We report on the calibration of the Compact Midwave Imaging Sensor (CMIS) which has been developed by The Johns Hopkins University - Applied Physics Lab (JHU/APL) under a grant from the NASA Earth Science Technology Office (ESTO). At the heart of the CMIS instrument is a newly-developed high operating temperature (HOT) detector made from III-V compounds in a Type II Superlattice design. The instrument is sensitive to 3 particular bands in the IR spectrum which have been noted for their usefulness in determining cloud coverage and temperatures. The bands used were centered at 2.25 μm, 3.75 μm and 4.05 μm. The focal plane array (FPA) was based on the FLIR ISC0405 640×512 pixel readout integrated circuit with 15 μm square pixels. The CMIS design included a 5 zone “butcher block” filter placed in close proximity to the FPA and refractive optical elements contained inside the barrel of the cold shield such that the optics were cooled to approximately the same temperature as the FPA. A small-size, low-power closed-cycle cooler was used to maintain the FPA and the optics at a temperature of 150 K, at which the dark current was low enough to allow integration times longer than 50 ms for cold background scenes. JHU/APL developed the camera control electronics (CCE) and data processing unit (DPU) for running the FPA, performing image processing functions on the data and storing it in memory. The CCE and DPU were designed for possible use on an orbital payload but for the airborne flight the commercial versions of some of the parts specified for spaceflight were used. This paper will describe the laboratory calibration procedures and results.
Plastics are often used in mine and IEDs. Difficult to detect with traditional approaches, plastics are spectrally active in the shortwave and mid-infrared due to vibrational absorptions from the C-H bonds of which they are composed; bonds and vibrations that are diagnostic of and spectrally vary with composition. Hyperspectral infrared imaging has proven exceedingly capable of detecting and categorizing plastics. Here we pursue a dual-band imaging approach that leverages the ubiquitous presence of the ~1.7-micron harmonic of the ~3.4-micron fundamental absorption feature for a low SWaP (Size, Weight, and Power) instrument concept. The 1.7-micron band is also in a spectral region free of telluric and almost all geologic absorption features, making its presence in a reflectance spectrum almost a unique marker for plastics. We have developed and tested a two-camera, dual-band sensor, emphasizing imaging over spectroscopy and implementing on-camera processing to achieve near real-time, partially autonomous detection and imaging of plastic objects. The sensor has proven successful in discriminating and imaging plastics such as fiberglass, styrene, and acrylics from background materials such as grass, dirt, rocks, and brush. The sensor is challenged by certain plastics, especially thin, transparent plastics (less relevant to mines and IEDs) even if they are spectrally active near 1.7 microns. Also, photometric variations in the observing conditions can mask weak plastic signatures. We will discuss our current measurement and technical approach, the results and the challenges that remain to implementing an effective low SWaP sensor for the detection and imaging of plastic objects.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is developing a compact, light-weight, and lowpower midwave-infrared (MWIR) imager called the Compact Midwave Imaging Sensor (CMIS), under the support of the NASA Earth Science Technology Office Instrument Incubator Program. The goal of this CMIS instrument development and demonstration project is to increase the technical readiness of CMIS, a multi-spectral sensor capable of retrieving 3D winds and cloud heights 24/7, for a space mission. The CMIS instrument employs an advanced MWIR detector that requires less cooling than traditional technologies and thus permits a compact, low-power design, which enables accommodation on small spacecraft such as CubeSats. CMIS provides the critical midwave component of a multi-spectral sensor suite that includes a high-resolution Day-Night Band and a longwave infrared (LWIR) imager to provide global cloud characterization and theater weather imagery. In this presentation, an overview of the CMIS project, including the high-level sensor design, the concept of operations, and measurement capability will be presented. System performance for a variety of different scenes generated by a cloud resolving model (CRM) will also be discussed.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has created a unique design for a compact, lightweight, and low-power instrument called the Compact Midwave Imaging Sensor (CMIS). Funded by the NASA ESTO Instrument Incubator Program (IIP), the goal of this CMIS development project is to increase the technical readiness of CMIS for retrieval of cloud heights and atmospheric motion vectors using stereo-photometric methods. The low-cost, low size, weight and power (SWaP) CMIS solution will include high operating temperature (HOT) MWIR detectors and a very low power cooler to enable spaceflight in a 6U CubeSat. This paper will provide an overview of the CMIS project to include the high-level sensor design.
The advanced imagers team at JHU APL and ECE has been advocating and developing a new class of sensor systems
that address key system level performance bottlenecks but are sufficiently flexible to allow optimization of associated
cost and size, weight, and power (SWaP) for different applications and missions. A primary component of this approach
is the innovative system-on-chip architecture: Flexible Readout and Integration Sensors (FRIS). This paper reports on
the development and testing of a prototype based on the FRIS concept. It will include the architecture, a summary of test
results to date relevant to the hostile fire detection challenge. For this application, this prototype demonstrates the
potential for this concept to yield the smallest SWaP and lowest cost imaging solution with a low false alarm rate. In
addition, a specific solution based on the visible band is proposed. Similar performance and SWaP gains are expected for
other wavebands such as SWIR, MWIR, and LWIR and/or other applications like persistent surveillance for critical
infrastructure and border control in addition to unattended sensors.
We present a bio-inspired system-on-chip focal plane readout architecture which at the system level, relies on an
event based sampling scheme where only pixels within a programmable range of photon flux rates are output.
At the pixel level, a one bit oversampled analog-to-digital converter together with a decimator allows for the
quantization of signals up to 26 bits. Furthermore, digital non-uniformity correction of both gain and offset
errors is applied at the pixel level prior to readout. We report test results for a prototype array fabricated in a
standard 90nm CMOS process. Tests performed at room and cryogenic temperatures demonstrate the capability
to operate at a temporal noise ratio as low as 1.5, an electron well capacity over 100Ge-, and an ADC LSB down
to 1e-.
The burial of objects disturbs the ground surface in visually perceptible ways. This project investigated how such
information can inform detection via imaging from visible through mid-infrared wavelengths. Images of the ground
surface where objects were buried were collected at multiple visible through mid-infrared wavelengths prior to burial
and afterward at intervals spanning approximately two weeks. Signs of soil disturbed by emplacement change over time
and exposure in the natural environment and vary in salience across wavelengths for different time periods. Transient
cues related to soil moisture or illumination angle can make signatures extraordinarily salient under certain conditions.
Longpass shortwave infrared and multi-band mid-infrared imaging can enhance the signature of disturbed soils over
visible imaging. These findings add knowledge and understanding of how soil disturbances phenomena can be exploited
to aid detection.
In recent years quantum well infrared (IR) photodetector (QWIP) focal plane array (FPA) technology has developed to the point where it may be considered a candidate for insertion into 3rd generation FLIR systems. Large format 1024x1024 pixels FPAs have been produced using QWIP technology. We report on the application of a large format FPAs to the challenges facing today's military. These include the collection of signatures of military vehicles for long-range target detection/identification. The FPA used was a 1024x1024 pixel array which is available commercially. from QWIP Technologies, Inc. We show imagery of military targets at ranges from 500 m to 5 km acquired in the field. The results of the performance in the field are compared to that predicted by computer models and the performance of the large format QWIP FPA will be evaluated in terms of the capabilities of a notional 3rd generation FLIR system.
In recent years quantum well infrared (IR) photodetector (QWIP) focal plane array (FPA) technology has developed to the point where it may be considered a candidate for insertion into 3rd generation FLIR systems. Both large format (1024x1024 pixels) and multicolor (MWIR/LWIR and LWIR/LWIR) FPAs have been produced using QWIP technology. We report on the application of these new FPAs to the challenges facing today's military. These include the collection of signatures of buried land mines with a LWIR/LWIR dual-color QWIP and long-range target detection/identification using a 1024x1024 FPA. The FPAs were produced from several sources. Large format LWIR FPAs were made by an ARL/NASA/Rockwell team using ARL’s C-QWIP optical coupling scheme. Another large-format FPA was obtained from QWIP Technologies, Inc. and is commercially available. The dual-color LWIR/LWIR FPA was produced by BAE Systems. Laboratory and field imagery from both types of FPAs are presented and analyzed.
We at Army Research Laboratory (ARL) have developed 2xD light emitting device (LED) arrays for possible application in infrared (IR) scene projection experiments. These LEDs emit light in the 3-4 μm wavelength region with peak at 3.75 μm when operate at room temperature. The epitaxial structure for LED was grown on GaSb substrate by molecular beam epitaxial (MBE) technology. Mesa sizes ranging from 30-100 μm diameters were used in the device fabrication. By comparing with radiation from blackbody source, we found that the brightness temperature of the infrared LED is in the range of 300-600 K. We obtained very good uniformity in device current and voltage (I-V) characteristics. This paper discusses the LED array design, fabrication and evaluation results.
In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x 1K), 8.4-9 μm infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are
currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.
We present imagery taken with a quantum well infrared photodetector (QWIP) dual-band infrared (IR) focal plane array (FPA) of the inaugural launch of the Atlas 5 launch vehicle. The FPA was developed under the Army Research Laboratory's Advanced Sensors Federated Laboratory program and used a read-out integrated circuit produced under the Air Force Research Laboratory's Advanced Multi-Quantum Well Technology program. The detectors are able to sense light in both the 3-5 micron (MWIR) and 8-12 micron (LWIR) atmospheric transmission windows such that the resulting LWIR and MIWR images are pixel registered and simultaneous. The FPA was installed in a camera system that used a closed-cycle cooler to operate at 60 K. The camera was placed at the prime focus of an all-reflective telescope on a computer-controlled tracking mount at the Innovative Sensor Technology Evaluation Facility (ISTEF) at the Kennedy Space Center. The launch was observed from ISTEF at a distance of 15 km from the pad. Before and after the launch, The FPA/camera system was calibrated using standard blackbody sources. The launch vehicle was observed from about 30 s after launch until approximately 4 minutes after launch. This corresponded to ranges between 15 km and more than 300 km and altitudes from just over 1 km to more than 100 km. Several interesting differences in the structure of the plume were observed. In addition, the hardbody of the rocket was seen in the LWIR imagery but was undetectable in the MWIR imagery. The imagery was unsaturated in both bands allowing us to obtain good measurements of the radiance of the plume in both the MWIR and LWIR bands.
The next generation of infrared (IR) focal plane arrays (FPAs) will need to be a significant improvement in capability over those used in present-day second generation FLIRs. The Army's Future Combat System requires that the range for target identification be greater than the range of detection for an opposing sensor. To accomplish this mission, the number of pixels on the target must be considerably larger than that possible with 2nd generation FLIR. Therefore, the 3rd generation FLIR will need to be a large format staring FPA with more than 1000 pixels on each side. In addition, a multi-spectral capability will be required to allow operability in challenging ambient environments, discriminate targets from decoys, and to take advantage of the smaller diffraction blur in the MWIR for enhanced image resolution. We report on laboratory measurements of a large format (1024 x 1024 pixels) single-color LWIR IR FPA made using the corrugated quantum well infrared photodetector (QWIP) structure by the ARL/NASA team. The pixel pitch is 18 μm and the spectral response peaks at 8.8 μm with a 9.2 μm cutoff. We report on recent results using a MWIR/LWIR QWIP FPA to image the boost phase of a launch vehicle for missile defense applications and a LWIR/LWIR FPA designed specifically for detecting the disturbed soil associated with buried land mines. Finally, we report on the fabrication of a new read-out integrated circuit (ROIC) specifically designed for multi-spectral operation.
We report on the development and application of dual-band infrared focal plane array (FPA) technology to problems of interest to the U. S. military. For tactical applications, we show the application of dual-band MWIR/LWIR FPAs to reconnaissance, surveillance, and target acquisition. We show field test results of dual-band imaging of military targets over a diurnal cycle. We describe the development of a new dual-band LWIR/LWIR FPA for detection of the disturbed soil features associated with buried land mines. Finally, we will describe the application of dual-band FPAs in the strategic defense arena. We present dual-band MWIR/LWIR imagery of commercial launch vehicles that shows the utility of such an FPA for a sensor in a boost-phase interceptor.
We report on the development and testing of a new dual-band infrared (IR) focal plane array (FPA) specifically designed to detect buried land mines. The detector response spectra were tailored to take advantage of the sharp spectral features associated with disturbed soils. The goal was to have a blue channel with peak response near 9.2 micrometers and a red channel with maximum response at 10.5 micrometers . The quantum well infrared photodetector (QWIP) is particularly suited for this application because of the flexibility available in designing the peak wavelength of the detector and the relatively narrow width of the response spectrum. FPAs were produced and tested under the U. S. Army Research Laboratory's Advanced Sensors Collaborative Research Alliance in co-operation with the Night Vision and Electronic Sensors Directorate. We report on laboratory measurements of the response spectra, the dark current as a function of operating temperature, and the conversion efficiency in both the blue and red channels. Imagery was taken in the field of buried anti-tank mines. The images were analyzed by combining the data from the two channels into single fused images.
This paper provides the design details for a new two-color quantum-well infrared photodetector for use in advanced thermal imaging. The single pixel experimental data used in the evolution of this design is discussed in significant detail. Using the knowledge gained from extensive measurements comparing miniband transport with bound-to-quasi-bound QWIPs and also double and triple coupled-well QWIPs with the more conventional single-well QWIPs, a two-color design is presented. The detector design provides for a lattice-matched growth and superior response in the MWIR spectral region, while keeping the dark currents from the LWIR portion of the detector to a minimum. The architecture will allow for the MWIR and LWIR stacks to be biased separately and also for the signals to be read independently.
We report on results of laboratory and field tests of dual- band MWIR/LWIR focal plane arrays (FPAs) produced under the Army Research Laboratory's Multidomain Smart Sensor Federated Laboratory program. The FPAs were made by DRS Infrared Technologies using the HgCdTe material system and by BAE Systems using QWIP technology. The HgCdTe array used the DRS HDVIPTM process to bond two single-color detector structures to a 640 X 480-pixel single-color read-out integrated circuit (ROIC) to produce a dual-band 320 X 240 pixel array. The MWIR and LWIR pixels are co-located and have a high fill factor. The images from each band may be read out either sequentially (alternating frames) or simultaneously. The alternating frame approach must be used to produce optimal imagery in both bands under normal background conditions. The QWIP FPA was produced using MBE-grown III-V materials. The LWIR section consisted of GaAs quantum wells and AlGaAs barriers and the MWIR section used InGaAs quantum wells with AlGaAs barriers. The detector arrays were processed with three ohmic contacts for each pixel allowing for independent bias control over both the MWIR and LWIR sections. The arrays were indium bump-bonded to an ROIC (specifically designed for two color operation) which puts out the imagery from both bands simultaneously. The ROIC has variable gain and windowing capabilities. Both FPAs were tested under similar ambient conditions with similar optical components. The FPAs were subjected to a standard series of laboratory performance tests. The relative advantages and disadvantages of the two material systems for producing medium-format dual-band FPAs are discussed.
We report on the results of laboratory and field tests on a pixel-registered, 2-color MWIR/LWIR 256 X 256 QWIP FPA with simultaneous integrating capability. The FPA studied contained stacked QWIP structures with spectral peaks at 5.1 micrometer and 9.0 micrometer. Normally incident radiation was coupled into the devices using a diffraction grating designed to operate in both spectral bands. Each pixel is connected to the read-out integrated circuit by three bumps to permit the application of separate bias levels to each QWIP stack and allow simultaneous integration of the signal current in each band. We found the FPA to have high pixel operability, well balanced response, good imaging performance, high optical fill factor, and low spectral crosstalk. We present data on measurements of the noise-equivalent temperature difference of the FPA in both bands as functions of temperature and bias. The FPA data are compared to single-pixel data taken on devices from the same wafer. We also present data on the sensitivity of this FPA to polarized light. It is found that the LWIR portion of the device is very sensitive to the direction of polarization of the incident light. The MWIR part of the device is relatively insensitive to the polarization. In addition, imagery was taken with this FPA of military targets in the field. Image fusion techniques were applied to the resulting images.
Corrugated quantum well IR photodetector (QWIP) focal plane arrays (FPAs) with cutoff wavelength of 11.2 and 16.2 micrometers were fabricated and tested. Each detector array has 256 X 256 pixel elements, indium bumped to a direct injection readout circuit manufactured by Rockwell Science Center. The rest of the supporting electronics were designed and built in-house to provide biases and clock functions to the FPAs. IR imageries with good aesthetic attributes were obtained from both FPAs. For the 11.2 micrometers FPA, background limited IR performance (BLIP) was obtained at 63 K under F/2 optics, consistent with the test results of a large area detector. This operating temperature is substantially higher than the grating coupled arrays with comparable cutoff wavelengths. On the other hand, the optics of the present camera were not optimized for wavelengths beyond 14 micrometers . As a result, the BLIP temperature for the 16.2 micrometers FPA, observed to be 38 K, was somewhat lower than the expected 42 K from the single detector characterization. Despite the reduced detector volume of a C-QWIP structure, the measured internal quantum efficiency remains to be high, being 20.5 percent and 25.4 percent at 2 V bias for the 11.2 micrometers and the 16.2 micrometers FPA, respectively.
Infrared sensor technology is critical to many commercial and military defense applications. Traditionally, cooled infrared material systems such as indium antimonide, platinum silicide, mercury cadmium telluride, and arsenic doped silicon (Si:As) have dominated infrared detection. Improvement in surveillance sensors and interceptor seekers requires large size, highly uniform, and multicolor IR focal plane arrays involving medium wave, long wave, and very long wave IR regions. Among the competing technologies are the quantum well infrared photodetectors based on lattice matched or strained III-V material systems. This paper discusses cooled IR technology with emphasis on QWIP and MCT. Details will be given concerning device physics, material growth, device fabrication, device performance, and cost effectiveness for LWIR, VLWIR, and multicolor focal plane array applications.
We describe here a study of Mini-Band Transport (MBT) Quantum Well Infrared Photodetector (QWIP) samples in which the binding energy of photoexcited electrons is systematically varied. Each sample has been characterized electrically and radiometrically. Results are reported for variation of absorption spectra, spectral response, IV characteristics, blackbody responsivity, detector noise, and detectivity vs. binding energy for dark current limited mode of operation.
Corrugated quantum well infrared photodetectors (C-QWIPs) use total internal reflection to couple normal incident light into the detectors. In this work, we report the performance of C- QWIPs at different wavelengths. Compared with 45 degrees edge coupling, a C-QWIP increases the background photocurrent to dark current ratio rI by a factor between 2.4 and 4.4, thereby increasing the background-limited temperature by 3 to 5 K. The detectivity D* is increased by a factor of 2.4. We applied the C-QWIP to two-color detection and obtained precision thermometric measurements. We have also fabricated and characterized a 256 X 256 C-QWIP array with cutoff wavelength at 11.2 micrometer. The uncorrected nonuniformity ((sigma) /mean) in the central 128 X 128 subarray is 2.3%. The NE(Delta) T at 63 K is estimated to be 23 mK. Furthermore, we have shown that rI can be further increased by fabrication of the C-QWIP into the corrugated hot-electron transistor structure. The enhanced performance of the corrugated structure, combined with its simple processing steps, greatly improves the QWIP technology.
A corrugated quantum well IR photodetector (C-QWIP) focal plane array (FPA) with cutoff at 11.2 micrometers has been fabricated and characterized. The C-QWIP array uses total internal reflection to couple normal incident light into the pixels. The processing steps involve only one chemical etching, one optional reactive ion etching, and one ohmic contact metalization. The detector array has 256 X 256 pixel elements, indium bumped to a direct injection readout circuit. The photocurrent to dark current ratio measured in this FPA, on which the noise equivalent temperature difference depends, is consistent with that of a large area test sample. The array shows good responsivity uniformity of 5.2 percent with no extra leakage resulted from array processing. The estimated noise equivalent temperature difference of this array, excluding the readout noise, is 17 mK at T equals 63 K. The fact that this FPA can be operated at a temperature similar to those of standard QWIP arrays with much shorter wavelengths shows that the C-QWIP structure can greatly increase array performance.
The MBT quantum-well detector is a new generation of detector materials and technology. Quantum-well detectors are based on mature GaAs materials growth and processing technologies that feature large wafers and outstanding material uniformity. These attributes combine to produce an affordable long wave infrared (LWIR) focal plane array (FPA). MBT quantum-well FPAs have demonstrated temporal noise equivalent temperature differences of 15 milliKelvin and operability in excess of 99.5%. The MBT detector can be bandgap engineered for peak spectral response between 3 micrometers and 19 micrometers and bandwidths from less than 0.5 micrometers to more than 4 micrometers . The MBT quantum-well detectors have been hybridized to 128 X 128 silicon multiplexers and are offered as an integrated sensor in the ImagIR, a turnkey imaging platform capable of real-time processing, display and storage of data.
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