Design, fabrication, and characterization of guided -mode resonance filters and waveguide -grating couplers

In this dissertation, two types of diffractive optical elements, guided-mode resonance filters and waveguide grating couplers, are studied theoretically and experimentally. The guided-mode resonance (GMR) filters are designed by rigorous coupled-wave theory and possess high efficiency filtering response and low sidebands extended over a large spectral range. High efficiency GMR filter with 98% peak reflectance and 5% sideband reflectance over 100 nm wavelength range was fabricated and characterized. The GMR filter was also used as a narrow-band mirror to demonstrate laser operation in a dye laser cavity. A GMR device was realized experimentally with a surface-relief grating made on a planar waveguide illuminated at the Brewster angle with a TM polarized wave producing a filter response with 94% peak reflectance and ∼1% low sidebandes over an extended wavelength range. Thus the principle of guided-mode resonance Brewster filter was verified. The experimental results on GMR Brewster filters are in excellent agreement with theoretical calculations. A new diffractive structure, photopolymer grating-sandwiched guided-mode resonance filter (GMRF), was invented, theoretically analyzed, fabricated, and tested. About 90% resonance efficiency was obtained experimentally with this new device. The idea of implementing a multi-line GMRF with a two-waveguide-grating-sandwiched structure was theoretically studied. The multiline filter is achieved by coupling several different diffracted orders from the sandwiched grating to the surrounding waveguides, which support multiple guided modes. This idea also revealed a new mechanism of polarization independent GMR filters in which coincident TE and TM resonances are excited in different surrounding waveguides by different diffracted orders. A new fabrication procedure that produces non-uniform gratings was developed by using a computer controlled moving shutter for precise control of the local exposure time during the recording of the laser interference pattern. This procedure was employed to fabricate waveguide-grating couplers with uniform output beam intensity. An output beam uniformity better than +/-5% was achieved over 20 mm coupling length with a total coupling efficiency of ∼80%. A new optical surface fabrication technique, photopolymer micro-surface molding, was invented and used successfully in the fabrication of both GMR filters and waveguide-grating couplers. This technique can duplicate delicate photoresist surface structures with complex patterns at sub-micron feature size level with excellent quality.