Wesley Peter Townsend

Refractive-diffractive micro-optics for permutation interconnects

Refractive and diffractive micro-optics are combined in monolithically fabricated array components for free-space permutation interconnects. Such space-variant optical interconnects are, e.g., of major importance for smart pixel architectures, which are proposed for photonic switching applications in telecommunication and data communication and for more general parallel information processing, for example, of images. The advantages of the considered optical concept and an experimental demonstration of a 2-D perfect shuttle interconnect with 8 x 8 optical channels are described. We also discuss the scaling behavior and the alignment and wavelength tolerances of the interconnect system.

Fabrication and measurement of fused silica microlens arrays

We report fabrication of refractive microlens arrays in fused silica (SiO2) with a variety of pitches, diameters, and focal lengths. Typical f-numbers range from f/1.5 to f/5. Melted photoresist lenses are made on a fused silica substrate, and etched into the SiO2 using reactive ion etching (RIE) by carefully controlling the etch ratio. Techniques for microlens testing and measurement are discussed.

Testing and measurement of microlenses

Microlenses and microlens arrays present challenging measurement problems to manufacturer and user alike. Standard techniques designed for testing larger optical components are impractical for lenses with dimensions of only a few hundred micrometers. We present several methods for characterizing the wavefront, focal length, surface profile, and other parameters of microlenses and microlens arrays. The use of Mach-Zehnder and Twyman-Green interferometers for wavefront and focal length measurement are discussed in some detail.

Performance and measurements of refractive microlens arrays

Refractive microlens arrays with f numbers ranging from f/1 to f/5 have been fabricated using a melted photoresist technique. The photoresist surface profile has been accurately reproduced in the underlying SiO2 substrate using etching techniques. Surface profile and optical performance characteristics of these microlenses are reported. Spherical microlenses are shown to have nearly diffraction-limited performance.