirp have different effects on the supercontinuum generation. The results show that the energy distribution of supercontinuum spectrum can be improved by selecting appropriate chirp value.

Effect of initial chirp on supercontinuum generation in dispersion decreasing fibers

Numerical simulations based on generalized nonlinear Schrödinger equation are used to study the effect of initial chirp on supercontinuum generation in dispersion decreasing fibers. The simulation results show that the effect of initial chirp on SC generation is highly related to the choices of pumping conditions and fiber parameters. When the pumping condition and the fiber parameters are different, the effect of initial chirp on SC generation may follow different patterns. To better discuss the effects of pulse parameters and fiber parameters on SC generation, the three normalized parameters: input soliton order, normalized dispersion slope and normalized effective fiber length are introduced. For a given input soliton order and a given normalized dispersion slope, there exists an optimal normalized effective fiber length for generating a flattest SC spectrum. On the condition of normalized effective fiber length in the vicinity of its optimal value, when DDF has small normalized dispersion slope, proper positive chirps can significantly enhance the SC bandwidth, while negative chirps or too large positive chirps suppresses the SC bandwidth. There is a wide range of positive chirps that can enhance the SC bandwidth, but the range of proper positive chirps become narrower as input soliton order decreases; When DDF has a large normalized dispersion slope and the pump pulse is a lower-order soliton, the enhancement of SC bandwidth by initial chirp is insignificant, and the widest SC spectrum is generated when the initial chirp is close to zero.

Effect of initial chirp on the broadband amplitude noise of supercontinuum generated in fiber normal dispersion region

Based on the generalized stochastic nonlinear Schrödinger equation, the effect of initial chirp on the broadband amplitude noise of supercontinuum generated in fiber normal dispersion regime is investigated numerically. The results show that, in the normal dispersion region, where the bandwidths of the obtained spectra are less sensitive to the initial chirp parameters of the input pulses, the nonlinear process is significantly affected by the initial chirp. An optimal input positive chirp will shorten the action time of intrapulse Raman scattering, and decrease the spectral broadband amplitude noise without bandwidth and flatness loss.

Effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier

Theoretical and experimental research on the effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier is carried out. The complex Ginzburg—Landau equation is used to simulate the propagation of the pulse in the fiber amplifier and the results show that pulses with negative initial chirp produce the widest supercontinuum and pulses with positive initial chirp produce the narrowest supercontinuum when the central wavelength of the pump lies in the normal dispersion region of the gain fiber. A self-made line width narrowing system is utilized to control the initial chirp of the nanosecond pump pulse and a four-stage master oscillator power amplifier configuration is adopted to produce a high power near-infrared suppercontinuum. The experimental results are in good agreement with simulations which can provide some guidance on further optimization of the system in future work.

Propagation of chirped laser pulses in a plasma channel

Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

Effect of initial chirp on supercontinuum generation by femtosecond pulse in photonic crystal fibers

The numerical simulations with the method of split-step Fourior were presented to investigate the effect of initial chirp on supercontinuum generation in photonic crystal fibers. According to the fiber length, the evolution of pulse in photonic crystal fibers was divided into three stages: initial broadening stage, dramatic broadening stage and saturation broadening stage. By discussing the differences in evolution of the chirp pulse and non-chirp pulse in each stage, we find that the initial chirp only affects the spectrum at the initial broadening stage and the dramatic broadening stage, and the chirp is profitable for spectrum broadening when β2C2C>0. In the saturation broadening stage, chirp does not affect the spectrum anymore. If we want to broaden the spectrum by using chirp pulse we must choose a right fiber length, and output the pulse in the dramatic broadening stage. These conclusions provide significant reference for supercontinuum generation in photonic crystal fibers with chirp pulse.