A new spectral detection method for confocal scanning microscopy is presented in this paper. The proposed spectral detector utilizes the natural dispersion of zero-order beams in an acousto-optic tunable filter (AOTF). A new method that compensates for the birefringence of an AOTF and maintains the consistency in dispersion is proposed. The proposed birefringence compensator adapts the principle of geometrical optics with a single beam displacer. Theoretical modeling and analyses were performed and the results were confirmed through confocal spectral imaging microscopy. These preliminary experiments demonstrate the feasibility of using AOTFs as fluorescence-dispersing beam splitters for spectral imaging microscopy.