Study of dynamic chirp in direct modulated DFB laser for C-OFDR application

A description of the chirp induced by direct modulated DFB laser is presented. Two approaches are considered: the first one is based on a resolution of laser rate equations; the second, on a simulation with a commercial software. We compare results of the two approaches, we demonstrate that the optical frequency can be controlled via the injected current. We also characterize the linear variation of the optical frequency in time (for triangular and sawtooth modulation), in order to choose the appropriate values of laser and modulation parameters for a perfect linearity of the chirp in time. This study will be very helpful to validate the use of direct linear modulated DFB laser as a tunable source in Coherent Optical Frequency Domain Reflectometry technique C-OFDR. We present a simulation result of Mach–Zehnder delay time measurement based on C-OFDR system using a direct modulated semiconductor laser source. The obtained results are very important because it depicts the beat frequencies relating to each delay time, with respect to the modulation format used. This is very encouraging for the implementation of an experimental C-OFDR.