Integration of Microspheres and Multi-Quantum-Well Modulators as Retro-Modulation Surfaces for Optical Wireless and Free-Space Optical Communication

In this work, we introduce a retro-modulator surface as a monolithic passive transceiver for short- to medium-range optical wireless and free-space optical communication links. It incorporates a sublayer of microspheres for retroreflection and multi-quantum-well structure for modulation over the optical communication C-band (1530–1565 nm) when driven by digital voltages (0–5 V). Our theoretical analyses show that LaSFN9 and BaTiO3microspheres, with refractive indices of 1.8 and 2.0, respectively, give optimal retroreflection for shorter and longer link lengths, respectively; our experimental analyses reveal that our AlGaInAs-based modulator imparts sufficiently deep modulation over the C-band. This lets our integrated retro-modulator surfaces with LaSFN9 or BaTiO3microspheres function with fields-of-view of 10.8° or 9.4°, respectively, and modulation depths of 3.4% or 5.3%, respectively (giving extinction ratios of 0.93 or 0.89, respectively). Our characterizations of error performance through links with weak, moderate, and strong turbulence then show error vector magnitudes of 3.7%, 9.2%, and 24%, respectively, with bit error rates below 10–3, below 10–3, and equal to 0.0183, respectively. We conclude that retro-modulator surfaces can be effective elements in passive transceivers for short- to medium-range optical wireless or free-space optical communication links, through weak or moderate turbulence, while offering minimal size, weight, and power.