Frequency modulation via the Doppler effect in optical fibers

We present the principle of optical frequency modulation via the Doppler ef fect obtained by rapidly stretching an optical fiber and thus modifying the optical path of the light propagating in the fiber. This procedure creates a pure frequency shift, with no degradation of the spectrum. Moreover, the effect is wavelength independent and can therefore be applied to any type of light source. We show an experimental realization in which a frequency e xcursion of similar to 100 MHz was obtained with a bobbin vibrating at 180 Hz. (C) 1999 Optical Society of America.