Figure 8.1-3 The bounce angles θm and the wavevector components of the modes of a planarmirror
waveguide (indicated by dots). The transverse components kym = k sin θm are spaced
uniformly at multiples of π/d, but the bounce angles θm and the propagation constants βm are not
equally spaced. Mode m = 1 has the smallest bounce angle and the largest propagation constant.