Effect of periodic strain on the leaky modes in single-mode fiber.

The effect of periodic strain on the beat wavelength between the guided LP(01) and the leaky LP(11) modes is approximated around the LP(11) mode cutoff. An abrupt change of the beat wavelength as a function of optical wavelength signifies the onset of the cutoff region. An order parameter is suggested to characterize the transition of the LP(11) mode from a guided to a cladding mode.