Geometric optics analysis of modal propagation in graded-index cylindrical fiber.

Methods of geometric optics are used to characterize a multimode optical fiber. The discrete propagation modes are derived by applying the phase resonance constraint to equations of constant phase surfaces. This constraint provides a very clear geometrical interpretation of discrete propagation modes, and provides a link between the well known Wentzel, Kramers, Brillouin (WKB) method and geometric optics.