Spectral broadening and the generation of supercontinuum are inherent features of nonlinear optics, and have been studied intensively for many years. Supercontinuum generation has been found numerous applications in such various fields as spectroscopy, pulse compression, and the design of tunable ultra-short femtosecond laser sources. Generally, supercontinuum is mainly generated by hyperbolic-secant soliton pulse. It is rarely investigated about the spectral broadening when pumping with pulse of a rectangle or quasi-rectangle shape, which is an interesting direction of supercontinuum generation. In this paper, supercontinuum generation based on soliton, quasi-rectangle, and rectangle pulses are investigated numerically. Firstly, we introduced the general nonlinear Schrödinger equation (GNLSE) to deduce the temporal and spectral evolution of pulse broadening in the photonic crystal fiber. Secondly, with different types of pulses, including hyperbolic-secant, ultra-Gaussian and rectangle pulses, we investigated the generation of new frequency and spectral broadening by numerical methods. Comparisons of characteristics of spectral and temporal evolution with different pulses are made in the following parts of paper. It is found that the generation of dispersive waves and Raman effect play main roles in the spectral broadening and generation of supercontinuum, as the broadband wave is generated by the coupling of Raman soliton and dispersive waves through cross-phase modulation. Apparent side-bands can be observed in our simulation under the condition of quasi-rectangle and rectangle pulses pumping, which affect the smooth of spectrum. Thus, to our acknowledge, a flat supercontinuum can be generated by changing the parameter of pulse to make a better coupling of the side-bands.
In recent years,tunable optical delay line has attracted much research interest for its applications in optical
communications,optical signal processing and optical control of phased array antennas in microwave communications.
Compared with optical delay line based on slow light techniques, all-optical wavelength conversion followed by signal
propagation in a dispersive medium presents an alternative approach to control the delay time because it is simpler and
more controllable. In this paper, a tunable optical delay line with a large time delay up to 650ps based on four-wave
mixing (FWM) wavelength conversion in 420m high nonlinearity fiber (HNLF) and dispersion in 8km standard single
mode fiber (SMF) is experimentally demonstrated.Our experimental results are in good agreements with the principle.
Passively mode-locked fiber laser (MLFL) has been widely used in many applications, such as optical communication system, industrial production, information processing, laser weapons and medical equipment. And many efforts have been done for obtaining lasers with small size, simple structure and shorter pulses. In recent years, nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA) has been studied and applied as a mode-locking mechanism. This kind of passively MLFL has faster operating speed and makes it easier to realize all-optical integration. In this paper, we had a thorough analysis of NPR effect in SOA. And we explained the principle of mode-locking by SOA and set up a numerical model for this mode-locking process. Besides we conducted a Matlab simulation of the mode-locking mechanism. We also analyzed results under different working conditions and several features of this mode-locking process are presented. Our simulation shows that: Firstly, initial pulse with the peak power exceeding certain threshold may be amplified and compressed, and stable mode-locking may be established. After about 25 round-trips, stable mode-locked pulse can be obtained which has peak power of 850mW and pulse-width of 780fs.Secondly, when the initial pulse-width is greater, narrowing process of pulse is sharper and it needs more round-trips to be stable. Lastly, the bias currents of SOA affect obviously the shape of mode-locked pulse and the mode-locked pulse with high peak power and narrow width can be obtained through adjusting reasonably the bias currents of SOA.