Dynamic indoor free-space optical communication enabled by beam steering and beam shaping.

Indoor free-space optical communication (FSO) provides orders of magnitude larger usable bandwidth compared to radio-frequency links but suffers from an intrinsic trade-off between areal coverage and received power. In this paper, we report a dynamic indoor FSO system enabled by a line-of-sight optical link featuring advanced beam control capabilities. The optical link herein utilizes a passive target acquisition scheme by combining a beam steering and beam shaping transmitter with a receiver adorned with a ring-shaped retroreflector. When controlled by an efficient beam scanning algorithm, the transmitter is capable of locating the receiver with millimeter-scale accuracy over a distance of 3 m with a full viewing angle of ±11.25∘ in the vertical direction and ±18.75∘ in the horizontal direction within 1.162±0.005s, regardless of the receiver's positions. We also demonstrate 1 Gbit/s data rate with bit error rates below 4×10-7 using an 850 nm laser diode with only 2 mW of output power.

One-volt silicon photonic crystal nanocavity modulator with indium oxide gate.

The ever-increasing global network traffic requires a high level of seamless integration between optical interconnect systems and complementary metal-oxide-semiconductor (CMOS) circuits. Therefore, it brings stringent requirements for future electro-optic (E-O) modulators, which should be ultracompact, energy efficient, high bandwidth, and in the meanwhile, able to be directly driven by the state-of-the-art CMOS circuits. In this Letter, we report a low-voltage silicon photonic crystal nanocavity modulator using an optimized metal-oxide-semiconductor (MOS) capacitor consisting of an In2O3/HfO2/p-Si stacked nanostructure. The strong light-matter interaction from the accumulated free carriers with the nanocavity resonant mode results in holistic improvement in device performance, including a high tuning efficiency of 250 pm/V and an average modulation strength of 4 dB/V with a moderate Q factor of ∼3700 and insertion loss of ∼6 dB using an ultrashort electrode length of only 350 nm. With 1 V driving voltage over a capacitive loading of only 13 fF, the silicon photonic nanocavity modulator can achieve more than 3 dB extinction ratio with energy consumption of only 3 fJ/bit. Such a low-voltage, low-capacitance silicon nanocavity modulator provides the feasibility to be directly driven by a CMOS logic gate for single-chip integration.