Abstract
We describe a prototype element for use in probing electro-optic retro-reflection in sensor applications, illuminating a planar-aligned nematic liquid crystal electro-optic cell with convergent light having a single, tunable angle of incidence (tunable conical illumination). This illumination is generated using a 100X, high numerical aperture, long working-distance microscope objective under conditions of extreme spherical aberration. The electro-optic effect observed is multiple-beam optical interference between polarized reflections from the two bounding plates of the cell, rendered tunable with voltage-controlled refractive index changes induced by molecular reorientation of the liquid crystal. Characterization of the reflectivity vs. angle of incidence and applied voltage enables identification of conditions of high-contrast, low power, electro-optic reflectivity control applicable to fiber optics.
Highlights
A variety of remote sensing applications are enabled by miniature optical sensing devices that generally report spectral changes in absorption or fluorescence and are interrogated at long range by retro-reflected laser light, delivered by fiber optic [1–4] or free space propagation [5–19]
We describe a prototype element for use in probing electro-optic retro-reflection in sensor applications, illuminating a planar-aligned nematic liquid crystal electro-optic cell with convergent light having a single, tunable angle of incidence, generated using a 100X, high numerical aperture, long working-distance microscope
The results show that the electro-optic contrast obtained depends strongly on angle of incidence, cell geometry and thickness, and Liquid crystal (LC) parameters, and enable the design of high-contrast, low power, electro-optic reflectivity control applicable to fiber optics
Summary
A variety of remote sensing applications are enabled by miniature optical sensing devices that generally report spectral changes in absorption or fluorescence and are interrogated at long range by retro-reflected laser light, delivered by fiber optic [1–4] or free space propagation [5–19] The addition, to these and other remote devices, of a capability to communicate local information by intensity or phase modulation of the retro-reflected light would enable a variety of significant enhancements [20–22]. The electro-optic effect observed is multiple-beam optical interference between polarized reflections from the two bounding plates of the cell, rendered tunable with voltage-controlled refractive index changes induced by molecular reorientation of the liquid crystal This geometry would be suitable for information transfer from a sensing device that communicates using light incident from an optical fiber by modulating its reflection back down the fiber. The results show that the electro-optic contrast obtained depends strongly on angle of incidence, cell geometry and thickness, and LC parameters, and enable the design of high-contrast, low power, electro-optic reflectivity control applicable to fiber optics
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