Graphene-based liquid-crystal microlens arrays for synthetic-aperture imaging

Abstract

In this paper, a new kind of liquid-crystal microlens array with graphene electrodes controlled electrically are designed and fabricated successfully. The graphene-based liquid-crystal microlens arrays (GLCMAs) exhibit excellent beam focusing performances in both the visible and near infrared (NIR) wavelength regions and also synthetic aperture imaging function. The graphene films used to fabricate the electrodes of the GLCMAs are grown by chemical vapor deposition over copper foils, demonstrating several characters of low sheet resistance and high transmittance in both wavelength ranges above. The key processes for shaping the GLCMAs include: transferring graphene films from copper foils to wafers selected, conventional UV-photolithography, ICP etching, and liquid-crystal encapsulation. Through performing common optical measurements, the point spread functions of incident lasers with different wavelength, such as red lasers of ∼600 nm, green lasers of ∼532 nm, and NIR lasers of ∼980 nm, have been obtained. Several key parameters including focal spots size, average normalized light intensity, focal length, average deviation rate and contrast ratio have been acquired and analyzed. A particular synthetic-aperture imaging based on the GLCMA is realized so as to certify a fact that a single target pattern can be constructed effectively based on some sub-aperture patterns with several tens or hundreds of micrometer scale, and thus highlight a way to fast process partial or small-zoned patterns for enhancing the detection efficiency of special targets.