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.
The development of a new optical device often faces the same challenges, more specifically at the concept validation level where their development risks are very high. It commonly leads to a laboratory proof-of-concept to test the principle usually built with commercially available off-the-shelf components with high degree of adjustments. The level of robustness, the compactness, and the portability of the device are limited by these adjustable mounts. A breadboard prototype is then developed integrating more custom mounts, but it may require substantial optomechanical effort to converge on an improved version. QuickPOZ, a new generation of mounts, has been developed to fill the gap between the concept idea and the first prototype runs. These standard mounts and breadboards are an easy way to build optical breadboards quickly and accurately robust. They can be used in the development process as soon as the proof-of-concept validation, and up to small run prototyping to test the market. These mounts combine the QuickCTR-edge technology to self-center optics and their mounts, with a high robustness level. QuickPOZ mount’s optical performance results are presented and discussed over a wide operating temperature range between -40°C up to 50°C.
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.
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.
Typical laboratory optical systems use commercially off-the-shelf components in which emphasis is oriented toward ease of assembly and a wide range of adjustability. However, these mounts often require individual alignments that, when each degree of adjustability is cumulated in a complex optical system, can be inefficient and time consuming. Furthermore, most of these optomechanical mounts lack the mechanical robustness required to maintain operational performances out of the laboratory environment. An optomechanical assembly method based on passively aligning design features is proposed to simplify breadboard level optical systems, to improve alignment accuracy and maintaining operational pointing stability. Given the recent improvements in lens passive centering techniques, it seemed worth exploring methods to reduce alignment time and improve the mechanical robustness of laboratory setups. Recent studies show that a typical optical lens centering of <1 arc min with respect to its mount can be achieved using patented auto centering and edge contact mounting technologies. To achieve similar position accuracy between multiple lenses on a portable breadboard, lens mounts should be designed and built with proper reference surfaces and a system should easily reference one mount with respect to the other. The use of reference spheres and dedicated optomechanical mounts is employed to leverage the standard threaded holes of laboratory breadboards and achieve precise lens mount positioning. A series of optomechanical mounts incorporating these techniques are therefore tested. Position accuracy and repeatability are measured mechanically with a coordinate measuring machine and optically with the active monitoring of a laser beam centroid position. Measured position accuracy at the optomechanical mount level is <50 μm with a repeatability of less than 5 μm per interface. The optomechanical mounts robustness is tested within typical storage temperature range of −46 ° C to 63°C and at vibrations levels exceeding typical shipping conditions. Measured optical pointing stability of a simple optical system after environmental testing was found to be under 25 μm. This method should be a promising solution to bridge the design technological gap between the early prototyping and the production phases.
We introduce a new type of drop-in technique used to passively and accurately center lenses in optical mounts. This lens mounting method is called edge contact mounting and uses the edge at the intersection of the cylindrical and optical surface of the lens as the mounting interface. By providing a spherical mounting seat for the lens on a simple standard threaded ring, it is possible to center accurately lenses of different geometries, diameters, and radius of curvatures. The method allows relaxation of some manufacturing tolerances compared with rim contact drop-in and is not subject to a minimum clamping angle as for the surface contact mounting. This innovative lens mounting method allows extension of the centering accuracy offered by passive lens centering methods to a next level without compromise on cost and complexity.
This paper introduces a new type of drop-in technique used to center passively and accurately lenses in optical mounts. This novel lens mounting method is called edge contact mounting and uses the edge at the intersection of the cylindrical and optical surface of the lens as the mounting interface. By providing a spherical mounting seat for the lens on a simple standard threaded ring, it is possible to center accurately lenses of different geometries, diameters and radius of curvatures. The method allows to relax some manufacturing tolerances compared to rim contact drop-in and is not subject to a minimum clamping angle as for the surface contact mounting. This innovative lens mounting method allows to extend the centering accuracy offered by passive lens centering methods to a next level without compromise on cost and complexity.
Mounting aspheres is often challenging because of the higher sensitivity to decenter and tilt compared with spherical lenses. This paper first describes aspheric surface decenter and tilt error as per ISO 10110 standard. Then, the most common lens mounting and alignment method for aspheric lenses are discussed in detail. Finally, an innovative mounting method that uses surface contact mounting is presented. This autocentering method uses the optical surfaces as mounting interfaces to provide a high level of centering accuracy for aspheric lenses. Centering measurement results for different aspheric lenses mounted using this method are also presented.
Mounting aspheres is often challenging because of the higher sensitivity to decenter and tilt compared to spherical lenses. This paper first describes aspheric surface decenter and tilt error as per ISO 10110 standard. Then, the most common lens mounting and alignment method for aspheric lenses are discussed in detail. Finally, an innovative mounting method that uses surface contact mounting is presented. This auto-centering method uses the optical surfaces as mounting interfaces to provide a high level of centering accuracy for aspheric lenses. Centering measurement results for different aspheric lenses mounted using this method are also presented.
The adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). Recently, INO has been involved in the optomechanical design of several subsystems of NFIRAOS, including the Instrument Selection Mirror (ISM), the NFIRAOS Beamsplitters (NBS), and the NFIRAOS Source Simulator system (NSS) comprising the Focal Plane Mask (FPM), the Laser Guide Star (LGS) sources, and the Natural Guide Star (NGS) sources. This paper presents an overview of these subsystems and the optomechanical design approaches used to meet the optical performance requirements under environmental constraints.
A convenient method to assemble optomechanical components is to use threaded interface. For example, lenses are often secured inside barrels using threaded rings. In other cases, multiple optical sub-assemblies such as lens barrels can be threaded to each other. Threads have the advantage to provide a simple assembly method, to be easy to manufacture, and to offer a compact mechanical design. On the other hand, threads are not considered to provide accurate centering between parts because of the assembly clearance between the inner and outer threads. For that reason, threads are often used in conjunction with precision cylindrical surfaces to limit the radial clearance between the parts to be centered. Therefore, tight manufacturing tolerances are needed on these pilot diameters, which affect the cost of the optical assembly. This paper presents a new optomechanical approach that uses threads as mechanical reference. This innovative method relies on geometric principles to auto-center parts to each other with a very low centering error that is usually less than 5 μm. The method allows to auto-center an optical group in a main barrel, to perform an axial adjustment of an optical group inside a main barrel, and to perform stacking of multiple barrels. In conjunction with the lens auto-centering method that also used threads as a mechanical reference, this novel solution opens new possibilities to realize a variety of different high precision optomechanical assemblies at lower cost.
We report on the design and instrumentation of an aircraft-certified far infrared radiometer (FIRR) and the resulting instrument characteristics. FIRR was designed to perform unattended airborne measurements of ice clouds in the arctic in support of a microsatellite payload study. It provides radiometrically calibrated data in nine spectral channels in the range of 8-50 μm with the use of a rotating wheel of bandpass filters and reference blackbodies. Measurements in this spectral range are enabled with the use of a far infrared detector based on microbolometers of 104-μm pitch. The microbolometers have a new design because of the large structure and are coated with gold black to maintain uniform responsivity over the working spectral range. The vacuum sealed detector package is placed at the focal plane of a reflective telescope based on a Schwarschild configuration with two on-axis spherical mirrors. The telescope field-of-view is of ~6° and illuminates an area of ~2.1-mm diameter at the focal plane. In operation, FIRR was used as a nonimaging radiometer and exhibited a noise equivalent radiance in the range of 10-20 mW/m2-sr. The dynamic range and the detector vacuum integrity of FIRR were found to be suited for the conditions of the airborne experiments.
The early-light facility adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). The science beam splitter changer mechanism and the visible light beam splitter are subsystems of NFIRAOS. This paper presents the opto-mechanical design of the NFIRAOS beam splitters subsystems (NBS). In addition to the modal and the structural analyses, the beam splitters surface deformations are computed considering the environmental constraints during operation. Surface deformations are fit to Zernike polynomials using SigFit software. Rigid body motion as well as residual RMS and peak-to-valley surface deformations are calculated. Finally, deformed surfaces are exported to Zemax to evaluate the transmitted and reflected wave front error. The simulation results of this integrated opto-mechanical analysis have shown compliance with all optical requirements.
In a typical optical system, optical elements usually need to be precisely positioned and aligned to perform the correct optical function. This positioning and alignment involves securing the optical element in a holder or mount. Proper centering of an optical element with respect to the holder is a delicate operation that generally requires tight manufacturing tolerances or active alignment, resulting in costly optical assemblies. To optimize optical performance and minimize manufacturing cost, there is a need for a lens mounting method that could relax manufacturing tolerance, reduce assembly time and provide high centering accuracy. This paper presents a patent pending lens mounting method developed at INO that can be compared to the drop-in technique for its simplicity while providing the level of accuracy close to that achievable with techniques using a centering machine (usually < 5 μm). This innovative auto-centering method is based on the use of geometrical relationship between the lens diameter, the lens radius of curvature and the thread angle of the retaining ring. The autocentering principle and centering test results performed on real optical assemblies are presented. In addition to the low assembly time, high centering accuracy, and environmental robustness, the INO auto-centering method has the advantage of relaxing lens and barrel bore diameter tolerances as well as lens wedge tolerances. The use of this novel lens mounting method significantly reduces manufacturing and assembly costs for high performance optical systems. Large volume productions would especially benefit from this advancement in precision lens mounting, potentially providing a drastic cost reduction.
Threaded rings are used to fix lenses in a large portion of opto-mechanical assemblies. This is the case for the low cost drop-in approach in which the lenses are dropped into cavities cut into a barrel and clamped with threaded rings. The walls of a cavity are generally used to constrain the lateral and axial position of the lens within the cavity. In general, the drop-in approach is low cost but imposes fundamental limitations especially on the optical performances. On the other hand, active alignment methods provide a high level of centering accuracy but increase the cost of the optical assembly.
This paper first presents a review of the most common lens mounting techniques used to secure and center lenses in optical systems. Advantages and disadvantages of each mounting technique are discussed in terms of precision and cost. Then, the different contributors which affect the centering of a lens when using the drop-in approach, such as the threaded ring, friction, and manufacturing errors, are detailed. Finally, a patent pending lens mounting technique developed at INO that alleviates the drawbacks of the drop-in and the active alignment approaches is introduced. This innovative auto-centering method requires a very low assembly time, does not need tight manufacturing tolerances and offers a very high level of centering accuracy, usually less than 5 μm. Centering test results performed on real optical assemblies are also presented.
Lens positioning accuracy and manufacturing cost are two main concerns for optomechanical engineers looking for solutions to reduce costs while meeting stringent optical and environmental requirements. Minimizing optical component positioning errors generally translates into significant cost increases. To maximize the precision-to-cost ratio, there are significant advantages in having both an accurate optomechanical tolerance calculation method and an effective technique to mount and align lenses. This paper presents a tool that has been developed at INO to easily perform complex optomechanical statistical tolerancing using Monte Carlo simulation to reduce manufacturing and alignment costs. This tolerancing method provides a more realistic prediction of optical component errors compared to the classical worst case and root sum square calculations. In addition, precision alignment using elastomeric lens mounting is presented. Thermal stability and often overlooked factors for effective alignments are discussed. Results of tests performed on real optical assemblies are presented for tolerancing, thermal stability and alignment performance. The use of these methods can considerably reduce cost while efficiently ensuring compliance with requirements.
KEYWORDS: Tolerancing, Error analysis, Monte Carlo methods, Manufacturing, Received signal strength, Lenses, Assembly tolerances, Optical components, Optics manufacturing, Indium oxide
Optical systems generally require a high level of optical components positioning precision resulting in elevated manufacturing cost. The optomechanical tolerance analysis is usually performed by the optomechanical engineer using his personal knowledge of the manufacturing precision capability. Worst case or root sum square (RSS) tolerance calculation methods are frequently used for their simplicity. In most situations, the chance to encounter the worst case error is statistically almost impossible. On the other hand, RSS method is generally not an accurate representation of the reality since it assumes centered normal distributions. Moreover, the RSS method is not suitable for multidimensional tolerance analysis that combines translational and rotational variations. An optomechanical tolerance analysis method based on Monte Carlo simulation has been developed at INO to reduce overdesign caused by pessimist manufacturing and assembly error predictions. Manufacturing data errors have been compiled and computed to be used as input for the optomechanical Monte Carlo tolerance model. This is resulting in a more realistic prediction of the optical components positioning errors (decenter, tilt and air gap). Calculated errors probabilities were validated on a real lenses barrels assembly using a high precision centering machine. Results show that the statistical error prediction is more accurate and that can relax significantly the precision required in comparison to the worst case method. Manufacturing, inspection, adjustment mechanism and alignment cost can then be reduced considerably.
INO has designed, assembled and tested the Raven Multi-Object Adaptive Optics demonstrator calibration unit. This
sub-system consists in a telescope simulator that will allow aligning Raven's components during its integration, testing
its Adaptive Optics performances in the laboratory and at the telescope, and calibrating the Adaptive Optics system by
building the interaction matrix and measuring the non-common path aberrations. The system is presented with the
challenges that needed to be overcome during the design and integration phases. The system test results are also
presented and compared to the model predictions.
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.
A prototype THz imaging system based on modified uncooled microbolometer detector arrays, INO MIMICII camera
electronics, and a custom f/1 THz optics has been assembled. A variety of new detector layouts and architectures have
been designed; the detector THz absorption was optimized via several methods including integration of thin film metallic
absorbers, thick film gold black absorbers, and antenna structures. The custom f/1 THz optics is based on high resistivity
floatzone silicon with parylene anti-reflection coating matched to the wavelength region of interest. The integrated
detector, camera electronics, and optics are combined with a 3 THz quantum cascade laser for initial testing and
evaluation. Future work will include the integration of fully optimized detectors and packaging and the evaluation of the
achievable NEP with an eye to future applications such as industrial inspection and stand-off detection.
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