Theoretical Study of Semiconductor Laser under Modulation

In this paper we present a description of the chirp induced in a direct modulated DFB laser. Our study is follows two different approaches. The first approach is based on a resolution of the rate equations of laser; the second, on a simulation of a heterodyne system with the Optisystem software. This study enables us to visualize the chirp in the RF field. We also characterize it according to the injection current i(t) parameters, such as the amplitude and the frequency of the modulation. The aim of our study is to choose the appropriate values of these parameters, in order to use the direct modulated DFB laser as an optical tunable source for Coherent Optical Frequency Domain Reflectometry technique (C‐OFDR). We demonstrate that the optical frequency of these lasers can be controlled via the injection current i(t) and it can be linearly swept (chirped) over some tens of gigahertz.