This PDF file contains the front matter associated with SPIE Proceedings Volume 12514, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this work, we design an InGaAs avalanche photodiode (APD) with a higher photocurrent to dark current ratio than a conventional APD. The improvement is based on optical confinement in an optical resonant metastructure, which increases the optical intensity in the detector volume and thus its quantum efficiency. With optical confinement, the absorbing layer can be 20 times thinner than the conventional APD, reducing the intrinsic generation-recombination dark current by the same amount and still be able to produce 90.9% of the photocurrent. The photocurrent to intrinsic dark current ratio can thus be increased theoretically by 18.2 times in concomitant with a lower operating voltage. Higher photocurrent can also be obtained using a thicker absorber. Besides APDs, the optical resonator structure can also be applied to p-i-n photodiodes for similar improvement. To further increase the detection sensitivity, we design an efficient InGaAsP light emitting diode (LED) having a similar resonator geometry. The resonator geometry enables more collimated emission and increases the optical power theoretically by more than 36 times compared to a conventional LED. Integrating the meta- APD and LED together will yield a powerful SWIR transceiver for various low light, LIDAR, and 3-dimensional imaging applications.

The detection of Nd: YAG laser emission at 1.064 microns is important for a number of applications such as active infrared imaging and space LIDAR. We propose a silicon avalanche photodiode (APD) based on micro-scaled photonic metastructures. In one approach, the metastructure contains a hexagonal hole array filled with SiO₂ to yield optical diffraction and trapping. With 3D electromagnetic modeling, we optimize the array dimensions and yield 26.0% theoretical absorption at 1.064 microns. It is 59 times larger than that of the planar structure with an additional 18% dark current reduction. In another approach, the metastructure contains a ring array fabricated on the top contact layer to excite localized surface plasmons. The theoretical QE is 52 times larger and the dark current is 8.6 times lower. In addition to active imaging and LIDAR, the present meta-APD designs are also useful for broadband passive imaging, in which I_p/I_d can be improved by 3.9 and 8.7 times, respectively. The ring metastructure can also be integrated with an InGaAsP light emitting diode to produce coherent, directional emission at 1.064 micron to further improve SWaP in active applications.

Based on the recent success of our strained-layer superlattice (SLS)-based infrared (IR) camera that performed Earth imaging from the International Space Station (ISS) in 2019 we have built, what we consider, to be the next generation multi-band SLS imaging system. The Compact Thermal Imager (CTI) was installed on the Robotic Refueling Mission 3 (RRM3) and attached to the exterior of the ISS. From this location we were able to capture 15 million images of a multitude of fires around the globe in 2019. This unexpected trove of data initiated quite a bit of scientific interest to further utilize this imaging capability but would include features to more precisely monitor terrestrial fires and other surface phenomena. To this end, we developed a technique to install specific bandpass filters directly onto the SLS detector hybrid assembly. Utilizing this technique we have built a CTI-2 camera system with two filters, 4 and 11μm, and have made a second detector assembly with six filter bands from 4- 12μm. This second system will also be used to supplement Landsat remote imaging monitoring approximate land surface temperatures, monitor evapotranspiration, sea ice and glacier dynamics. The CTI-2 camera is based on a 1,024x1,024 (1kx1k) format SLS detector hybridized to a FLIR ISC0404 readout integrated circuit (ROIC). The six band SLS focal plane array is based on the 640x512 FLIR ISC 9803 ROIC. This camera system is based on the Landsat 8 and 9 Thermal IR Sensors (TIRS) instrument and one of its purposes is to perform ground truthing for the Landsat 8/9 data at higher spectral resolution. Both Landsat TIRS instruments are dual band thermal IR sensors centered on 11 and 12μm (each with about a 1μm bandpass). Both of our SLS systems utilize a Ricor K548 cryocooler. To streamline costs and development time we used commercial optics and both commercial and custom NASA electronic components. A primary feature of these camera systems is the incorporation of specific filters to collect fire data at ~3.9μm and thermal data at ~11μm. The CTI- 2 instrument is designed for 37 m /pixel spatial resolution from 410km orbit (ISS orbit). In this paper, we will present the design and performance of the focal plane, optics, electronics and mechanical structure of the dual-band CTI-2 and the focal plane performance of the six-band focal plane.

Photon detectors are increasingly utilizing quantum features to enhance their performance. Cutting down on dark current by reducing absorber thickness necessitates electron/hole carrier transport engineering to obtain gain via quantum features. Superlattices, barrier-based detectors, and quantum materials such as Floquet engineered systems are poorly served by semi-classical transport modeling approaches and a fully quantum approach is warranted to capture all quantum features from a bottom-up fashion. These effects include non-parabolic and low-dimensional bandstructures, tunneling, resonant transport, dynamic (Floquet) and low-dimensional (Anderson) localization, transport mediation via phonons, plasmons, and photons, as well as various recombination and carrier generation/multiplication methods. In this work we present a systematic framework for quantum transport modeling of detectors via the Non-Equilibrium Green’s Function (NEGF) formalism. This formalism is highly modular in terms of extending the transport related physics, as well robust in handling arbitrary material stack, given a Hamiltonian description. This method has been successfully used in analysis of highly scaled, 2D and nanowire transistor devices, transport in novel quantum materials, and in non-equilibrium thermal transport, and therefore forms a solid foundation for building our platform. However, many open challenges remain in doing so, and in this work, we describe our recent efforts towards advancing this framework for its adoption as a preferred tool for next generation quantum enhanced photon-detectors.

Free space coupled, InGaAs PIN + TIA Quad Photoreceivers enable multiple space applications that require differential wavefront sensing, such as gravitational wave detectors, and position sensing and tracking, for example inter-satellite optical communication links. Optical crosstalk between the individual quadrants of the 2 × 2 photoreceiver array is a key parameter that limits the position and/or direction sensing error of the system. Therefore, it is imperative to ensure low crosstalk in the quad photoreceivers throughout the mission life. We present 1 mm, 1.5 mm, and 2 mm diameter low noise Quad Photoreceivers that demonstrate crosstalk < -30 dB up to 20 MHz frequency. These devices were subjected to 100 MeV Protons and 100 MeV/n Helium Ions up to a fluence of 1 × 1010 cm^-2. These tests not only validate the devices for Geostationary Orbit missions, but also for deep space missions outside of Earth’s protective magnetosphere where Galactic Cosmic Rays are a significant component of the radiation environment. All devices were found to be fully functional after radiation, and their crosstalk was essentially unchanged in all cases. Pre- and Post- radiation results were also measured for Dark Current vs. Reverse Bias Voltage for the Quad Photodiodes, DC Responsivity of the Quad Photodiodes, Conversion Gain and Bandwidth of the PIN + TIA Quad Photoreceiver, TIA Drive Current, and Input Equivalent Noise Density of PIN + TIA. Although we observed an increase in dark current due to radiation induced displacement damage in the Quad Photodiode, we did not observe any change in any other parameter for Quad Photoreceivers.

Polarimetry imaging technology has progressed rapidly in recent years. It promises advances in various fields of application, including remote sensing, medical imaging, molecular sensing, and many areas of defense and homeland security application. Conventional polarimetry is not flexible and has remained difficult to implement due to the complexity of optics and moving parts, and generally, it is bulky and costly. Recent advances in the design, micro/nanofabrication, and testing of metasurfaces have opened tremendous opportunities by simplifying the optics pathway. These sub-wavelength and flat structures can be engineered to transform the propagation, phase, and polarization of light. It is now conceivable to replace the carefully aligned optical components with a single well-designed metasurface. In this work, we present the design, fabrication, and integration of a multiplexed dielectric metasurface operating at 532 nm, which is of great interest for underwater imaging. The metasurface developed in this work spatially diffracts polarizations, resulting in demultiplexing the polarization, and the intensity of each polarization was recorded to determine the Stokes parameters. We will discuss the optimization process of designing the dielectric metasurface to recover the Stokes parameters for imaging and the degree of polarization. With the FDTD simulation, we explored the metasurface design parameter space to achieve better transmission and phase control. The incorporation of Pancharatnam–Berry phase and cross-talk among the orthogonal components of linearly and circularly polarized light were evaluated. The designed metasurface was fabricated using electron beam lithography and ICP-RIE etching. Finally, the fabricated metasurface was integrated with a time-of-flight multi-pixel imager.

The development of a scalable, low cost, low power, and room temperature operating MWIR detector technology capable of high spatial resolution infrared (IR) imaging is of substantial interest and utility towards the advancement of space and satellite technologies, including remote sensing and earth observation capabilities. However, conventional mid-wave infrared (MWIR) band photodetectors based on HgCdTe material typically require external cooling to achieve sufficient sensing performance, adding significant size, weight, and power restrictions and requirements. By incorporating bilayers of p⁺-doped graphene to function as a high mobility channel enhancing recombination of photogenerated carriers within HgCdTe absorbing material, a graphene-enhanced HgCdTe photodetector capable of providing uncooled detection over the 2-5 μm MWIR band has been developed. This high performance MWIR band detector technology comprises graphene bilayers initially deposited on Si/SiO₂ doped with boron and annealed using a spin-on dopant (SOD) process, that are subsequently transferred onto HgCdTe. Raman spectroscopy, secondary-ion mass spectroscopy (SIMS), and I-V photocurrent testing were used to analyze dopant levels, structural properties of the bilayer graphene prior to and following doping and transfer, and detector IR photoresponse, respectively, of the graphene-enhanced detector devices through various stages of the development process. These room-temperature operating graphene-HgCdTe MWIR detectors have demonstrated enhanced MWIR detection performance to benefit certain NASA Earth Science, defense, and commercial applications.

Event-based sensors are a novel sensing technology which capture the dynamics of a scene via pixel-level change detection. This technology operates with high speed (>10 kHz), low latency (10 μs), low power consumption (<1 W), and high dynamic range (120 dB). Compared to conventional, frame-based architectures that consistently report data for each pixel at a given frame rate, event-based sensor pixels only report data if a change in pixel intensity occurred. This affords the possibility of dramatically reducing the data reported in bandwidth-limited environments (e.g., remote sensing) and thus, the data needed to be processed while still recovering significant events. Degraded visual environments, such as those generated by fog, often hinder situational awareness by decreasing optical resolution and transmission range via random scattering of light. To respond to this challenge, we present the deployment of an event-based sensor in a controlled, experimentally generated, well-characterized degraded visual environment (a fog analogue), for detection of a modulated signal and comparison of data collected from an event-based sensor and from a traditional framing sensor.

This paper reports on the characteristics of the plasmonic phenomena in diamond FET devices at THz frequencies. We present a detailed numerical study of the terahertz resonant response of n-diamond TeraFETs as a function of temperature and channel length, demonstrate their potential for emerging terahertz applications, and compare their performance with that for p-diamond devices. The results show that short channel n-diamond TeraFETs exhibit a resonant response at room and cryogenic temperatures. We also report on the impact of the amplitude of the impinged THz signal and gate-to-channel separation on the induced voltage response. In our analysis, we have accounted for the effect of the viscosity of the electron fluid in the channel which is one of the major contributors to the damping of the plasma waves.

This study examines estimation of dielectric functions, based on the ability of pseudo-broadened DFT-calculated IR spectra to have very high correlation with measured IR-spectra, on the macroscale. For the case of dielectric-function estimation, one seeks by means of pseudo broadening, a best or most reasonable approximation of macroscale absorbance spectra using DFT spectra. Specifically, this study examines scalability of DFT-calculated IR spectra with respect to meso and macro scales, characteristic of dielectric response as measured using different IR spectroscopies. A case study analysis concerning scalability of IR spectra for caffeine is described.

This study describes a parametric model of diffuse reflectance, based on reduction of absorption spectra for NIR-SWIR absorbing dyes on substrates, using critical feature isolation and projection. The critical features are identified through a structural analysis of the peaks, troughs, and points of inflection in the calculated Kubelka-Munk absorption spectra from diffuse reflectance measurements. These features are then parameterized and projected into a reduced feature subspace to effectively capture the fundamental characteristics of the absorbing dyes. The parametric model is structured for combination with effective-medium models of mixtures and deposit-on-substrate micro or meso structure

As modern displays continue to increase in resolution, means of capturing images and videos at such high resolutions can be prohibitively expensive. This is especially true in the infrared domain. Image super-resolution, or upsampling, has often been applied to improve the aforementioned problem. Deep learning models have been proposed to reconstruct high quality high-resolution images from a low-resolution base. Previous solutions require a massive number of parameters which necessitate a large amount of free memory and computation power or they fall apart when applied to the infrared domain. As a result, many modern super-resolution models are not entirely practical. One difficult aspect in IR super-resolution is that IR images are inherently noisy, causing a poor signal-to-noise ratio, due to characteristics of IR sensors and internal reflections within the lenses. Because of this, super-resolution in IR must also act somewhat as a denoiser. Therefore, we propose a highly efficient, super-resolution model capable of producing single-image super-resolution in the IR domain.

The growth and development of antireflection (AR) coatings comprising alternating optical layers has enabled reduced losses due to reflection of radiation off substrates and optical components, with associated substantial improvements in overall optical and imaging performance for a wide range of devices and applications. A novel means of enhancing transmission for improved detector and system performance has involved the growth of nanostructured optical layers offering tunable refractive index properties that provide broadband and omnidirectional suppression of light reflection/scattering while increasing transmission. These nanostructured AR coatings can be custom designed for specific wavebands from the ultraviolet (UV) to long-wave infrared (LWIR) for various photonic applications, such as when the need for increased sensitivity over a given wavelength range requires maximizing the transmission of light, e.g., onto the surfaces of detectors and imaging devices. We have developed advanced, optimized nanostructured AR coatings fabricated using a proprietary e-beam deposition process on GaSb, Si and various other types of substrates and sensors to provide broadband high AR performance, particularly for IR band sensing applications. These nanostructured coatings provide substantial improvements over conventional thin film AR coating technologies including quarter wavelength stacks by further minimizing reflection losses and increasing transmission over a wide range of light incidence angles on optical detectors and focal plane array (FPA) imaging devices. Here we review the latest developments of this high-performance nanoengineered AR coating technology in view of advancing NASA Earth Science sensing and imaging infrared (IR) band applications.

Significant efforts have been made on realizing deep ultraviolet (UV) – (200 – 280 nm) detectors; however, target detection elements remain inefficient, bulky, and low sensitivity. An ideal detector, particularly avalanche photodetectors (APDs) for this region must have high gain, high efficiency, and low noise. Ultrawide bandgap (UWB) AlxGa1-xN material system has shown promise to enable the design of high quantum efficient (QE), radiation-hard detectors capable of operating at high temperatures in this region. However, achieving high quality material becomes more difficult at higher Al compositions due to challenges associated with nonuniformity and doping efficiency. Current APDs are unable to provide high QE, low dark current, high multiplication gain, and solar blindness without coatings. We are developing III-Nitrite based APDs for single photon detection to operate filter-free in the deep-UV band. Toward this objective, we present results on development of high quality, high Al composition AlxGa1-xN with high conductivity, and demonstrate first in the world fabricated Separate Absorption and Multiplication (SAM) APD devices with 65% Al composition. Physics-based TCAD simulations utilizing the material system, and device measurement results are also presented. The proposed APD and its array, with single photon detection capability using III-N material systems will have earth science, space, defense, and commercial applications including UV spectroscopy, non-line of sight communications, portable chemical and biological identification systems.

The effects of climate change, such as drought and pest infestation, will pose new challenges for forest management in the coming years to ensure the preservation of biodiversity and vegetation balance. A combination of various sensor technologies enables early detection of changes and initiation of necessary mitigation steps. Here, hyperspectral cameras provide direct measurement of the health status on the plants themselves. The achievable spatial and spectral resolutions have been steadily increasing due to the use of drones instead of airplanes and satellites. Nevertheless, only canopy measurement is possible in this case. The measurement below the tree canopy can grant new insights and increase the resolution up to the level of the leaf. The aim of this work is to define the basic requirements for a spectral system suitable for this purpose. For these high-resolution spectral images of typical plants of the mid-mountain range during desiccation were acquired. On the basis of these, various vegetation indices were calculated and the influence of filter properties such as the half-width were simulated. During this investigation, a clear reaction to desiccation was observed in all samples after a brief period of time. Different vegetation indices show a comparable behavior despite the application of different wavelengths.

We demonstrate the design of a transmission filter that can switch the 850nm transmission band on and off to enable a single silicon camera to perform day time and night time (NIR) imaging. In a prior work we demonstrated imaging trials using a tunable reflection-mode filter, but it required a separate dual band static filter for proper operation. Our new design is a self-contained filter that does not require a second filter. It utilizes GSST (Ge2Sb2Se4Te1) as a phase change material to dynamically alter the transmission spectrum. The design consists of a DBR cavity with an active layer consisting of the phase change material and a compensating dielectric film.

We present a novel method to extract phase information of a diffuse object illuminated by linearly polarized light. This method involves the combination of off-axis digital holography (DH) and the transport of intensity equation (TIE) where the hologram is recorded with two reference waves that have orthogonal linear polarization states, simultaneously interfered with the object beam illuminated with a random linear polarization state. Thus, phase information of both polarization states can be obtained. This technique of using TIE along with DH reconstruction using Fresnel propagation has been shown as an effective phase unwrapping technique to uncover either the phase of transmissive objects or the topography of contoured objects.

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Remote sensing is an objective monitoring of the dynamics of changes in the resource potential of the tourism component of the country's modern economy. This paper proposes the information storage model for creating a global space monitoring system for the presence of municipal solid waste objects with elements of economic analysis and recreation of the health of potential tourists and the ecology of recreational areas around the world. The proposed model uses methods for decoding remote sensing images by fractal-percolation image analysis and elements of convolutional neural networks. The purpose of the work is to design a model of a global automatic monitoring system for waste disposal facilities, including industrial ones, using Earth remote sensing technologies in recreational areas, followed by an economic analysis to reduce the resource potential in the tourism business in the face of deteriorating ecology of the studied areas.