Loïc Le Noc

A microbolometer-based THz imager

THz imaging is a very promising field rapidly growing in importance. This expanding field is at its early stage of development but already a large number of applications are foreseen. THz imaging promises to be a key technology in various fields, such as defense & security where it can be used to defeat camouflage. Based on its many years of experience in uncooled bolometers technology, INO has developed, assembled and characterized a prototype THz imager. The cameras 160 × 120 pixel array consists of pixels with a 52 μm pitch that have been optimized for the THz region. Custom camera electronics and an F/1 THz lens barrel complete the imager design. Real-time imaging at video rate of 30 frame/sec has been performed with a 3 THz quantum cascade laser set-up. THz images of numerous object-obscurant combinations are presented, proving the feasibility of video imaging in security screening applications.

Flexible 640 x 480 pixel infrared camera module for fast prototyping

In various military, space and civilian infrared-based applications, there is an important need for fast prototyping. At the very heart, stands a requirement for flexible camera modules that provides a multitude of output formats as well as fast adaptability. Based on this concept, INO has developed an advanced compact camera module that can provide both raw data output as well as fully processed images under a variety of formats such as NTSC, PAL, VGA and GigE. This tool can be used to perform a rapid demonstration of an application concept. The IRXCam-640 camera core is a very flexible module that is based on a 640 x 480 pixels uncooled FPA but which may be rapidly modified to accommodate for other resolutions and sensor types. Providing 16-bit raw signal and 8-bit final image outputs at 60 Hz, the electronics gives total access to the detector configuration parameters. The output is available in NTSC, PAL, and GigE. An additional VGA output can be used as input for a microdisplay. TECless operation minimizes module size and power consumption. If required for absolute measurements, a TEC integrated to the detector package can be controlled with external electronics. The camera core can be configured for outdoors operation from -30°C to +60°C with 200°C scene dynamic range at maximum sensitivity. Windowing capability provides flexibility of frame frequency and operating field of view. The camera can be further coupled with a microscan mechanism to provide a high resolution 1280 x 960 pixel image. In this paper, the camera module is reviewed as well as its performances.

1280 x 960 pixel microscanned infrared imaging module

The needs of surveillance/detection operations in the infrared range, for industrial, spatial and military applications continuously tend toward larger field of view and resolution while maintaining the system as compact as possible. To answer this need, INO has developed a 1280x960 pixel thermal imager, said HRXCAM, with 22.6° field of view. This system consists in the assembly of a catadioptric optics with microscan mechanism and a detection electronic module based on a 640x480 25μm pitch pixel bolometric detector. The detection module, said IRXCAM, is a flexible platform developed for fast prototyping of varied systems thanks to its ability to support a large range of infrared detectors. With its multiple hardware and software functionalities, IRXCAM can also be used as the complete electronic module of a finalized system. HRXCAM is an example of fast prototyping with IRXCAM and an optical lens that fully demonstrates the imaging performance of the final system. HRXCAM provides 1280x960 pixel images at a nominal 5-15 Hz frequency with 60 mK NETD. It can also be used in the 640x480 mode at 58 Hz with the same sensitivity. In this paper, the catadioptric optics with integrated microscan and IRXCAM architecture and specifications are reviewed. Some typical examples of image obtained with HRXCAM in outdoor conditions are presented.

Towards very high-resolution infrared camera core

In various military, space and civilian infrared applications, there is an important need for fast prototyping. For example, detectors with small pitch compared to the diffraction limited spot radius are now available and their specificities must be studied to optimize the design of the next imaging systems. At the very heart stands a requirement for flexible camera modules that provide a multitude of output formats as well as fast adaptability. Based on this concept, INO has developed an advanced compact camera module IRXCAM that can provide both raw data as well as fully processed images under a variety of outputs: NTSC, DVI, VGA, GigE and Camera Link. This tool can be used to perform a rapid demonstration of concept for a specific application. IRXCAM now supports the bolometric detectors INO IRM160A (160 x 120 52 μm pitch pixels, LWIR and THz), Ulis 04 17 1 (640 x 480 25 μpitch pixels, LWIR) and Ulis 05 25 1 (1024 x 768 17 μm pitch pixels). Reduction of the pixel pitch is a way to improve the compromise between the spatial resolution and the dimensions of an imaging system, mainly by reducing the required optical focal length with constant numerical aperture. Microscanning is another way that provides excellent results in terms of spatial resolution for pixel pitches as small as 25 μm in the LWIR range for F/1 optics. Microscanning also preserves the field of view without increasing the number of pixels of the detector. Finally, microscanning is an efficient way to reduce the aliasing effect of a non unity filling factor, a parameter that becomes increasingly important for small pixels. This paper presents the IRXCAM-1024 camera module, its performances, and its use for microscanning with 17 μm pitch pixels and commercial F/1 and F/0.86 refractive optical lenses.

Evolution of INO Uncooled Infrared Cameras Towards Very High Resolution Imaging

Along the years INO has been involved in development of various uncooled infrared devices. Todays, the infrared imagers exhibit good resolutions and find their niche in numerous applications. Nevertheless, there is still a trend toward high resolution imaging for demanding applications. At the same time, low-resolution for mass market applications are sought for low-cost imaging solutions. These two opposite requirements reflect the evolution of infrared cameras from the origin, when only few pixel-count FPAs were available, to megapixel-count FPA of the recent years. This paper reviews the evolution of infrared camera technologies at INO from the uncooled bolometer detector capability up to the recent achievement of 1280×960 pixels infrared camera core using INOs patented microscan technology.

Pressure sensing in vacuum hermetic micropackaging for MOEMS-MEMS

Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. Uncooled IR bolometers require a vacuum atmosphere of 1 mTorr and can be integrated with the IR bolometers in a die-level packaging process or microfabricated simultaneously on the same die. We present the typical performance and measurement uncertainty of these pressure sensors along with a reading method that provides a pressure measurement with a dependence on the package temperature as low as 0.7%/°C. A complex reading circuit or temperature control of the packages are not required, making the pressure sensor well adapted for low-cost high-volume production and integration with IR bolometer arrays.

Review of a high resolution catadioptric optical module

The alignment method of a fast catadioptric optical module with very large field of view is presented in this paper. The module is made of three aspheric optical components: a primary mirror, a secondary mirror and a field lens. To achieve the 22.6 degrees field of view, the secondary mirror makes a large obscuration requiring an F/0.75 working f-number to achieve the effective F/1.05. The catadioptric optical module was integrated with the IRXCAM-640 uncooled camera module made by INO. System spatial resolution is improved with the use of a 4-position microscan mechanism.

Subwavelength imaging challenges in the infrared and THz wavebands

Subwavelength imaging has recently seen increased interest in multiple fields. There are various applications and distinct contexts for performing subwavelength imaging. The technological ways to proceed as well as the benefits obtained are as various as the applications foreseen. To benefit from subwavelength imaging a way around standard imaging procedure is often required. INO is also involved in this activity mainly for the infrared and the THz wavebands. In the infrared band a detector with 17 um pixel pitch, larger than the pixel, was used in conjunction with a microscanning device to oversample the image at a pitch much smaller than the wavelength. In this case the pixel size is in the order of the wavelength but the sampling is at subwavelength level. In the THz band a 35 um pixel pitch is used at wavelength ranging from 70 um to 1,063 mm to perform imaging through various objects. In this case, the pixel itself is smaller than the wavelength. Subwavelength imaging is not without its challenges, though. For instance, while the use of ultra-fast optics provides better definition, their design becomes more challenging as the models used are at their very limits. Questions about information content of images can be raised as well. New research avenues are being investigated to help address the challenges of subwavelength imaging with the goal of achieving higher imaging system performance. This paper discusses aspects to be considered, review some results obtained and identify some of the key issues to be further addressed.

Portable LWIR hyperspectral imager based on MEMS Fabry-Perot interferometer and broadband microbolometric detector array

The fast growing consumer electronics market of connected and wearable devices is driving a wealth of new applications. Personal capability for detecting and monitoring substances part of our everyday life (food, cosmetics, drugs, etc.) by spectroscopic means will soon become a reality as a number of new miniature spectrometers are being reported. These devices mostly operate in the visible and near infrared spectral region due to the readily available lowcost detectors in these spectral regions. However, enhanced selectivity is achievable in the molecular fingerprint spectral region (7-20 μm), allowing for applications that would be difficult or impossible at lower spectral wavelengths. To this end, a compact, portable, Long-Wave Infrared (LWIR) hyperspectral imager was developed. It is based on INO’s MICROXCAM-384 camera featuring a 384 x 288 pixel, 35 μm pitch uncooled bolometric broadband Focal Plane Array (FPA) and Fraunhofer ENAS’ 2 mm x 2 mm aperture MEMS tunable Fabry-Pérot Interferometer (FPI). The INO’s broadband FPA exhibits a Noise Equivalent Temperature Difference (NETD) lower than 25 mK (for the 8-12 μm range at 300 K, 50 fps and f/1) and a flat spectral response from 3 to 14 μm. The footprint of the hyperspectral imager is 7 cm x 8 cm x 10 cm excluding the source. The spectral resolution varies from 55 to 220 nm depending on the type of FPI used. The Noise Equivalent Spectral Radiance (NESR) is 430 mW/(m2 .sr.μm) at 9 μm. Using this hyperspectral imager, spectra of various substances including polymers were recorded in the transmission, reflection and transflectance configurations. A good agreement was found with spectra obtained by applying the FPI transfer function to spectra recorded with a commercial FTIR spectrometer. The LWIR configuration of the imaging spectrometer will be described and test results presented.

Software thermal imager simulator

A software application, SIST, has been developed for the simulation of the video at the output of a thermal imager. The approach offers a more suitable representation than current identification (ID) range predictors do: the end user can evaluate the adequacy of a virtual camera as if he was using it in real operating conditions. In particular, the ambiguity in the interpretation of ID range is cancelled. The application also allows for a cost-efficient determination of the optimal design of an imager and of its subsystems without over- or under-specification: the performances are known early in the development cycle, for targets, scene and environmental conditions of interest. The simulated image is also a powerful method for testing processing algorithms. Finally, the display, which can be a severe system limitation, is also fully considered in the system by the use of real hardware components. The application consists in Matlabtm routines that simulate the effect of the subsystems atmosphere, optical lens, detector, and image processing algorithms. Calls to MODTRAN® for the atmosphere modeling and to Zemax for the optical modeling have been implemented. The realism of the simulation depends on the adequacy of the input scene for the application and on the accuracy of the subsystem parameters. For high accuracy results, measured imager characteristics such as noise can be used with SIST instead of less accurate models. The ID ranges of potential imagers were assessed for various targets, backgrounds and atmospheric conditions. The optimal specifications for an optical design were determined by varying the Seidel aberration coefficients to find the worst MTF that still respects the desired ID range.