We investigate the feasibility of additively manufacturing optical components to accomplish task-specific classification in a computational imaging device. We report on the design, fabrication, and characterization of a non-traditional optical element that physically realizes an extremely compressed, optimized sensing matrix. The compression is achieved by designing an optical element that only samples the regions of object space most relevant to the classification algorithms, as determined by machine learning algorithms. The design process for the proposed optical element converts the optimal sensing matrix to a refractive surface composed of a minimized set of non-repeating, unique prisms. The optical elements are 3D printed using a Nanoscribe, which uses two-photon polymerization for high-precision printing. We describe the design of several computational imaging prototype elements. We characterize these components, including surface topography, surface roughness, and angle of prism facets of the as-fabricated elements.
A 4-color imaging pyrometer was developed to investigate the thermal behavior of laser-based metal processes, specifically laser welding and laser additive manufacturing of stainless steel. The new instrument, coined a 2x pyrometer, consists of four, high-sensitivity silicon CMOS cameras configured as two independent 2-color pyrometers combined in a common hardware assembly. This coupling of pyrometers permitted low and high temperature regions to be targeted within the silicon response curve, thereby broadening the useable temperature range of the instrument. Also, by utilizing the high dynamic range features of the CMOS cameras, the response gap between the two wavelength bands can be bridged. Together these hardware and software enhancements are predicted to expand the real-time (60 fps) temperature response of the 2x pyrometer from 600 °C to 3500 °C. Initial results from a calibrated tungsten lamp confirm this increased response, thus making it attractive for measuring absolute temperatures of steel forming processes.
The goal of this study is to understand how to optimize the performance of micro-mirrors for a variety of optical microsystem applications. Our approach relies on a number of process variations and mirror designs to ultimately produce relatively large (500μm to mm-scale), smooth (for nm RMS), and flat mirrors (greater than 1m curvature). White-light interferometric measurements, and finite element models are discussed in support of these findings. Stress gradients and residual stresses have been measured for accurate modeling of micro-mirrors. Through this modeling study, we have identified relevant structural parameters that will optimize SUMMiT V MEMS mirrors for optical applications. Ways of mitigating surface topography, print-through effects, and RMS roughness are currently being investigated.
The optical system properties of a reconfigurable surface micromachined micro-electro-mechanical system (MEMS) interconnect are presented. An array of optical signals from a singlemode MT connector is first collimated by a refractive lenslet array. Each beam may be individually redirected by a rotatable, 45 degree flip-up MEMS mirror. The second, complimentary MEMS mirror folds the optical beam back through the lenslet array and couples it into a second fiber row on the MT connector. Much work has been presented promoting the utility of MEMS configurations to manipulate optical signals. This work examines, with ray tracing simulations, the proposed configuration from the detailed optical system perspective.
A slow-speed optical fiber cross-connect has been developed around surface-micromachined MEMS mirrors that pop up 45 degrees relative to the substrate and rotate 360 degrees about the normal axis. Various assembly, latching, and rotational mechanisms have been evaluated and tested, with current work focusing on demonstrating functionality. Routing capability has been characterized for 2 × 2 arrays of micromirrors, the feedback from which has been applied to second-generation designs with improved control and greater precision. The cross-connect described here is scalable and represents an important building block in a general-purpose photonic infrastructure.
The recent encouraging results on compliant substrates have made them a promising technology for innovative optoelectronic devices and circuits involving lattice mismatched semiconductors. Different from traditional bulk semiconductor substrates, compliant substrates are flexible templates that can accommodate the lattice strain produced during heteroepitaxial growth. This article discusses one special class of compliant substrates, namely twist-bonded compliant substrates. A twist-bonded compliant substrate contains a 30-100A thin layer bonded to a bulk crystal with a high-angle twist boundary at the interface. Experiment has shown that the twist-bonded thin layer functions as a compliant template to absorb the mismatch strain through elastic and plastic deformation. We have fabricated twist-bonded GaAs and Si compliant substrates and grown InGaAs (1.5% mismatch) and InSb (14.7% mismatch) layers on GaAs compliant substrates and Ge layers (4% mismatch) on Si compliant substrates. Cross sectional TEM results have shown a significant reduction in threading dislocation density for all these films. The crosshatch free InGaAs surface indicates that substrate compliance indeed provides a new strain release mechanism than forming dislocation half loops in the heteroepitaxial layers. The photoluminescence data from InGaAs multiquantum- wells also confirm the superior quality of heteroepitaxial layers grown on compliant substrates. Future research is directed to enhancement of our understanding of substrate compliance mechanisms, improvement of processing technology, and demonstration of critical photonic devices on compliant substrates.
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