TABLE OF CONTENTS The rationale for inserting the frequency-selective 'Bragg' grating into a semiconductor laser has been met in Sections 1.5 and 1.6 and the effect of a periodic permittivity on the energy exchange has been considered in Section 4.4. The next two chapters provide a relatively self-contained account of the physics and some numerical modelling for uniform and phase-shifted 'Bragg' lasers. There is a slightly arbitrary labelling of 'basic' and 'advanced' features before the detailed numerical time-domain modelling is discussed in Chapter 7. This present chapter starts with a more physical derivation of the coupled-mode equations than the mathematics of Chapter 4 and Appendix 5 and moves on to new features such as the eigenmodes for the analytic solutions, the influence of grating parameters on the dispersion diagram and the 'stopband' of nonpropagating frequencies.
Readers familiar with energy-band-distance diagrams in semiconductor devices will not be surprised to find that stopband-distance diagrams are similarly helpful when discussing Bragg lasers. The deficiencies of the uniform Bragg laser over single-mode selection have already been mentioned and are pursued further here to show the benefits of the insertion of phase shifts at judicious places into an otherwise uniform Bragg grating. The chapter concludes with an outline of the frequency-domain-modelling technique using transfer matrices. This is one of a number of numerical methods for simulating the performance of DFB lasers. The reader will be able to contrast these with time-domain techniques discussed in Chapter 7.
