Hemispherical retro-modulation technologies for passive free-space optical communication links

Alexander C. MacGillivray; Sayra Gorgani; Ilija R. Hristovski; Matthias F. Jenne; Nikolai I. Lesack; Jonathan F. Holzman

doi:10.1117/12.2655454

15 March 2023 Hemispherical retro-modulation technologies for passive free-space optical communication links

Alexander C. MacGillivray, Sayra Gorgani, Ilija R. Hristovski, Matthias F. Jenne, Nikolai I. Lesack, Jonathan F. Holzman

Author Affiliations +

Proceedings Volume 12413, Free-Space Laser Communications XXXV; 124130L (2023) https://doi.org/10.1117/12.2655454
Event: SPIE LASE, 2023, San Francisco, California, United States

Abstract

In this work, we introduce the concept of a hemispherical retro-modulator for the realization of passive free-space optical communication links. The hemispherical retro-modulator is implemented with a high-refractive-index glass (S-LAH79) hemisphere on a semi-insulating-InP (SI-InP) layer, whose thickness dictates the effectiveness of both retroreflection and modulation. A voltage is applied across transparent indium tin oxide (ITO) and gold (Au) films on either side of the SIInP layer to bring about the desired modulation. The overall device is designed to enable low divergence on the retroreflected beam, as defined by a small divergence angle, and deep modulation on the retroreflected beam, as a result of electroabsorption in the SI-InP layer. To this end, the device is analysed with a ray-based model for retroflection and a unified Franz-Keldysh/Einstein model for modulation in the SI-InP layer. The theoretical results show strong agreement with the experimental results from our prototype. Moreover, the results show effective retroflection and deep modulation—with an applied electric field of 2.167 kV/cm yielding modulation depths of 13%, 34%, and 50% for our 980-nm photons and SI-InP layer thicknesses of 200, 600, and 1,000 μm, respectively. From this, we deem the SI-InP layer thickness of 600 μm to be optimal given its combined capabilities for retroflection and modulation. Ultimately, the introduced hemispherical retro-modulator is shown to be an effective element for future realizations of passive freespace optical communication links.

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Alexander C. MacGillivray, Sayra Gorgani, Ilija R. Hristovski, Matthias F. Jenne, Nikolai I. Lesack, and Jonathan F. Holzman "Hemispherical retro-modulation technologies for passive free-space optical communication links", Proc. SPIE 12413, Free-Space Laser Communications XXXV, 124130L (15 March 2023); https://doi.org/10.1117/12.2655454

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