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International audience; In the field of spectral imaging, numerous instruments use scanning-based technologies. However, the temporal dimension of these systems, whether to scan the spectrum or scan the scene, can be an issue for some applications. This is particularly the case when trying to observe and identify rapid temporal variations in a fixed scene or detecting objects of interest when moving. In this case, it is suitable to observe the desired spectral information of the scene simultaneously, and so-called snapshot systems have been thus investigated. In this paper, we study the ability of a kaleidoscope-based multiview camera to acquire multispectral information in the long wavelength infrared. Several strategies and technologies will be compared to add the spectral function inside the different blocks of a kaleidoscope-based camera: the front lens, the kaleidoscope, or the reimaging lens. The studied camera uses an uncooled infrared detector and thus must deal with the issue of having a large aperture.; Dans le domaine de l'imagerie multispectrale, de nombreux instruments utilisent des technologies basées sur le balayage. Cependant, la dimension temporelle de ces systèmes, qu'il s'agisse de balayer le spectre lumineux ou la scène, peut poser problème pour certaines applications. C'est notamment le cas lorsqu'il s'agit d'observer et d'identifier des variations temporelles rapides dans une scène fixe ou de détecter des objets d'intérêt en mouvement. Dans ce cas, il convient d'observer simultanément les informations spectrales souhaitées de la scène et les systèmes à acquisition simultanée des images spectrales ont donc été étudiés. Dans cet article, nous étudions la capacité d'une caméra multi-vues basée sur l'utilisation d'un kaléidoscope à acquérir des informations multispectrales dans l'infrarouge lointain (LWIR). Plusieurs stratégies et technologies seront comparées pour ajouter la fonction spectrale à l'intérieur des différents blocs d'une caméra kaléidoscope : la lentille de tête, le kaléidoscope ou le réimageur. La caméra étudiée utilise un détecteur infrarouge non refroidi et les solutions doivent donc être compatible aux grandes ouvertures.

International audience; Multi-view snapshot systems are used for a wide range of applications in all the spectral ranges. In this Letter, we present the study and the realization of an optical system using a kaleidoscope in the long wavelength infrared (LWIR), compatible with uncooled infrared detectors such as microbolometers. The optical system has a high numerical aperture and a wide field of view, and it uses a single focal plane array. Here, we establish the advantages of this technology on other design strategies and its design rules for every subset of the optical architecture, and we present the results of a first demonstrator.; compatible with uncooled infrared detectors such as microbolometers. The optical system has a high optical aperture, a wide field of view and uses a single focal plane array. We establish here the advantages of this technology on other design strategies, its design rules for every subset of the optical architecture and present the results of a first demonstrator.Les systèmes multi-images snapshot sont utilisés pour un large éventail d'applications dans toutes les gammes spectrales.Nous soumettons ici l'étude et la réalisation d'un système optique utilisant un kaléidoscope dans l'infrarouge bande III (LWIR) et compatible avec les détecteurs infrarouges non refroidis tels que les microbololomètres. Le système optique présente une ouverture numérique élevée, un large champ de vision et utilise un détecteur unique. Nous établissons ici les avantages de cette technologie sur d’autres stratégies de conception, ses règles de conception pour chaque sous-ensemble de l’architecture optique et nous en présentons les résultats d'un premier démonstrateur.

International audience; Multi imaging snapshot systems are used for a wide range of applications in all the spectral ranges. We propose here a study and a realization of a multi-view snapshot system using a kaleidoscope in the Long-Wave Infrared (LWIR) and compatible with uncooled infrared detectors such as microbolometers. The optical system has a high numerical aperture, a wide range of fields of view and uses a single focal plane array. We will establish here the advantages of this technology on other design strategies and especially the kaleidoscope design will be compared with the TOMBO design. Then the optical conception rules for every subset of the kaleidoscope architecture will be described and the results of a first demonstrator will be presented. The features of this system will be compared with a TOMBO-based system with a front afocal.; Les systèmes permettant l'acquisition de plusieurs images simultanément, dits "snapshot", sont utilisés pour une large gamme d'applications dans toutes les gammes de longueur d'onde. Nous proposons ici une étude et une réalisation d'un système snapshot multi-image utilisant un kaléidoscope dans l'infrarouge lointain (LWIR) et compatible avec des détecteurs infrarouges non refroidis tels que les microbolomètres. Le système optique dispose d'une grande ouverture numérique, d'une large plage de champs de vue accessibles et utilise un seul détecteur pour toutes les images. Nous établirons ici les avantages de cette technologie sur d'autres stratégies de conception et les performances de l'architecture kaléidoscope seront comparées à celles de l'architecture TOMBO. Ensuite, les règles de conception optique pour chaque sous-ensemble de l'architecture du kaléidoscope seront décrites et les résultats d'une première maquette seront présentés. Les caractéristiques de ce système seront comparées à celles d'un système type TOMBO couplé à un afocal.

International audience; Birefringent interferometers are often used for compact static Fourier transform spectrometers. In such devices, several uniaxial birefringent parallel or prismatic plates are stacked, with their optical axes set so that there is an efficient coupling from ordinary to extraordinary and extraordinary to ordinary eigen-modes of two successive plates. Such coupling, aside from few particular cases, is however not perfect, an effect that may adversely affect performance. In order to help the design and the tolerancing of these in-terferometers, we have developed a numerical modeling, based on the propagation of plane waves inside and through the interface of birefringent media. This tool evaluates the traveled optical path length and the amplitude of the different polarization modes, enabling to predict both the optical path differences on the interferometer outputs and the unwanted coupling strengths and related stray wave amplitudes. The tool behavior is illustrated on Savart and Double-Wollaston interferometers, and compared with experimental characterization of a calcite Double-Wollaston prism.

We present an ultra-compact infrared cryogenic camera integrated inside a standard SOFRADIR’s Detector Dewar Cooler Assembly (DDCA) and whose field of view is equal to 120°. The multichannel optical architecture produces four non-redundant images on a single SCORPIO detector with a pixel pitch of 15μm. This ultra-miniaturized optical system brings a very low additional optical and mechanical mass to be cooled in the DDCA: the cool-down time is comparable to the one of an equivalent DDCA without an imagery function. Limiting the number of channels is necessary to keep the highest number of resolved points in the final image. However, optical tolerances lead to irregular shifts between the channels. This paper discusses the limits of multichannel architectures. With an image processing algorithm, the four images produced by the camera are combined to process a single full-resolution image with an equivalent sampling pitch equal to 7.5μm. Experimental measurements on MTF and NETD show that this camera achieves good optical performances.

This paper is devoted to the presentation of a new technique of characterization of the intra-pixel sensitivity variations (IPSVs) of astronomical detectors. The IPSV is the spatial variation of the pixel response function (PRF). In the case of under-sampled instruments for high quality imaging and accurate photometry, IPSV can contribute to the instrument global error and it should be considered carefully. Our measurement technique is based in the Fourier transform (FT) approach. It consists into the sampling of the pixel transfer function (PTF) by projecting high-resolution periodic patterns onto the whole sensor without classic optics but using the self-imaging property (the Talbot effect) of a continuously self imaging grating (CSIG) illuminated by a plane wave. The PRF is determined by computing the inverse FT. Our measurement technique permits to determine the PRF with a resolution of pixel/10 (10 times Nyquist frequency).

Compact and hand-held spectrometers may be very interesting for the measurement of spectral signatures of chemicals or objects. To achieve this goal, ONERA and IPAG have developed a new on chip Fourier Transform Spectrometer operating in the visible spectral range with a high spectral resolution (near 2 cm-1), named visible HR SPOC (visible High Resolution Spectrometer On Chip). It is directly inspired from the MICROSPOC infrared spectrometer, studied at ONERA in the past years. This spectrometer is made of a stair-step two-wave interferometer directly glued on a CMOS detector making it a very compact prototype. After calibrating the optical path difference, measurements of experimental spectra are presented.

Designing a cryogenic camera is a good strategy to miniaturize and simplify an infrared camera using a cooled detector. Indeed, the integration of optics inside the cold shield allows to simply athermalize the design, guarantees a cold pupil and releases the constraint on having a high back focal length for small focal length systems. By this way, cameras made of a single lens or two lenses are viable systems with good optical features and a good stability in image correction. However it involves a relatively significant additional optical mass inside the dewar and thus increases the cool down time of the camera. ONERA is currently exploring a minimalist strategy consisting in giving an imaging function to thin optical plates that are found in conventional dewars. By this way, we could make a cryogenic camera that has the same cool down time as a traditional dewar without an imagery function. Two examples will be presented: the first one is a camera using a dual-band infrared detector made of a lens outside the dewar and a lens inside the cold shield, the later having the main optical power of the system. We were able to design a cold plano-convex lens with a thickness lower than 1mm. The second example is an evolution of a former cryogenic camera called SOIE. We replaced the cold meniscus by a plano-convex Fresnel lens with a decrease of the optical thermal mass of 66%. The performances of both cameras will be compared.

Hyperspectral imaging from small unmanned aerial vehicles (UAVs) arouses a growing interest, as well for military applications as for civilian applications like agriculture management, pollution monitoring or mining. This paper establishes a quick state of the art of cameras of which the capabilities in small-UAVs embedded campaigns have been demonstrated. We also introduce a novel compact hyperspectral camera operating in mid-infrared spectral range embeddable on small UAVs. This camera combines birefringent interferometer for size reduction and cooled imaging optics for a better signal noise ratio. The design of a first prototype and first results from a ground-based measurement campaign, of which the goal was an optical concept validation, is also discussed. Finally, we present the design modifications for the small-UAVs-embeddable version.

We present an ultracompact infrared cryogenic camera integrated inside a standard Sofradir's detector dewar cooler assembly (DDCA) whose field of view is equal to 120°. The multichannel optical architecture produces four nonredundant images on a single SCORPIO detector with a pixel pitch of 15 μm. This ultraminiaturized optical system brings a very low additional optical and mechanical mass to be cooled in the DDCA: the cool-down time is comparable to an equivalent DDCA without an imagery function. Limiting the number of channels is necessary to keep the highest number of resolved points in the final image. However, optical tolerances lead to irregular shifts between the channels. This paper discusses the limits of multichannel architectures. With an image-processing algorithm, the four images produced by the camera are combined to process a single full-resolution image with an equivalent sampling pitch equal to 7.5 μm. Experimental measurements on the modulation transfer function and noise equivalent temperature difference show that this camera achieves good optical performance.

We evaluated the performance of long-wavelength infrared (LWIR, λ c = 9.0 μm at 80 K) mercury cadmium telluride electron-injected avalanche photodiodes (e-APDs) in terms of gain, excess noise factor, and dark current, and also spectral and spatial response at zero bias. We found an exponential gain curve up to 23 at 100 K and a low excess noise factor close to unity (F = 1–1.25). These properties are indicative of a single carrier multiplication process, which is electron impact ionization. The dark current is prevailed by a diffusion current at low reverse bias. However, tunneling currents at higher reverse bias limited the usable gain. The measurements of the pixel spatial response showed that the collection width, and, especially, the amplitude of the response peak, increased with temperature. Furthermore, we developed a Monte Carlo model to understand the multiplication process in HgCdTe APDs. The first simulation results corroborated experimental measurements of gain and excess noise factor in mid-wavelength infrared (MWIR, x = 0.3) and LWIR (x = 0.235) e-APDs at 80 K. This model makes it possible for phenomenological studies to be performed to identify the main physical effects and technological parameters that influence the gain and excess noise. The study of the effect of the n −-layer thickness on APD performance demonstrated the existence of an optimum value in terms of gain.

Les progres fulgurants en microtechnologie durant la derniere decennie ont abouti a la realisation de plans focaux infrarouge (PFI) de grand format, integrant une importante densite de detecteurs au centimetre carre. Prochainement, les grands plans focaux bispectraux ou multispectraux verront le jour. Pour suivre voire anticiper cette course a la resolution spatiale et spectrale, le laboratoire de caracterisation des detecteurs de l'Onera a developpe de nouvelles techniques de mesures permettant d'extraire les reponses spatiales et spectrales des centaines de milliers de pixels formant le PFI. Ainsi, un banc de mesure de cartographies hyperspectrales a ete mis au point, dont le principe de mesure sera presente. On montrera des exemples de mesures obtenues avec ce banc de test et les parametres utiles que l'on peut en extraire. Pour les caracterisations en reponse spatiale, la projection de mires couvrant toute la surface du PFI et contenant des details sub-pixels est necessaire pour extraire les fonctions d'etalement de chaque detecteur elementaire. Pour cela, des techniques de projection sans optiques, reposant sur les proprietes auto-imageantes de mires periodiques ont ete elaborees. Les premiers resultats obtenus et les potentialites de cette approche originale seront discutes.

We study the optical coupling in quantum well photodetectors, focusing on finite size effects. We introduced a finite-element model of the detector and we show experimentally that the optical coupling efficiency is strongly dependent on the pixel size and that in very small detectors diffraction dominates the grating coupling. A 640 × 512 QWIP focal plane array was characterized to show that the optical response of thinned samples may depend on the substrate thickness noticeably. These results are in much closer agreement with predictions obtained with our model than using standard techniques.

International audience; We designed a compact infrared cryogenic camera using only one lens mounted inside the detector area. In the field of cooled infrared imaging systems, the maximal detector area is determined by the dewar. It is generally a sealed and cooled environment dedicated to the infrared quantum detector. By integrating an optical function inside it, we improve the compactness of the camera as well as its performances. The originality of our approach is to use a thin integrated optics which is a high quality Fresnel lens on a thin germanium substrate. The aim is to reduce the additional mass of the optical part integrated inside the dewar to obtain almost the same cool down time as a conventional dewar with no imaging function. A prototype has been made and its characterization has been carried out.

International audience; Today huge efforts are made in the research and industrial areas to design compact and cheap uncooled infrared optical systems for low-cost imagery applications. Indeed, infrared cameras are currently too expensive to be widespread. If we manage to cut their cost, we expect to open new types of markets. In this paper, we will present the cheap broadband microimager we have designed. It operates in the long-wavelength infrared range and uses only one silicon lens at a minimal cost for the manufacturing process. Our concept is based on the use of a thin optics. Therefore inexpensive unconventional materials can be used because some absorption can be tolerated. Our imager uses a thin Fresnel lens. Up to now, Fresnel lenses have not been used for broadband imagery applications because of their disastrous chromatic properties. However, we show that working in a high diffraction order can significantly reduce chromatism. A prototype has been made and the performance of our camera will be discussed. Its characterization has been carried out in terms of modulation transfer function (MTF) and noise equivalent temperature difference (NETD). Finally, experimental images will be presented.

This paper is devoted to the presentation of a new technique of characterization of the Intra-Pixel Sensitivity Variations (IPSVs) of astronomical detectors. The IPSV is the spatial variation of the sensitivity within a pixel and it was demonstrated that this variation can contribute to the instrument global error. Then IPSV has not to be neglected especially in the case of under-sampled instruments for high quality imaging and accurate photometry. The common approaches to measure the IPSV consist in determining the pixel response function (PRF) by scanning an optical probe through the detector. These approaches require high-aperture optics, high precision mechanical devices and are time consuming. The original approach we will present in this paper consists in projecting high-resolution periodic patterns onto the whole sensor without classic optics but using the self-imaging property (the Talbot effect) of a Continuously Self Imaging Grating (CSIG) illuminated by a plane wave. This paper describes the test bench and its design rules. The methodology of the measurement is also presented. Two measurement procedures are available: global and local. In the global procedure, the mean PRF corresponding to the whole Focal Plane Array (FPA) or a sub-area of the FPA is evaluated. The results obtained applying this procedure on e2v CCD 204 are presented and discussed in detail. In the local procedure, a CSIG is moved in front of each pixel and a pixel PRF is reconstructed by resolving the inverse problem. The local procedure is presented and validated by simulations.

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.

Today, both military and civilian applications require miniaturized and cheap optical systems. One way to achieve this trend consists in decreasing the pixel pitch of focal plane arrays (FPA). In order to evaluate the performance of the overall optical systems, it is necessary to measure the modulation transfer function (MTF) of these pixels. However, small pixels lead to higher cut-off frequencies and therefore, original MTF measurements that are able to extract frequencies up to these high cut-off frequencies, are needed. In this paper, we will present a way to extract 1D MTF at high frequencies by projecting fringes on the FPA. The device uses a Lloyd mirror placed near and perpendicular to the focal plane array. Consequently, an interference pattern of fringes can be projected on the detector. By varying the angle of incidence of the light beam, we can tune the period of the interference fringes and, thus, explore a wide range of spatial frequencies, and mainly around the cut-off frequency of the pixel which is one of the most interesting area. Illustration of this method will be applied to a 640×480 microbolometer focal plane array with a pixel pitch of 17µm in the LWIR spectral region.

In the original Talbot experiment, a grating made of thin slits was illuminated in polychromatic light. Reconstituting this simple experiment, we have observed that at a certain distance from the grating, achromatic lines are formed whose transverse-resolution remains unaffected over a wide propagation-distance range. To our knowledge, this phenomenon has never been reported before. A theoretical explanation of this achromatic and continuous self-imaging regime is given and experimental results are reported.

In this Letter, we propose a method to perform 3D imaging with a simple and robust imaging system only composed of a continuously self-imaging grating (CSIG) and a matrix detector. With a CSIG, the intensity pattern generated by an object source is periodic and propagation invariant, apart from a dilatation factor that depends on the distance of the object. We demonstrate, theoretically and experimentally, how to exploit this property to analyze a scene in three dimensions. Such an imaging system can be used, for example, for tomographic applications.

Recent developments in the Mid Wave InfraRed (MWIR) optical domain were made on materials, optical design and manufacturing. They answer increasing demands for more compact, less temperature dependent optical systems with increased optical performances and complexity (multi- or hyper- spectral imagery). At the same time, the characterization of these components has become strategic and requires solutions with higher performance. The optical quality of such devices is measured by wave front sensing techniques. PHASICS previously developed wave front sensors based on Quadri-Wave Lateral Shearing Interferometry (QWLSI) using broadband microbolometers cameras for infrared measurements. However they suffer from reduced light sensitivity in the MWIR domain, which limits their use with broadband sources such as black bodies. To meet metrology demands, we developed an innovative wave front sensor. This instrument combines the metrological qualities of QWLSI with the radiometric performances of a last generation detection block (Infrared Detector Dewar Cooler Assembly, IDDCA) with a quantum infrared focal plane array (IRFPA) of HgCdTe technology. The key component of QWLSI is a specific diffractive grating placed a few millimeters from the focal plane array. This requirement implies that this optics should be integrated inside the IDDCA. To achieve this, we take advantage of the experience acquired from recent developments with optics integrated in IDDCA. Thanks to this approach, we developed a high spatial resolution MWIR wave front sensor (160x128 points) with a high sensitivity for accurate measurements under low-flux conditions. This paper will present the instrument technological solutions, the development key steps and experimental results on various metrology applications.

The SYSIPHE system is the state of the art airborne hyperspectral imaging system developed in European cooperation. With a unique wide spectral range and a fine spatial resolution, its aim is to validate and quantify the information potential of hyperspectral imaging in military, security and environment applications. The first section of the paper recalls the architecture of the project. The second one describes the SIELETERS sensors, their implementation onboard the platform and the data processing chain. The last section gives illustrations on the work in progress.

International audience; We present the design and the realization of a compact and robust imaging spectrometer in the mid-infrared spectral range. This camera combines a small static Fourier transform birefringent interferometer and a cooled miniaturized infrared camera in order to build a robust and compact instrument that can be embedded in an unmanned aerial vehicle for hyperspectral imaging applications. This instrument has been tested during a gas detection measurement campaign. First results are presented.

The SYSIPHE system is the state of the art airborne hyperspectral imaging system developed in European cooperation. With a unique wide spectral range and a fine spatial resolution, its aim is to validate and quantify the information potential of hyperspectral imaging in military, security and environment applications. The first section of the paper recalls the objectives of the project. The second one describes the sensors, their implementation onboard the platform and the data processing chain. The last section gives illustrations on the work in progress.

A new simple and cost-effective method has been developed for the fabrication of both plano-convex and plano-concave lens arrays with potentially important sag heights. The process is based on the use of potassium bromide (KBr) powder. At ambient temperature and under pressure, KBr powder is compressed on a molding die with the desired shape to form a solid lens array. The quality of the lens arrays has been assessed, and we present the first image produced by a converging KBr lens array.

An InfraRed (IR) cooled camera is generally composed by an optical block (warm lenses outside a dewar) and a detection block (a cooled focal plane array inside the dewar). A minimalist approach to design a compact and robust camera consists in giving the dewar an imaging function by replacing the cold pupil by a Diffractive Optical Element (DOE). In this paper we present different DOE that can be used to design the camera. We present first a pinhole camera that validates this approach but that is limited in radiometric performances and in angular resolution. We replace then the pinhole by a continuously self-imaging DOE, such as the diffractive axicon, to improve both the radiometric performances and the angular resolution. Finally, the MALDA is introduced to improve the performances of the axicon. Diffraction effects and Talbot effect under polychromatic light are exposed for such DOE and two different design rules are derived from those effects to allow the design of a compact camera with dimensions compatible with the size of an industrial dewar. Experimental prototypes are presented and radiometric performances are compared and show the best performances for the MALDA.

International audience; Stationary Fourier transform spectrometry is an interesting concept for building reliable field or embedded spectroradiometers, especially for the mid- and far- IR. Here, a very compact configuration of a cryogenic stationary Fourier transform IR (FTIR) spectrometer is investigated, where the interferometer is directly integrated in the focal plane array (FPA). We present a theoretical analysis to explain and describe the fringe formation inside the FTIR-FPA structure when illuminated by an extended source positioned at a finite distance from the detection plane. The results are then exploited to propose a simple front lens design compatible with a handheld package.

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). A dewar is a sealed environment where the detector is cooled on a cold plate. We show in this paper that wide field of view imagery functions can be simply added to the dewar. We investigate two ways of integration and make two demonstrators. The first one called FISBI consists in replacing the window by a fish-eye lens and in integrating a lens in the cold shield. This optical system has a field of view of 180°. The second one, called IR-Cam-on-Chip, consists in integrating the optics directly on the focal plane array. This optical system has a field of view of 120°. The additional mass of the optics is sufficiently small to be compatible with the cryogenic environment of the DDCA. The performance of these cameras will be discussed and several evolutions of these cameras will be introduced too.

International audience; We present a compact infrared cryogenic multichannel camera with a wide field of view equal to 120 degrees. By merging the optics with the detector, the concept is compatible with both cryogenic constraints and wafer-level fabrication. The design strategy of such a camera is described, as well as its fabrication and integration process. Its characterization has been carried out in terms of the modulation transfer function and the noise equivalent temperature difference (NETD). The optical system is limited by the diffraction. By cooling the optics, we achieve a very low NETD equal to 15 mK compared with traditional infrared cameras. A postprocessing algorithm that aims at reconstructing a well-sampled image from the set of undersampled raw subimages produced by the camera is proposed and validated on experimental images. (C) 2012 Optical Society of America

Multi-lateral shearing interferometry [1] is an evolution of the classical lateral shearing interferometry: a grating based technique used for optical testing. Firstly developed for adaptive optics, for ultra-intense lasers characterization, or for lens testing, in visible or infrared, it has now been applied to visible quantitative phase microscopy of biological samples. The purpose of this paper is to present the transfer of this technique to the X-ray domain, stressing on the basic property of propagation invariance.

International audience; Diffractive Optical Elements (DOE), that generate a propagation-invariant transverse intensity pattern, can be used for metrology and imaging application because they provide a very wide depth of focus. However, exact implementation of such DOE is not easy, so we generally code the transmittance by a binary approximation. In this paper, we will study the influence of the binary approximation of Continuously Self-Imaging Gratings (CSIG) on the propagated intensity pattern, for amplitude or phase coding. We will thus demonstrate that under specific conditions, parasitic effects due to the binarization disappear and we retrieve the theoretical non-diffracting property of CSIG's.

International audience; A design of a miniaturized stationary Fourier transform IR spectrometer has been developed that produces a two-dimensional interferogram. The latter is disturbed by effects like parasitic interferences or disparities in the cutoff wavelength of the pixels. Thus, a simple Fourier transform cannot be used to estimate the spectrum of the scene. However, as these defects are deterministic, they can be measured and taken into account by inversion methods. A regularization term can also be added. The first experimental results prove the efficiency of this processing methodology.

We have recently shown that dewar-level integration of optics is a promising way to develop compact IR cameras. Indeed, the integration of optics into the dewar leads to simple and entirely cooled optical architectures dedicated to imaging applications with large-field of view. Here, we review the optical elements we could add in those devices to make a hyper- or multispectral imager. Among them, we find specific focal-plane arrays with a built-in spectrometry function, plasmonic filters combined with a multichannel optical design, and birefringent interferometers. Several optical architectures will be detailed with first experimental results.

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 array (FPA) with micro-sized pixels, this miniaturisation will become feasible with the integration of optical functions in the detector area. In the field of cooled infrared imaging system, the detector area is the Detector-Dewar-Cooler Assembly (DDCA). A dewar is a sealed environment where the detector is cooled on a cold plate. We show in this paper that an imagery function can be added to the dewar by simply integrating a single meniscus inside the cold shield. An infrared system with a wide field of view and high throughput is thus obtained without adding optics outside the dewar. The additional mass of the optic is sufficiently small to be compatible with the cryogenic environment of the DDCA. The temperature stabilization of the optic and the reduction of the background radiation are the main advantages of this system. The performance of this camera will be discussed and several evolutions of this camera will be introduced too.

International audience; We present a optical system with an extended point-spread function (PSF) for the localization of point sources in the visible and IR spectral ranges with a subpixel precision. This compact system involves a random phase mask (RPM) as its unique component. It exhibits original properties, because this RPM is used in a particular regime, called the ''filamentation regime,'' before the speckle region. The localization is performed by calculating the phase correlation between the PSF and the image obtained under off-axis illumination. Numerical simulations are presented to assess the basic optical properties of this RPM in the filamentation regime.

International audience; We present the range of optical architectures for imaging systems based on a single optical component, an aperture stop, and a detector. Thanks to the formalism of third-order Seidel aberrations, several strategies of simplification and miniaturization of optical systems are examined. Figures of merit are also introduced to assess the basic optical properties and performance capabilities of such systems; by this way, we show the necessary trade-off between simplicity, miniaturization, and optical performance.

We present a new method to measure the modulation transfer function (MTF) beyond the Nyquist frequency of a multichannel imaging system for which all the channels have parallel optical axes. Such a multichannel optical system produces a set of undersampled subimages. If the subimages contain nonredundant information, high spatial frequencies are folded between low spatial frequencies, leading to the possible extraction of frequencies higher than the Nyquist frequency. The measurement of the MTF of the multichannel system leads to the estimation of the resolution enhancement of the final image that can be obtained by applying a postprocessing algorithm to the collection of undersampled subimages. Experimental images are presented to validate this method.

Over the past decade, several technological breakthroughs have been achieved in the field of optical detection, in terms of spatial and thermal resolutions. The actual trend leads to the integration of new functions at the vicinity of the detector. This paper presents two types of integrated optics in the cryo-cooler, close to the MCT (CdHgTe) infrared detector array. The first one, for spectro-imaging applications, is a Fourier-transform microspectrometer on chip (MICROSPOC), developed for very fast acquisition of spectral signatures. Experimental results will be presented. The second one, for large field of view applications, illustrates the high potentiality of the integration of advanced optical functions in the Dewar of MCT detectors.

International audience; A new configuration of micro-spectrometer based on an infrared stationary Fourier transform (FTIR) interferometer has been developed at ONERA. Our device is based on a classic infrared focal plane array (FPA) of HgCdTe technology with a built-in two-wave wedge-like interferometer. This new architecture generates research works in several domains. Technological researches are conducted in collaboration with the CEA to optimize the manufacturing process and reduce the technological defects. In parallel, researches in optical design are conducted to implement the FTIR-FPA in a complete system. For this, theoretical work is needed to understand and describe the fringes formation inside the detection structure when illuminated by a wave which is not ideal, i.e. emitted by an extended source positioned at a finite distance from the detection plane. The results of this theoretical study are presented. These results are exploited to design a compact spectrometer with a very simple optical architecture. First experimental data are presented and discussed.

Today’s infrared focal plane arrays concentrate in a small volume of typically 1 cm 3 the results of three decades of research in microelectronics and packag ing. Several technological breakthroughs have already been achieved leading to the development of infrared focal plane arrays (IRFPA’s) for high-performances applications requiring spatial and thermal resolution, also for low-cost and high-manufacturing volumes (technology of uncooled micro-bolometers). The next step is to reduce the optics and make it compatible wi th the successful IRFPA’s fabri cation technology. This paper presents some methods and technologies we are exploring for high-performance and small infrared systems. These developments have led to a tool box of micro-concepts described by an optical function (imagery or spectrometry) integrated in the vicinity of the IRFPA. For this, old optical concepts have been revisited (pinhole optics, Talbot effect) and first demonstrations of original IRFPA-based micro-optical assemblies will be given. Keywords: infrared, focal plane array, spectrometer, micro-camera

International audience; We present an original and compact optical system inspired by the unusual eyes of a Strepsipteran insect called Xenos peckii. It is designed for a field of view of 30° and is composed of multiple telescopes. An array of prisms of various angles is placed in front of these telescopes in order to set a different field of view for each channel. This type of camera operates in the [ 3−5 μm] spectral bandwidth and is entirely integrated in a Dewar in order to maximize its compactness. Experimental images are presented to validate this design.

The original Talbot experiment in white light has been reconstituted, using an amplitude grating made of thin slits and a colour CCD camera and a model has been developed to describe the field diffracted by the grating illuminated in polychromatic light with a known spectral density. Above the historical interest of this study, the possibility of applying this effect to make spectral measurements is explored and a new concept of Talbot spectrometer is proposed.

We present the application of Quadri-Wave Lateral Shearing Interferometry (QWLSI), a wave front sensing technique, to characterize optical beams at infrared wavelengths from 2 to 16μm with a single instrument. This technique can be used to quantify the quality of optical systems (like thermal infrared lenses) by measuring their aberrations. It can also evaluate laser sources in the infrared range like some gas lasers (HeNe laser or CO2 laser), infrared Optical Parametric Oscillator laser sources or Quantum Cascade Laser sources. In all cases, QWLSI offers the crucial advantage that it yields an analyzed wave front without the use of a reference arm and consequent time consuming alignment. In this paper, we first present the single interferometer which can be used with wavelength within 2 and 16μm, covering this way the MWIR (λ within 3 and 5μm) and LWIR (λ within 8 and 14μm) ranges. We then present the characterization of two gas lasers: an infrared HeNe lasers (λ=3.39μm) and a CO2 laser (λ=10.6μm) with this instrument. We finally show the experimental analysis of an infrared lens at two different wavelengths, one in the MWIR range (λ=3.39μm) and the other in the LWIR range (λ=10.6μm). λ

International audience; The performances of a compact infrared optical system using advanced pinhole optics for wide field applications are given. This concept is adapted from the classical Tisse design in order to fit with infrared issues. Despite a low light gathering efficiency and a low resolution in comparison with classical lenses, pinhole imagery provides a long depth of field and a wide angular field of view. Moreover, by using a simple lens that compresses the field of view, the angular acceptance of this pinhole camera can be drastically widened to a value around 180{\textdegree}. This infrared compact system is named pinhole fisheye since it is based on the field lens of a classical fisheye system.

We present the application of Quadri-Wave Lateral Shearing Interferometry (QWLSI), a wave front sensing technique, to characterize thermal infrared lenses for wavelengths within 8 and 14μm. Wave front sensing is not only a tool to quantify optical quality, but also to map the local (dust, scratches) or global possible defects. This method offers the crucial advantage that it yields an analyzed wave front without the use of a reference arm and consequent time consuming alignment. Moreover thanks to the acceptance of QWLSI to high numerical aperture beams, no additional optics is required. This makes lens characterization convenient and very fast. We particularly show the experimental characterization of single Germanium lens and finally present the characterization of complex optical imaging systems for high-performance infrared cameras. The analysis is made in conditions that are very close to the usual conditions of the camera use; that is to say, directly in the convergent beam and in polychromatic (black body) light.

Sub-wavelength gratings allow to code complex transmittance functions that introduce both amplitude andphase variations in the propagation of a given wavefront. These micro-structures are a promising techniqueto miniaturize optical functions such as light polarizing, light con“nement, spectral “ltering... Realizations inthe visible and the infrared domain have been ful“lled: for example micro-lenses, anti-re”ection coatings orsinusoidal-transmittance can easily be coded. This technique is all the more advantageous in the mid-wavelengthinfrared(MWIR) or long-wavelengthinfrared (LWIR) spectral range since there are only a few materials availablein this spectral range. However the chara cterization of these structures is problematical, since it involves phaseand amplitude measurements. It is even more complicated in the far infrared domain (8 Š 14 µ m), as will bedetailed. Besides, the “nite size of the gratings introduces phase steps, which is well-known to be a problematicissue. We describe here a dedicated bench to characterize sub-wavelength gratings in the LWIR spectral range.The core of the bench is a quadri-wave lateral shearing interferometer based on a dir action grating, which allowsa complete two-dimensional characterization of both phase and amplitude in a single measurement. We presenthere theoretical and experimental results of a characterization of such a sub-wavelength grating.Keywords: Interferometry, nanotechnology, sub-wavelength structures, infrared

Circular diffraction gratings (also called diffractive axicons) are optical components producing achromatic non-diffracting beams. They thus produce a focal line rather than a focal point for classical lenses. We have recently shown in the visible spectral range that this property can be used to design a simple imaging system with a long depth of focus and a linear variable zoom by using and translating a diffractive axicon as the only component. We have then adapted this principle for the mid-wavelength infrared (MWIR) spectral range and the long-wavelength infrared (LWIR) spectral range. A LWIR low-cost micro-camera, called MICROCARD, has been designed and realized. First images from this camera will be shown. Moreover a way to design a compact MWIR micro-camera with moveable parts integrated directly into the cryostat will be presented.

A novel configuration of stationary Fourier transform infrared (FTIR) spectrometer is presented. Contrary to classic configurations, the interferometer is directly integrated in the focal plane array (FPA) during its process of fabrication. A first, to the best of our knowledge, demonstration of the spectrometric function has been achieved departing from a well-known structure of an HgCdTe photodetector. We show that the obtained FTIR-FPA can be described by intrinsic parameters such as an optical path difference and a so-called spectrometric efficiency. First experimental results are presented.

We propose to add a specific phase chessboard to the classical Hartmann mask used for wave-front sensing. By doing this we obtain a pseudoguiding of the energy issuing from this mask, allowing for an increase in the sensitivity of the Hartmann test. This property is illustrated by experiment, and a comparison between classical and new Hartmanngrams is presented.

International audience; Diffractive axicons are optical components producing achromatic nondiffracting beams. They thus produce a focal line rather than a focal point for classical lenses. This gives the interesting property of a long focal depth. We show that this property can be used to design a simple imaging system with a linear variable zoom by using and translating a diffractive axicon as the only optical component. (c) 2008 Optical Society of America.