Signals of an intermodal fiber interferometer induced by laser frequency modulation

Signals of an intermodal fiber interferometer induced by laser optical frequency modulation are studied. Dependences of signal amplitudes and spectra on the laser frequency deviation are examined theoretically and experimentally for various optical fibers. It is established that the sensitivity of the intermodal fiber interferometer to the laser frequency variation essentially depends on the fiber refractive index profile. The minimal sensitivity corresponds to graded-index ($\alpha\approx$ 2) multimode optical fibers. Step-index optical fibers ($\alpha=\infty$) are more sensitive to the laser frequency variation by more than a factor of 100.