Light Sci. Appl. 6, e17053 (2017)

Integrated photonic circuits typically rely on fixed waveguides to route light around a chip, but it can be desirable to have more flexibility and dynamic control over the routing opportunities. Now, Carlos García-Meca, Sergio Lechago and colleagues from the Universitat Politècnica de València in Spain have done away with conventional interconnecting waveguides, demonstrating reconfigurable ‘optical wireless’ links between ports on an integrated optical chip. The approach makes use of silicon nanoantennas with high directivity and thermo-optical tuning to provide the reconfigurability. The antennas are formed by a taper and an arrangement of rectangular director bars to enhance directivity. A simple two-director geometry with a directivity of 114 was deemed sufficient for many applications. The concept allows broadband operation with a –3 dB bandwidth of over 900 nm around the 1,550 nm telecommunications window. In experiments, cross-talk was low enough to allow transmission of 160 Gb s–1 over a 100-μm-long free-space link by using four channels to simultaneously transmit at 40 Gb s–1. Another set-up, with 100-nm-thick titanium heater elements, exploited the thermo-optic effect to shift phase and allow beam steering from a four-element phased-array antenna. The team were able to steer the beam in a 30° window (–3 dB), allowing switching between 100-μm links with switching time and power of 5.2 μs and 8.3 mW, respectively.