Tolerance analysis is a critical part of the optical design process because it helps predict system real performance, after manufacturing and assembly. To obtain reliable predictions, it is mandatory to use realistic optomechanical models. INO developed Comet software, a powerful standalone application for realistic optical tolerancing analysis. A previous paper demonstrates how a better modeling helps avoid the production of overly expensive optical systems with excellent performances, or on the other hand, the production of inexpensive optical systems with unexpectedly erratic performances. This article presents the methodology used to find the best centering method for an infrared dual-band objective. INO’s Comet standalone software application is used to perform the optomechanical tolerance analysis and computes the perturbations to be applied in the optical tolerance analysis. It will be demonstrated how Comet is quick and easy to use for comparing several centering concepts, helping to find the best trade-off between optical performances and ease of manufacturing. The studied infrared dual-band lens requires almost diffraction limited performances to fulfill the needs of the foreseen application. Therefore, two accurate centering techniques are considered: the active alignment and the QuickCTR autocentering technique. The active alignment is the most accurate method for centering optical elements, but requires expensive instrumentation, human manipulation, and cure time for the adhesive. The QuickCTR auto-centering techniques are almost as accurate as the active alignment but requires a fraction of the effort for centering, thus is less expensive to implement. The presented methodology will show how to get the best compromise by using both techniques.
Achieving realistic tolerance analysis requires a good understanding of lenses optomechanical movements, which is long and tedious task often neglected by designers. This paper presents tolerance analysis results comparison for simplified and realistic optomechanical models.
The ISO-10110 metrics summarize in a few figures the gist of the form error of an optical surface. The values of a few ISO-10110 metrics are usually sufficient to tell if the optical elements are of adequate quality to allow the construction of an optical system with the desired performance. In the context of tolerance analysis, surface form deviations (SFD) are simulated by adding a random sum of generic surfaces on top of a nominal surface. A Matlab-based tool was created to convert the 2D continuous mathematical models of SFD into ISO-10110 metrics. The tool works directly on the raw data of the Monte-Carlo files produced by OpticsStudio during the tolerance analysis process. Not only ISO-10110 metrics are calculated by the tool, but also many mechanical metrics and other optical metrics. The entire set of metrics is calculated for all the surfaces, elements or groups and this for each of the Monte-Carlo optical configurations. Both rotationally symmetric and cylindrical surfaces can be processed by the tool. The calculation of the irregularities is done by a decomposition of the SFD functions into Zernike polynomials and bivariate Legendre polynomials respectively for rotationally symmetric and cylindrical surfaces. A bar graph is used to display all the results of a given type on a single graph. A distance correlation is implemented in the tool to help identify the worst sources of performance degradation. Therefore, the tool can also be used for the iterative tightening of the most significant tolerance operands during the entire tolerance analysis.
Optical tolerance analysis is a very important step in optical systems development. It ensures that appropriate optical performances will be achieved considering all the manufacturing errors involved in the assembly. To perform an accurate tolerance analysis, a realistic optomechanical tolerance model and appropriate perturbations simulation are required in the optical design code. Most of the time, optomechanical lens mounting is not taken into account accurately in classical optical tolerancing method. To improve optical system tolerancing process, an integrated opto-mechanical tolerance analysis is proposed. This paper first describes typical tolerancing process and iteration performed between optical designers and optomechanical engineers in the development of optical systems. Then, the optomechanical tolerance analysis that involves interactions between lenses and mounts, as well as manufacturing errors is presented. Simulation methods to consolidate optical and optomechanical tolerance analysis are discussed. Finally, an integrated optomechanical tolerance analysis is described, and a new optomechanical tolerancing software is introduced. The intent of this new modeling method is to perform accurate optical simulations that are representative of the optomechanical mounting and centering methods. This result in a more efficient allocation of the tolerances and a more accurate prediction of the optical system performances.
An innovative software application for a more realistic tolerance analysis has been developed recently by INO. The application is using optical and mechanical manufacturing databases as well as several equations to translate realistic manufacturing tolerances, optomechanical mounting interfaces, and centering methods into tilts and decenters perturbations, easily transferable to Zemax OpticStudio. The standalone application can be used by the optical designer to quickly verify the feasibility of a mounting and alignment technique according to the specific sensibilities of the current design. The optomechanical engineer can also easily validate or choose a better centering method as well as update the mechanical tolerance parameters. Once the parameter is fixed, the optical designer can export the new parameters into a Zemax OpticStudio file, updating Lens Data Editor and Tolerance Data Editor. Communication between both optical and optomechanical specialists is straightforward with this powerful tool, making the design process easier, quicker, and more accurate. This paper presents how INO is using its standalone application for tolerance analysis to overcome the complex simulation of various centering techniques. Through real examples, it will show how realistic tolerancing simulations impact the choice of appropriate centering method for the lens assembly.
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.
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.
The ability of millimeter waves (1-10 mm, or 30-300 GHz) to penetrate through dense materials, such as leather, wool, wood and gyprock, and to also transmit over long distances due to low atmospheric absorption, makes them ideal for numerous applications, such as body scanning, building inspection and seeing in degraded visual environments. Current drawbacks of millimeter wave imaging systems are they use single detector or linear arrays that require scanning or the two dimensional arrays are bulky, often consisting of rather large antenna-couple focal plane arrays (FPAs). Previous work from INO has demonstrated the capability of its compact lightweight camera, based on a 384 x 288 microbolometer pixel FPA with custom optics for active video-rate imaging at wavelengths of 118 μm (2.54 THz), 432 μm (0.69 THz), 663 μm (0.45 THz), and 750 μm (0.4 THz). Most of the work focused on transmission imaging, as a first step, but some preliminary demonstrations of reflection imaging at these were also reported. In addition, previous work also showed that the broadband FPA remains sensitive to wavelengths at least up to 3.2 mm (94 GHz). The work presented here demonstrates the ability of the INO terahertz camera for reflection imaging at millimeter wavelengths. Snapshots taken at video rates of objects show the excellent quality of the images. In addition, a description of the imaging system that includes the terahertz camera and different millimeter sources is provided.
The evolution of infrared imaging technology has always followed, from a distance, the evolution of the technology in the visible waveband with ever increasing resolutions and decreasing pixel pitch. With such evolution the cameras in the visible are smaller than ever and display high quality imaging. Nowadays the size of the pixels in the infrared is generally much larger than its counterpart in the visible. However, the ratio of the size of the pixel to the wavelength is much smaller in the infrared than in the visible with the consequence that the gain on the pixel size could be limited considering today's rules of design. In the infrared, the recent advent of large 1024 x 768 pixel focal plane arrays based on 17 um pixel for the 8 to 12 um waveband raises development challenges. Nevertheless, it was recently shown that sampling a scene at a frequency higher than the one corresponding to the pixel pitch is an efficient way of increasing the resolution of an image for given pixel size and FPA dimensions. Following this strategy a 2048 x 1536 pixel imager with integrated microscan was developed based on an uncooled bolometer FPA. Due to its very small 8.5 um efficient pixel pitch the imager offers very high resolution and large field-of-view (FOV) using a short 50 mm focal length. Furthermore, since the size of the FPA is maintained at a reasonable size and the pixel pitch is very small the optics is compact and lightweight and the level of aberrations at the larger angles of the FOV is kept to a minimum offering excellent imaging quality. Such a platform could thus be used for very compact surveillance system and remote sensing instrumentation. This paper reviews the optics developed to perform the microscanned acquisition, the acquisition electronics and presents examples of high-resolution imaging. Finally, comparison of imaging with and without microscan is provided illustrating the usefulness of the microscan system despite the fact that the efficient pixel pitch is very close to the lower limit of the 8 to 12 um infrared waveband.
INO has developed infrared camera systems with microscanning capabilities in order to increase image resolution. It has
been shown in previous works that the image quality may be improved even if the pixel pitch is smaller than the point
spread function.
This paper introduces a catadioptric optics system with fully integrated microscan for improved resolution in the THz
band. The design, inspired by the INO's HRXCAM infrared camera core and adapted for terahertz wavelengths, includes
two mirrors and one refractive element. It has a 11.9 degree full field of view and an effective F-number of 1.07 over a
wide spectral range, from 100 μm to 1.5 mm wavelength. This diffraction limited optics is used to provide video rate
high quality THz images. A THz camera, with 160 x 120 pixel and 52 μm pitch detector, is combined with the microscan
objective to provide a 320 x 240 pixel image with a 26 μm sampling step.
Preliminary imaging results using a THz illumination source at 118 μm wavelength are presented. A comparison
between standard and microscanned images is also presented.
Uncooled microbolometer detectors are well suited for space applications due to their low power consumption while still exhibiting adequate performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet different mission requirements. If radiometric measurements are required, the radiometric error induced by variation of the temperature of the detector environment must be minimized. In a radiometric package, the detector environment is thermally stabilized by means of a temperature-controlled radiation shield. The radiation shield must be designed to prevent stray radiation from reaching the detector. A radiometric packaging technology for uncooled microbolometer FPAs is presented. The selection of materials is discussed and the final choices presented based on thermal simulations and experimental data. The radiometric stability with respect to stray light and variation of the temperature of the environment as well as the different noise components studied by means of the Allan variance are presented. It is also shown that the device successfully passed the prescribed environmental tests without degradation of performance.
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.
Loïc Le Noc, Bruno Tremblay, Anne Martel, Claude Chevalier, Nathalie Blanchard, Martin Morissette, Luc Mercier, François Duchesne, Lucie Gagnon, Patrick Couture, Frédéric Lévesque, Nichola Desnoyers, Mathieu Demers, Frédéric Lamontage, Hubert Jerominek, Alain Bergeron
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.
High resolution is in demand for the new applications based on the use of infrared technology. For observation task, high
resolution provides more information either under the form of better resolving power or larger field-of-view. Various
solutions can be envisioned to achieve high resolution imaging. In this paper, a combination of high resolution detector
and microscanning system is proposed. This strategy results in higher resolution and reduced aliasing. A catadioptric
configuration is preferred when a microscan is required to increase the spatial sampling frequency. Among the
catadioptric configurations, the Schmidt-Cassegrain has wide angle capability due to its aspherical entrance window.
However, when the system is used in harsh environment, this compensator window may have to be replaced often. In
this case, a flat window would be preferred because it can be removed or easily replaced at reasonable cost. The
reduction of the aberrations to an acceptable level without compensator window requires that the mirrors of the telescope
be aspherized.
In this paper, we present a modified Cassegrain telescope with two aspherical mirrors and one field lens. Due to the large
obscuration of the secondary mirror, the effective F/1.05 necessitates a larger working F-number of 0.75. The spectral
band ranges from 7.0 to 14.0 microns and the focal length is 50mm. The system is designed for the ULIS UL04171
microbolometer detector with 640 x 480 pixels and 25 microns pixel pitch. With this sensor, the total field of view of
the system is 22.6 degrees, which is very large for a catadioptric system. A microscan increases the system maximal
spatial sampling frequency from 20 to 40 cycles per millimeter. Despite of the compactness, there is enough room
between the field lens and the detector to insert a shutter. A baffle extending ahead of the device is needed in this large
field of view design to avoid undesired rays reaching the detector.
INO has extensive experience in the design and fabrication of focal plane arrays (FPAs) of uncooled microbolometers.
In particular, the FPA of 512×3 microbolometers, developed in collaboration with the Canadian Space Agency (CSA),
has been selected for use in the NIRST (New Infrared Sensor Technology) radiometer of the SAC-D Aquarius mission.
The FPA has been designed for pushbroom scanning of the Earth to provide radiometric data in the mid- and long-wave
infrared for the monitoring of fires as well as thermal mapping of ocean temperature. Uncooled microbolometer
detectors are suited for space applications due to their low power consumption while still exhibiting adequate
performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet
different mission requirements. In order to ensure that the detector receives only the thermal contribution from the
desired target and to minimize radiometric error due to variation of the temperature of the surrounding during the
measurements, a radiometric package is required. In a radiometric package the detector environment is thermally
stabilized by means of a temperature controlled radiation shield. The radiation shield should also be designed to prevent
stray radiation from reaching the detector.
Under the Space Technology Development Program of the CSA, INO has designed, assembled and tested a radiometric
package in order to characterize its performance and compatibility with the space environment. The operating spectral
band is defined by the spectral characteristics of a bandpass filter placed in front of the FPA. For typical space missions,
the package must pass standard environmental tests without degradation of its performance (thermal cycling from -55 to
+85 °C according to MIL-STD-810, random acceleration up to 14 G RMS from 20-2000 Hz and shock up to 75 G). In
order to ensure reliability in those conditions while maintaining optimum performance, an adequate selection of
materials is necessary.
In this paper, INO's radiometric packaging technology for uncooled microbolometer FPA's will be presented. The
selection of materials will be discussed and the final choices presented based on thermal simulations and experimental
data. The effects of different design parameters on the performance, such as material, shape and thickness of radiation
shield and choice of adhesive have been studied. An instantaneous noise equivalent temperature difference (NETD) of
~ 20 mK was obtained under the measurement conditions (broadband LWIR, 140 ms integration time, f/1 optics,
characterization in flood exposure). The design of the package reduced the contribution of environmental temperature
variations on the offset of the sensor. The equivalent response of the package varied less than 0.08 °C per degree of
variation of the temperature of the package. The package also showed low sensitivity to stray radiation as a result of the
effectiveness of the radiation shield design. The device successfully passed the prescribed environmental tests without
degradation of performance.
The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its new science satellite, SCISAT-1. Dr. Peter Bernath of the University of Waterloo is the ACE Mission Scientist, and ABB Bomem is the industrial contractor for the development of the ACE primary instrument. The principal goal of the ACE mission is to measure and to understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in a low earth orbit. A high inclination, low earth orbit will allow coverage of tropical, mid-latitude and polar regions. The ACE primary instrument is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible and near infrared imager. The FTS, operating from 2.4 to 13.3 microns, will measure at high resolution (0.02 cm-1) the infrared absorption signals that contain information on different atmospheric layers to provide vertical profiles of atmospheric constituents. Its highly folded design results in a very high performance instrument with a compact size. The imager will monitor aerosols based on the extinction of solar radiation using two filtered detectors at 1.02 and 0.525 microns. The instrument also includes a suntracker, which provides the sun radiance to both the FTS and the imager during solar occultation of the earth's atmosphere. This paper will describe the recent developments on the ACE instrument. Results obtained with the engineering model will be given and the latest status of the flight model will be presented.
Cost-effective optical correlators are now available for industrial applications. One such application field is the real-time automatic inspection of textile web, in which the high data throughput of the optical correlator over-performs that of the electronic computer. Two approaches for defect enhancement using of wavelet and Wiener filters are proposed. The band-pass wavelet filter is designed to give higher weights in the frequency band, where the energy of defect is higher than that of the web, and to suppress the zero, first and all higher diffracted orders. The Wiener filters are designed based on an average defect shape, with the web texture considered as noise. Using the technique developed at INO (National Optics Institute), a set up of the Vander Lugt type correlator demonstrates experimentally the relevancy of the algorithms. Simulation and optical results are presented.
Improvements on spatial light modulation made available cost-effective correlators suitable for industrial applications. One such application field is the real-time automatic inspection of textile web. Our approaches for defect enhancement make use of wavelet and Wiener amplitude- based filtering. Simulation and optical results are presented.
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