Theoretical Investigating On Optical Pulse Compression Technique

The generation of ultra-short optical pulse with high repetition rate is one of the key techniques in the high-speed optical time-division multiplexing (OTDM) system. The higher the transmission speed is, the shorter the optical pulse width is expected to be. Nowadays, the optical pulse used in the OTDM system is often generated by the gain-switched distributed-feedback (GS-DFB) semiconductor laser, which has a large pulse width and negative chirp. Therefore, in order to satisfy the demand of the OTDM system, the technique of optical pulse compression must be adopted. Based on the previous works, many teasible schemes about pulse compression have been proposed and investigated in this paper, through which the pulse can be compressed effectively.A novel designed model of optical pulse compressor, which is based on the dispersion decreasing fiber in the normal-dispersion regime (ND-DDF), single mode fiber (SMF) and nonlinear optical fiber loop mirror (NOLM), has been presented. When a pulse is propagating in the ND-DDF, the central part of the pulse will generate linear up-chirp, which can be compressed through propagating in a single mode fiber with reasonable length, and a nonlinear optical fiber mirror is used for further compression and pedestal suppression.Standing from the adiabatic compression theory, a new pulse adiabatic compression mode based on the nonlinearity increasing fiber has been suggested and investigated. The numerical results show that the pulse compression process in this kind of fiber satisfies the adiabatic condition by selecting the reasonable systematic parameters. For the nonlinear coefficients increases with the increase of propagating distance, the higher order nonlinear effects, especially the Raman self-frequency-shift, will be enhanced, which will lead to time-delay between the output and the input pulse. High quality compressed pulse can still be obtained even if the higher order effects are involved.The above results can provide an instructive insight to obtain ultra-short optical pulse with high repetition rate.