13 June 2012

Sofradir boosts performance of high-operating temperature MWIR detector

In stand F360,-hall 6 at Eurosatory, the biennial land defence and security exhibition near Paris (11-15 June), Sofradir of Châtenay-Malabry, near Paris, France (which makes cooled infrared detectors based on mercury cadmium telluride (MCT/HgCdTe) for military, space and commercial applications) is demonstrating a prototype high-operating-temperature L-HOT mid-wavelength infrared (MWIR) integrated detector cooler assembly (IDCA) that offers a significantly improved detection range over earlier models.

Sofradir says that the L-HOT MWIR demonstrator meets system integrators’ requirements to reduce SWaP (Size, Weight and Power) in military equipment.

“Producing infrared detectors that are compact, lighter and save energy is driving much of our developments at Sofradir,” says VP R&D David Billon-Lanfrey. “L-HOT MWIR ensures that customers get a high-operating-temperature IR detector with all the gains and no trade-off in image quality and NETD [noise-equivalent temperature difference] in order to keep the highest detection range,” he adds.

Sofradir says that NETD (the signal-over-noise ratio of the IR detector) is an important attribute for evaluating image quality and detection range (the ability to see smaller objects at greater distances in all weather conditions). An IR chip with high standard NETD performance is more apt at detecting slight differences in temperature between objects. This provides more detail and more accurate images, which is desirable for users looking for SWaP reductions in hand-held thermal imagers, small gimbals for small unmanned aerial vehicles (UAVs) as well as long-endurance systems, such as border surveillance or 24hr surveillance.

Yet, with high-operating-temperature IR detectors and increased power efficiency comes dark current (useless information such as noise) that can interfere with NETD. By using a p-on-n MCT photodiode technology, Sofradir says that it has overcome the dark current problem, while keeping the nominal 5µm cut-off wavelength.

“To achieve a cut-off wavelength at 5µm that enables L-HOT MWIR to offer low power consumption in a full-performance IR detector with no trade-off in NETD, Sofradir switched to a p-on-n photodiode technology,” says Billon-Lanfrey. “With a cut-off wavelength at 4µm obtained with other technologies, there are fewer input photons on the IR detector and the NETD is degraded,” he claims. “Our L-HOT MWIR prototype has a cut-off wavelength of 5µm at 150K.”

The TV-format 15µm-pitch L-HOT MWIR integrated detector cooler assembly (IDCA) prototype operates at 150K (-123°C), which is 60K higher than standard MCT IR detectors (90K, -183°C) in 3-5µm waveband and consumes less than 2 watts. Currently, the prototype achieves the same NETD (better than 20mK) as Sofradir’s standard full-performance mid-waveband IR detectors.

Tags: Sofradir HgCdTe MCT IR detectors

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