Highlighted Articles from Optica Publishing Group Journals
Spotlight Summary by Francesco Morichetti
High-performance modified uni-traveling carrier photodiode integrated on a thin-film lithium niobate platform
Photonic integration is constantly looking for novel material platforms to implement more advanced functionalities operated at higher speed and reduced power consumption. When a new photonic technology is born, it is necessary to develop a complete portfolio of photonic building blocks; some of them appear early, others remain in the wish list for years or decades. A new story has recently begun with lithium niobate on insulator (LNOI) technology, which has brought to the nanophotonic scale one of the mostly used materials in optics - lithium niobate - thanks to its electro-optic, nonlinear and transparency properties. Starting from optical modulators and wavelength converters, a number of other devices have been integrated on LNOI, such as frequency comb generators and laser sources. Yet, high-speed photodetectors were still to appear.
Now this gap has been filled by X. Guo and coauthors, who succeeded in integrating a fast photodiode on a LNOI platform. By carefully optimizing the thicknesses of a InGaAs/InP layer stack, they demonstrated a heterogeneously integrated photodiode with a detection bandwidth of 80 GHz, a responsivity of 0.6 A/W and a dark current as low as 3 nA. Notably the fabrication process of this photodiode is based on scalable wafer die bonding approach that is fully compatible with the realization of other devices, like modulators and resonators on the same LNOI wafer. With this new piece of the puzzle, we have now all we need to build complete systems on chip integrated on a LNOI platform. In doing so, we may realize that something is still missing, so the search for other components is still open.