Study of Reduction of Nonlinear Chirp Distortion Directly Modulated Semiconductor Lasers by Using Pulse Shaping

Abstract

A modulation of the device current leads to laser-power modulation and is useful for transmitting information as a sequence of optical pulses .However , modulation of the current also affects the optical frequency which emphasize that carriers influence the optical phase . The center frequency of the out put laser shifts by an amount during modulation . The phenomenon of the dynamic shift of the laser frequency is referred to as frequency chirping or wavelength chirping . The chirp is directly proportional to the line-width enhancement factor and has its origin in the carrier induced index change that accompanies any gain change in semiconductor laser . This chirp may be reduced by a suitable shaping of the injection current.