Thin-Film Lens Technology Applied To Integrated Optical Spectrum Analyzers

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Abstract
Thin-film Luneburg lenses are an alternative to geodesic and grating type lenses for optical microelectronic devices requiring the collimation or focusing of a guided optical wave on a substrate. They have the advantage of circular symmetry and ease of fabrication by semiconductor-type sputtering processes. However, close tolerance levels must be maintained for control of refractive index, loss and scatter, profile and position. These issues have been addressed theoretically, with Luneburg-type lens structures, and experimentally, with films of niobium pentoxide (Nb2O5) on Ti-indiffused lithium niobate (Ti:LiNb03) planar waveguides. Films with loss levels of 0.5 dB/cm and low in-plane scatter were obtained by using reactive rf sputtering from a niobium target. Refractive indices near 2.29 at X = 0.633 Am can be repeatedly obtained with partial pressure-controlled and gas-analyzed sputter environment. Tolerance levels on refractive index have been theoretically determined and are compared to experimental values. Time-temperature experiments have determined aging and environmental ruggedness. The data indicate that high index thin-film lenses can be reproducibly fabricated that meet inte-grated, optical spectrum analyzer requirements.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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