Through the Nonlinear Laser Lithography method, we demonstrate the first computer generated holograms fabricated deep inside Silicon. Fourier and Fresnel holograms are fabricated buried inside Si wafers, and a generation algorithm is developed for hologram fabrication. © OSA 2016

Elahi P.

Makey G.

Pavlov I.

Tokel O.

Turnali A.

Yavuz O.

Ömer Ilday F.

Yavuz Ö.

Ilday F.Ö.

Bilkent University Institutional Repository

Holograms deep inside silicon

JW4A.2.pdf 2016 Imaging and Applied Optics Congress (3D, AO, AIO,COSI, DH, IS, LACSEA, MATH) © OSA 2016Holograms Deep Inside SiliconGhaith Makey1, Onur Tokel1, Ahmet Turnali2, Ihor Pavlov1, Parviz Elahi1,Özgün Yavuz2 and F. Ömer Ilday1,21Department of Physics, Bilkent University, 06800 Ankara, Turkey2Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara, Turkeyg.makey@fen.bilkent.edu.trAbstract: Through the Nonlinear Laser Lithography method, we demonstrate the firstcomputer generated holograms fabricated deep inside Silicon. Fourier and Fresnel hologramsare fabricated buried inside Si wafers, and a generation algorithm is developed for hologramfabrication.OCIS codes: 090.1760, 320.7130Recently we have demonstrated the use of ultrafast lasers for creating extremely uniform structures over indefinitelarge surfaces with Nonlinear Laser lithography (NLL) [1]. The method relies on a novel physical mechanism whichenables a plethora of laser created nanostructures on surfaces. Now with the extension of this mechanism to thethird dimension, for the first time, we can create buried structures in silicon (Si) wafers without damaging the wafersurface [2–4]. The importance of this achievement is hard to overemphasize, since Si is the fundamental material inelectronics, silicon photonics and solar cell technologies. Further, it has desired properties at the mid-infrared wherefunctional optical elements are hard to fabricate. Here we demonstrate the first functional holograms created inside Siwafers. The phase delay along the fabricated micro-structures inside Si enables the translation of diffractive optics andholography lexicon to Si optics in unprecedented fashion. As a capability demonstration of the plethora of functionaldiffractive optical elements buried inside Si, here we present the first computer generated holograms; namely Fourierholograms to project high detailed 2D images, and Fresnel holograms to reconstruct 3D image projection.a b cd eFig. 1 (a) The target image (source image). (b) Part of the generated hologram in Si. (c) Microscope image of portion of the fabricatedhologram. (d) The reconstructed image by simulation (1st order only). (e) The optically reconstructed image (1st order only).JW4A.2.pdf 2016 Imaging and Applied Optics Congress (3D, AO, AIO,COSI, DH, IS, LACSEA, MATH) © OSA 2016In comparison to computer generated holograms (CGH) written on the surface of Si [5], which are based onamplitude modulation, Si embedded CGHs are based on phase modulation. The pixel based phase modulation enablesimplementing buried kinoforms (phase holograms), which also reduces the number of pixels in the hologram requiredto recreate an image. Moreover, the micro-structures inside Si exhibit high refractive index difference, in contrast toglass embedded CGHs, which increases the applicability of kinoforms inside Si compared to glass.To design the kinoform binary holograms that can reconstruct both binary and gray-scale images at high fidelity,we developed and customized an algorithm. For Fourier holograms, we implemented a modified version of theadaptive-additive Iterative Fourier Transform Algorithm (IFTA) [6]. The modifications include customizing thespectral condition of adaptive-additive algorithm to yield binary phase holograms, and increasing the noise spaceof the algorithm to improve the quality of the reconstructed image. The result of the application of our algorithm isshown in Fig. 1, which shows the target image (the Mona Lisa, Fig 1a), part of the generated subsurface hologram(Fig. 1b), and simulation of the reconstructed image (Fig. 1d). The experimental result of the image generated bythe hologram is given in Fig 1e. For the Fresnel hologram, we used the same algorithm to generate a stack of binaryholograms, each able to create a slice of the intended 3D projection at a different distance. Then, we superimposedthe generated holograms together and finally binarized the resulting hologram. The presented 3D projection of theFresnel hologram was chosen to be rectangular twisted channel of 4 slices (Fig. 2).Experimentally, the holograms were fabricated using a home-build 1.55 µm master oscillator power amplifier(MOPA) fiber laser. The silicon sample was processed on a three-axis motorized stage to enable precise positioning ofthe sample. The pixel size was chosen as 10 µm to keep the scalar wave equation valid, and also to reconstruct largeimages. A portion of the fabricated hologram is shown in Fig.1(c), where dark zones indicate processed areas. Theholograms were fabricated up to 800 by 600 pixels in size.Fig. 2 The optical setup used to reconstruct Fresnel images of silicon subsurface holograms, and the optical constructed images ofthe 3D twisted channel (a,b,c,d).JW4A.2.pdf 2016 Imaging and Applied Optics Congress (3D, AO, AIO,COSI, DH, IS, LACSEA, MATH) © OSA 2016For Fourier holograms, the optical setup uses a 1 µm home-made fiber laser system, a digital camera after removingits IR filter, and focusing optics. Fig. 1(e) shows the final optical reconstruction of the image. As for Fresnel hologram,the reconstruction setup implemented the same laser, while the same camera was mounted on one-axis motorizedstage to capture the different slices of the 3D projection. Fig. 2 shows both the optical reconstruction setup of Fresnelhologram and images of the optical reconstructed slices of the hologram’s 3D projection. Diffraction efficiency isdefined as the power ratio of the diffraction’s first order to zeroth order, which is measured approximately as 200 %corresponding to a phase modulation depth of 0.73 π .In conclusion, the first deeply buried silicon holograms are made possible by Nonlinear Laser Lithography. Thealgorithm for generating the embedded holograms was developed and optimized to reconstruct detailed 2D images viaFourier diffraction, and 3D projections by Fresnel diffraction. The presented holograms prove the ability to create avariety of diffractive optical elements inside Si, that can be used in wavefront correction and micro-optical applications.References1. B. Öktem, I. Pavlov, S. llday, H. Kalaycıoğlu, A. Rybak, S. Yavaş, M. Erdoğan, and F. Ö. llday, “Nonlinear laserlithography for indefinitely large-area nanostructuring with femtosecond pulses,” Nature Photon. 7, 897 (2013).2. O. Tokel, A. Turnali, I. Pavlov and F. Ömer Ilday, ”Laser writing deep inside silicon for 3D information pro-cessing,” presented at CLEO/EU-EQEC, Munich, Germany, 21–25 June 2015.3. O. Tokel, A. Turnali, I. Pavlov, F. Ömer Ilday , ”Physical model for subsurface silicon writing,” presented atCLEO-PR, Busan, Korea, 24–28 Aug 2015.4. O. Tokel, A. Turnali, E. Ergecen, I. Pavlov, F. Ömer Ilday , ”3D Functional Elements Deep Inside Silicon withNonlinear Laser Lithography,” presented at APS, Baltimore, Maryland, USA, 14–18 March 2016.5. K. J. Waedegaard and P. Balling, ”High-resolution computer-generated reflection holograms with three-dimensional effects written directly on a silicon surface by a femtosecond laser,” Opt. Exp. 19, 3434 (2011)6. ER. Dufresne, GC. Spalding, MT. Dearing, SA. Sheets and DG. Grier, ”Computer generated holographic opticaltweezer arrays,” Review of Scientific Instruments 72, 1810 (2001)

Holograms deep inside Silicon

Through the Nonlinear Laser Lithography method, we demonstrate the first computer generated holograms fabricated deep inside Silicon. Fourier and Fresnel holograms are fabricated buried inside Si wafers, and a generation algorithm is developed for hologram fabrication. © OSA 2016. © OSA 2016

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Holograms deep inside Silicon

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Bilkent University Institutional Repository

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Bilkent University Institutional Repository

Bilkent University Institutional Repository

Bilkent University Institutional Repository

Bilkent University Institutional Repository