The simulation of light waves propagating in fibers oppositely has to handle the extremely huge volume of data when employing sequential and unidirectional methods, where the simulation is in a coordinate system that moves along with the light waves. Therefore, alternative simulation algorithm should be used when calculating counter propagating light waves. Parallelizable and bidirectional (PB) algorithm simulates the light waves matching in time domain instead of space domain, does not need iteration, and permits efficient parallelization on multiple processors. The PB method is proposed to calculate the propagation of dispersing Gaussian pulse and a bit stream in fibers. However, PB method also has apparent advantages when simulating pulses in fiber laser amplifiers, which has not been investigated detailed yet. In this paper, we perform the simulation of pulses in a rare-earth-ions doped fiber amplifier. The influence of pump power, signal power, repetition rate, pulse width and fiber length on the amplifier’s output average power, peak power, pulse energy and pulse shape are investigated. The results indicate that the PB method is effective when simulating high power amplification of pulses in fiber amplifier. Furthermore, nonlinear effects can be added into the simulation conveniently. The work in this paper will provide a more economic and efficient method to simulate power amplification of fiber lasers.
The spectrum generated in tapered Photonic Crystal Fiber (PCF) by ultrashort laser pulses is demonstrated via means of numerical simulations of the generalized Nonlinear Schrödinger Equation. Our simulations are able to deliver the spectral evolution of the pulses along the fiber axis at desired propagation distances. Differences of the output spectra and the propagation of laser pulses depending on the different structures of the PCF tapers are investigated. The results show that the variation of the diameter of a tapered PCF along the fiber axis crucially influences the soliton dynamics, the spectral evolution as well as the generation of a supercontinuum (SC). The diameter of a tapered fiber along the fiber axis can be used as a new degree of freedom to tailor the spectrum generated by ultrashort laser pulses.
The concept of cascading Photonic Crystal Fiber (PCF) tapers is proposed, and the numerical model of supercontinuum
(SC) generation in cascaded PCF tapers is clarified. Using self-compiled program, the SC generation in cascaded PCF
tapers with identical and different structural parameters are numerically simulated. Hence the function of cascading is
illustrated. Via cascading PCF tapers with same structural parameter, we can overcome the limitation of the tapering rig
to enhance the nonlinear interaction length. Via cascading PCF tapers with different structural parameter, we can not only
enhance the interaction length, but also obtain higher nonlinearity and more manageable dispersion to increase the
qualities of SC, such as spectral range and flatness.