François Duchesne

Introducing a 384x288 pixel terahertz camera core

Terahertz is a field in expansion with the emergence of various security needs such as parcel inspection and through-camouflage vision. Terahertz wavebands are characterized by long wavelengths compared to the traditional infrared and visible spectra. However, it has recently been demonstrated that a 52 μm pixel pitch microscanned down to an efficient sampling pitch of 26 μm could provide useful information even using a 118.83 μm wavelength. With this in mind, INO has developed a terahertz camera core based on a 384x288 pixel 35 μm pixel pitch uncooled bolometric terahertz detector. The camera core provides full 16-bit output video rate.

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.

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.

MEMS-based flexible reflective analog modulators (FRAM) for projection displays: a technology review and scale-down study

A MEMS based technology for projection display is reviewed. This technology relies on mechanically flexible and reflective microbridges made of aluminum alloy. A linear array of such micromirrors is combined with illumination and Schlieren optics to produce a pixels line. Each microbridge in the array is individually controlled using electrostatic actuation to adjust the pixels intensities. Results of the simulation, fabrication and characterization of these microdevices are presented. Activation voltages below 250 V with response times below 10 μs were obtained for 25 μm × 25 μm micromirrors. With appropriate actuation voltage waveforms, response times of 5 μs and less are achievable. A damage threshold of the mirrors above 8 kW/cm2 has been evaluated. Development of the technology has produced projector engines demonstrating this light modulation principle. The most recent of these engines is DVI compatible and displays VGA video streams at 60 Hz. Recently applications have emerged that impose more stringent requirements on the dimensions of the MEMS array and associated optical system. This triggered a scale down study to evaluate the minimum micromirror size achievable, the impact of this reduced size on the damage threshold and the achievable minimum size of the associated optical system. Preliminary results of this scale down study are reported. FRAM with active surface as small as 5 μm × 5 μm have been investigated. Simulations have shown that such micromirrors could be activated with 107 V to achieve f-number of 1.25. The damage threshold has been estimated for various FRAM sizes. Finally, design of a conceptual miniaturized projector based on 1000×1 array of 5 μm × 5 μm micromirrors is presented. The volume of this projector concept is about 12 cm3.

Development of a DVI-Compatible VGA Projector Engine Based on Flexible Reflective Analog Modulators

The development of a Digital Video Interface (DVI) - compatible VGA projector engine based on Flexible Reflective Analog Modulator (FRAM) is reported. The FRAM technology development began a few years ago in response to a need for a new projection technology allowing the achievement of ultrahigh resolution for high fidelity simulations. This technology relies on simple micromirrors produced using typical Micro Opto Electro Mechanical System (MOEMS) manufacturing processes. It has the advantages of offering a simple fabrication process (three masking layers), a quick response time (5 µs) and to be wavelength insensitive over large spectral ranges. Additionally, the light modulation with these microdevices does not require the achievement of a very high quality optically flat state of the micromirrors which is typically difficult to obtain yet necessary for other MOEMS modulation technologies.

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.

Overcoming the challenges of active THz/MM-wave imaging: an optics perspective

Imaging in the Terahertz (THz) and millimeter-wave (mm-wave) bands offer advantages over doing do in other conventional bands, such as the visible, infrared (IR). The THz band ranges from 300 GHz to 3 THz or in wavelength, 1 mm to 100 μm. These longer wavelengths allows THz radiation to pass unobscured through some materials allowing for imaging hidden threats or defects within such materials. Going further, millimeter-waves cover the spectral band of 30 – 300 GHz, or 10 cm to 1 mm. In addition to passing through denser materials, they also have much less atmospheric absorption, thus are ideal for imaging in adverse weather conditions. In the THz/mm-wave, the greatest challenge to real-time active imaging was previously the lack of compact sensor arrays. INO has overcome this by optimizing its microbolometer focal plane array (originally developed for the infrared) for the longer wavelengths, covering both the THz and mm-wave bands. The remaining challenge for active imaging is how to obtain useful imagery using coherent sources. INO has been working on improving the quality of the illumination beam over the past few years, as well as designing high quality fast imaging optics. This paper will focus on the different techniques that have been tested across the THz and into the mm-wave bands in both transmission and reflection imaging modes. The impact on image quality will be demonstrated, and their implications to developing useful systems for different applications will be discussed.

Optical, mechanical and electronic design and integration of POMM, a polarimeter for the Observatoire du mont Mégantic

A polarimeter, to observe exoplanets in the visible and infrared, was built for the “Observatoire du Mont Mégantic” (OMM) to replace an existing instrument and reach 10-6 precision, a factor 100 improvement. The optical and mechanical designs are presented, with techniques used to precisely align the optical components and rotation axes to achieve the targeted precision. A photo-elastic modulator (PEM) and a lock-in amplifier are used to measure the polarization. The typical signal is a high DC superimposed to a very faint sinusoidal oscillation. Custom electronics was developed to measure the AC and DC amplitudes, and characterization results are presented.