Geolocation is the process of calculating a target position based on bearing and range relative to the known location of
the observer. A high performance thermal imager with integrated geolocation functions is a powerful long range
targeting device. Firefly is a software defined camera core incorporating a system-on-a-chip processor running the
AndroidTM operating system. The processor has a range of industry standard serial interfaces which were used to
interface to peripheral devices including a laser rangefinder and a digital magnetic compass. The core has built in Global
Positioning System (GPS) which provides the third variable required for geolocation. The graphical capability of Firefly
allowed flexibility in the design of the man-machine interface (MMI), so the finished system can give access to
extensive functionality without appearing cumbersome or over-complicated to the user. This paper covers both the
hardware and software design of the system, including how the camera core influenced the selection of peripheral
hardware, and the MMI design process which incorporated user feedback at various stages.
Raising the operating temperature of mercury cadmium telluride infrared detectors from 80K to above 160K creates new applications for high performance infrared imagers by vastly reducing the size, weight and power consumption of the integrated cryogenic cooler. Realizing the benefits of Higher Operating Temperature (HOT) requires a new kind of infrared camera core with the flexibility to address emerging applications in handheld, weapon mounted and UAV markets. This paper discusses the Firefly core developed to address these needs by Selex ES in Southampton UK. Firefly represents a fundamental redesign of the infrared signal chain reducing power consumption and providing compatibility with low cost, low power Commercial Off-The-Shelf (COTS) computing technology. This paper describes key innovations in this signal chain: a ROIC purpose built to minimize power consumption in the proximity electronics, GPU based image processing of infrared video, and a software customisable infrared core which can communicate wirelessly with other Battlespace systems.
In 2012 Selex ES demonstrated High Operating Temperature (HOT) MCT detectors with 5μm cut-off wavelength and f/4 aperture operating at temperatures above 200K. These detectors are grown by Metal Organic Vapour Phase Epitaxy (MOVPE) which enables fine control over the photo-diode structure. Since 2012 Selex has created two further generations of MOVPE HOT MCT, progressively improving operability and yield. This paper presents performance data for Selex’s third generation of HOT MCT technology and describes the improvements to the diode design and materials processing that have enabled these advances. A parallel program has developed miniature Dewars with lower heatload and reduced manufacturing costs. When integrated with the latest generation of miniature linear cryo-engines the required cooler power is reduced to the region of 1W at temperatures of 200K. This paper will present example imagery from a detector operating with <1 Watt cooler input power. The combination of third generation HOT MCT, high efficiency Dewars and miniature linear coolers will allow a drastic reduction in SWAP-C for long range hand-held thermal imagers.
Detector arrays using Metal-Organic Vapour Phase Epitaxy (MOVPE) grown HgCdTe (MCT) on GaAs substrates have been in production at SELEX Galileo for over 10 years and are a mature technology for medium wave, long wave, and dual-band tactical applications. The mesa structure used in these arrays is optimised for MTF, quantum efficiency and dark currents. Further development of the technique has migrated to very long wave and short wave bands, mainly for space and astronomy applications, and for mid wave applications towards smaller pixels and higher operating temperatures. The emphasis of this paper is on recent experiments aimed at further improving HOT performance.
Raising the operating temperature of infrared detectors has benefits in terms of reduced cooler power and increased life
and enables an overall reduction in size and weight for handheld applications. With MCT the composition can be tuned
to achieve the required wavelength range at a given temperature. Work on detectors operating in the 3-5μm atmospheric
transmission window at operating temperatures up to 210K will be described. The influence of limiting factors such as
excess noise, radiation shield emission, dark current and injection efficiency will be presented.
Packaging aspects will be discussed emphasizing the importance of achieving low cost, weight and power for handheld
applications. The impact of the detector design on overall system size and performance is considered with specific
attention to time to image, passband and f-number.
Finally images will be presented showing performance from a high operating temperature (HOT) camera.
This paper summarises measurements and calculations of HOT performance in Selex Galileo's MW
detectors and demonstrates that high quality imagery can be achieved up to 175K. The benefits of HOT
operation for cooler performance and power dissipation are also quantified.
The variable band gap of MCT provides the ability to optimise the cut-off wavelength for a wide range
of operating temperatures. In particular, it provides the means to produce a MW detector that is well
matched to the 3-5μm atmospheric transmission window at any temperature in the range from 80K up
to room temperature. Competing InSb technology is disadvantaged at higher operating temperatures by
a narrowing band gap, increasing cut-off wavelength, and inadequate EO performance.
The practical upper limit of operating temperature for near-background limited performance is
influenced by several factors, which fall into two categories: the fundamental physics of thermal dark
current generation and black body emission from the cooled radiation shield, and the technology
limitations of MCT diode leakage currents, excess noise, dark current due to defects, and injection
efficiency into the ROIC.
This paper describes progress in the development of dual-band (MW / LW) infrared detectors made from HgCdTe grown
by Metal-Organic Vapor Phase Epitaxy. The technologies of LW and MW single band detectors, which feed into dualband
capability, are discussed. The performance of single-band detectors is detailed to give an indication of the quality
that can be achieved through MOVPE processes. For single-band detectors, pixel resolution has reached 1024 x 786,
while pixel pitch has been reduced to 16μm. Operability for single-band detectors has exceeded 99.98% in both bands.
Full-TV (640 x 512 pixels) dual-band arrays on 24μm and 20μm pitches have been developed. MW median NETD
values achieved are 10mK and 14mK for the 24μm and 20μm pitch arrays respectively. The corresponding LW median
NETD values are 23mK and 27mK respectively.