This paper demonstrates a phase tunable holographic fabrication of three-dimensional photonic lattice structures using a single optical element. A top-cut four-side prism is employed to generate five-beam three-dimensional interference patterns. A silica glass slide is inserted into the optical path to adjust the phase of one interfering beam relative to other four beams. The phase control of the interfering laser beam renders the lattice of the interference pattern from a face-center tetragonal symmetry into a high contrast, interconnecting diamondlike symmetry. This method provides a flexible approach to fabricating three-dimensional photonic lattices with improved photonic band structures

Chen, Kevin P.

Harb, Ahmad

Lin, Yuankun

Lozano, Karen

Rodriguez, Daniel

Xu, Di

English

Scholarworks@UTRGV Univ. of Texas RioGrande Valley

University of Texas Rio Grande Valley ScholarWorks @ UTRGV Mechanical Engineering Faculty Publications and Presentations College of Engineering and Computer Science 6-10-2009 Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element Di Xu University of Pittsburgh Kevin P. Chen University of Pittsburgh Ahmad Harb The University of Texas Rio Grande Valley Daniel Rodriguez The University of Texas Rio Grande Valley Karen Lozano The University of Texas Rio Grande Valley, karen.lozano@utrgv.edu See next page for additional authors Follow this and additional works at: https://scholarworks.utrgv.edu/me_fac  Part of the Mechanical Engineering Commons Recommended Citation Xu, Di; Chen, Kevin P.; Harb, Ahmad; Rodriguez, Daniel; Lozano, Karen; and Lin, Yuankun, "Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element" (2009). Mechanical Engineering Faculty Publications and Presentations. 23. https://scholarworks.utrgv.edu/me_fac/23 This Article is brought to you for free and open access by the College of Engineering and Computer Science at ScholarWorks @ UTRGV. It has been accepted for inclusion in Mechanical Engineering Faculty Publications and Presentations by an authorized administrator of ScholarWorks @ UTRGV. For more information, please contact justin.white@utrgv.edu, william.flores01@utrgv.edu. Authors Di Xu, Kevin P. Chen, Ahmad Harb, Daniel Rodriguez, Karen Lozano, and Yuankun Lin This article is available at ScholarWorks @ UTRGV: https://scholarworks.utrgv.edu/me_fac/23 ?????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ???????????????????? ????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Phase tunable holographic fabrication for three-dimensional photoniccrystal templates by using a single optical elementDi Xu,1 Kevin P. Chen,1,a Ahmad Harb,2 Daniel Rodriguez,2 Karen Lozano,2 andYuankun Lin2,b1Department of Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh,Pennsylvania 15261, USA2College of Science and Engineering, University of Texas-Pan American, Edinburg, Texas 78541, USAReceived 18 February 2009; accepted 10 May 2009; published online 10 June 2009This paper demonstrates a phase tunable holographic fabrication of three-dimensional photoniclattice structures using a single optical element. A top-cut four-side prism is employed to generatefive-beam three-dimensional interference patterns. A silica glass slide is inserted into the optical pathto adjust the phase of one interfering beam relative to other four beams. The phase control of theinterfering laser beam renders the lattice of the interference pattern from a face-center tetragonalsymmetry into a high contrast, interconnecting diamondlike symmetry. This method provides aflexible approach to fabricating three-dimensional photonic lattices with improved photonic bandstructures. © 2009 American Institute of Physics. DOI: 10.1063/1.3149705Three-dimensional 3D photonic crystal structures havebeen the subject of intense scientific and engineering inter-ests since the first introduction in 1987.1,2 The existence of aphotonic bandgap in photonic crystals gives rise to a numberof peculiar optical properties useful for photonic engineer-ing. However, the fabrication of 3D photonic crystals with acomplete bandgap in visible and near infrared regimes re-mains a great challenge.3 This is because the existing photo-mask lithography-based fabrication approach widely used insemiconductor industries cannot be inherited for 3D nano-fabrication. Nevertheless, various approaches have been em-ployed to fabricate photonic crystals with complex 3D peri-odic lattices.4–7Among these methods, holographic laser lithography is apowerful technique to fabricate 3D photonic crystals.7,8 Theholographic lithography constructs 3D interference patternsof multiple coherent laser beams in a photoresist to form 3Dstructures. The complexity and symmetry of the 3D photonicstructures can be controlled by the number of interfering la-ser beams, their relative interference angles, and their respec-tive phases.Recently, a number of papers have demonstrated the la-ser holographic fabrication of 3D photonic crystal structuresusing a single optical element such as a refractive opticalelement e.g., a top-cut prism9–11 or a diffractive optical el-ement e.g., a phase mask12. The optical element splits asingle incoming laser beam into multiple coherent laserbeams with desired interfering angles for 3D holographicpattern formation. The adaptation of single optical element inholographic lithography drastically reduces the fabricationcomplexity.Technically, it is relatively easy to produce multiple co-herent laser beams with precise interference angles by asingle optical element.9–12 However, holographic lithographytechniques using a single optical element presented so farlack precise phase control of the interfering beams. Precisephase control of interfering laser beams is critical to the fab-rication of complex, highly symmetric photonic structuressuch as the diamondlike structures which possess large pho-tonic bandgaps.13,14In this paper, we demonstrate a phase tunable holo-graphic fabrication of 3D photonic structures using a singleoptical element. The technique demonstrated in this paperprovides a simple approach to finely tune and optimize pho-tonic band structures with large photonic bandgap width.The single optical element used to construct the five-beam interference pattern is a top-cut, four-side prism. Fivebeams are selected by a set of apertures from one incomingcollimate beam. The use of the apertures prevents laserbeams from hitting corners and edges of the prism. As shownin the inset of Fig. 1, all five laser beams are incident fromthe bottom side of the prism. After total internally reflected atfour lateral surfaces of the prism, Beam 2–5 refract throughthe top surface of the prism and recombine with beam 1 toform interference patterns. To perform the phase modulation,a thin microscope glass cover slide with a uniform thicknessCorning, BK7 glass, d=130 m, n=1.52 is inserted intoone of five beams used to form interference patterns labeledaElectronic mail: kchen@engr.pitt.edu.bElectronic mail: linyk@utpa.edu.FIG. 1. Color online Experiment setup of the five-beam interference withone beam modulated by a glass slide. Inset: phase modulation  as afunction of the glass slide rotational angle .APPLIED PHYSICS LETTERS 94, 231116 20090003-6951/2009/9423/231116/3/$25.00 © 2009 American Institute of Physics94, 231116-1as beam 5 in Fig. 1. By rotating the glass slide, the phase ofthe beam 5 can be adjusted continuously.The rationale of the phase control of one interferingbeam can be briefly described as the following. The intensityprofile of the five-beam interference pattern can be calculatedasI = i=15Ei2 + ij5EiEj coski − kjr + ij , 1where Ei is electric field strength and ki is wave number. Theinsertion of the phase control glass slide in the beam 5 in-duces an additional phase modulation , which only affectson the last term of Eq. 1 and we can rewrite Eq. 1 asImod = Inonmod + i=15EiE5 coski − k5r +  , 2where Imod and Inonmod denote the isosurface of the intensitypattern related to and not related to the phase modulation,respectively. The additional phase modulation  as a func-tion of the glass slide rotation angle  can be described as =2	 dcos 	nglass − nair cos − 	− nglass − naird , 3where 	=arcsinsin  /nglass and  is the incident wave-length. Figure 1 inset illustrates the relation between thephase change  and the rotation angle  from Eq. 3. Fromthis curve, we can see that 6.1° of rotation of the glass slideis enough to produce a  phase retardation using the currentsetup. Figure 2 shows the variation in unit cell lattices for thefive-beam interference pattern as the phase change evolves from 0 to  with a 0.2 increment. The evolution ofthe phase change  renders the interference pattern or ho-lographic photonic crystal from face-centered-cubic or face-centered-tetragonal FCT structure into interconnectedstructures. When the phase modulation reaching the optimalvalue =, a diamondlike network is formed.13,14To experimentally validate the phase tuning and struc-ture controlling, 3D photonic crystal templates were fabri-cated in a negative-toned photoresist mixture. It contains88.93 wt % dipentaerythritol penta/hexaacrylate monomerfrom Aldrich, 0.22 wt % photoinitiator rose bengal, 0.82wt % coinitiator N-phenyl glycine and 10.03 wt % chain ex-tender N-vinyl pyrrolidinone.15 The mixture was spin-coatedon glass slides at 2000 rpm for 2 min. No prebake procedurewas used before receiving exposure.A 514.5 nm circularly polarized laser beam from Ar ionlaser Coherent Inc. was cleaned, expanded, and collimatedby spatial filter and collimating lens. The BK7 microscopeslide used for phase tuning was mounted on a rotationalstage. The exposure dose in use is tested in the range of100–1000 mJ /cm2. After exposure, the photoresist sampleswere developed directly in propylene glycol methyl etheracetate for 20 s, followed by rinsing in isopropanol for 10 sand then left to dry in air.Figure 3 shows the scanning electric microscope SEMpictures for the recorded five-beam interference pattern in thephotoresist. In this case, the glass slide for phase modulationwas not used. Without the phase modulation, the developedphotoresist did not form interconnected networks. Only onelayer of developed photoresist was left on the glass slide.Two-dimensional structures shown in the SEM is in goodagreement with the simulated one see insert in Fig. 3.In a sharp contrast, the introduction of a phase tuningmechanism in the five-beam holographic lithography usingthe prism yields overlapping diamondlike structures. Figure4a shows the SEM image for the photonic crystal templateformed in photoresist with diamondlike structures, whichwere achieved by the phase tuning of the beam 5. As pre-dicted by the simulation in Fig. 4b, the fine phase tuningtransforms the photonic crystal template from the FCT sym-metry to diamondlike symmetry. The interference patternlocked in photoresist clearly shows interlaced structures withdiamondlike symmetries in Fig. 4. The period of diamond-like structure in the Fig. 4a in x or y direction is measuredto be 0.85 m, in good agreement with a theoretic predic-tion of 0. 84 m with an interference angle of 37.5° and aperiod of 0.82 m in Fig. 3 for the fabricated one-layerstructure.A detail examination of the SEM photo shows that vari-ous interlaced structures were produced periodically on thesurface of the photoresist with a period of around 8.6 m,which is approximately ten times as large as the diamondlikelattice period. Zoom-in SEM pictures, as shown in Figs.4c–4f, present detailed features of various interlacedFIG. 2. Color online Isosurface of the unit cells of the phase modulatedfive-beam interference pattern, Imod. The phase change  varies from 0 to with 0.2 increment.FIG. 3. Color online SEM pictures of fabricated structures in the photo-resist through the five-beam interference without a phase modulation. Insetsare the zoom in view of the bottom layer and a simulation for a comparison.231116-2 Xu et al. Appl. Phys. Lett. 94, 231116 2009structures in the developed photoresist. These structuralvariations could be attributed to a slight misalignment of thesample. The surface of the photoresist film is not completelyperpendicular to the normal incident laser beam, but cutthrough the 001 surface of the diamondlike structure at asmall angle. This will result in surface topology representingdiamondlike structures at different depth. The comparisonbetween the simulation and the experiment showed in Fig. 4confirms this speculation. Figures 4g–4j shows the com-puted five-beam interference pattern where one beam has aphase retardation of  relative to other four beams, and itsselected cross-section planes along height z direction. Thefabricated topographic images shown in Figs. 4c–4fmatch well with those simulation planes.It should be pointed out that the photonic bandgap prop-erties of the photonic crystal can be improved by such phasemodulation. Theoretical simulation predicts that the photonicstructure templates duplicated from the five-beam interfer-ence patterns can have complete bandgap if the templatesor their inverse replica structures are translated into high-index materials. Such inversion processes have beenwell-documented.16 If the template structure shown in Fig. 4is translated into a 3D photonic structure consisting of airfilled voids and high refractive index dielectric materialssuch as Si, the phase modulation  from 0 to  will lead toan improvement of photonic bandgap width bandgap width/bandgap central frequency from 3.8% to 25%, with achange in bandgap location from band 8–9 to band2–3.13,14,17In summary, we have demonstrated phase tunable holog-raphy fabrication of 3D diamondlike photonic crystal tem-plates using a top-cut prism as a refractive optical elementand a glass slide as a phase modulator. The phase modulationcan transfer the template from FCT structure to diamondlikestructure, as confirmed through SEM images. This paper pro-vides a simple and versatile method to control holographicinterference patterns to fabricate photonic crystal with opti-mized optical properties.This work was supported by research grants from theU.S. National Science Foundation under Grant Nos. DMI-0556086 K.P.C., CMMI-0609345 Y.L. and K.L. andDMR-0722754 Y.L..1S. John, Phys. Rev. Lett. 58, 2486 1987.2E. Yablonovitch, Phys. Rev. Lett. 58, 2059 1987.3M. Maldovan and E. L. Thomas, Nature Mater. 3, 593 2004.4K. M. Ho, C. T. Chan, C. M. Soukoulis, R. Biswas, and M. Sigalas, SolidState Commun. 89, 413 1994.5S. H. Park, D. Qin, and Y. Xia, Adv. Mater. Weinheim, Ger. 10, 10281998.6M. Deubel, G. V. Freymann, M. Wegener, S. Pereira, K. Busch, and C. M.Soukoulis, Nature Mater. 3, 444 2004.7M. Campbell, D. N. Sharp, M. T. Harrison, R. G. Denning, and A. J.Turberfield, Nature London 404, 53 2000.8Y. V. Miklyaev, D. C. Meisel, A. Blanco, G. V. Freymann, K. Busch, W.Koch, C. Fnkrich, M. Deubel, and M. Wegener, Appl. Phys. Lett. 82,1284 2003.9L. Wu, Y. Zhong, C. T. Chan, K. S. Wong, and G. P. Wang, Appl. Phys.Lett. 86, 241102 2005.10Y. Zhong, L. Wu, H. Su, K. S. Wong, and H. Wang, Opt. Express 14, 68372006.11Y. K. Pang, J. C. Lee, C. T. Ho, and W. Y. Tam, Opt. Express 14, 91132006.12Y. Lin, P. R. Herman, and K. Darmawikarta, Appl. Phys. Lett. 86, 0711172005.13T. Y. M. Chan, O. Toader, and S. John, Phys. Rev. E 71, 046605 2005.14O. Toader, T. Y. M. Chan, and S. John, Appl. Phys. Lett. 89, 1011172006.15Y. Lin, A. Harb, D. Rodriguez, K. Lozano, D. Xu, and K. P. Chen, Opt.Express 16, 9165 2008.16N. Tétreault, G. V. Freymann, M. Deubel, M. Hermatschweiler, F. P. Wil-lard, S. John, M. Wegener, and G. A. Ozin, Adv. Mater. Weinheim, Ger.18, 457 2006.17D. Xu, K. P. Chen, K. Ohlinger, and Y. Lin, Appl. Phys. Lett. 93, 0311012008.FIG. 4. Color online Color Online a SEM pictures for the photoresisttemplates of the interconnecting diamondlike structure, produced by thefive-beam interference with phase retardation. b Computed five-beam in-terference pattern and its selected cross-section planes along height z di-rection; c–f Structure variation described by the zoom in SEM views ofthe diamondlike template and their corresponding simulation planes fromb.231116-3 Xu et al. Appl. Phys. Lett. 94, 231116 2009

Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element

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Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element

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