High photon efficiency (HPE) techniques, using pulse modulation, capacity approaching error correcting codes, and photon counting receivers, can be used to significantly reduce the size, weight, and power (SWaP) of an optical communication system by reducing aperture size and transmit laser power requirements. Low-SWaP systems also require compact, low-power receivers capable of photon-limited performance. We investigate the use of semiconductor optical amplifiers (SOAs) to achieve near-photon limited performance in low-SWaP HPE systems. SOAs are significantly smaller and require less external support compared with Erbium-doped fiber amplifiers (EDFAs). We build and test a low-noise optical pulse receiver using a semiconductor optical amplifier and avalanche photodiode (APD). Pulse-to-pulse variations, amplified spontaneous emission (ASE) levels, and background noise levels are measured and used to evaluate an expected bit error rate (BER) as a function of signal photons per pulse. Overall power draw of the system, including SOA drive current, thermo-electric cooler (TEC) drive, and APD bias and temperature control and trans-impedance amplifier, are evaluated to assess the overall impact of the SOA receiver on optical terminal power requirements. We show that SOA receivers can be used as near-photon limited receivers in HPE optical communication systems.
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 μm×24 μm) 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 μm 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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.