The continuing need to miniaturize mechanisms with wide range of motion for use in free-space optical communications has motivated the design of a low size, weight, and power (SWaP), two-axis gimbal with an optical fiber wrap as the key enabling feature. Our efforts to design a small gimbal with 100 micro-radian pointing accuracy for free-space optical communications have resulted in an unconventional optical fiber wrap design in order to achieve the low optical noise needed to meet system performance goals. Traditionally, fiber optic leads are installed in a stationary configuration to ensure maximum life and performance for the component. The fiber wrap design employed by Applied Technology Associates utilizes a combination of supplier design specifications and “mechanical spring” design techniques to construct a dynamic, innovative fiber mechanism, with life expectancy scaled to expected on-orbit operations and with negligible performance degradation. An engineering mockup was created to test both life expectancy and polarization performance at accelerated lifetime rates to verify the design. Presented in this paper is the design approach, test configuration approach, resulting lifetime testing (from cyclical stress testing), and polarization performance test outcomes. The polarization performance test outcomes show that the design results exceed planned lifetime goals, and maintain optical performance throughout the testing process. These test results confirm that fiber wrapping is a viable and available tool for miniature mechanisms in compact optical communications gimbals.
A technique employing a 3D morphological image-registration algorithm is demonstrated for stitching together high-resolution surface im- ages obtained with a commercial atomic-force microscope (AFM), producing 3D surface images up to 1mm long with lateral resolution ~ 100nm: These images can be applied to reflectance modeling by extracting surface parameters to be used as inputs for reflectance models, for instance the previously-published Coherence Model [BG. Hoover and VL. Gamiz, J. Opt. Soc. Am. A 23, 314 (2006)], which utilizes the surface roughness and autocorrelation derivatives in the large-roughness approximation. Surface moments estimated from extended-range AFM images demonstrate lower uncertainty at all frequencies and substantial reduction of sampling artifacts at low frequencies, enabling improved estimates of surface parameters. The autocorrelation of a nearly monoscale diffuse-gold surface is measured out to 800μm separation, and the autocorrelation of a multiscale tin surface provides parameters that verify the Coherence Model t to the measured quasimonostatic BRDF.
We propose to utilize confocal Raman spectroscopy combined with high resolution atomic force microscopy (AFM) for nondestructive characterisation of the sidewalls of etched and passivated small pixel (24 <i>μ</i>m×24 <i>μ</i>m) focal plane arrays (FPA) fabricated using LW/LWIR InAs/GaSb type-II strained layer superlattice (T2SL) detector material. Special high aspect ratio Si and GaAs AFM probes, with tip length of 13 <i>μ</i>m and tip aperture less than 7°, allow characterisation of the sidewall morphology. Confocal microscopy enables imaging of the sidewall profile through optical sectioning. Raman spectra measured on etched T2SL FPA single pixels enable us to quantify the non-uniformity of the mesa delineation process.