Appendix 3: Group refractive index of laser waveguides
The group velocity is the velocity of a wave packet (i.e. the velocity of energy) that is centred on a central carrier frequency f = ω/2π. The group velocity is different from the phase velocity for two reasons: (i) the waveguide changes the propagation coefficient as a function of frequency; and (ii) the material permittivity changes with frequency so that the propagation coefficient in the material changes with frequency. This appendix illustrates these two roles using a symmetric three-layer waveguide so that one can appreciate the physics through putting numbers into an analytic solution.
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Appendix 3: Group refractive index of laser waveguides, Page 1 of 2
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