Wide-angle acousto-optic diffraction spectral selectivity enhancement by optoelectronic feedback introduction

Abstract

One of the acousto-optic (AO) tunable filters applications is the filtration of divergent optical beams, for exampleimage spectral filtration. In this case, the so-called wideangle or tangential AO interaction geometry is used. Unfortunately, such AO devices usually do not have a high spectral resolution, and an increase in the light beam divergence leads to an even greater widening of the AO device transmission function, since the AO phase matching condition for the lateral components of the optical beam spatial spectrum differs from those for the axial components. In this paper we examine the possibility of improving the spectral resolution of a wide-angle AO tunable filter by introducing optoelectronic feedback connecting the optical output of the AO cell and its piezoelectric transducer. The study is carried on the example of collinear AO interaction (a special case of highfrequency wide-angle diffraction). It is shown that the feedback introduction makes it possible to improve the spectral contrast and narrow the AO filter passband up to 20 times, while AO cell transfer function, which determines the value of AO filter angular aperture, remains unchanged.