Maxime Savard

Large-deviation achromatic Risley prisms pointing systems

As part of the Infrared Eye project, this article describes the design of large-deviation, achromatic Risley prisms scanning systems operating in the 0.5 - 0.92 and 8 - 9.5 μm spectral regions. Designing these systems is challenging due to the large deviation required (zero - 25 degrees), the large spectral bandwidth and the mechanical constraints imposed by the need to rotate the prisms to any position in 1/30 second. A design approach making extensive use of the versatility of optical design softwares is described. Designs consisting of different pairs of optical materials are shown in order to illustrate the trade-off between chromatic aberration, mass and vignetting. Control of chromatic aberration and reasonable prism shape is obtained over 8 - 9.5 μm with zinc sulfide and germanium. The design is more difficult for the 0.5 - 0.92 μm band. Trade-offs consist in using sapphire with Cleartran® over a reduced bandwidth (0.75 - 0.9 μm ) or acrylic singlets with the Infrared Eye in active mode (0.85 - 0.86 μm). Non-sequential ray-tracing is used to study the effects of fresnelizing one element of the achromat to reduce its mass, and to evaluate detector narcissus in the 8 - 9.5 μm region.

A real-time high-resolution optical SAR processor

An optical SAR processor prototype exhibiting real-time and fine sampling capabilities has been successfully developed and tested. Synthetic Aperture Radar (SAR) images are typically processed digitally applying dedicated Fast Fourier Transform (FFT) algorithms. These operations are time consuming and require a large amount of processing power and are often performed in one dimension at a time. A true two dimensional Fourier transform may be instead performed through optics, as optical processing provides inherent parallel computing capabilities. By processing the azimuth and slant range directions simultaneously, a reduction in processing time and power is achieved. In addition, the configuration of the optics is such that high resolution images may be obtained at no additional processing cost. The optical SAR processor is also designed to adapt to SAR system parameter changes. It has the capability to produce full Envisat / ASAR scenes from the various image mode swaths (IS1 - IS7) within tens of seconds. This paper reviews the design of the real-time high resolution optical SAR processor prototype and discusses the results of images reconstructed from simulated point targets as well as from Envisat / ASAR data sets.

A global review of optronic synthetic aperture radar/ladar processing

Synthetic aperture (SA) techniques are currently employed in a variety of imaging modalities, such as radar (SAR) and ladar (SAL). The advantage of fine resolution provided by these systems far outweighs the disadvantage of having large amounts of raw data to process to obtain the final image. Digital processors have been the mainstay for synthetic aperture processing since the 1980’s; however, the original method was optical that is, it employed lenses and other optical elements. This paper provides a global review of a compact light weight optronic processor that combines optical and digital techniques for ultra-fast generation of synthetic aperture images. The overall design of the optronic processor is detailed, including the optical design and data control and handling. As well, its real-time capabilities are demonstrated. Example ENVISAT/ASAR images generated optronically are also presented and compared with ENVISAT Level 1 products. As well, the extended capabilities of optronic processing, including wavefront correction and interferometry are discussed. Finally, a tabletop synthetic aperture ladar system is introduced and SAL images generated using the exact optronic processor designed for SAR image generation are presented.

Ultra-rapid optronic processor for instantaneous ENVISAT/ASAR scene observation

This paper introduces a real-time compact optronic SAR processor that has the capability to generate ENVISAT/ASAR image swaths of 100 km × 100 km in 10 seconds exhibiting slant plane sampling distances of 4 meters in azimuth and 1 meter in range. It may be instantaneously reconfigured to process data from any of the 7 ASAR image swath modes. In this respect, numerous SAR image sets may be produced immediately on-demand without bottleneck. A rapid SAR processor that also provides fine ground sampling distances in both azimuth and range directions could provide benefits for such applications as ship detection, landslide and flood monitoring, snow and ice coverage and glacier monitoring.

Real-time optical processor prototype for remote SAR applications

A Compact Real-Time Optical SAR Processor has been successfully developed and tested. SAR, or Synthetic Aperture Radar, is a powerful tool providing enhanced day and night imaging capabilities. SAR systems typically generate large amounts of information generally in the form of complex data that are difficult to compress. Specifically, for planetary missions and unmanned aerial vehicle (UAV) systems with limited communication data rates this is a clear disadvantage. SAR images are typically processed electronically applying dedicated Fourier transformations. This, however, can also be performed optically in real-time. Indeed, the first SAR images have been optically processed. The optical processor architecture provides inherent parallel computing capabilities that can be used advantageously for the SAR data processing. Onboard SAR image generation would provide local access to processed information paving the way for real-time decision-making. This could eventually benefit navigation strategy and instrument orientation decisions. Moreover, for interplanetary missions, onboard analysis of images could provide important feature identification clues and could help select the appropriate images to be transmitted to Earth, consequently helping bandwidth management. This could ultimately reduce the data throughput requirements and related transmission bandwidth. This paper reviews the design of a compact optical SAR processor prototype that would reduce power, weight, and size requirements and reviews the analysis of SAR image generation using the table-top optical processor. Various SAR processor parameters such as processing capabilities, image quality (point target analysis), weight and size are reviewed. Results of image generation from simulated point targets as well as real satellite-acquired raw data 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.

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.

Recent advances in a linear micromirror array for high-resolution projection

The visual displays of contemporary military flight simulators lack adequate definition to represent scenes in basic fast-jet fighter tasks. For example, air-to-air and air-to-ground targets are not projected with sufficient contrast and resolution for a pilot to perceive aspect, aspect rate and object detail at real world slant ranges. Simulator display geometries require the development of ultra-high resolution projectors with greater than 20 megapixel resolution at 60 Hz frame rate. A new micromirror device has been developed to address this requirement; it is able to modulate light intensity in an analog fashion with switching times shorter than 5 μs. When combined with a scanner, a laser and Schlieren optics, a linear array of these flexible micromirrors can display images composed of thousands of lines at a frame rate of 60 Hz. Recent results related to evaluation of this technology for high resolution projection are presented. Alternate operation modes for light modulation with flexible micromirrors are proposed. The related importance of controlling the residual micromirror curvature is discussed and results of experiments investigating the use of the deposition pressure to achieve such control are reported. Moreover, activities aiming at minimizing the micromirror response time and, so doing, maximizing the number of image columns per image frame are discussed. Finally, contrast measurement and estimate of the contrast limit achievable with the flexible micromirror technology are presented. All reported activities support the development of a fully addressable 2000-element micromirror array.

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.

Optical Design of Beam Delivery System for Laser Micromachining

We present the design of a UV Beam Delivery System working at 248 nm. The system has the capability of drilling uniform 2 um hole pattern in polymer over a field of 6.5 x 6.5 mm.