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16 March 2015 Continuous beam divergence control via wedge-pair for laser communication applications
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Abstract
Lasercom terminals often scan an area of uncertainty during acquisition with a wide-divergence beacon beam. Once the terminal has established cooperative tracking with the remote terminal, a narrow divergence beam is used for communication. A mechanism that enables continuous beam divergence control can provide significant size, weight, and power (SWaP) benefits to the terminal. First, the acquisition and the communication beams can be launched from the same fiber so only a single high-power optical amplifier is required. Second, by providing mid-divergences, it eases the remote terminal’s transition from the acquisition phase to the communication phase. This paper describes a mechanism that provides gradual, progressive adjustment of far-field beam divergence, from wide divergence (> 300 μrad FWHM) through collimated condition (38 μrad FWHM) and that works over a range of wavelengths. The mechanism is comprised of a variable-thickness optical element, formed by a pair of opposing wedges that is placed between the launch fiber and the collimating lens. Variations in divergence with no beam blockage are created by laterally translating one wedge relative to a fixed wedge. Divergence is continuously adjustable within the thickness range, allowing for a coordinated transition of divergence, wavelength, and beam power. Measurements of this low-loss, low-wavefront error assembly show that boresight error during divergence transition is maintained to a fraction of the communication beamwidth over wavelength and optical power ranges.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Keith M. Hinrichs, Alan E. DeCew, Lawrence E. Narkewich, and Timothy H Williams "Continuous beam divergence control via wedge-pair for laser communication applications", Proc. SPIE 9354, Free-Space Laser Communication and Atmospheric Propagation XXVII, 93540L (16 March 2015); https://doi.org/10.1117/12.2084557
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