A FIBER OPTIC FREQUENCY SHIFTER

A fiber optic frequency shifter capable of shifting the frequency of l ight traveling through the fiber has been designed, constructed, and t ested. The frequency of the transmitted light is shifted by stretching and contracting the optical fiber that is wound around two piezoelect ric ceramic tubes. The frequency of the light is shifted by Linearly c hanging the path length along which the light must travel. The diamete rs of two piezoelectric ceramic tubes are changed when a linearly incr easing electric field is applied to the tubes. A servo control system is used to comet and compensate for nonlinearity of the piezoelectric material and assembly. A frequency shift of up to 305 Hz for up to 2.5 s with a linewidth of less than 1 Hz is achieved with the present set up. This frequency shifter has been successfully applied to a laser li ght scattering apparatus for which heterodyne experiments are made for particle electrophoretic mobility and zeta potential measurements. (C ) 1997 American Institute of Physics.