An asymmetric slab waveguide is shown in Figure 13.26. In this case, the regions above and below the slab have unequal refractive indices, where n₁> n₃> n₂.

(a) Write, in terms of the appropriate indices, an expression for the minimum possible wave angle, θ₁, that a guided mode may have.

(b) Write an expression for the maximum phase velocity a guided mode may have in this structure, using given or known parameters.

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