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Experimental implementation of an optical multiple-aperture antenna for space communications

An optical multiple-aperture antenna whose subantenna fields are phased should permit nonmechanical steering of the outgoing laser beam in analogy to the microwave regime. Corresponding theoretical analysis showed promising results. To our knowledge, however, little experimental evidence of optical phasing exists, prompting a beam steering experiment having 'proof-of-concept' character. Our design foresees a small optical antenna array consisting of three subapertures fed by a diode-pumped Nd:YAG ring laser via single-mode fibers. A measurement and control unit generates the necessary phase adjustment signals applied to piezoelectric fiber stretchers acting as phasing actuators. To this end, a 'pilot-beam' concept was developed. The individual subantenna beams are phased with respect to the pilot beam, which defines the direction of the antenna axis.