A new family of geodesic lenses for waveguide optical devices

A new family of geodesic lenses is described. The design procedure is analytical and allows one to project lenses with diffraction limited aperture larger than 60 percent of the dimple diameter. A simplified profile of the outer rim has been introduced which avoids any critical region both for radiation and transition losses; as a consequence total losses of
5 \times 10^{-2}
dB become achievable. Moreover the simplified profile should make the substrate grinding and polishing easier. Two lenses belonging to this new family have been fabricated on glass with ion exchanged waveguides. The substrate shaping was performed by means of a simple machine for optical manufacturing and a talystep to check up the profile. With a beam width equal to 50 percent of the total lens diameter, focal spot sizes of
15-18 \mu
m have been achieved. There was no evidence of additional losses due to the lenses.