Today, both military and civilian applications require miniaturized optical systems in order to give an imagery function to vehicles with small payload capacity. After the development of megapixel focal plane arrays (FPA) with micro-sized pixels, this miniaturization will become feasible with the integration of optical functions in the detector area. In the field of cooled infrared imaging systems, the detector area is the Detector-Dewar-Cooler Assembly (DDCA). SOFRADIR and ONERA have launched a new research and innovation partnership, called OSMOSIS, to develop disruptive technologies for DDCA to improve the performance and compactness of optronic systems. With this collaboration, we will break down the technological barriers of DDCA, a sealed and cooled environment dedicated to the infrared detectors, to explore Dewar-level integration of optics. This technological breakthrough will bring more compact multipurpose thermal imaging products, as well as new thermal capabilities such as 3D imagery or multispectral imagery. Previous developments will be recalled (SOIE and FISBI cameras) and new developments will be presented. In particular, we will focus on a dual-band MWIR-LWIR camera and a multichannel camera.
New applications require high sensitivity infrared (IR) sensors in order to detect very low incident fluxes. Laser
gated imaging has, in particular, additional specific needs. IR sensors for this type of application are synchronized
with eye-safe lasers, and have to detect a weak signal backscattered from the target on the order of 10 photons per
pulse. They also have to be able to operate with a very short integration time, typically one hundred nanoseconds,
to gate the backscattered signal around the target. In partnership with Sofradir, CEA/LETI (France) has developed
high quality HgCdTe avalanche photodiodes satisfying these requirements. In parallel, specific studies have been
carried out at the Read-Out Circuit level to develop optimized architectures. Thanks to these advances, a new
Integrated Dewar Detector Cooler Assembly has been developed. This new product is the first step in a road-map
to address low flux infrared sensors in the next few years.
Photocurable thin films have been deposited using the Aerosol-gel process. 3-(Trimethoxysilyl) propyl methacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid have been used as sol-gel precursors. The films were characterized with respect to their chemical, structural, optical, and photopolymerization properties.
Optically active films in the system Y2Ti2O7-Er2Ti2O7 have been deposited using the Aerosol-gel process. Photoluminescence properties closely depend on the film crystallization state. Dilution of erbium ions within a crystalline Y2Ti2O7 matrix allows to prevent photoluminescence concentration quenching induced by short range distance interactions. Consequently, heavily doped films with good photoluminescence properties can be obtained.
YETO (Y2-xErxTi2O7) thin films of good optical quality have been successfully deposited using the Aerosol-gel process. Strong photoluminescence (PL) emission centered at 1.53 μm was detected when pumping in a waveguiding configuration at 980 nm. Different heat-treatment procedures have been used in order to study the relationship between the spectroscopic properties and the thin films microstructure. A clear correlation between microstructure and spectroscopic properties was observed, when passing from amorphous to crystallized YETO. A single exponential PL decay with a lifetime of 7.5 ms was found for crystalline YETO films. The erbium quenching concentration in crystalline YETO is 1021 ions/cm3 and the corresponding PL lifetime is 3.5 ms. Our work shows that the dilution of the erbium ions within a Y2Ti2O7 (YTO) matrix allows to prevent short range distance interactions between the active Er3+ ions and therefore improves the spectroscopic properties with respect to pure ETO.