A directional coupler acoustooptic filter with reduced sidelobe levels

A two-waveguide directional coupler filter with an acoustically induced grating structure is proposed. The directional coupler filter has the advantage that it does not require input and output polarizers and does not require specific birefringent material properties. Since multiple acoustic waves could be applied simultaneously, this property could be used to couple both TE and TM polarizations from one waveguide to the other. This allows for filtering the required optical wavelength from both polarizations simultaneously. A notable weakness of acoustooptical filters and all mode-coupling filters is the high sidelobe levels in their optical transmission spectrum. A technique to suppress these high sidelobe levels in the proposed acoustooptic filter is presented. It is based on simultaneous application of several acoustic waves on the optical waveguide. This technique could be applied to any existing configuration of acoustooptic filters