Patent ID: 7680371

Claim:
An interface device for performing mode transformation in optical waveguides, comprising: a first optical waveguide core for propagating light of a particular wavelength or a plurality of wavelengths in a longitudinal direction through said first optical waveguide core between an input face and an output face; a subwavelength grating embedded in said first optical waveguide core; said subwavelength grating having a series of transverse grating elements arrayed in said longitudinal direction between said input face and said output face such that light propagating in said first waveguide core between said input face and said output face successively passes said transverse grating elements; said grating elements having a pitch sufficiently less than the wavelength of the light to frustrate diffraction; and wherein a property of said subwavelength grating varies to effect a gradual change in effective mode index of said first optical waveguide core in the longitudinal direction, said property being selected from the group consisting of: duly ratio, width, pitch, modulation depth, material composition, and any combination thereof; and whereby the propagation mode of the light is modified during passage through said first waveguide core between said input face and said output face as said light passes said grating elements.