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.<p> </p> 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.
Proc. SPIE. 9190, Thirteenth International Conference on Solid State Lighting
KEYWORDS: Light emitting diodes, LED lighting, Detection and tracking algorithms, Sensors, Calibration, Control systems, Light sources and illumination, Temperature metrology, RGB color model, Color and brightness control algorithms
Accurate color control of LED lighting systems is a challenging task: noticeable chromaticity shifts are commonly observed in mixed-color and phosphor converted LEDs due to intensity dimming. Furthermore, the emitted color varies with the LED temperature. We present a novel color control method for tri-chromatic and tetra-chromatic LEDs, which enable to set and maintain the LED emission at a target color, or combination of correlated color temperature (CCT) and intensity. The LED color point is maintained over variations in the LED junctions’ temperatures and intensity dimming levels. The method does not require color feedback sensors, so to minimize system complexity and cost, but relies on estimation of the LED junctions’ temperatures from the junction voltages. If operated with tetra-chromatic LEDs, the method allows meeting an additional optimization criterion: for example, the maximization of a color rendering metric like the Color Rendering Index (CRI) or the Color Quality Scale (CQS), thus providing a high quality and clarity of colors on the surface illuminated by the LED. We demonstrate the control of a RGBW LED at target D65 white point with CIELAB color difference metric triangle;a,bE < 1 for simultaneous variations of flux from approximately 30 lm to 100 lm and LED heat sink temperature from 25°C to 58°C. In the same conditions, we demonstrate a CCT error <1%. Furthermore, the method allows varying the LED CCT from 5500K to 8000K while maintaining luminance within 1% of target. Further work is ongoing to evaluate the stability of the method over LED aging.
Wavefront sensing is one of the key elements of an Adaptive Optics System. Although Shack-Hartmann WFS are the
most commonly used whether for astronomical or biomedical applications, the high-sensitivity and large dynamic-range
of the Pyramid-WFS (P-WFS) technology is promising and needs to be further investigated for proper justification in
future Extremely Large Telescopes (ELT) applications. At INO, center for applied research in optics and technology
transfer in Quebec City, Canada, we have recently set to develop a Pyramid wavefront sensor (P-WFS), an option for
which no other research group in Canada had any experience. A first version had been built and tested in 2013 in
collaboration with NRC-HIA Victoria. Here we present a second iteration of demonstrator with an extended spectral
range, fast modulation capability and low-noise, fast-acquisition EMCCD sensor. The system has been designed with
compactness and robustness in mind to allow on-sky testing at Mont Mégantic facility, in parallel with a Shack-
Hartmann sensor so as to compare both options.
The Laser Tomographic Adaptive Optics system for Giant Magellan Telescope (GMT) uses a single conjugated
deformable mirror, the segmented Adaptive Secondary Mirror (ASM), to correct atmospheric wavefront aberrations with
the help of a constellation of six laser beacons equally spaced on the sky. We will present different approaches for the
design of the Laser Guide Star (LGS) Wave Front Sensor (WFS) system for GMT to cover all sodium emission altitudes
and telescope elevations, from 80 km to 200 km range and how the preliminary design was derived from these
approaches. The designed LGS WFS system includes a defocus-compensation mechanism working with a simple
zooming optics to achieve the pupil image with constant pupil size, nearly constant wavefront correction, as well as pupil
distortion correction. Either a trombone-mirror structure or a direct LGS-WFS translation is used for the defocus
compensation, when conjugating the LGS altitudes in the sky. In the designs, a zooming collimator images the ASM in
the GMT at the exit pupil of the LGS WFS system, where the designed lenslet-array is tailored for the selected CCD
format for the required plate scale on the sky. Additionally, we have proposed a novel and simple solution for pupilimage
segmentation when working with smaller CCD arrays. This novel solution consists of a single multi-aperture
blaze grating for pupil segmentation in the system.
As a ground-layer adaptive optics (GLAO) system can correct the wavefront errors caused by turbulence close to the
Canada-France-Hawaii telescope (CFHT), an intensive study is in progress to determine the feasibility and the
pertinence of equipping the CFHT of such a GLAO system. More specifically, the study concerns the implementation
of GLAO capabilities using a deformable mirror inserted into the optical path of an optical relay. The studied system
called IMAKA would be used both for the dynamic correction of the wavefront errors caused by air turbulence and the
increases of the telescope effective field of view. The objective pursued by IMAKA is to achieve a PSF with Full Width
at Half Maximum of less than 0.15" over a 1-degree field of view for extended wavebands within the spectral waveband
of 470 nm - 900 nm. This paper presents the main results of a study conducted by INO about the optical design
challenges of the IMAKA system. INO has proposed 4 different approaches for the realization of the system and made
preliminary optical designs for each of them. The science camera and deformable mirror in the proposed designs are
located below the Cassegrain environment for three of the proposed configurations and between the primary mirror and
the top ring for the fourth design. In all the proposed configurations, the effective focal length of the telescope with the
added correction relay is about 20.63 m for a working focal ratio of about 5.74. The design configurations included in
this paper have achieved nearly diffraction limited performances with a deformable mirror having a diameter inferior to
0.5 m and flat or mild curvature nominal shape. Based on our preliminary optical design and performance analysis with
the 4 optical design approaches, it seems possible to achieve most of the IMAKA requirements.
Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space
Administration (NASA) of the United States of America (USA) and the Comisión Nacional de Actividades Espaciales
(CONAE) of Argentina. The overall mission targets the understanding of the total Earth system and the consequences of
the natural and man-made changes in the environment of the planet. Jointly developed by CONAE and the Canadian
Space Agency (CSA), the New IR Sensor Technology (NIRST) instrument will monitor high temperature events on the
ground related to fires and volcanic events, and will measure their physical parameters. Furthermore, NIRST will take
measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities.
NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the
thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um. The temperature range is
from 300 to 600 K with an NEDT < 0.5 K for the mid-infrared band and from 200 to 400 K with an NEDT < 0.4 K for
the thermal bands. The baseline design of the NIRST is based on micro-bolometer technology developed jointly by INO
and the CSA. Two arrays of 512x3 uncooled bolometric sensors will be used to measure brightness temperatures. The
instantaneous field-of-view is 534 microradians corresponding to a ground sampling distance of 350 m at the subsatellite
point. A pointing mirror allows a total swath of +/− 500 km. This paper describes the detailed design of the
NIRST camera module. Key performance parameters are also presented.
A null-lens based on a Computer Generated Hologram (CGH) is designed to test the primary off-axis aspherical mirror of the GAIA space telescope. This custom-designed and fabricated CGH includes five zones (null CGH, alignment CGH, and beam-projection CGH) on the same substrate. The optical test configuration is simple and the designed five-zones CGHs can simultaneously provide the aberrated wavefront correction for null tests, CGH alignment with a commercial interferometer, pre-positioning of the mirror under test in a cryogenic chamber, and isolation of the diffraction orders in the test setup. Positioning of the five zones with respect to each other is extremely critical for the success of this custom-made CGH null testing. For this reason, the fringes of all five zones were manufactured on a single photolithographic mask. With INO's special micro-fabrication processes, including its photolithographic, etching, and coating technologies, this 4.5-inch in diameter CGH was successfully made. The RMS wavefront error is estimated at 7.33 nm for the fabricated null CGH.
The control of optical distortion is useful for the design of a variety of optical system. The most popular is the F-theta lens used in laser scanning system to produce a constant scan velocity across the image plane. Many authors have designed during the last 20 years distortion control corrector. Today, many challenging digital imaging system can use distortion the enhanced their imaging capability. A well know example is a reversed telephoto type, if the barrel distortion is increased instead of being corrected; the result is a so-called Fish-eye lens. However, if we control the barrel distortion instead of only increasing it, the resulting system can have enhanced imaging capability. This paper will present some lens design and real system examples that clearly demonstrate how the distortion control can improve the system performances such as resolution. We present innovative optical system which increases the resolution in the field of view of interest to meet the needs of specific applications. One critical issue when we designed using distortion is the optimization management. Like most challenging lens design, the automatic optimization is less reliable. Proper management keeps the lens design within the correct range, which is critical for optimal performance (size, cost, manufacturability). Many lens design presented tailor a custom merit function and approach.
It is well known that a fish-eye lens produces a circular image of the scene with a particular distortion profile. When using a fish-eye lens with a standard sensor (e.g. 1/3", 1/4",.), only a part of the rectangular detector area is used, leaving many pixels unused. We proposed a new approach to get enhanced resolution for panoramic imaging. In this paper, various arrangements of innovative 180-degree anamorphic wide-angle lens design are considered. Their performances as well as lens manufacturability are also discussed. The concept of the design is to use anamorphic optics to produce elliptical image that maximize pixel resolution in both axis. Furthermore, a non-linear distortion profile is also introduced to enhance spatial resolution for specific field angle. Typical applications such as panoramic photography, video conferencing, and homeland/transportation security are also presented.
A global iterative coding method for computer-generated holograms (CGH) is introduced. The method is based on the iterative correction of a CGH with the use of standard Lee coding. The correction, i.e. the difference between the desired and the obtained reconstruction, is coded and added to the current CGH. The learning factor and the weighting factor are introduced in order to control the speed of convergence and the signal-to-noise ratio (SNR). Advantages lie in low computing time as well as improvement of the object SNR, the neighborhood SNR and the background SNR. Reducing the standard deviation of the phase of the reconstructed object also results. A slight improvement of the diffraction efficiency is also observed. The comparison is realized using the Lee interferogram method as a reference.
A global iterative coding method for computer-generated holograms (CGH) is introduced. The method is based on the iterative correction of a CGH using standard Lee coding. The correction, i.e., the difference between the desired and the obtained reconstruction, is coded and added to the current CGH. The coding and weighting factors are introduced to control the speed of convergence and the SNR. Advantages lie in low computing time and improvement of the object SNR, the neighborhood SNR, and the background SNR. Reducing the standard deviation of the phase of the reconstructed object also results. A slight improvement of the diffraction efficiency is also observed. The comparison is realized using the Lee interferogram method as a reference. This method is tested on binary and complex gray-level objects. Simulation results and optical reconstruction are also presented.