Acousto-optic filter with near-ideal bandpass characteristics

A filter for filtering multiwavelength electromagnetic radiation having a single polarization state to selectively change the polarization state of at least one of the wavelengths comprising:

• an electromagnetic waveguide which receives at an input end said multiwavelength electromagnetic radiation and which outputs at an output end said multiwavelength electromagnetic radiation with at least one of the wavelengths having a changed polarization state,
• a structure for generating another wave which interacts with said multiwavelength electromagnetic radiation in said electromagnetic waveguide with an interaction profile that oscillates in phase polarity and that is damped and that has a propagation constant equal to a change in propagation constant of the selected wavelength,
• wherein said structure for generating a wave comprises:
• a first waveguide in which said other waves propagate,
• a second waveguide coupled to the first waveguide in which other waves propagate, said second waveguide containing said electromagnetic waveguide, and
• a damping structure for damping other waves propagating in said first and second waveguides,
• said other waves propagating in said first waveguide being coupled into said second waveguide so that said other waves in said second waveguide have said interaction profile.

An acousto-optic filter for receiving multiple wavelength optical radiation with a single polarization state and for changing the polarization state of one of the optical wavelengths comprising:

• a substrate,
• first and second coupled acoustic waveguides formed on said substrate, said acoustic waveguides tapering toward each other at least over a portion of their length located near one end of the substrate,
• a transducer for launching surface acoustic way in said first acoustic waveguide, said surface acoustic waves coupling into said second acoustic waveguide,
• a structure for damping said surface acoustic waves in said acoustic waveguides, and
• an optical waveguide formed on said substrate within said second acoustic waveguide, said optical waveguide receiving said multiwavelength optical radiation at an input near said one end of said substrate and outputting said multiwavelength radiation with the polarization state of one wavelength changed at an output, wherein said surface acoustic waves coupled into said second acoustic waveguide have an acousto-optic interaction profile which oscillates in phase polarity and is damped.