Acousto-Optic Cell Non-Linearity Fed by Two-Frequency Acoustic Signal
V.Parygin, A.V.Vershoubskiy (Department of Oscillation Physics, Faculty of Physics, Moscow State University, Moscow, Russia)
Acousto-optic (AO) cell is the device that is linear relative to an optic signal and non-linear relative to an acoustic signal. This non-linearity is associated with the dependence of the diffracted light intensity on the acoustic wave amplitude. As a first approximation this non-linearity may be approximated by a cubic polynomial. In such approximation an optical beam diffracted by two-frequency acoustic signal contains, besides two main maxima, two spurious maxima that decrease the dynamic band of AO cell working as an acoustic signal spectrum analyzer. The amplitudes distribution of main and spurious maxima is analyzed in the work presented. It is shown that an appropriate preliminary distortion of an input signal makes it possible to lessen the spurious maxima level substantially. Moreover, the optimal coefficient of non-linear distortion does not depend on the Bragg condition mismatch. The results testify that under the condition of weak AO interaction the proposed distortion method allows to increase the dynamic band of AO spectrum analyzer by 20 dB. However, if the AO interaction efficiency is high, the preliminary distortion of an input signal does not effect the dynamic band. Thus, the AO interaction non-linearity can be compensated effectively in a wide range and improve the characteristics of an AO spectrum analyzer.
Section : 9