It has been investigated of nonlinear propagation of femosecond pulse and supercontinuum generation (SCG) in three
photonic crystal fibers (PCFs) with different dispersion profile in the 1550nm window by numerical stimulation. The
influence of higher-order effects on supercontinuum, including higher-order dispersion (HOD), self-steepening (SS), and
stimulated Raman scattering (SRS), are discussed in detail as well. The results of numerical simulations show that group
velocity dispersion and self-phase modulation take main effect in the initial stage. In the PCF with anomalous dispersion,
SRS plays main role when the propagation distance increases, which induces a red-shift of the central wavelength,
suggesting the appearance of soliton self-frequency shift. In the PCF with near-zero anomalous dispersion, HOD plays
main role. This results in the fission of higher-order solitons and remarkable broadening of the pulse spectrum. In the
PCF with normal dispersion, higher-order effects have almost no effect on the pulse. The Gaussian pulse wave broadens
to rectangular symmetrically, and the pulse spectrum broadens symmetrically, too. However, the broadening is smaller
than the former two cases.
Based on the Maxwell-Bloch formalism, operation of a passively mode-locked fiber laser is numerically investigated. It
is found that even with the effects of coherence stable solitary waves can still be obtained in the laser due to the cavity
pulse peak clamping effect. And the discrepancies between the results obtained by the coupled GLEs and the Maxwell-
Bloch formalism will increase as the linear phase delay bias increases.
Effect of the initial chirp on picosecond pulse breakup in the presence of noise is analyzed through numerically solving
the modified nonlinear Schrödinger equation, using the standard split-step Fourier method. It is found that, for shorter
pulses, the pulse breakup is caused by pulse collapse resulted from high-order soliton compression, even in the presence
of noise. For longer pulse, pulse breakup is triggered by nonlinear amplification of noise caused by modulation
instability. The effect of initial chirp on pulse breakup is closely related to the mechanism of pulse breakup, and the
process of short pulse breakup depends strongly on the strength of negative initial chirp.
The characteristics of femtosecond pulse trapping in photonic crystal fibers are investigated. Numerical simulations show that the efficiency of pulse trapping can be improved by adjusting the parameters of pump pulse. For a given pulse width, the trapping efficiency is fluctuant as the temporal delay increases and has a maximal value. The blue-shift of signal pulse and the red-shift of pump pulse, however, have no matter with temporal delay. The maximal trapping efficiency and the corresponding temporal delay both decrease as the pulse width increases.
In the paper, we have numerically studied how the initial conditions influence the mode-locked soliton formation in the passively mode-locked fiber laser by using the nonlinear polarization rotation technique. We find that once the laser gain is fixed, a soliton with fixed peak power and pulse width will be formed, which is independent of the initial seed pulse conditions. Further numerical simulations have shown that both the peak power and the pulse width of the mode-locked soliton are varied with the linear cavity delay bias setting. We identified that the larger the linear cavity phase setting, the higher the soliton peak and the narrower the soliton pulse achievable in certain range, and adjustable pulse width passively mode-locked fiber laser can be formed by turning the linear cavity delay bias.
We have demonstrated an all optical switching by use of pulse trapping in photonic crystal fiber (PCF). A train of four pulses with temporal separation of 1 ps is used as the signal pulses, in which only one pulse is trapped by the soliton pulse in the PCF. The wavelength of the trapped pulse is blue shifted, and thus the trapped pulse can be picked off easily by use of a wavelength filter such as a fiber Bragg grating. In addition, The characteristics of the ultrafast all optical switching are analyzed numerically. The trapping efficiency decreases as the temporal separation increases. The low trapping efficiency impairs the performance of optical switching.
We report on the theoretical investigation of the amplification of highly chirped pulse with ultrabroad bandwidth. Based on the analysis of the properties of the pulse with a very big chirp, we build a theoretical model for the amplification of highly chirped pulse. The model includes the effects of homogeneous and inhomogeneous broadening. Based on our model, the difference
between the inhomogeneously and homogeneously broadening amplification is identified by numerical simulations. We believe that the obtained model can be used to evaluate the laser-performance, and optimize the laser design.
Proc. SPIE. 5627, High-Power Lasers and Applications III
KEYWORDS: Diffraction, Modulation, High power lasers, Free space, Laser beam propagation, Wave propagation, Near field diffraction, Pulsed laser operation, Light wave propagation, Laser systems engineering
We report on a numerical investigation of propagation property of high-power broadband laser beam in free space. We use Hankel transformation to solve Helmholtz equation numerically in the frequency domain. The modulation property of the broadband laser beam propagating in the Fresnel diffraction region is disclosed. It is found that the number of diffractive modulation rings equals to half the Fresnel number corresponding to the central wavelength of the broadband laser beam. The intensity modulation contrast of the broadband laser beam is smaller than that of monochromatic laser beam, suggesting that the broadband laser beam can suppress the harmful effect of near-field diffraction to some extent. Furthermore, it is demonstrated that the uniformity of near-field diffraction profile is determined by Fresnel number and bandwidth of the broadband beam.