Assessing the performance of Digital Micromirror Devices for use in space-based multi-object spectrometers

A current need in space-based instrumentation is a reconfigurable slit mask. Several techniques for slit masks have been employed for ground-based astronomical spectrographs. These ground-based instruments have used large discrete components, which are impractical for remote operation in space-based deployment. The Texas Instruments\u27 Digital Micromirror Device (DMD) was originally conceived purely for display purposes, but is a viable candidate to be use as a slit mask in a space-based multi-object spectrograph (MOS). The Integrated Circuit (IC) manufacturing industry has enabled the robust integration of both silicon transistors and Micro-Electrical Mechanical Systems (MEMS) optical components into a very reliable monolithic chip (the DMD). The focus of this work was in three areas that addressed the suitability of proposing DMDs for future space missions. The DMDs were optically characterized to assess their utility in a spectrograph. The DMDs were also cooled in a liquid nitrogen dewar to determine their minimum operating temperature. The low temperature tests indicated that the DMD can operate to temperatures as low as 130 K. In addition, several DMDs were irradiated with high-energy protons at the LBNL 88 Cyclotron to determine how robust the devices are to ionizing radiation (protons). The radiation testing results indicate that DMDs would survive medium to long duration space missions with full operability. Based on preliminary tests in these three areas, the DMD should be considered as an excellent candidate for deployment in future space missions

Optical MEMS

Optical microelectromechanical systems (MEMS), microoptoelectromechanical systems (MOEMS), or optical microsystems are devices or systems that interact with light through actuation or sensing at a micro- or millimeter scale. Optical MEMS have had enormous commercial success in projectors, displays, and fiberoptic communications. The best-known example is Texas Instruments’ digital micromirror devices (DMDs). The development of optical MEMS was impeded seriously by the Telecom Bubble in 2000. Fortunately, DMDs grew their market size even in that economy downturn. Meanwhile, in the last one and half decade, the optical MEMS market has been slowly but steadily recovering. During this time, the major technological change was the shift of thin-film polysilicon microstructures to single-crystal–silicon microsructures. Especially in the last few years, cloud data centers are demanding large-port optical cross connects (OXCs) and autonomous driving looks for miniature LiDAR, and virtual reality/augmented reality (VR/AR) demands tiny optical scanners. This is a new wave of opportunities for optical MEMS. Furthermore, several research institutes around the world have been developing MOEMS devices for extreme applications (very fine tailoring of light beam in terms of phase, intensity, or wavelength) and/or extreme environments (vacuum, cryogenic temperatures) for many years. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) novel design, fabrication, control, and modeling of optical MEMS devices based on all kinds of actuation/sensing mechanisms; and (2) new developments of applying optical MEMS devices of any kind in consumer electronics, optical communications, industry, biology, medicine, agriculture, physics, astronomy, space, or defense

Modeling and simulation of adaptive multimodal optical sensors for target tracking in the visible to near infrared

This work investigates an integrated aerial remote sensor design approach to address moving target detection and tracking problems within highly cluttered, dynamic ground-based scenes. Sophisticated simulation methodologies and scene phenomenology validations have resulted in advancements in artificial multimodal truth video synthesis. Complex modeling of novel micro-opto-electro-mechanical systems (MOEMS) devices, optical systems, and detector arrays has resulted in a proof of concept for a state-of-the-art imaging spectropolarimeter sensor model that does not suffer from typical multimodal image registration problems. Test methodology developed for this work provides the ability to quantify performance of a target tracking application with varying ground scenery, flight characteristics, or sensor specifications. The culmination of this research is an end-to-end simulated demonstration of multimodal aerial remote sensing and target tracking. Deeply hidden target recognition is shown to be enhanced through the fusing of panchromatic, hyperspectral, and polarimetric image modalities. The Digital Imaging and Remote Sensing Image Generation model was leveraged to synthesize truth spectropolarimetric sensor-reaching radiance image cubes comprised of coregistered Stokes vector bands in the visible to near-infrared. An intricate synthetic urban scene containing numerous moving vehicular targets was imaged from a virtual sensor aboard an aerial platform encircling a stare point. An adaptive sensor model was designed with a superpixel array of MOEMS devices fabricated atop a division of focal plane detector. Degree of linear polarization (DoLP) imagery is acquired by combining three adjacent micropolarizer outputs within each 2x2 superpixel whose respective transmissions vary with wavelength, relative angle of polarization, and wire-grid spacing. A novel micromirror within each superpixel adaptively relays light between a panchromatic imaging channel and a hyperspectral spectrometer channel. All optical and detector sensor effects were radiometrically modeled using MATLAB and optical lens design software. Orthorectification of all sensor outputs yields multimodal pseudonadir observation video at a fixed ground sampled distance across an area of responsibility. A proprietary MATLAB-based target tracker accomplishes change detection between sequential panchromatic or DoLP observation frames, and queries the sensor for hyperspectral pixels to aid in track initialization and maintenance. Image quality, spectral quality, and tracking performance metrics are reported for varying scenario parameters including target occlusions within the scene, declination angle and jitter of the aerial platform, micropolarizer diattenuation, and spectral/spatial resolution of the adaptive sensor outputs. DoLP observations were found to track moving vehicles better than panchromatic observations at high oblique angles when facing the sensor generally toward the sun. Vehicular occlusions due to tree canopies and parallax effects of tall buildings significantly reduced tracking performance as expected. Smaller MOEMS pixel sizes drastically improved track performance, but also generated a significant number of false tracks. Atmospheric haze from urban aerosols eliminated the tracking utility of DoLP observations, while aerial platform jitter without image stabilization eliminated tracking utility in both modalities. Wire-grid micropolarizers with very low VNIR diattenuation were found to still extinguish enough cross-polarized light to successfully distinguish and track moving vehicles from their urban background. Thus, state-of-the-art lithographic techniques to create finer wire-grid spacings that exhibit high VNIR diattenuation may not be required

COMPRESSIVE IMAGING AND DUAL MOIRE´ LASER INTERFEROMETER AS METROLOGY TOOLS

Metrology is the science of measurement and deals with measuring different physical aspects of objects. In this research the focus has been on two basic problems that metrologists encounter. The first problem is the trade-off between the range of measurement and the corresponding resolution; measurement of physical parameters of a large object or scene accompanies by losing detailed information about small regions of the object. Indeed, instruments and techniques that perform coarse measurements are different from those that make fine measurements. This problem persists in the field of surface metrology, which deals with accurate measurement and detailed analysis of surfaces. For example, laser interferometry is used for fine measurement (in nanometer scale) while to measure the form of in object, which lies in the field of coarse measurement, a different technique like moire technique is used. We introduced a new technique to combine measurement from instruments with better resolution and smaller measurement range with those with coarser resolution and larger measurement range. We first measure the form of the object with coarse measurement techniques and then make some fine measurement for features in regions of interest. The second problem is the measurement conditions that lead to difficulties in measurement. These conditions include low light condition, large range of intensity variation, hyperspectral measurement, etc. Under low light condition there is not enough light for detector to detect light from object, which results in poor measurements. Large range of intensity variation results in a measurement with some saturated regions on the camera as well as some dark regions. We use compressive sampling based imaging systems to address these problems. Single pixel compressive imaging uses a single detector instead of array of detectors and reconstructs a complete image after several measurements. In this research we examined compressive imaging for different applications including low light imaging, high dynamic range imaging and hyperspectral imaging

Evaluating the performance of digital micromirror devices for use as programmable slit masks in multi-object spectrometers

Multi-object spectrometers are extremely useful astronomical instruments that allow simultaneous spectral observations of large numbers of objects. Studies performed with ground-based multi-object spectrometers (MOSs) in the last four decades helped to place unique constraints on cosmology, large scale structure, galaxy evolution, Galactic structure, and contributed to countless other scientific advances. However, terrestrial MOSs use large discrete components for object selection, which, aside from not transferable to space-based applications, are limited in both minimal slit width and minimal time required accommodate a change of the locations of objects of interest in the field of view. There is a pressing need in remotely addressable and fast-re-configurable slit masks, which would allow for a new class of instruments - spacebased MOS. There are Microelectromechanical System (MEMS) - based technologies under development for use in space-based instrumentation, but currently they are still unreliable, even on the ground. A digital micromirror device (DMD) is a highly capable, extremely reliable, and remotely re-configurable spatial light modulator (SLM) that was originally developed by Texas Instruments Incorporated for projection systems. It is a viable and very promising candidate to serve as slit mask for both terrestrial and space-based MOSs. This work focused on assessing the suitability of DMDs for use as slit masks in space-based astronomical MOSs and developing the necessary calibration procedures and algorithms. Radiation testing to the levels of orbit around the second Lagrangian point (L2) was performed using the accelerated heavy-ion irradiation approach. The DMDs were found to be extremely reliable in such radiation environment, the devices did not experience hard failures and there was no permanent damage. Expected single-event upset (SEU) rate was determined to be about 5.6 micro-mirrors per 24 hours on-orbit for 1-megapixel device. Results of vibration and mechanical shock testing performed according to the National Aeronautics and Space Administration (NASA) General Environmental Verification Standard (GEVS) at NASA Goddard Space Flight Center (GSFC) suggest that commercially available DMDs are mechanically suitable for space-deployment with a very significant safety margin. Series of tests to assess the performance and the behaviour of DMDs in cryogenic temperatures (down to 78 K) were also carried out. There were no failures or malfunctions detected in commercially-available devices. An earlier prototype of a terrestrial DMD-based MOS (Rochester Institute of Technology Multi-Object Spectrometer (RITMOS)) was updated with a newer DMD model, and the performance of the instrument was evaluated. All the experiments performed strongly suggest that DMDs are highly reliable and capable devices that are extremely suitable for use as remotely programmable slit masks in MOS

Advances in Raman hyperspectral compressive detection instrumentation for fast label free classification, quantitation and imaging

Multiple prototypes of hyperspectral compressive detection (CD) Raman spectrometers have previously been constructed in the Ben-Amotz lab and have proven to be useful for fast, label-free chemical identification, quantitation and imaging. The CD spectrometer consists of a volume holographic grating (VHG) that linearly disperses the Raman photons into its component wavelengths and all wavelengths are focused onto a digital micromirror devise (DMD). The DMD is an optical modulator that consists of an array of programmable 10μm mirrors that can reflect photons in either +12° or -12° to the incoming light. The DMD is tilted such that the +12° photons go back through the focusing lens and the VHG and is focused onto a single 150μm photon counting avalanche photodiode detector(APD). In chapter 1 of the thesis I describe the construction of a new CD Raman spectrometer capable of fast hyperspectral imaging that has better photon collection efficiency and fewer photon losses compared to its predecessors. The new spectrometer consists of a VHG and a DMD, however, the DMD is not tilted but is perpendicular to the incoming Raman photons. All the Raman photons modulated by the DMD are symmetrically detected in the +12° and -12° by two photon counting photomultiplier tube(PMT) detector modules. The new spectrometer avoids a double pass through the optics and hence has fewer losses associated due to reflection transmission of the optics. Full spectral measurements are made by consecutively scanning through columns of the DMD mirrors and measuring the intensity of photons associated with each wavelength. CD measurements are made by multiplexing wavelengths channels onto the detectors and can be done by applying optimal binary(OB) or Hadamard filters. The new optical design has a spectral window from 150cm-1 to 4000 cm-1 and the improvement in the photon collection efficiency allows classification and imaging speeds of 10μs per point with 13mW of laser power on the sample, and is significantly faster than measurements made with the previous prototype. In chapter 2 of the thesis I describe the construction of a new instrument which is equipped with both a hyperspectral CD spectrometer as well as a traditional Czerny Turner spectrometer. A flip mirror after the Raman microscope directs the Raman scattered beam either towards the CD spectrometer (with the mirror down) or towards the Czerny Turner spectrometer. This instrument allows us to perform head to head comparisons of the two spectrometers using the same Raman scattered photons emitted by the sample. The CD spectrometer uses hardware optical filters to perform compressed chemometric measurements to classify chemicals. The traditional spectrometer uses the CCD to measure full spectral data and chemometric analysis is performed to extract lower dimensional chemical information post measurement. Chemical classification results obtained using two sets of chemicals with differing degrees of spectral overlap show that CD classification is comparable to full spectral classification in the high signal regime. However, for signals consisting of less than 1000 total photon counts, CD classification outperforms full spectral classification. In chapter 3 of the thesis, Raman spectroscopy is used to probe changes in vibrational spectra of nucleotide solutions and hanging droplets containing RNA crystals at different pH. Self-modeling curve resolution (SMCR) applied to full Raman is used to extract solute correlated (SC) Raman spectral components that contain solute spectra with minimal interference from the surrounding solvent. The goal of these studies is to show that Raman spectroscopy can be used to study biological molecules in aqueous environments, with minimal sample preparation and without the need of labels