Silicon nanomembrane-based compact true-time-delay module on unconventional substrates

Abstract

We demonstrate several building blocks of true-time-delay (TTD) network, including subwavelength grating couplers, photonic crystal waveguide TTD lines, and multimode interferometer (MMI) power splitters fabricated on silicon nanomembrane (SiNM) transferred onto unconventional substrates, such as glass, Kapton. Bending tests performed on flexible gratings demonstrate operation even at ~15mm bending radius, with about 5dB loss. The 1x16 cascaded multimode interference (MMI) based power splitter demonstrates uniformity of 0.96dB across all the 16 output channels, and an insertion loss of 0.56dB.The photonic crystal waveguides are designed to provide large time delay values within a short length. Photonic crystal tapers are implemented at the strip-photonic crystal waveguide interfaces to minimize loss and provide larger time delay values. A large group index of ~28.5 is calculated from the measurement data, thus indicating achievability of time delay larger than 58ps per millimeter length of the delay line within a tuning range of 20nm. The demonstrated building blocks present a viable path for obtaining scalable TTD modules on unconventional substrates.