TABLE OF CONTENTS Chapter 5 considered some basic features of DFB lasers, concentrating on the static performance. However, several key features for high-performance lasers were not discussed such as linewidth, the influence of reflections and especially the phase of weak-facet reflections, the role of complex gratings and what happens on designing for power levels in the hundreds of milliwatt range rather than the milliwatt range of conventional communication lasers. These more advanced problems of the static design of lasers are outlined here and the chapter ends with a discussion on some results of modelling the dynamic performance of DFB lasers, considering problems associated with carrier transport into quantum wells. The dynamic performance of DFB lasers highlights yet further the problems that have already been met with a uniform grating in a uniform DFB laser. Change of mode with time, dynamic instabilities, yield of devices with the right mode etc. prove to be major problems unless the laser has additional features.
As seen in Chapter 5, the use of one or more phase shifts offers considerable improvement in the performance of a laser, and this chapter concentrates on the dynamic performance of a DFB laser with two phase shifts. It is generally agreed that one phase shift [1], although stabilising the mode at low power levels, does not offer the solution to all the dynamic problems. Three phase shifts have been advocated [2], and continuous changes in the grating period/ coupling constant along the laser can be of interest [3, 4] but,...
