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Publication Open Access A MEMS based visible-NIR Fourier transform microspectrometer - art. no. 61860C(Society of Photo-optical Instrumentation Engineers (SPIE), 2006) Wolter, A.; Department of Electrical and Electronics Engineering; Ataman, Çağlar; Ürey, Hakan; Işıkman, Serhan Ömer; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 8579; N/ADesign, fabrication and characterization of a novel out-of-plane vertical comb-drive actuator based Fourier transform microspectrometer (FTS) is presented. The spectrometer utilizes resonant mode vertical comb actuators as a variable-depth diffraction grating and a single photodetector to monitor the 0th order of the diffraction pattern. The spectrum of the source illuminating the gratings is computed by Fourier transforming the 0th order intensity as a function of the optical path difference. The vertical comb actuators have a travel range of 100 mu m under atmospheric pressure with 28V excitation, which yields a theoretical spectral resolution of 0.5nm in the visible and better than 5nm in the telecom wavelengths.
Publication Metadata only A wideband silicon photonic duplexer constructed from a deep photonic network of custom Mach-Zehnder interferometers(Society of Photographic Instrumentation Engineers (SPIE), 2024) Department of Electrical and Electronics Engineering; Amiri, Ali Najjar; Görgülü, Kazım; Mağden, Emir Salih; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of EngineeringUsing a highly-scalable and physics-informed design platform with custom Mach-Zehnder interferometers (MZIs), we design and experimentally demonstrate a 1 x 2 wideband duplexer on silicon operating within 1450-1630 nm. The device is constructed from six layers of cascaded MZIs whose geometries are optimized using an equivalent artificial neural network, in a total timeframe of 75 seconds. Experimental results show below 0.72 dB deviation from the arbitrarily-specified target response, and less than 0.66 dB insertion loss. Demonstrated capabilities and the computational efficiency of our design framework pave the way towards the scalable deployment of custom MZI networks in communications, sensing, and computation applications.Publication Open Access Addendum to 'Unidirectionally invisible potentials as local building blocks of all scattering potentials'(American Physical Society (APS), 2014) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; Department of Physics; College of Sciences; 4231In [Phys. Rev. A 90, 023833 (2014)], we offer a solution to the problem of constructing a scattering potential v(x) which possesses scattering properties of one's choice at an arbitrarily prescribed wave number. This solution involves expressing v(x) as the sum of n <= 6 finite-range unidirectionally invisible potentials. We improve this result by reducing the upper bound on n from 6 to 4. In particular, we show that we can construct v(x) as the sum of up to n = 3 finite-range unidirectionally invisible potentials, unless if it is required to be bidirectionally reflectionless.Publication Open Access Adiabatic series expansion and higher-order semiclassical approximations in scattering theory(Institute of Physics (IOP) Publishing, 2014) Department of Mathematics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; College of Sciences; 4231The scattering properties of any complex scattering potential, nu: R -> C, can be obtained from the dynamics of a particular non-unitary two-level quantum system. S-nu. The application of the adiabatic approximation to S-nu yields a semiclassical treatment of the scattering problem. We examine the adiabatic series expansion for the evolution operator of S-v and use it to obtain corrections of arbitrary order to the semiclassical formula for the transfer matrix of S-nu. This results in a high-energy approximation scheme that unlike the semiclassical approximation can be applied for potentials with large derivatives.Publication Metadata only An LED-based super resolution GPU implemented structured illumination microscope(Spie-Int Soc Optical Engineering, 2020) Aydin, Musa; N/A; N/A; N/A; Department of Physics; Uysallı, Yiğit; Özgönül, Ekin; Morova, Berna; Kiraz, Alper; PhD Student; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; College of Sciences; N/A; N/A; N/A; 22542Fluorescence imaging of sub-cellular structures with sizes below the diffraction limit is vital in understanding cellular processes. Relying on exciting the sample with different illumination patterns and image processing for the elimination of background fluorescence, Structured Illumination Microscopy (SIM) provides imaging capability beyond diffraction limit using relatively simple optical setups. Here, we present a laser-free, DLP projector-based, and GPU-implemented SIM super resolution microscope. Sub-diffractive biological structures were imaged with a lateral resolution of similar to 150 nm. The microscopy system is LED-based and entirely home-built which enables customizable operation at a low cost.Publication Open Access Applications of augmented reality in ophthalmology [invited](Optical Society of America (OSA), 2021) Artal, Pablo; Department of Physics; Department of Electrical and Electronics Engineering; Aydındoğan, Güneş; Kavaklı, Koray; Ürey, Hakan; Şahin, Afsun; Faculty Member; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; College of Engineering; School of Medicine; N/A; N/A; 8579; 171267Throughout the last decade, augmented reality (AR) head-mounted displays (HMDs) have gradually become a substantial part of modern life, with increasing applications ranging from gaming and driver assistance to medical training. Owing to the tremendous progress in miniaturized displays, cameras, and sensors, HMDs are now used for the diagnosis, treatment, and follow-up of several eye diseases. In this review, we discuss the current state-of-the-art as well as potential uses of AR in ophthalmology. This review includes the following topics: (i) underlying optical technologies, displays and trackers, holography, and adaptive optics; (ii) accommodation, 3D vision, and related problems such as presbyopia, amblyopia, strabismus, and refractive errors; (iii) AR technologies in lens and corneal disorders, in particular cataract and keratoconus; (iv) AR technologies in retinal disorders including age-related macular degeneration (AMD), glaucoma, color blindness, and vision simulators developed for other types of low-vision patients.Publication Open Access Artificial eye model and holographic display based IOL simulator(Society of Photo-optical Instrumentation Engineers (SPIE), 2023) N/A; Department of Electrical and Electronics Engineering; N/A; Şahin, Afsun; Ürey, Hakan; Aygün, Uğur; Kavaklı, Koray; Akyazı, Deniz; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; School of Medicine; College of Engineering; Graduate School of Sciences and Engineering; 171267; 8579; N/A; N/A; N/ACataract is a common ophthalmic disease in which a cloudy area is formed in the lens of the eye and requires surgical removal and replacement of eye lens. Careful selection of the intraocular lens (IOL) is critical for the post-surgery satisfaction of the patient. Although there are various types of IOLs in the market with different properties, it is challenging for the patient to imagine how they will perceive the world after the surgery. We propose a novel holographic vision simulator which utilizes non-cataractous regions on eye lens to allow the cataract patients to experience post-operative visual acuity before surgery. Computer generated holography display technology enables to shape and steer the light beam through the relatively clear areas of the patient’s lens. Another challenge for cataract surgeries is to match the right patient with the right IOL. To evaluate various IOLs, we developed an artificial human eye composed of a scleral lens, a glass retina, an iris, and a replaceable IOL holder. Next, we tested different IOLs (monofocal and multifocal) by capturing real-world scenes to demonstrate visual artifacts. Then, the artificial eye was implemented in the benchtop holographic simulator to evaluate various IOLs using different light sources and holographic contents.Publication Open Access Augmented reality 3d display using head-mounted projectors and transparent retro-reflective screen(Society of Photo-optical Instrumentation Engineers (SPIE), 2017) Department of Electrical and Electronics Engineering; Soomro, Shoaib Rehman; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; N/A; 8579A 3D augmented reality display is proposed that can provide glass-free stereo parallax using a highly transparent projection screen. The proposed display is based on a transparent retro-reflective screen and a pair of laser pico projectors placed close to the viewer's head. The retro-reflective screen directs incident light towards its source with little scattering so that each of the viewer's eyes only perceives the content projected by the associated projector. Each projector displays one of the two components (left or right channel) of stereo content. The retro-reflective nature of screen provides high brightness compared to the regular diffused screens. The partially patterned retro-reflective material on clear substrate introduces optical transparency and facilitates the viewer to see the real-world scene on the other side of screen. The working principle and design of the proposed see-through 3D display are presented. A tabletop prototype consisting of an in-house fabricated 60x40cm(2) see-through retro-reflective screen and a pair of 30 lumen pico-projectors with custom 3D printed housings is demonstrated. Geometric calibration between projectors and optimal viewing conditions (eye box size, eye-to-projector distance) are discussed. The display performance is evaluated by measuring the brightness and crosstalk for each eye. The screen provides high brightness (up to 300 cd/ m2 per eye) using 30 lumens mobile projectors while maintaining the 75% screen transparency. The crosstalk between left and right views is measured as < 10% at the optimum distance of 125-175 cm, which is within acceptable range.Publication Metadata only Biaxial MEMS raster scanner with linear ramp drive(IEEE, 2003) Sprague, Randall; Department of Electrical and Electronics Engineering; Ürey, Hakan; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 8579A biaxial MEMS raster scanner is developed for laser scanning displays. We discuss microfabrication, packaging, and design aspects, and how to minimize power consumption and linearity error by optimizing the vertical scanner resonant frequency and drive waveform.Publication Open Access Blowing up light: a nonlinear amplification scheme for electromagnetic waves(Optical Society of America (OSA), 2018) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Ghaemidizicheh, Hamed; Hajizadeh, Sasan; Faculty Member; PhD Student; Department of Mathematics; Department of Physics; Graduate School of Sciences and Engineering; 4231; N/A; N/AWe use the blow-up solutions of nonlinear Helmholtz equations to introduce a nonlinear resonance effect that is capable of amplifying electromagnetic waves of a particular intensity. To achieve this, we propose a scattering setup consisting of a Kerr slab with a negative (defocusing) Kerr constant placed to the left of a linear slab in such a way that a left-incident coherent transverse electric wave with a specific incidence angle and intensity realizes a blow-up solution of the corresponding Helmholtz equation whenever its wavenumber k takes a certain critical value, k(*). For k = k(*), the solution blows up at the right-hand boundary of the Kerr slab. For k < k(*), the setup defines a scattering system with a transmission coefficient that diverges as (k - k(*))(-4) for k -> k(*). By tuning the distance between the slabs, we can use this setup to amplify coherent waves with a wavelength in an extremely narrow spectral band. For nearby wavelengths, the setup serves as a filter. Our analysis makes use of a nonlinear generalization of the transfer matrix of the scattering theory as well as properties of unidirectionally invisible potentials.