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1. Freeform optics for dynamic illumination

   https://doi.org/10.1117/12.2568785  

   Shadalou, Shohreh ; Suleski, Thomas J. ( August 2020 , 785 Event: SPIE Optical Engineering + Applications, 2020, Online Only)

   Winston, Roland ; Yablonovitch, Eli (Ed.)

   Abstract Dynamic illumination can improve functionality for multiple application areas, including lighting, AR/VR, automotive, medicine, and security. Some applications require a uniform illumination pattern of continuously variable divergence or size for improved functionality. Such dynamic functionality has previously been achieved, for example, by longitudinally moving a source relative to a curved reflector, which can result poor uniformity, or through zoom configurations in which the longitudinal distances between lenses in the system are dynamically adjusted. Advances in high precision manufacturing methods such as diamond machining have facilitated the practical implementation of freeform optical components, enabling new design approaches and concepts for illumination systems. In this paper, we explore the use of arrays of transmissive pairs of freeform surfaces to enable efficient and uniform dynamic illumination in a compact package. This work builds on the Alvarez lens concept, in which a pair of transmissive XY-polynomial freeform surfaces generates variable optical power through lateral relative shifts. Design approaches and simulation results are presented. 

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2. MEMS-actuated metasurface Alvarez lens

   https://doi.org/10.1038/s41378-020-00190-6  

   Han, Zheyi ; Colburn, Shane ; Majumdar, Arka ; Böhringer, Karl F. ( October 2020 , Microsystems & Nanoengineering)

   Miniature lenses with a tunable focus are essential components for many modern applications involving compact optical systems. While several tunable lenses have been reported with various tuning mechanisms, they often face challenges with respect to power consumption, tuning speed, fabrication cost, or production scalability. In this work, we have adapted the mechanism of an Alvarez lens – a varifocal composite lens in which lateral shifts of two optical elements with cubic phase surfaces give rise to a change in the optical power – to construct a miniature, microelectromechanical system (MEMS)-actuated metasurface Alvarez lens. Implementation based on an electrostatic MEMS generates fast and controllable actuation with low power consumption. The utilization of metasurfaces – ultrathin and subwavelength-patterned diffractive optics – as optical elements greatly reduces the device volume compared to systems using conventional freeform lenses. The entire MEMS Alvarez metalens is fully compatible with modern semiconductor fabrication technologies, granting it the potential to be mass-produced at a low unit cost. In the reported prototype operating at 1550 nm wavelength, a total uniaxial displacement of 6.3 µm was achieved in the Alvarez metalens with a direct-current (DC) voltage application up to 20 V, which modulated the focal position within a total tuning range of 68 µm, producing more than an order of magnitude change in the focal length and a 1460-diopter change in the optical power. The MEMS Alvarez metalens has a robust design that can potentially generate a much larger tuning range without substantially increasing the device volume or energy consumption, making it desirable for a wide range of imaging and display applications.

    

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3. Precision glass molding of freeform optics

   https://doi.org/10.1117/12.2320574  

   Gurganus, Dustin ; Owen, Joseph D. ; Davies, Matthew A. ; Dutterer, Brian S. ; Novak, Spencer ; Symmons, Alan ; Rascher, Rolf ; Williamson, Ray ; Kim, Dae Wook ( September 2018 , Optical Manufacturing and Testing XII)

   Precision glass molding is a viable process for the cost-effective volume production of freeform optics. Process development is complex, requiring iterative trials of mold manufacture and metrology, glass mold prototyping, metrology and functional testing. This paper describes the first iteration in the development of a process for an Alvarez lens for visible light. The challenges of this optic are extremely tight band-RMS tolerances on a freeform shape over a maximum clear aperture of 45 mm, a 16:1 aspect ratio and a freeform departure of 329 micrometers. A freeform glass mold for an Alvarez lens was manufactured by coordinated-axis diamond turning in a mold substrate using a custom tool error correction method. The results of prototype precision glass molding are also reported. Mold surfaces and molded optical surfaces are analyzed with scanning white light interferometry. A surface roughness of approximately 3 nm RMS is obtained for both the mold substrate and the glass optic with high-fidelity reproduction of micro-surface structure in the glass. These measurements also identify challenging areas, particularly the presence of mid-spatial frequency errors on the optic originating from the machine thermal control system. The form of the molds was also measured with a profilometer; however, the mold surface does not agree with the expected prescription with an overall deviation in form of approximately 10 μm. The machining process is expected to have sub-micrometer error and the sources of this discrepancy are still being determined. Metrology of the glass optics is currently in progress. 

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4. Variable extended depth of field imaging using freeform optics

   https://doi.org/10.1117/12.2568723  

   Moein, Sara ; Suleski, Thomas J. ( August 2020 , SPIE Optical Engineering + Applications, 2020, Online Only)

   Hahlweg, Cornelius F. ; Mulley, Joseph R. (Ed.)

   Increasing depth of field in imaging systems can be beneficial, particularly for systems with high numerical apertures and short depth of field, such as microscopy. Extending depth of field has been previously demonstrated, for example, using non-rotationally symmetric (freeform) components such as cubic and logarithmic phase plates. Such fixed phase plates are generally designed for a specific optical system, so a different phase plate is required for each system. Methods that enable variable extended depth of field for multiple optical systems could provide benefits by reducing the number of required components and costs. In this paper, we explore the design of a single pair of transmissive freeform surfaces to enable extended depth of field for multiple lenses with different numerical apertures through relative translation of the freeform components. This work builds on the concept of an Alvarez lens, in which one pair of transmissive XY-polynomial freeform surfaces generates variable optical power through lateral relative shifts between the surfaces. The presented approach is based on the design of multiple fixed phase plates to optimize the through-focus Modulation Transfer Function (MTF) for imaging lenses of given numerical apertures. The freeform surface equation for the desired variable phase plate pair is then derived and the relative shift amounts between the freeform surfaces are calculated to enable extended depth of field for multiple imaging lenses with different numerical aperture values. Design approaches and simulation results will be discussed. © (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. Citation Download Citation Sara Moein and Thomas J. Suleski "Variable extended depth of field imaging using freeform optics", Proc. SPIE 11483, Novel Optical Systems, Methods, and Applications XXIII, 114830G (21 August 2020); https://doi.org/10.1117/12.2568723 

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5. General design method for dynamic freeform optics with variable functionality

   https://doi.org/10.1364/OE.460078  

   Shadalou, Shohreh ; Suleski, Thomas J. ( January 2022 , Optics Express)

   We propose and demonstrate a general design method for refractive two-element systems enabling variable optical performance between two specified boundary conditions. Similar to the Alvarez lens, small, relative lateral shifts in opposite directions are applied to a pair of plano-freeform elements. The surface prescriptions of the boundary lenses and a maximum desired shift between freeform plates are the main design inputs. In contrast to previous approaches, this method is not limited to boundaries with similar optical functions and can enable a wide range of challenging, dynamic functions for both imaging and non-imaging applications. Background theory and design processes are presented both for cases that are conducive to analytical surface descriptions, as well as for non-analytic surfaces that must be described numerically. Multiple examples are presented to demonstrate the flexibility of the proposed method. 

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