Noise and synamics in semiconductor lasers

Abstract

In this thesis, theoretical and experimental work on the noise and dynamics in continuous wave and mode-locked semiconductor lasers is presented. The main focus is on semiconductor cascade lasers and semiconductor mode-locked lasers. In semiconductor cascade lasers, multiple gain stages are connected electrically in series. Each electron injected into a cascade laser is capable of producing more than one photon, and the differential quantum efficiency of cascade lasers can be much larger than that of conventional semiconductor lasers. The photon emission events in different gain stages in cascade lasers are highly positively correlated, and these correlations increase the noise in the laser output compared to a conventional laser. The work on cascade lasers has required a revision of the previous work on laser noise, and the development of self-consistent theoretical models for the current noise and the photon noise in semiconductor lasers. The current and photon noise in both interband cascade lasers and intersubband quantum cascade lasers are studied in this thesis. The noise in optical pulses in semiconductor mode-locked lasers is also studied in this thesis. In contrast to the previous work in this field, the models presented here are fully quantum mechanical, self-consistent, and also take into account the effects of group velocity dispersion, active phase and amplitude modulation, and pulse chirp on the pulse noise. In semiconductor mode-locked lasers, as a result of the carrier density dependent refractive index, pulses are heavily chirped. The pulse noise is found to be significantly affected by the magnitude of the pulse chirp.

(cont.) The noise in harmonically mode-locked semiconductor lasers is also discussed, and it is shown that the correlations in the noise of different pulses inside the laser cavity can significantly affect the results when the pulse noise is measured experimentally.