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 BaTiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> microspheres, 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 BaTiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> microspheres 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<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–3</sup>, below 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–3</sup>, 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.