UK OPTICAL DESIGN MEETING
Thursday 25th September 2014
University of Glasgow
Kelvin Conference Centre
Glasgow, Scotland
Abstracts
Design of a Manufacturable Freeform Three-Mirror Imaging Telescope
Jannick P. Rolland1 , Kyle Fuerschach1, and Kevin P. Thompson2,1
1The Institute of Optics, University of Rochester
2Synopsys - Optical Solutions Group
Recently, the field of optical design with freeform surfaces has burst onto the scene. A system that demonstrates the potential for phi polynomial freeform surfaces to revolutionize optical design forms was conceived in 2010 [1-2]. In the intervening time it has been fabricated, the individual surfaces tested, and assembled. It is now operational as a fully unobscured all-reflective telescope with a 10° full field of view operating at F/1.9. This talk will describe the methods that were used to create this telescope and present the first images.
[1] J.P. Rolland and K. Fuerschbach, “Nonsymmetric optical design and design method for nonsymmetric optical system”, US Patent 8,616,712 B2 (December 31, 2013).
[2] K. Fuerschbach, J.P. Rolland, and K.P. Thompson, “A new family of optical systems employing φ polynomial surfaces”, Optics Express, 19(22), 21919-21928 (2011).
Some Fascinating Empirical Limits in Lens Design and a Path to Violating Them
Kevin P. Thompson1,2
1Synopsys - Optical Solutions Group
2The Institute of Optics, University of Rochester
Computational imaging is changing the landscape in many dimensions. This work will first present some interesting empirical limits in lens design and then go on to discuss the potential impacts on optical system design when an imaging system leverages computational methods that extend depth of focus. Computational methods were introduced to the lens design community with the work of Dowski and Cathey [1] that initiated the field of computational imaging in the context of application to imaging optical design. For a lens designer, the challenge in nearly all imaging optical systems is to create high performance imagery on a flat detection plane. One perspective on the impact of computational methods that create extended depth of focus across a field of view is that it can enable a successful optical imaging system that is designed with a curved surface of best imagery. This condition can dramatically simplify the complexity of any optical system for a given level of performance. To put the impact of allowing curved focal surfaces into perspective, some examples to the limits of lens design will be demonstrated. Here, it is found that there is a specific bounding line that is not crossed by any lens design. In this talk we will show that a lens enabled by computation imaging could cross the line, dramatically.
[1] E. R. Dowski and W. T. Cathey, “Extended depth of field through wavefront coding,” Appl. Opt. 34, 1859–1866 (1995).
Development of Motion Picture Camera Zoom Lenses
Iain A. Neil, ScotOptix, Switzerland
A chronology of Academy Award® winning zoom lens optical designs are described in terms of technical innovation and artistic impact on cinematography. In addition, trends in cine zoom lens development are discussed with reference to optical design examples taken from US Patents and published papers as well as optical technology. Also, some recent zoom lens products are used to illustrate how diverse motion picture zoom lenses are becoming.
Computational Imaging: inspired by communications
Andy R Harvey1, Guillem Carles1, Paul Zammit1, Nick Bustin2 and Andy Wood2
[1] School of Physics and Astronomy, University of Glasgow
[2] Qioptiq, St Asaph
While the performance of imaging systems is fundamentally limited by diffraction, the design and manufacture of practical systems is intricately associated with the control of optical aberrations. Traditional optical design typically aims for a compact point-spread function (PSF) across an extended field of view in the presence of chromatic aberrations and imperfect manufacture. In the design of computational imaging systems, a more pertinent criteria is the overall system PSF, or modulation-transfer function (MTF), and the optical PSF is only an intermediate measure of the transfer of information via the detector to post-detection digital recovery of a high-quality image. This is closely related to transmission of information through an imperfect communication system: it is the recovery of high fidelity information at the output that is the prime concern. This presentation will discuss the similarity between imaging and communications systems.
Hybrid computational imaging, involving optimisation of antisymmetric pupil-plane phase functions, yields an extended PSF and approximately defocus-invariant MTF enabling image recovery for an extended depth-of-field [1]. Reduced sensitivity to defocus-related aberrations enables simplified lens design (for example high numerical-aperture imaging with a singlet or a single-element zoom lens). Image-replication artifacts due to strong phase effects can significantly degrade image quality, however the use of complementary imaging and recovery kernels can enable their eradication [2] as will be demonstrated in the presentation.
The resolution of many practical systems is limited, not by diffraction or optical aberrations, but by the finite size of detector pixels and so recorded images are aliased. In such circumstances high-angular resolution may be maintained using an array of shorter-focal length lenslets, typically with an array of lenses of total width equal to the width of the detector array [3] and this limits angular resolution. Higher resolution, using an optical aperture much wider than the detector array, requires more complex optical designs. The consequent distortion and a space-variant PSF, can be incorporated into the recovery of the final image to yield a high-resolution super-resolved image. Angular resolution may also be maintained by super resolving the images recorded by an array of independent cameras [4], exploiting randomisation of image aliasing to improve image recovery [5]. An alternative to the design and manufacture of optics of increasing complexity to achieve increasing field of view is to provide local correction of a primary lens by a segmented correction element over a small field of view [6] followed by computational image reconstruction. In this case the PSF exhibits multiple separated main lobes, but high-quality image recovery is nevertheless possible, with a much more compact and lower cost lens than could be achieved by traditional optical design.
These so-called computational imaging approaches have strong analogy with conventional communication systems: for example: in hybrid imaging, optical coding and digital decoding with spatial dispersion of optical spatial frequencies [7] is equivalent to the function of an electronic MODEM; multi-aperture imaging [4, 5] is similar to the sub-Nyquist sampling of band-limited temporal frequencies routinely used in high-frequency digitisation; and image recovery for the multi-valued PSF of multiscale imaging is redolent of the use of a Rake receiver to combat multi-path effects in cluttered free-space communication [8]. Digital communication systems routinely combine these coding and decoding techniques to maximise information transmission through imperfect channels to enhance system performance, robustness and logistics. Computational imaging offers the potential to provide the same overall system benefits for imaging. In some cases simplification of optics is possible but with the quid pro quo of more complex digital processing.
[1] T. Vettenburg, N. Bustin and A.R. Harvey, “Fidelity optimization for aberration-tolerant hybrid imaging sys- tems”, Opt. Exp., 18, 9220–9228 (2010)
[2] P. Zammit, G. Carles and A.R. Harvey, OSA Conf on Comp. Opt. Sens. and Imag, Hawaii (2014)
[3] K. Nitta, R. Shogenji, S. Miyatake and J. Tanida, “Image reconstruction for thin observation module by bound optics by using the iterative backprojection method”, App. Opt. 45, 2893–2900 (2006)
[4] G. Carles, J. Downing and A.R.Harvey,“Super-resolution imaging using a camera array”,Opt. Let.,39, 1889– 1892, (2014)
[5] J. Downing, E. Findlay, G. Muyo and A.R. Harvey, “Multichanneled finite-conjugate imaging”, JOSA A,29, 6, 921–927, (2012).
[6] D.J. Brady and N. Hagan, “Multiscale lens design”, Opt. Exp. 17, 10659–10674 (2009)
[7] G. Muyo and A.R. Harvey,“Decomposition of the optical transfer function: wavefront coding imaging system”, Opt. Let., 30, 2715–2717, (2005)
[8] G.E. Bottomley, T. Ottosson and Y-P.E. Wang,“A generalized RAKE receiver for interference suppression”, IEEE J. on Sel. Areas Comm., 18, 8, 1536–1545, (2000)
Feasibility Study of the Enhancement of Three Camera Systems VIS and IR for Deuterium-Tritium Operation in JET
A. Manzanares1,4 C. Ruiz de Galarreta1, G. Arnoux2, I. Balboa2, R. Clarkson2, N. Conway2, D. Croft2,3, J. Figueiredo3, C. Hidalgo4, C. Marren2, D. Martin2, A. Meigs2, D. Price2, M. Stamp2, S. Whetham2, and JET-EFDA Contributors
JET-EFDA, Culham Science Centre, Abingdon OX14 3DB, United Kingdom
[1] Greenlight Solutions S.L., Madrid, Spain
[2] Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
[3] Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, P-1049-001 Lisboa, Portugal
[4] Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain
The CDT project is part of the JET component of the EFDA 2012 Work Programme which includes 4 enhancement projects foreseen to work during the D-D and D-T campaings in 2017. The CDT project includes the upgrade of three imaging systems: two IR 3-5um diagnostics (wide angle and divertor FoV) and one wide angle FoV visible diagnostic. The JET visible and infrared cameras are presently installed at a very close distance to the tokamak (typically 2 - 4 meters from the plasma boundary). The neutron yield during 50-50 D-T operation is likely to cause irreversible damage to these cameras or, in the best case, white out the sensor during a plasma pulse. Shielding these cameras from the neutrons is the only way to keep these diagnostics functional during D-T operations. The best shield is to increase the distance between the neutron source and the cameras and insert a concrete wall in the middle. As the torus hall is quite crowed, the increment of the optical line implies the re-design of the diagnostics, partially using new optical components and partially sharing the path with other diagnostics. This contribution will show the status and results of these three re-designs.
Optical Design for Laser-Interferometric Gravitational Wave Detectors
Stefan Hild
SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, UK
The hunt for the direct detection of gravitational waves, tiny ripples in spacetime that have been predicted by Albert Einstein in his theory of general relativity, is carried out with kilometer scale Michelson interferometers. These instruments, using up to one Megawatt (CW) optical power in their arms, obtain strain sensitivities of the order of 10^(-23)/sqrt(Hz) and can measure their kilometer long test ranges to an accuracy of about 1/1000th of a proton diameter. In order to obtain such sensitivities requires very careful optical design of the optical resonators, a diligent treatment of stray light and ultra-low loss optics featuring absorption losses of less than 0.5ppm/cm and scatter losses of less than 50ppm per surface. In this talk I will give an overview of the optical design and relevant techniques for future gravitational wave detectors such as upgrades to the Advanced LIGO detectors or the planned European Einstein Telescope.
Methodology for lens transmission measurement in the 8-13 micron waveband: Integrating sphere versus camera-based
Norbert Schuster, Jan Verplancke, Bergeron Salethaiyan, John Franks
Umicore Electro-Optic Materials (Belgium)Transmission is a key parameter in describing an IR-lens, but is also often the subject of controversy. One reason is the misinterpretation of “transmission” in infrared camera practice. If the camera lens is replaced by an alternative one the signal will be affected by two parameters: proportional to the square of the effective aperture based F-number and linearly to the transmission. The measure to collect energy is defined as the Energy Throughput ETP, and the signal level of the IR-camera is proportional to ETP. Most published lens transmission values are based on spectrophotometric measurement of plane-parallel witness pieces obtained from coating processes. Published aperture based F-numbers derive very often from ray tracing values in the on-axis bundle.
The following contribution is about transmission measurement. It highlights the bulk absorption and coating issues of infrared lenses. Two different setups are built and tested, an Integrating Sphere (IS)-based setup and a Camera-Based (CB) setup. The comparison of the two principles also clarifies the impact of the F-number. One difficulty in accurately estimating lens transmission lies in measuring the ratio between the signal of ray bundles deviated by the lens under test and the signal of non-deviated ray bundles without lens (100% transmission). There are many sources for errors and deviations in LWIR-region including: background radiation, reflection from “rough” surfaces, and unexpected transmission bands. Care is taken in the set up that measured signals with and without the lens are consistent and reproducible.
Reference elements such as uncoated lenses are used for calibration of both setups. When solid angle-based radiometric relationships are included, both setups yield consistent transmission values. Setups and their calibration will be described and test results on commercially available lenses will be published.
Lightpipe design and optimization using simultaneous multi surface design method and LightTools
Murzyn, Pawel
Visteon, UK
Lightpipes are widely used for illumination designs in automotive interiors, i.e. instrument clusters and centre stack electronics. Increasingly demanding requirements and design constraints require the use of more sophisticated design methods to accomplish successful designs. We have applied a 2D simultaneous multi-surface design method to optimize lightpipe sections, e.g. LED coupling sections.
We have developed a number of design cases, which can be adapted for similar designs by changing relevant design parameters. This tool has also been linked with LightTools optical simulation software, allowing recreating designed sub-components directly into optical CAD. This substantially speeds up the design process and allows for re-use of similar concepts and customization to a specific case.
Technology review: Layered polymeric GRIN lenses and their benefits to optical designs
Andrew Boyd
Qioptiq, UK
Gradient Index or GRIN lenses have been known for many years to provide performance benefits to optical systems. The primary barrier to widespread adoption of this technology has been the cost and complexity of manufacture. Recent developments in layered polymer GRIN technology (known as L-GRIN) have the potential to overcome this barrier. This paper reviews the benefits and versatility of this method to visible waveband optical systems. A variety of lens designs based on this manufacturing technique have been developed. We present the optical performance of these lens designs and comment on the challenges of producing them in commercial optical design software.
Feasibility and performance of the implementation of a grism based slit spectroscopy mode in the current SAFARI imaging FTS for the SPICA mission
Carmen Pastor1, Tomás Belenguer1, Willem Jellema2, Pablo Zuluaga1, Luis Miguel González Fernández1 , Josefina Torres Redondo3, Francisco Najarro3, Martin Eggens2 Peter Paul Kooijman2, Jaap Evers2
[1] Instituto Nacional de Técnica Aeroespacial (INTA), Madrid, Spain
[2] SRON Netherlands Institute for Space Research, Department of Low Energy Astrophysics, Groningen, The Netherlands
[3] Centro de Astrobiología (INTA-CSIC), Madrid, Spain
This paper describes the optical feasibility study of a new mode of spectroscopy to be implemented in the reference design instrument concept of SAFARI, and based in grism slit spectroscopy. The reference design of the SAFARI instrument, is a cryogenic far-infrared imaging Fourier transform spectrometer (iFTS) for the JAXA’s SPICA mission, designed to perform background-limited spectroscopic and photometric imaging in the far-infrared (34-210 μm). The instrument will be sharing the SPICA telescope with other instruments and it will be covering a 2’x2’ instantaneous field of view. The instrument shall provide direct imaging, with diffraction limited performance in three spectral bands over 34-210μm. The study is motivated by the possibility of expanding the observing efficiency of SAFARI for strong (> 1Jy) point-like sources, and to overcome sensitivity limitations due to dominating detector background levels. The study presented in this paper is an assessment of the spectroscopic performance that can be achieved due to the implementation of a dispersive element (grism) in the current SAFARI optical design.
Design of NVIS-white compatible illumination using LEDs
Ralf Jedamzik
SCHOTT AG, Advanced Optics, Mainz, Germany
LEDs change the requirements for optical design rules of illumination. Especially, the colour design for night vision compatible equipment has changed dramatically, because the colour locus of LED based illumination no longer defines a one-to-one correspondence of the spectral energy distribution. A so-called NVIS compatible illumination has a specific color and at the same time a very low near infrared radiation. Therefore, modern illumination in cabins and displays requires a combination of filter and LED, which is specific to the LED model. This implies that the filter has to be calculated specifically for each LED model or bin.
The algorithm for the design of a balanced filter and LED combination is presented and some rules of thumb are given for obtaining feasible LED and filter combinations.