New moldable, infrared (IR) transmitting glasses and diffusion-based gradient index (GRIN) optical glasses enable simultaneous imaging across multiple wavebands including short-wave infrared, midwave infrared, and long-wave infrared, and offer potential for both weight savings and increased performance in optical sensors. Lens designs show potential for significant reduction in size and weight and improved performance using these materials in homogeneous and GRIN lens elements in multiband sensors. An IR-GRIN lens with Δn = 0.2 is demonstrated.
Optical design requires an accurate knowledge of the dispersion functions for the materials in each lens. For systems to work over a wide range of temperature, knowing the temperature dependence of these functions is as important as knowing the coefficients of thermal expansion. The dispersion curves of several NRL-developed infrared glasses were measured over a temperature range that spanned, at minimum, -20°C to 60°C. Details concerning the data fidelity, data modeling, fit results, and physical implications of the results will be provided in this work.
Vendor-supplied calibration curves for fixed-grating, fixed-detector-array portable spectrometers typically provide wavelength accuracies of about ±1 pixel on the array. Independent calibration using atomic lamp spectra is hampered by the sparsity of available lines: interpolation between atomic lines typically leads, again, to pixel-width errors or greater. We provide a technique that combines information from sparse atomic line spectra with densely populated peaks from the transmission spectrum of an air-spaced etalon to generate calibration curves capable of ~1/10th pixel accuracies across entire detector arrays. Subsequent transmission spectra through solid etalons of well-characterized glass samples validate the calibration procedure.
New moldable, infrared (IR) transmitting glasses from NRL and graded index (GRIN) optical materials enable simultaneous imaging across multiple wavebands including SWIR, MWIR and LWIR and offer potential for both weight savings and increased performance in optical sensors. Lens designs show the potential for significant SWaP reduction benefits and improved performance using NRL materials and IR-GRIN lens elements in multiband sensors.
Starting with a literature-based design for a rifle scope, we demonstrate the potential to replace large, heavy glass lenses with polymer-based GRIN lenses with little optical penalty, while saving 50% of the lens weight in the system. Several properties of the primary design are chosen to favor manufacturability, such as leaving glass for the external surfaces and choosing polymers and GRIN geometries based on proven fabrication techniques. Compared to the reference design which weighed 154 g, the GRIN-substituted design weighed 78 g while maintaining visually constant performance from 0-40°C.
Previous work developed a first-order theory for picking optimal pairs of materials for gradient index (GRIN) achromatic singlets. This work extends that concept to include the addition of a third material to a GRIN blend, to improve performance further. Several ternary-based GRIN lens designs are compared to binary versions. Implications for material development in gradient index optics are discussed.
Previous work identified a lens design in which a polymer GRIN element was able to simultaneously correct for firstorder color and temperature variations of a glass singlet. This work presents a materials-based theory, rooted in paraxial optics, that explains this correction and identifies relationships among the GRIN and glass materials which must hold for the correction to be effective. This result provides a path for using polymer optics, with their relatively large thermophysical and thermo-optic coefficients, in passively corrected optical systems over significant temperature ranges.
An optical design is shown which provides simultaneous color correction over the visible spectrum and passive thermal
compensation, for an f/4 doublet made of a glass and a polymer gradient index (GRIN) element. The design is enabled
by a new optical model for the thermally varying GRIN element, which incorporates measured material properties from
20-40°C (limited only by the extent of the measured data set). The design is made possible because of the GRIN degrees
of freedom available to the material. A color-corrected doublet is most efficient when there is a large ratio of the
dispersion strength (Abbe number) between the two materials. To make that doublet athermal, however, there needs to
be an equally high ratio between the thermal coefficients. The large ratio of polymer to glass thermal coefficients
presents a unique advantage for GRIN: the effective GRIN dispersion coefficient can have just as large a ratio to the
glass as the thermal coefficients, making for a powerful athermal achromat. To our knowledge, this is the first example
of a polymer GRIN used for simultaneous chromatic and thermal correction.
A new figure of merit is developed for ranking pairs of materials as candidates for gradient index (GRIN) optics capable
of good color correction. The approach leverages recent work which derives a connection in GRIN lenses between the
optical properties of constituent materials and the wavelength dependence of the lens power. We extend the analysis
here, the effectiveness of which is evidenced by a simulated f/3 GRIN lens with diffraction-limited performance over the
visible spectrum, using the top material pair selected out of a database of >60,000 possible candidates.
This paper presents new multispectral IR glasses with transmission from 0.9 to > 14 μm in wavelength and refractive
index from 2.38 to 2.17. These new glasses are designed to have comparable glass softening temperatures and
compatible coefficients of thermal expansion to allow bonding and co-molding of multilayer optics. With large variation
in their Abbe numbers and negative to near-zero dn/dT, optics made from these new glasses can significantly reduce the
size/weight or complexity of the multispectral imaging systems for weight sensitive platforms.
Hybrid quantum systems can be formed that combine the strengths of multiple platforms while avoiding the weaknesses. Here we report on progress toward a hybrid quantum system of neutral atom spins coupled to superconducting qubits. We trap laser-cooled rubidium atoms in the evanescent field of an ultrathin optical fiber, which will be suspended a few microns above a superconducting circuit that resonates at the hyperfine frequency of the Rb atoms, allowing magnetic coupling between the atoms and superconductor. As this will be done in a dilution refrigerator environment, the technical demands on the optical fiber is severe. We have developed and optimized a tapered fiber fabrication system, achieving optical transmission in excess of 99.95% , and fibers that can sustain 400 mW of optical power in a UHV environment. We have also optimized tapered fibers that can support higher order optical modes with high transmission (> 97%), which may be useful for different optical potential geometries. We have developed an in-situ tunable high-Q superconducting microwave resonator that can be tuned to within the resonator linewidth of the 6.8 GHz frequency of the Rb hyperfine transition.
We have demonstrated efficient propagation of the first excited TE01, TM01, and HE21 modes in a nanofiber
with a radius of 400 nm. As we decrease the taper angle from 4 mrad to 1 mrad, the propagation becomes more
adiabatic and the transmission improves from 20% to 85%. We have also demonstrated that the choice of drawn
fiber can have a significant impact on the propagation characteristics.
Polymers are receiving considerable attention as components in novel optical systems because of the tailored
functionality, ease of manufacturing, and relatively low cost. The processing of layered polymeric systems by
coextrusion is a method to produce films comprising hundreds to thousands of alternating layers in a single, one-step
roll-to-roll process. Several layered polymer optical systems have been fabricated by coextrusion, including gradient
refractive index lenses, tunable refractive index elastomers, photonic crystals, and mechanically tunable photonic
crystals. Layered polymeric optical systems made by coextrusion can also incorporate active components such as
photoreactive additives for multilayered patterning and laser dyes for all-polymer laser systems. Coextrusion is a process
which allows for the flexible design of polymeric optical systems using layers with thickness spanning the nanoscale to
This paper reviews recent progress in the design and fabrication of bio-inspired gradient index lenses. Inspired by the
gradient index distributions of the protein layers in biological eyes, we employ nested layers of polymer composites to
create smoothly-varying index distributions within bulk lens substrates. Because the fabrication technique allows for
independent control of the index layers, the index contours, and the final lens surfaces, optical power can be combined
with aberration control in a single element. Gradient-index singlets which correct for spherical aberration and singlets
which correct for chromatic aberration are described as examples of the utility of this class of optics.
The design, fabrication, and properties of one of a new class of gradient-index lenses are reported. The lens is an f/2.25 GRIN singlet based on a nanolayered polymer composite material, designed to correct for spherical aberration. The light
gathering and focusing properties of the polymer lens are compared to a homogeneous BK7 glass singlet with a similar
f-number. The modulation transfer function of the polymer GRIN lens exceeded that of the homogeneous glass lens at
all spatial frequencies and was as much as 3 times better at 5 cyc/mm. The weight of the polymer lens was
approximately an order of magnitude less than the homogeneous glass lens.