Waveguide-to-fiber coupling using a second-order grating and an anamorphic binary optic

There exists a need for packaging devices with multiple fiber outputs, that have been gang-aligned, efficiently coupled, and hermetically sealed. (The latter item will be very important in automotive or aerospace applications.) Instead of trying to have fiber penetrate the package wall. This has been accomplished by sending out the light normal to the waveguides and collecting it with a binary optic that focuses it on to a fiber outside the package. The optical design of this system requires that the beam be nearly collimated as it leaves the surface of the device. To accomplish this, a second-order grating was etched into a 200 km-long section of an adiabatically expanded single-mode waveguide. The entire test structure consisted of three features, a straight waveguide, an adiabatically expanded waveguide, designed to be cleaved for evaluation, and an adiabatically expanded waveguide with gratings etched into it. All devices were planarized with polymide and portions of the waveguide were metallized to provided a modulator structure. The modulators could be biased to observe any possible effects of voltage on the structure and to make it easy to discern modulated output light and to aid in loss measurements. An SEM of the grating is shown. A full description of modulator efficiency and binary optic coupling performance will be presented.