Two-sided through-wafer interconnect for optical spiral delay line

True-time-delay devices could significantly contribute to improving the performance of many optical systems in applications such as sensing, ranging, communication and signal processing. Delay devices based on spiral optical waveguides are of special interest due to their small size and relatively low power attenuation. In this paper, we propose to fabricate spirals on both sides of a wafer, where the coupling between them is through a vertical interconnect. The novel through-wafer interconnect has a level of attenuation that compares competitively with that obtained with a conventional s-shaped interconnect between two interleaved spirals and considerably simplifies the waveguide design and fabrication.