REPORTS the formation of sn ngle-domain, elongated phors to build polarized light-emitting diodes(Fig 4, 15. L Carbone et al., Nano Lett. 7, 2942 (2007) e superparticles with /=11+ 4 um G to J, and fig S27) 16. D. V. Talapin et al, Nano Left. 7, 2951(2007) 1.1±03μm(Fg.4, B and c). These Our results show that anisotropic interactions 17. See supplementary materials on Science Online single-domain superparticles have a different mor- of CdSe-Cds nanorods can be used to synthesize Angew. Chem. Int. Ed. 47, 220B(2008)do 18.]. Q Zhuang, H M. Wu, Y. G. Yang, Y.C. phology from those multidomain superparticles colloidal superparticles with multiple well-defined 19. D B. Williams, C.B. Carter, Transmission Electron made from identical nanorods without incubation supercrystalline domains under thermodynamic treatment(fig. S21, C to E). equilibrium. Functionality-based anisotropic inter- during the superparticle Montagne, Y C. Cao 40% and are indefinitely stable in solvents with ing to the formation of single-domain, needle-like ma8.843(2012) strong polarity, such as water or ethanoL. However, rticles. We anticipate that these findings can 23. P. Ball, The sel -Made Tapestry: Pattern Formation m these particles can undergo intraparticle ripening be extended for the self-assembly of nano-objects 24. Y. N. Xia, Y. D. Yin, Y. Lu, L. McLellan, Adv. Funct. Mater. in lower-polarity solvents such as ethylene glycol, having other anisotropic shapes, as well as the 13, 907(2003) demonstrating that the needle-like morphology is self-assembly of two or more types of anisotropic 25. D. V. Talapin et al, Nano Lett. 3, 1677(2003) not an equilibrium shape(fig. S23). The meso- nano-objects into well-defined mesoscopic and 26. A Sitt, A Salant, G. Menagen, U Banin, Nano Lett. 11. scopic sizes of these needle-like superparticles macroscopic complex architectures(1-3) 27.]. F. Wang, M. S. Gudiksen, X. F. Duan, Y. allow them to be easily aligned into unidirec- C. M. Lieber, Science 293, 1455 (2001) tional line patterns on Si, N4 substrates through rces wnich can References and notes readily transferred into uniform and removable G. M Whitesides, B Grzybowski, Science 295, 2418 Acknowledgments: Supported by Office of Naval Research thin films of polydimethylsiloxane(PDMS)with 4-09-1-0441 ( Y CC), NSF Career Awar 2.5.Mann,Nat.Mate.8,781(2009) DMR-0645520, and the Cornell High Energy Synchrotro sizes as large as 5.0 cm x 5.0 cm(Fig 4, D andE, 3. S C. Glotzer, M 1. Solomon, Nat. Mater. 6. 557(2007). Source through NSF award DMR-0936384We thank SZou for and fig S25). The resulting thin films exhibit strong 4. M.R. Jones et al, Nat. Mater. 9, 913(2010) inearly polarized PL at 579 nm with a typical emission polarization ratio [p=(n-I+I, 6. M. Rycenga, ]. M. McLellan, Y. N. Xia, Adv. Mater. 20. cted at the Major Analytical Instrumentation Center University of Florida. A PCT Intermational Patent where /y and l, are the intensities parallel (/p) and perpendicular(1)to the nanorod long axis) of 7. A Salant, E. Amitay-Sadovsky, U Banin, Am. Chem. Application has been filed(docket no.995xC1PCT,"Laterally 0.88(Fig. 4F and fig S26), which is substantially 8.M.L. Tang, N Liu, J.A. Dionne, A P. Alivisatos, 1 Am. PCT/US2012/0429,ods Assemblies, "serial no 0C.128,10006(2006). Aligned Colloidal Na hem5a133,1320(2011). o5巴o higher than that of individual single CdSe-Cds 9. 5. Wei ef al, Am Chem. Soc. 131, 9728(2009) inside the elongated needle-like superparticles 12. J.J. Urban, D V. Talapin, E V Shevchenko, CR.Kagan, table? to s277 rials nanorods[0.75(25, 26)]. This PL anisotropy 10. C T Black, C.B. Murray, R.L. Sandstrom, S H Sun, enhancement can be attributed to a combinatio Materials and Method of dielectric effect and collective electric dipole 11. A. Courty, A Mermet, P. A. Albouy, E.Duval, MP.Pileni coupling effects among the CdSe-Cds nanorods Nat. Mater.4,395(2005) embedded in PDMS films(26-28). In addition, 13. Y Yamada et al. Nat. Chem. 3. 372(2011) 品E we show that the superparticle-embedded PDMS 14.1 Q. Zhuang et al. I. Am. Chem. Soc. 131, 6084 3 May 2012: accepted 6 September 2012 Integrated Compact Optical Vortex miniaturization, and scalability compared with bulk optics(13). Compact, robust, and efficient Beam emitters ceivers are critical elements, as they can be in- s planar waveguide-based OAM emitters and re- tegrated in large numbers and interconnected via Marc Sorel, Jeremy L. o'Brien,2 Mark G. Thompson, Siyuan Yu4 ris, Jiangbo Zhu, 4,5 Xinlun Cai, Jianwei Wang, 2 Michael ] Strain, Benjamin Johnson-Mc waveguides with each other and with lasers and detectors to form photonic integrated circuits (PICs). Recently, a waveguide-based device has Emerging applications based on optical beams carrying orbital angular momentum(OAM) will probably been reported for multiplexing and demultiplex require photonic integrated devices and circuits for miniaturization, improved performance, and ing of oAM beams as a means of realizing multi- enhanced functionality. We demonstrate silicon- integrated optical vortex emitters, using angular gratings channel optical communication(5, 14). However to extract light confined in whispering gallery modes with high OAM into free-space beams with ts large size(2.5 by 1.5 mm)and phase-sensitive well-controlled amounts of oAM. The smallest device has a radius of 3.9 micrometers. Experimental rayed waveguide structure do not yet support characterization confirms the theoretical prediction that the emitted beams carry exactly defined and large-scale integration. Here, we report micrometer- adjustable OAM Fabrication of integrated arrays and demonstration of simultaneous emission of multiple sized silicon photonic waveguide OAM devices identical optical vortices provide the potential for large-scale integration of optical vortex emitters complementary metal-oxide-semiconductor compatible silicon chips for wide-ranging applications Photonics Group, Merchant ers School of K.Department of Elec- T the discovery that photons in optical vortices involve passing free-space light beams tronics and Electrical Engineering, University of Glasgo vortices-light beams with helical phase through optical elements, including computer- UK. State Key Laboratory of Optoelectronic Materials and fronts and an azimuthal component of the generated holograms(4, 8), spiral phase plates Technologies and School of Physics and Engineering, Sun wave vector-can carry orbital angular momentum (9), inhomogeneous birefringent elements(10), Applicaton-Specific Integrated Circuits and Systems and De- (OAM)()may lead to wide-ranging applications subwavelength gratings(ID), and nanoantennas(12) rtment of Communication Saence and Engineering, Fudan in optical microscopy(2), micromanipulation (3), Photonic integration has been a major pro- University, Shanghai, China Gbe-space communication(4, 5, and quantum in- pellant for widespread application of photonic "To whom correspondence should be addressed. E-mail nation(6, 7). Techniques for generating optical technologies due to advantages in reliability, s. u@bristol. acuk www.sciencemag.orgScieNceVol33819ocTober2012 363leading to the formation of single-domain, elongated needle-like superparticles with l = 11 T 4 mm and d = 1.1 T 0.3 mm (Fig. 4, B and C). These single-domain superparticles have a different mor￾phology from those multidomain superparticles made from identical nanorods without incubation treatment (fig. S21, C to E). The needle-like superparticles from unopti￾mized syntheses exhibit a PL quantum yield of ~40% and are indefinitely stable in solvents with strong polarity, such as water or ethanol. However, these particles can undergo intraparticle ripening in lower-polarity solvents such as ethylene glycol, demonstrating that the needle-like morphology is not an equilibrium shape (fig. S23). The meso￾scopic sizes of these needle-like superparticles allow them to be easily aligned into unidirec￾tional line patterns on Si3N4 substrates through capillary forces (24) (fig. S24), which can be readily transferred into uniform and removable thin films of polydimethylsiloxane (PDMS) with sizes as large as 5.0 cm × 5.0 cm (Fig. 4, D and E, and fig. S25). The resulting thin films exhibit strong linearly polarized PL at 579 nm with a typical emission polarization ratio [r = (I|| – I⊥)/(I|| + I⊥), where I|| and I⊥ are the intensities parallel (I||) and perpendicular (I⊥) to the nanorod long axis] of 0.88 (Fig. 4F and fig. S26), which is substantially higher than that of individual single CdSe-CdS nanorods [0.75 (25, 26)]. This PL anisotropy enhancement can be attributed to a combination of dielectric effect and collective electric dipole coupling effects among the CdSe-CdS nanorods inside the elongated needle-like superparticles embedded in PDMS films (26–28). In addition, we show that the superparticle-embedded PDMS films can be used as energy downconversion phos￾phors to build polarized light-emitting diodes (Fig. 4, G to J, and fig. S27). Our results show that anisotropic interactions of CdSe-CdS nanorods can be used to synthesize colloidal superparticles with multiple well-defined supercrystalline domains under thermodynamic equilibrium. Functionality-based anisotropic inter￾actions between these nanorods can be kinetically introduced during the superparticle synthesis, lead￾ing to the formation of single-domain, needle-like particles. We anticipate that these findings can be extended for the self-assembly of nano-objects having other anisotropic shapes, as well as the self-assembly of two or more types of anisotropic nano-objects into well-defined mesoscopic and macroscopic complex architectures (1–3). References and Notes 1. G. M. Whitesides, B. Grzybowski, Science 295, 2418 (2002). 2. S. Mann, Nat. Mater. 8, 781 (2009). 3. S. C. Glotzer, M. J. Solomon, Nat. Mater. 6, 557 (2007). 4. M. R. Jones et al., Nat. Mater. 9, 913 (2010). 5. K. Miszta et al., Nat. Mater. 10, 872 (2011). 6. M. Rycenga, J. M. McLellan, Y. N. Xia, Adv. Mater. 20, 2416 (2008). 7. A. Salant, E. Amitay-Sadovsky, U. Banin, J. Am. Chem. Soc. 128, 10006 (2006). 8. M. L. Tang, N. Liu, J. A. Dionne, A. P. Alivisatos, J. Am. Chem. Soc. 133, 13220 (2011). 9. Q. S. Wei et al., J. Am. Chem. Soc. 131, 9728 (2009). 10. C. T. Black, C. B. Murray, R. L. Sandstrom, S. H. Sun, Science 290, 1131 (2000). 11. A. Courty, A. Mermet, P. A. Albouy, E. Duval, M. P. Pileni, Nat. Mater. 4, 395 (2005). 12. J. J. Urban, D. V. Talapin, E. V. Shevchenko, C. R. Kagan, C. B. Murray, Nat. Mater. 6, 115 (2007). 13. Y. Yamada et al., Nat. Chem. 3, 372 (2011). 14. J. Q. Zhuang et al., J. Am. Chem. Soc. 131, 6084 (2009). 15. L. Carbone et al., Nano Lett. 7, 2942 (2007). 16. D. V. Talapin et al., Nano Lett. 7, 2951 (2007). 17. See supplementary materials on Science Online. 18. J. Q. Zhuang, H. M. Wu, Y. G. Yang, Y. C. Cao, Angew. Chem. Int. Ed. 47, 2208 (2008). 19. D. B. Williams, C. B. Carter, Transmission Electron Microscopy: A Textbook for Materials Science (Springer, New York, ed. 2, 2009). 20. L. D. Marks, D. J. Smith, Nature 303, 316 (1983). 21. L. D. Marks, J. Cryst. Growth 61, 556 (1983). 22. Y. Nagaoka, T. Wang, J. Lynch, D. LaMontagne, Y. C. Cao, Small 8, 843 (2012). 23. P. Ball, The Self-Made Tapestry: Pattern Formation in Nature (Oxford Univ. Press, Oxford, 2000). 24. Y. N. Xia, Y. D. Yin, Y. Lu, J. McLellan, Adv. Funct. Mater. 13, 907 (2003). 25. D. V. Talapin et al., Nano Lett. 3, 1677 (2003). 26. A. Sitt, A. Salant, G. Menagen, U. Banin, Nano Lett. 11, 2054 (2011). 27. J. F. Wang, M. S. Gudiksen, X. F. Duan, Y. Cui, C. M. Lieber, Science 293, 1455 (2001). 28. S. Y. Wang et al., Nat. Commun. 2, 364 (2011). Acknowledgments: Supported by Office of Naval Research grant N00014-09-1-0441 (Y.C.C.), NSF Career Award DMR-0645520, and the Cornell High Energy Synchrotron Source through NSF award DMR-0936384. We thank S. Zou for helpful discussions and X. Liu for providing line-patterned Si3N4 substrates. Transmission electron microscope work was conducted at the Major Analytical Instrumentation Center at the University of Florida. A PCT International Patent Application has been filed (docket no. 995XC1PCT, “Laterally Aligned Colloidal Nanorods Assemblies,” serial no. PCT/US2012/042958). Supplementary Materials www.sciencemag.org/cgi/content/full/338/6105/358/DC1 Materials and Methods Supplementary Text Figs. S1 to S27 Table S1 References (29–32) 3 May 2012; accepted 6 September 2012 10.1126/science.1224221 Integrated Compact Optical Vortex Beam Emitters Xinlun Cai,1 Jianwei Wang,2 Michael J. Strain,3 Benjamin Johnson-Morris,1 Jiangbo Zhu,4,5 Marc Sorel,3 Jeremy L. O’Brien,2 Mark G. Thompson,2 Siyuan Yu1,4* Emerging applications based on optical beams carrying orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract light confined in whispering gallery modes with high OAM into free-space beams with well-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for large-scale integration of optical vortex emitters on complementary metal-oxide–semiconductor compatible silicon chips for wide-ranging applications. The discovery that photons in optical vortices—light beams with helical phase fronts and an azimuthal component of the wave vector—can carry orbital angular momentum (OAM) (1) may lead to wide-ranging applications in optical microscopy (2), micromanipulation (3), free-space communication (4, 5), and quantum in￾formation (6, 7). Techniques for generating optical vortices involve passing free-space light beams through optical elements, including computer￾generated holograms (4, 8), spiral phase plates (9), inhomogeneous birefringent elements (10), subwavelength gratings (11), and nanoantennas (12). Photonic integration has been a major pro￾pellant for widespread application of photonic technologies due to advantages in reliability, miniaturization, and scalability compared with bulk optics (13). Compact, robust, and efficient planar waveguide–based OAM emitters and re￾ceivers are critical elements, as they can be in￾tegrated in large numbers and interconnected via waveguides with each other and with lasers and detectors to form photonic integrated circuits (PICs). Recently, a waveguide-based device has been reported for multiplexing and demultiplex￾ing of OAM beams as a means of realizing multi￾channel optical communication (5, 14). However, its large size (2.5 by 1.5 mm2 ) and phase-sensitive arrayed waveguide structure do not yet support large-scale integration. Here, we report micrometer￾sized silicon photonic waveguide OAM devices 1 Photonics Group, Merchant Venturers School of Engineering, University of Bristol, Bristol, UK. 2 Centre for Quantum Pho￾tonics, University of Bristol, Bristol, UK. 3 Department of Elec￾tronics and Electrical Engineering, University of Glasgow, UK. 4 State Key Laboratory of Optoelectronic Materials and Technologies and School of Physics and Engineering, Sun Yat-sen University, Guangzhou, China. 5 State Key Laboratory of Application-Specific Integrated Circuits and Systems and De￾partment of Communication Science and Engineering, Fudan University, Shanghai, China. *To whom correspondence should be addressed. E-mail: s.yu@bristol.ac.uk www.sciencemag.org SCIENCE VOL 338 19 OCTOBER 2012 363 REPORTS on October 23, 2012 www.sciencemag.org Downloaded from