Analysis and Experimental Demonstration of Conformal Adaptive Phase-Locked Fiber Array for Laser Communications and Beam Projection Applications
| dc.contributor.advisor | Vorontsov, Mikhail A. | en_US |
| dc.contributor.author | Liu, Ling | en_US |
| dc.contributor.department | Electrical Engineering | en_US |
| dc.contributor.publisher | Digital Repository at the University of Maryland | en_US |
| dc.contributor.publisher | University of Maryland (College Park, Md.) | en_US |
| dc.date.accessioned | 2009-01-24T06:45:11Z | |
| dc.date.available | 2009-01-24T06:45:11Z | |
| dc.date.issued | 2008-10-07 | en_US |
| dc.description.abstract | The primary goal of this research is the analysis, development, and experimental demonstration of an adaptive phase-locked fiber array system for free-space optical communications and laser beam projection applications. To our knowledge, the developed adaptive phase-locked system composed of three fiber collimators (subapertures) with tip-tilt wavefront phase control at each subaperture represents the first reported fiber array system that implements both phase-locking control and adaptive wavefront tip-tilt control capabilities. This research has also resulted in the following innovations: (a) The first experimental demonstration of a phase-locked fiber array with tip-tilt wavefront aberration compensation at each fiber collimator; (b) Development and demonstration of the fastest currently reported stochastic parallel gradient descent (SPGD) system capable of operation at 180,000 iterations per second; (c) The first experimental demonstration of a laser communication link based on a phase-locked fiber array; (d) The first successful experimental demonstration of turbulence and jitter-induced phase distortion compensation in a phase-locked fiber array optical system; (e) The first demonstration of laser beam projection onto an extended target with a randomly rough surface using a conformal adaptive fiber array system. Fiber array optical systems, the subject of this study, can overcome some of the drawbacks of conventional monolithic large-aperture transmitter/receiver optical systems that are usually heavy, bulky, and expensive. The primary experimental challenges in the development of the adaptive phased-locked fiber-array included precise (<5>microrad) alignment of the fiber collimators and development of fast (100kHz-class) phase-locking and wavefront tip-tilt control systems. The precise alignment of the fiber collimator array is achieved through a specially developed initial coarse alignment tool based on high precision piezoelectric picomotors and a dynamic fine alignment mechanism implemented with specially designed and manufactured piezoelectric fiber positioners. Phase-locking of the fiber collimators is performed by controlling the phases of the output beams (beamlets) using integrated polarization-maintaining (PM) fiber-coupled lithium niobate phase shifters. The developed phase-locking controllers are based on either the SPGD algorithm or the multi-dithering technique. Subaperture wavefront phase tip-tilt control is realized using piezoelectric fiber positioners that are controlled using a computer-based SPGD controller. Both coherent (phase-locked) and incoherent beam combining in the fiber array system are analyzed theoretically and experimentally. Two special fiber-based beam-combining testbeds have been built to demonstrate the technical feasibility of phase-locking compensation prior to free-space operation. In addition, the reciprocity of counter-propagating beams in a phase-locked fiber array system has been investigated. Coherent beam combining in a phase-locking system with wavefront phase tip-tilt compensation at each subaperture is successfully demonstrated when laboratory-simulated turbulence and wavefront jitters are present in the propagation path of the beamlets. In addition, coherent beam combining with a non-cooperative extended target in the control loop is successfully demonstrated. | en_US |
| dc.format.extent | 5970401 bytes | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://hdl.handle.net/1903/8773 | |
| dc.language.iso | en_US | |
| dc.subject.pqcontrolled | Physics, Optics | en_US |
| dc.subject.pqcontrolled | Engineering, System Science | en_US |
| dc.subject.pqcontrolled | Engineering, Electronics and Electrical | en_US |
| dc.subject.pquncontrolled | conformal adaptive phase-locked fiber array | en_US |
| dc.subject.pquncontrolled | coherent beam combining | en_US |
| dc.subject.pquncontrolled | adaptive optics | en_US |
| dc.subject.pquncontrolled | phase-locking | en_US |
| dc.subject.pquncontrolled | subaperture tip-tilt control | en_US |
| dc.subject.pquncontrolled | stochastic parallel gradient descent (SPGD) | en_US |
| dc.title | Analysis and Experimental Demonstration of Conformal Adaptive Phase-Locked Fiber Array for Laser Communications and Beam Projection Applications | en_US |
| dc.type | Dissertation | en_US |
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