Numerical study on self-similar pulses in mode-locking fiber laser by coupled Ginzburg-Landau equation model

A theoretical model is established to study the self-similar pulses in nonlinear polarization evolution (NPE) mode-locked fiber lasers. The propagation of pulse in single mode fibers and gain fibers are described by coupled Ginzburg- Landau equation (GLE). Two wave plates and a polarizer are considered to realize the NPE mechanism in simulation. This model describes the laser completely and provides some useful pulses\u27 information. In our simulation the laser generates high quality self-similar pulses output. The region of steady self-similar pulses operation is found. The polarization states of different parts across the pulse are simulated along the laser cavity. It is found that polarization states across the pulse are modulated from elliptical to almost circular before the pulse passing through the polarizer

Femtosecond second-harmonic generation in periodically poled lithium niobate waveguides written by femtosecond laser pulses

We present in this Letter the second-harmonic generation of femtosecond pulses in double-line-written waveguides fabricated in periodically poled lithium niobate (PPLN) with femtosecond laser pulses. In a 10-mm-long sample, a normalized conversion efficiency of 12.6% W−1 cm−2 has been achieved for 40 fs pump pulses with the wavelengths centered at 1550 nm. Simulation results show that in PPLN waveguides the FWHM of wavelength tuning curve for 40 fs pump pulses is 42 nm, which is 15 times of that for 40 ps pump pulses

Theoretical study on instantaneous linewidth of Fourier-domain mode-locked fiber lasers

We have numerically simulated the operation of the Fourier-domain mode-locked (FDML) fiber laser based on the wavelength reconstruction method instead of numerical solving the nonlinear Schrödinger equation. We studied the influences of the filter bandwidth and the relative time delay caused by the fiber chromatic dispersion on the instantaneous linewidth of the FDML fiber laser. The results show that the instantaneous linewidth broadens as the filter bandwidth and the relative time delay increase. When the filter has the bandwidth of 0.02 nm, the narrowest and broadest instantaneous linewidths are 0.024 and 0.042 nm, respectively. We give an understanding for the oscillation of the instantaneous linewidth of FDML. The presented result can be used to evaluate the performance achievable in the FDML fiber lasers. 2012 Elsevier B.V. All rights reserved

Second harmonic generation by femtosecond Yb-doped fiber laser source based on PPKTP waveguide fabricated by femtosecond laser direct writing

The frequency doubling of femtosecond pulses from an Yb-doped fiber laser source was demonstrated in a PPKTP waveguide fabricated by femtosecond laser direct writing. The PPKTP waveguide contains a fixed period of 8.9 μm and the feomtosecond fundamental pulses have a central wavelength of 1044 nm. A maximum SHG power of 406 mW was produced, yielding a conversion efficiency of 5.6%. Numerical simulations were carried out to investigate the property of frequency doubling for femtosecond pulses. The results show that the SHG process proceeds even the quasi-phase-matching (QPM) condition is not well satisfied, which is significantly different from that of long pulses or CW light and is accorded with the experimental results