Abstract

Lenses are among the key components in optical signal processing and computing systems⁽¹⁾. Realization of such optical systems in a waveguide substrate has long been considered one of the major applications of integrated optics. Recently, the prospects for this realization are significantly advanced through progress in guided-wave microoptic components of both active and passive types. Aside from the study on integrated acoustooptic RF spectrum analyzers⁽²⁾ that has become an international effort, serious attempts to utilize the integrated optic devices for optical computation of both analog and digital data are also being made at various research institutions. Accordingly, it is of great importance to develop viable techniques for fabrication of waveguide lenses with application to optical computing. A variety of planar waveguide lenses including the geodesic, chirp-grating, Fresnel, and Luneburg types have been reported in the literature. A common characteristic of these lenses is a relatively long focal length and a relatively small numerical aperture. It is to be noted that a channel waveguide lens involving multiple coupled-waveguides has also been proposed most recently⁽³⁾. In this paper we report on the single-mode planar waveguide microlenses and microlens arrays in LiNbO₃ that are formed using titanium indiffused-proton exchange technique⁽⁴⁾. These waveguide lenses have demonstrated desirable properties including very short focal length, large numerical aperture, very small focal spot size for a wide range of focal length, and low optical insertion loss at the 6328 Å He-Ne laser wavelength.

© 1985 Optical Society of America