MODIFIED INTEGRATED-OPTIC FRESNAL LENS FOR WAVE-GUIDE-TO-FIBER COUPLING

The traditional design procedure for the waveguide Fresnel lens was ca rried over from those of bulk optics. In this design it is assumed tha t the lens thickness is negligibly small with respect to This criterio n does not hold for many integrated optic devices, in particular those with small mode-index modulations and long wavelengths. Under these c onditions, the focal properties of the lens become unpredictable and t he lens efficiency is reduced, both of which severely limit the useful ness of the lens as a waveguide-to-fiber coupler. To correct for this shortcoming, the standard Fresnel lens design procedure was modified t o acocunt for the thickness of the lens explicitly. Both the standard and the modified Fresnel lens designs are outlined. A comparison of th e limitations of the two lenses predicts better performance for the mo dified Fresnel lens. This is supported through computer-simulation res ults for a pair of test lenses.