Frequency chirp and spectral dynamics in semiconductor lasers

Citation

Feng, Jing (1997) Frequency chirp and spectral dynamics in semiconductor lasers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/mahd-9t42. https://resolver.caltech.edu/CaltechETD:etd-06032005-160031

Abstract

A study of the effects of the longitudinal distribution of optical intensity and carrier density on the static and dynamic characteristics of semiconductor lasers has been performed. Through a self-consistent way, a static model for above threshold operation of a single mode distributed feedback (DFB) laser is developed by calculating the longitudinal optical intensity and carrier density distribution. A dynamic model for large signal modulation of the DFB laser is also presented based on time-dependent coupled-mode equation for electric traveling waves in the laser. The spatial hole burning (SHB) has been analyzed in a quarter wavelength shifted DFB laser and a conventional DFB laser.

A small-signal model is developed by including the optical intensity and carrier density distributions. Expressions are derived for the intensity modulation and resonance frequency, the frequency chirp and FM modulation, and the linewidth enhancement factor. Theoretical analysis of the frequency chirp in the DFB lasers has been used to support our experimental results. The model has led us to a new understanding of frequency chirp in DFB lasers and discovery of the ultra small chirp lasers.

The spectral dynamics and high speed response of uncooled DFB lasers have been studied. The most distinguished element differentiating the uncooled DFB lasers from uncooled FP lasers is that in uncooled DFB lasers; the wavelength detuning plays an important role in determining their spectral and high speed characteristics at high temperatures. Comparing with lasers lasing at gain peak, the DFB lasers with large negative wavelength detune could have better high speed performance at room temperature, but they might have higher threshold current. We can achieve optimum performance of uncooled DFB lasers by choosing wavelength detuning properly based on the laser applications.

Thesis Files