Copious Imaging is commercializing a digital-readout integrated circuit (DROIC) technology that not only digitizes, but also performs computations on the signal at each pixel. When the DROIC is mated to a photodiode detector array, the device forms a Computational Pixel Imager (CPI). The technology was in development for many years at MIT Lincoln Laboratory, and now also at Copious Imaging for new application areas. CPI technology is fundamental to the operation of WISP – the Wide-Area Infrared System with Persistence. WISP is a 500-Mpix longwave infrared (LWIR) motion imaging sensor that produces imagery covering the complete surroundings, more than 2π steradians, every 2 seconds. WISP utilizes a fast scanner to cover the scene quickly. The WISP sensor is coupled with a real-time processing system that stiches the scene together from scanned swaths, performs a non-uniformity compensation, stabilizes the imagery to sub-pixel accuracy, detects motion, and tracks all moving objects of interest. The system has machine learning built-in to aid in identifying objects of interest while ignoring clutter. WISP is in use for many applications and in development for several more. We are currently evaluating WISP for use in screening for fevers.
Since 2006, MIT Lincoln Laboratory has been developing Digital-pixel Focal Plane Array (DFPA) readout integrated
circuits (ROICs). To date, four 256 × 256 30 μm pitch DFPA designs with in-pixel analog to digital conversion have
been fabricated using IBM 90 nm CMOS processes. The DFPA ROICs are compatible with a wide range of detector
materials and cutoff wavelengths; HgCdTe, QWIP, and InGaAs photo-detectors with cutoff wavelengths ranging from
1.6 to 14.5 μm have been hybridized to the same digital-pixel readout. The digital-pixel readout architecture offers high
dynamic range, A/C or D/C coupled integration, and on-chip image processing with low power orthogonal transfer
operations. The newest ROIC designs support two-color operation with a single Indium bump connection.
Development and characterization of the two-color DFPA designs is presented along with applications for this new
digital readout technology.
We compare a more complete characterization of the low temperature performance of a nominal 1.7um cut-off
wavelength 1kx1k InGaAs (lattice-matched to an InP substrate) photodiode array against similar, 2kx2k HgCdTe
imagers to assess the suitability of InGaAs FPA technology for scientific imaging applications. The data we present
indicate that the low temperature performance of existing InGaAs detector technology is well behaved and comparable
to those obtained for state-of-the-art HgCdTe imagers for many space astronomical applications. We also discuss key
differences observed between imagers in the two material systems.
A persistent question in the infrared scene projection community has been the spectral characteristics of resistive array emission. This paper describes the results of a comprehensive study performed on two resistive array technologies; the Nuclear Optical Dynamic Display System (NODDS) and the Santa Barbara Infrared (SBIR) Large Format Resistive Array (LFRA) product lines. A Fourier Transform Infrared (FTIR) spectral radiometer is used to measure the spectral radiant emission of both resistive array technologies at multiple drive levels and substrate temperatures. Application of the results to scene projection and cross spectral non-uniformity correction is discussed.
Precision near infrared (NIR) measurements are essential for the next generation of ground and space based instruments. The SuperNova Acceleration Probe (SNAP) will measure thousands of type Ia supernovae up to a redshift of 1.7. The highest redshift supernovae provide the most leverage for determining cosmological parameters, in particular the dark energy equation of state and its possible time evolution. Accurate NIR observations are needed to utilize the full potential of the highest redshift supernovae. Technological improvements in NIR detector fabrication have lead to high quantum efficiency, low noise detectors using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7 μm. The effects of detector quantum efficiency, read noise, and dark current on lightcurve signal to noise, lightcurve parameter errors, and distance modulus fits are simulated in the SNAPsim framework. Results show that improving quantum efficiency leads to the largest gains in photometric accuracy for type Ia supernovae. High quantum efficiency in the NIR reduces statistical errors and helps control systematic uncertainties at the levels necessary to achieve the primary SNAP science goals.
A description of the plans and infrastructure developed for CCD testing and characterization for the DES focal plane detectors is presented. Examples of the results obtained are shown and discussed in the context of the device requirements for the survey instrument.
We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
Large format (1k × 1k and 2k × 2k) near infrared detectors manufactured by Rockwell Scientific Center and Raytheon Vision Systems are characterized as part of the near infrared R&D effort for SNAP (the Super-Nova/Acceleration Probe). These are hybridized HgCdTe focal plane arrays with a sharp high wavelength cut-off at 1.7 μm. This cut-off provides a sufficiently deep reach in redshift while it allows at the same time low dark current operation of the passively cooled detectors at 140 K. Here the baseline SNAP near infrared system is briefly described and the science driven requirements for the near infrared detectors are summarized. A few results obtained during the testing of engineering grade near infrared devices procured for the SNAP project are highlighted. In particular some recent measurements that target correlated noise between adjacent detector pixels due to capacitive coupling and the response uniformity within individual detector pixels are discussed.