Lithographically Fabricated Planar Holographic Bragg Reflectors

Planar holographic Bragg reflectors (HBRs) are computer-generated slab-waveguide holograms. They operate in two dimensions to provide powerful free-space-like spectral and spatial processing of optical signals in an integrated optics environment. An HBR typically images an input port to an output port while applying a specific spectral filtering function. HBRs are fully consistent with robust photolithographic or imprint-based fabrication and can be flexibly designed to offer a wide range of spatial wavefront control and single and multichannel spectral transfer functions. We report on lithographically fabricated, focusing HBRs implemented in the silica-on-silicon format whose spectral and spatial performances reach fundamental device limits set, respectively, by Fourier transform and diffractive constraints. We also demonstrate that HBRs support a unique process-friendly approach to apodization and overlay that uses fixed-depth etching and partial contour writing to achieve continuous reflective amplitude control of constitutive diffractive elements.