We demonstrate a scalable photo-thermal process which enables manufacturing of infrared (IR) transmissive glass-ceramic films with gradient refractive index (GRIN) profiles. Spatiallycontrolled laser irradiation creates Pb-rich amorphous phases within Ge-As-Pb-Se glass films, which are subsequently crystallized and become high index phases upon heat treatment. The density of the high index nanocrystals is shown to be controlled by the laser irradiation power, and the extent of fraction crystallized is controlled by post heat treatment time and temperature. Both of these variables can be optimized to realize a localized effective refractive index change, enabling a spatially-modulated refractive index change up to ~ +0.1. We demonstrate IR GRIN functionality within 1 inch diameter GAP-Se films with thicknesses ranging from 1 to 40 μm, confirming the scalability of our photo-thermal process to component-relevant geometries.
The large number of surface types that are manufacturable today provide many available paths to the optical designer. It is not always clear which path provides the optimal balance of merit function complexity, convergence speed, and image quality after optimization. This paper shows that Q-type polynomials provide a strong benefit in both convergence speed and image quality after optimization when the footprint comprises a large portion of the area inside the normalization radius, but for off-axis systems with large decenters this benefit is weakened. Also, the sensitivity of several unobscured reflective designs is compared to show that although surface types with more degrees of freedom can reduce some sensitivities, the design form is the primary driver and a system that occupies a smaller volume will tend to have higher sensitivities to misalignments regardless of surface type.
BAE Systems has developed an improved tool for exporting optical design coordinates to Computer-Aided Drafting (CAD) software. Existing scripts within common lens design packages export element shapes and rays which is enough for standard systems, but complex system design requires knowledge of surface vertices and coordinates for each component. Fixed coordinates for each element allows the mechanical engineer to place parts more accurately than allowed by the standard surface export algorithms, as well as locking optical elements in space so that mating surfaces do not inadvertently move optical elements during mechanical optimization. Including optical element vertex coordinates is useful for rotationally-symmetric systems, especially after multiple design iterations, and is essential for multi-channel, off-axis systems where apertures are not centered on surface vertices.
Coatings of various metalized patterns are used for heating and electromagnetic interference (EMI) shielding
applications. Previous work has focused on macro differences between different types of grids, and has shown good
correlation between measurements and analyses of grid diffraction. To advance this work, we have utilized the
University of Arizona's OptiScan software, which has been optimized for this application by using the Babinet Principle.
When operating on an appropriate computer system, this algorithm produces results hundreds of times faster than
standard Fourier-based methods, and allows realistic cases to be modeled for the first time. By using previously
published derivations by Exotic Electro-Optics, we compare diffraction performance of repeating and randomized grid
patterns with equivalent sheet resistance using numerical performance metrics. Grid patterns of each type are printed on
optical substrates and measured energy is compared against modeled energy.
We have recently demonstrated the ability to measure the absolute change in optical power (focus) of a 152 mm diameter flat mirror in vacuum between room and cryogenic temperatures (133K) with a peak-to-valley measurement error of only 22nm. Such a measurement would be crucial to the verification of the focus of a cryogenic instrument during ground testing.
The testing utilized a vibration-insensitive interferometer and a reference mirror maintained at room temperature located within the thermal vacuum chamber. Special considerations were taken to ensure that the reference mirror experienced low axial thermal gradients, since structural modeling indicated that axial thermal gradients and axial variation of substrate coefficient of thermal expansion are critical in maintaining flatness under cryogenic test conditions. This paper will discuss the testing equipment and methodology and the corresponding analysis and results.
A microring resonator, a circular waveguide adjacent to a straight waveguide, performs selective band-stop filtering for optical telecommunications. Small size and versatility of functionality allow many microrings to be incorporated into a single integrated optic circuit. We desire small size, less than 20 micron radius; low insertion loss in band-stop outside resonance; perfect cancellation to zero in band-stop at resonance; and low refractive index difference between core and cladding. These requirements are conflicting: conventional silicon waveguides cannot achieve low enough loss at the desired bend radius. Current approaches use different materials with higher refractive index differences. Analysis and simulation provide evaluation of the trade-offs. Further, we propose, for the first time, conventional waveguides using Bragg reflectors surrounding the microring to reduce loss for improved performance. Simulation shows feasibility of this approach.
The Levinson-Durbin (LD) algorithm has been used for decades as an alternative to Fast-Fourier Transforms (FFTs) in cases where several cycles of a signal are not available or too expensive to obtain. We describe a new application of this LD algorithm using spectral estimation to locate a magnetic dipole, such as a submarine or magnetic mine, relative to a high-sensitivity probe (i.e. gradiometer/magnetometer sensor) moving through the magnetic field. The weakness of the FFT is assuming periodic inputs, thus when the sample ends at a different level than the input, the FFT incorrectly inserts a step at the 'break' between cycles; the LD algorithm benefits by assuming that nothing outside the sampling window will change the spectrum. The iterative LD algorithm is also well suited for real-time operations since it can be solved continuously while the probe moves toward the subject. By establishing spectral templates for different measurement paths relative to the source dipole, we use correlation in the spectral domain to estimate the distance of the dipole from our current path. Direction, and thus location, is obtained by simultaneously sending a second probe to complement the information gained by the first probe, together with a multidimensional LD algorithm.