Polarization self-modulation in semiconductor lasers.

摘要

A method to generate modulated light using a semiconductor laser is proposed and experimentally tested. The basic idea behind this method is simple. Most semiconductor lasers lase in the TE (transverse electric) polarization state instead of the TM (transverse magnetic) state. However, if a polarization converter is inserted into the cavity which forces the polarization to rotate by 90{dollar}spcirc{dollar}, then the light may be induced to periodically change its polarization state every round trip through the cavity.; Experimentally, this idea was tested with external cavity semiconductor laser configurations, for reasons of convenience. Linear cavity as well as ring cavity structures were tried, and polarization self-modulation was successfully observed in both these cases. In addition, optical chaos was also observed in the linear cavity configuration. For the ring cavity configuration, additional higher frequency self-modulation phenomena were observed, with the frequencies always odd harmonics of the fundamental. With the use of these higher frequency effects, self-modulation at GHz frequencies was achieved.; Theoretical work undertaken to examine this phenomena by the development of a model showed that self-modulation at very high frequencies, tens of GHz, should be possible, which is very promising from an application point of view. The model was also able to simulate the higher frequency oscillations very well, adding further credibility to the model being used.; Finally, a possible use of this effect to optical-microwave applications was considered. It was experimentally shown that the intensity-modulated light obtained after passing through a polarizer could be continuously phase-shifted by simply rotating the polarizer. A method of electronically phase-shifting the modulation was also developed. This ability to implement phase shifts is very useful for phased array antenna applications, as the steering of the antenna beam is dependent on these phase shifts.