A new PSPICE model for laser diode has been determined, which represents a basic element in the digital transmission using optical fiber links compared to the diode LED which has a less optical power. It is necessary to control the optical power emitted by the laser diode before connecting it with the optical fiber. Also, the new generations of the laser diode comprise a transmitting laser diode and a photodiode PIN which makes it possible to monitoring the optical power. In order to use this new model and discuss the results we have with a real model of MITSUBISHI Laser diode, this work enabled us to meet the needs for simulation of high speed digital transmission using optical fiber before any realization.