KEYWORDS: Sensors, Spectroscopy, Digital micromirror devices, Video, Data acquisition, Reconstruction algorithms, Cameras, Hyperspectral imaging, Detection and tracking algorithms, Video compression
We present the system integration and validation tests of a compressive Multi-Mission Electro-Optical Sensor (MMEOS). With the unique algorithm implementation, the sensor exhibits exceptional agility enabling both multispectral (MS) sensing for wide area situational awareness and hyperspectral (HS) sensing for target recognition and identification. The sensor enables seamless mission changes on-the-fly via only software configuration of the operational parameters such as spatial, spectral and temporal resolutions based on mission requirements.
A Multispectral Polarized Scene Projector (MPSP) had been developed in the short-wave infrared (SWIR) regime for the test & evaluation (T&E) of spectro-polarimetric imaging sensors. This MPSP generates multispectral and hyperspectral video images (up to 200 Hz) with 512×512 spatial resolution with active spatial, spectral, and polarization modulation with controlled bandwidth. It projects input SWIR radiant intensity scenes from stored memory with user selectable wavelength and bandwidth, as well as polarization states (six different states) controllable on a pixel level. The spectral contents are implemented by a tunable filter with variable bandpass built based on liquid crystal (LC) material, together with one passive visible and one passive SWIR cholesteric liquid crystal (CLC) notch filters, and one switchable CLC notch filter. The core of the MPSP hardware is the liquid-crystal-on-silicon (LCoS) spatial light modulators (SLMs) for intensity control and polarization modulation.
This newly developed prototype Multispectral Polarized Scene Projector (MPSP), configured for the short wave
infrared (SWIR) regime, can be used for the test & evaluation (T&E) of spectro-polarimetric imaging sensors. The
MPSP system generates both static and video images (up to 200 Hz) with 512×512 spatial resolution with active spatial,
spectral, and polarization modulation with controlled bandwidth. It projects input SWIR radiant intensity scenes from
stored memory with user selectable wavelength (850-1650 nm) and bandwidth (12-100 nm), as well as polarization
states (six different states) controllable on a pixel by pixel basis. The system consists of one spectrally tunable liquid
crystal filter with variable bandpass, and multiple liquid crystal on silicon (LCoS) spatial light modulators (SLMs) for
intensity control and polarization modulation. In addition to the spectro-polarimetric sensor test, the instrument also
simulates polarized multispectral images of military scenes/targets for hardware-in-the loop (HIL) testing.
A newly fabricated Infrared Scene Projector (IRSP) configured for the Long Wave IR (LWIR) regime has
demonstrated simulated apparent temperatures exceeding 1500 oC, more than doubling the maximum
temperature capability of prior pixilated scene projector devices. Since the entire array surface is capable of
this high temperature output, the same device can be used to generate both the moderate temperature scene
background and an unlimited number of high temperature targets in the scene, without having to optically
combine a few discrete "hot spot" generators. This performance was enabled by advances in a new large pixel,
high voltage, 16-bit backplane Spatial Light Modulator (SLM) coupled with an intense spectral illumination
source, and special formulation liquid crystal (LC). The new LC formulation and SLM configuration also
achieves an effective usable frame rate of up to 200Hz capability. Performance characterization and resulting
data will be discussed in the paper.
Various single layer reflective polarizers are introduced based on cholesteric liquid crystal materials containing one polymeric liquid crystal component and other non-reactive liquid crystals. A non-linear pitch gradient has been created during a process called polymerization induced molecular re-distribution. The polarizers in the visible exhibits a high extinction ration (over 30:1) over a bandwidth from 400 to 1,000 nm. When tuned to the near infrared, the polarizer reflects from 700 to 2,000 nm. In addition, field controllable broadband polarizers will be briefly introduced. Finally, applications will be described.
The liquid crystal display industry relies on low cost high performance polarizers. In this paper we will describe a novel reflective polarizer, based on a special cholesteric liquid crystal (CLC) blend which results in a single layer polarizer having a super broad band approaching 2,000 nm. The novel polarizer overcomes many of the limitations of the conventional dichroic polarizers. It also improves the band width of prior art CLC polarizer invented by Phillips. While the latter relies on creating a linear pitch gradient and requires a special UV dye to obtain the broadband polarizer. Reveo's invention, in contrast, eliminates the need for special UV dye and uses a non-linear pitch distribution to create a band pass of about 2,000 nm in a film thickness of 20 microns.
A novel approach to optical storage based on layering of cholesteric liquid crystal (CLC) media is being pioneered by Reveo, Inc. CLC media have been chosen due to their unique property of selective reflection, wherein a CLC film reflects light of its characteristic wavelength and polarization handedness at near-zero loss while transmitting all other light. The new technology has the potential of making possible Terabyte storage on a single optical disk. This results from the ability to place 2 MN CLC layers on a single disk and reading selectively one or more such layers. Here M refers to the number of `decks' selected by depth- of-focus means. Each `deck' has 2 N layers selected by means of N wavelengths and two polarization states. It is projected that an enhancement factor of 2 MN of 400 is possible for M equals 10 and N equals 20. Furthermore, reading many layers in parallel promises to increase the data rate. The novel concept has been demonstrated in a 6-layer experiment. This, along with computer simulation indicate that the technology is viable and can go to market earlier than other storage technologies.
Diacetylenic monomers have been synthesized in order to obtain long conjugation to provide high nonlinear optical response. We report the preparation of nonadeca-10:12-diynoic acid and used as precursor for the following compounds: (1) 4-cyanobiphenyl-4'-(nonadeca-10:12- diynoate), and (2) 2,3,6,7,10,11-triphenylene-hexa(nonadeca-10:12-diynoate). The polymerizations of these monomers were carried out by UV-irradiation of the monomers in bulk and in 25 (mu) thickness of quartz cells. The cyanobiphenyl-containing diacetylenic monomer exhibits monotropic nematic phase and the polymer displays enantiotropic nematic phase. The diacetylenic discotic monomer is not polymerizable and exhibit no mesophase. The nonlinear absorption properties of the diacetylenic discotic monomer was studied by using 532 nm frequency-doubling output from a Q-switched Nd:YAG laser with a pulse width of 7 ns.
In order to study third order optical nonlinearities of nematic liquid crystals on the nanosecond timescale, we have carried out Z-scan measurements using a Q-switched Nd:YAG laser at 532 nm. The nonlinear refractive indices and absorption coefficients were determined for a number of liquid crystals at different temperatures. For the cyano-biphenyl 5CB, we used a two-pulse technique to estimate the response time, and we studied the intensity and wavelength dependence of the response to determine the dominant contributing mechanism. The correlation between the observed nonlinearities and the molecular structures is discussed.
Measurements of second harmonic generation (SHG) by polymer dispersed liquid crystal (PDLC) films have been carried out using nanosecond pulses from a Q-switched Nd:YAG laser. The PDLC films consist of micron-sized droplets of liquid crystal dispersed in a polymer matrix. The liquid crystal-polymer interface breaks inversion symmetry, allowing SHG, and the large surface to volume ratio may enhance the signal intensity. The intensity of the signal depends on the dielectric permittivity difference across the interface, and thus changes in orientational order or configuration of the liquid crystal in the inclusions give rise to changes in the second harmonic intensity. The authors have measured the temperature dependence of the SH signal from PDLC films at temperatures both below and above the nematic-isotropic transition temperature of the liquid crystal in the film. An externally applied electric field can affect the orientation of the liquid crystal, and hence affect the SHG. The modulation of the intensity of the second harmonic signal by a low frequency voltage applied across the film, as well as the effects of droplet size on SHG in PDLC films, have been studied. Possible mechanisms responsible for the measured results are discussed.
Liquid crystals consist of anisotropic organic molecules which are orientationally ordered
in the nematic phase. The birefringence of these materials gives a measire of the degree of
orientational order. In addition to the linear birefringence, liquid crystals possess large third
order nonlinear susceptibilities. Due to the bulk anisotropy of these materials, the nonlinear
refractive index 2 depends on the direction of polarization of light with respect to the nematic
director. We have used the Z-scan technique' to determine the third-order nonlinear refractive
indices n2 and nonlinear absorption coefficients j3 of the pure liquid crystal 5CB (4-cyano-4'--npentylbiphenyl)
in both the nematic and the isotropic phases. We have measured the nonlinear
refractive indices n211 and n21 for light polarized parallel and perpendicular to the director, using
both a CW Ar laser and a nanosecond frequecy-.doubled Nd:YAG laser. The nonlinear index n2
of 5CB in its nematic phase, measured with 7ns Nd:YAG laser pulses, is more than two orders of
magnitude larger than that of CS2, and originates in a self-defocusing process. We have also
observed strong nonlinear birefringence, the divergence of the nonlinear refractive indices as the
nematic-isotropic transition is approached from below, and strong polarization dependent
nonlinear absorption.
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