Coherent optical processors
Date
2020
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Publisher
University of Delaware
Abstract
In the evolving landscape of mobile communications, the need for spatial and temporal (frequency) agility is increasing exponentially. With the number of wireless broadband subscriptions expected to surpass global population in the next five years~\cite{Erics1}, novel, efficient techniques for spatial and spectral channel separation become critical in ensuring quality signal delivery for every user and every device. Currently, the advent of photonic up-conversion has unlocked spectral capacity previously unheard of for purely electrical approaches; countless 4G~LTE signals of 10~MHz bandwidth can be modulated onto a single laser beam operating at 193~THz and transmitted through optical fibers with loss orders of magnitude less than the equivalent loss through coaxial cables alone. Coherent spatial processing of multiple optical feeds as received from an RF-photonic phased array has shown that spatial demultiplexing can be achieved using an optical Fourier transform, with current efforts dedicated to recovery of the received and upconverted signal(s) once they have been isolated spatially \cite{Phased1}. Further, spectral demultiplexing performed through \textbf{k}-space tomography leverages a similar system layout incorporating a computed tomography algorithm. While system layouts follow a general formula, the performance of any particular RF-photonic imaging system depends upon many components. This thesis starts with a discussion of the subsystems constituting an RF-photonic imager, followed by an examination of optical components, their trade spaces, and system performance characteristics for different RF photonic aperture configurations. Specifically, the effects of varying the waist of launch and pickup beams into the optical processor on the optical coupling efficiency, for an on-axis beam as well as for the limiting off-axis case, are investigated. The motivation for creation and validation of an accurate analytical model for such a system is the broad range of potential applications to ongoing and future work. In general, the validation of this process is directly applicable to system calibration for all RF-Photonic imaging and receiving systems, removing the need to perform lengthy calibration routines in the lab and potentially in the field. In particular, analytical and parametric models of certain system variation may significantly decrease the lengthy calibration cost of RF-Photonic \textbf{k}-space tomography.
Description
Keywords
Mobile communications, Photonic up-conversion, Spatial processing