### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2pUW33. The relationship between rays and modes in a waveguide with
large-scale inhomogeneities.

**Anatoly L. Virovlyansky
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*Inst. of Appl. Phys., 46 Ulyanov St., 603600 Nizhny Novgorod, Russia
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The well-known results of Tindle and Guthrie, Felsen, and other authors on
studying the relationship between rays and normal modes in a range-independent
waveguide are generalized for a waveguide with large-scale inhomogeneities of
refractive index. It is shown that in complete analogy with the
range-independent case, the raylike behavior of a cluster of normal modes takes
place. The notion of Fresnel zones for normal modes is introduced, which is
analogous to the usual Fresnel zones introduced for rays. Using Fresnel zones
for modes one can simplify the analysis of mode scattering at large-scale
inhomogeneities (such as an opaque screen or an inhomogeneity of refractive
index) in a waveguide. Simple and statistical averaging-suited formulas are
deduced to calculate mode amplitude variations under scattering at
inhomogeneities of refractive index, which are ``mode analogues'' of the
formulas of geometrical optics and those of the Rytov method.