Research Project: Holografik ekran teknolojisi ve artırılmış gerçeklik sistemleri geliştirilmesi (HOLOAGES)
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Contributors
Funders
ID
TB.00578
Authors
Ürey, Hakan
Faculty Member
Publications
Intraocular lens simulator using computational holographic display for cataract patients
(Public Library of Science, 2024) Akyazı, Deniz; Aygün, Uğur; Şahin, Afsun; Ürey, Hakan; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; School of Medicine; Yes; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; SCHOOL OF MEDICINE
Purpose To develop and validate a holography based vision simulator for the demonstration of expected postoperative vision corresponding to monofocal and multifocal intraocular lenses (IOL) to cataract patients before surgery.Methods An artificial eye model is used to measure the optical performance of different IOL types. The resultant aberrations and degradations are then modeled using phase holograms and shown to subjects on a holographic display. We measure the contrast and resolution loss, halos around the light sources, and point spread function (PSF) corresponding to three different IOLs. We tested the holography based vision simulator on 13 healthy subjects and 6 cataract patients.Results Monofocal, bifocal, and trifocal IOLs exhibited a contrast decrease of 5%, 42%, and 45% and a resolution limit of 4.49, 4.00, and 4.00 lp/mm (using 0.05 MTF criteria), respectively. Monofocal IOLs have the best resolution and contrast at the optimal focus distance, and multifocal lenses offer extended depth-of-field but exhibit prominent halos and reduced contrast/resolution.Conclusion We confirmed that the visual functions of IOLs could be successfully modeled using phase holograms and simulated using a holographic display without using a physical IOL. Patients can experience the effects of different IOL options prior to surgery, which helps with IOL selection, expectation management, and patient satisfaction.
Cascaded laser scanning towards high-resolution LiDAR
(Elsevier Sci Ltd, 2024) Ürey, Hakan; Khodapanahandeh, Mehrdad; Zolfaghari, ParvizFerhanoglu, Onur; Department of Electrical and Electronics Engineering; Yes; College of Engineering
We present and demonstrate a cascaded laser scan architecture to achieve a three-fold gain in scan angle. We cascaded multiple piezoelectric MEMS scanners using a high numerical aperture relay lens pair in between scanners, which are located at optical conjugate planes. The cascaded scan architecture comprising 3 scanners is simulated using ray-tracing software. Finally, we conduct experiments using the folded architecture, where the incoming laser beam bounces off the first scan mirror (twice) and the second scan mirror, having nearly identical resonant frequencies of 27.59 kHz, yielding a total optical scan angle of 90 degrees. The observed scan angle exceeds the angle achieved by any single MEMS scanner. One can exploit the use of the back surface of the mirrors, as well as higher numerical aperture lenses to improve the achievable total optical scan to more than double, up to 210 degrees. With further development, the proposed architecture can be integrated into LiDAR systems to achieve high number of resolvable spots on the target, with unprecedented speed and form factor, far beyond what can be achieved with rotating motor or polygon mirror-based architectures.
Fabrication and characterization of a 2D PZT MEMS resonant scanner
(Iop Publishing Ltd, 2025) Zolfaghari, Parviz; Khodapanahandeh, Mehrdad; Ürey, Hakan; Khodapanahandeh, Mehrdad; Optical Microsystems Laboratory (MEMS); Graduate School of Sciences and Engineering; Department of Electrical and Electronics Engineering; Yes; Research Center; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Engineering
This work presents the design, simulation, fabrication, and characterization of a novel architectural compact two-dimensional (2D) resonant MEMS scanning mirror actuated by thin-film lead zirconate titanate (PZT). The device employs an innovative mechanically coupled dual-axis architecture fabricated using a three-mask process on an silicon-on-insulator PZT deposited wafer, significantly reducing system complexity while achieving high performance. The scanner integrates a 1 x 1.4 mm oval mirror within a 7 x 4.7 mm die, actuated by PZT thin-film elements optimized for resonant operation at 3.6 kHz (vertical) and 54.2 kHz (horizontal) under 12 Vp-p periodic pulse driving. The system achieves optical scan angles of 4.8 degrees and 11.5 degrees in vertical and horizontal directions, respectively, with quality factors of 750 (vertical) and 1050 (horizontal). These values contribute to high scanning bandwidth-efficiency products of 24.2 degrees mm kHz (vertical) and 623 degrees mm kHz (horizontal), among the higher values reported for 2D PZT-MEMS scanners. Finite element analysis confirmed minimal stress and mirror deformation, and experimental validation demonstrated excellent agreement with simulation results. This architecture demonstrates the feasibility of high-resolution laser scanning, as required in applications such as optical coherence tomography, light detection and ranging, and displays, by achieving performance levels in line with those used in such systems.
Dynamic accommodation measurement using Purkinje reflections and machine learning
(Nature Research, 2023) Aygün, Uğur; Özhan, Faik Ozan; Ürey, Hakan; Şahin, Afsun; KUTTAM (Koç University Research Center for Translational Medicine); Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; School of Medicine; Yes; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Research Center; SCHOOL OF MEDICINE
Quantifying eye movement is important for diagnosing various neurological and ocular diseases as well as AR/VR displays. We developed a simple setup for real-time dynamic gaze tracking and accommodation measurements based on Purkinje reflections, which are the reflections from front and back surfaces of the cornea and the eye lens. We used an accurate eye model in ZEMAX to simulate the Purkinje reflection positions at different focus distances of the eye, which matched the experimental data. A neural network was trained to simultaneously predict vergence and accommodation using data collected from 9 subjects. We demonstrated that the use of Purkinje reflection coordinates in machine learning resulted in precise estimation. The proposed system accurately predicted the accommodation with an accuracy better than 0.22 D using subject’s own data and 0.40 D using other subjects’ data with two-point calibration in tests performed with 9 subjects in our setup. © 2023, The Author(s).
Multi-color holograms improve brightness in holographic displays
(Association for Computing Machinery, 2023) Kavaklı, Koray; Ürey, Hakan; Shi, Liang; Urey, Hakan; Matusik, Wojciech; Aksit, Kaan; Graduate School of Sciences and Engineering; Department of Electrical and Electronics Engineering; Yes; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Engineering
Holographic displays generate Three-Dimensional (3D) images by displaying single-color holograms time-sequentially, each lit by a single-color light source. However, representing each color one by one limits brightness in holographic displays. This paper introduces a new driving scheme for realizing brighter images in holographic displays. Unlike the conventional driving scheme, our method utilizes three light sources to illuminate each displayed hologram simultaneously at various intensity levels. In this way, our method reconstructs a multiplanar three-dimensional target scene using consecutive multi-color holograms and persistence of vision. We co-optimize multi-color holograms and required intensity levels from each light source using a gradient descent-based optimizer with a combination of application-specific loss terms. We experimentally demonstrate that our method can increase the intensity levels in holographic displays up to three times, reaching a broader range and unlocking new potentials for perceptual realism in holographic displays.
