Analysis of the Additional Modulation of Semiconductor Lasers Using Optical Heterodyne Techniques

In this letter, the power spectrum of a cooled distributed feedback laser module is measured using the self-heterodyne technique. Periodical oscillation peaks have been observed in the measurement. Further investigation shows that the additional modulation signal is coupled from the thermal electric cooler (TEC) controller to the laser driver, and then applied to the laser diode. The additional modulation can be eliminated by properly isolating the laser driving source from the TEC controller.

I. Introduction

Pure optical spectrum and narrow linewidth of the light source is predominant for communication applications [1]. Although the purity of laser has been confirmed, some external circuit and optical links can still affect the performance of the device and whole system [2].