Distributed Feedback Semiconductor Lasers

Appendix 1: Maxwell, Plane Waves and Reflections

This appendix provides a summary of plane-wave interactions at dielectric interfaces and a summary of special cases which are of importance in laser-diode design, in particular, indicating one reason why TE modes are slightly more strongly reflected from a cleaved facet than TM modes.

A1.1 The Wave Equation

Start with Maxwell's two famous equations [1 3] for the electromagnetic fields:

(A1.1)
(A1.2)

In this work, the optical waveguide is formed from uniform layered slabs of different relative permittivity ? r = n 2 = ( n r+ j n i,) 2, giving the material's complex refractive index n with n r determining the real refractive index and n i determining the optical gain (Appendix 5). Taking the notation of Figure 3.1, the normal to the optical slab guides is in the O y direction and the TE (TM) waves may be classified as those modes with the E (H) field in the plane of the slabs i.e. in the Ox direction. With a uniform permittivity within each slab, elimination of H from eqns. A1.1 and A1.2 leads to the wave equation

(A1.3)

A1.2 Linearly Polarised Plane Waves (in a Uniform 'infinite' Material)

Taking an infinite uniform isotropic slab of material where there is no variation over the xy plane ( ?/ ?x = ?/ ?y=0) but only electric fields E x with optical frequencies ?, these fields propagate in the...

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