Beaconless pointing and tracking for bidirectional optical links using MEMS mirror nutation

Ondrej Čierny; Paul Serra; Kerri Cahoy

doi:10.1117/12.2582615

5 March 2021 Beaconless pointing and tracking for bidirectional optical links using MEMS mirror nutation

Ondrej Čierny, Paul Serra, Kerri Cahoy

Proceedings Volume 11678, Free-Space Laser Communications XXXIII; 116780I (2021) https://doi.org/10.1117/12.2582615
Event: SPIE LASE, 2021, Online Only

Abstract

Free-space laser links traditionally utilize an independent spatial tracking channel with a beacon laser and tracking sensors to meet stringent pointing requirements. In this work, we propose a miniaturized monostatic beaconless fiber transceiver that infers fine tracking information using existing receiver optoelectronics and a small injected pointing dither (nutation). A single MEMS steering mirror is used to both fine-point the beams and inject nutation. While this results in some additional link loss due to disturbed fiber coupling and transmit beam pointing, our analysis shows the loss becomes negligible for sufficient SNR. Links without point-ahead correction need an SNR of about 35 dB to minimize the dither loss below 0.1 dB and also maintain the RMS spatial tracking noise below a tenth of the beam divergence. Since the pointing and tracking bandwidth is typically many orders of magnitude slower than the receiver communication bandwidth, such SNR is usually achievable on the receiver with appropriate filtering. If point-ahead correction is needed, we show that depending on the available link margin, a transceiver based on single-mode fiber can reach up to about 1 beamwidth of correction, while a few-mode fiber design can reach up to about 1.75 beamwidths due to improved coupling sensitivity at higher point-ahead offsets. Finally, we propose the use of double-clad fiber with a secondary detector to help further minimize the incurred coupling loss.

Conference Presentation

Citation Download Citation

Ondrej Čierny, Paul Serra, and Kerri Cahoy "Beaconless pointing and tracking for bidirectional optical links using MEMS mirror nutation", Proc. SPIE 11678, Free-Space Laser Communications XXXIII, 116780I (5 March 2021); https://doi.org/10.1117/12.2582615

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