Honors & Awards

  • Carl E. Anderson Outstanding Doctoral Dissertation Award in Laser Science, American Physical Society (2015)
  • Michael H. Granof Awards for Excellence Outstanding Dissertation Award, the University of Texas at Austin (2014)
  • Nanoscience & Nanotechnology Portfolio Travel Award, the University of Texas at Austin (2013)
  • Professional Development Award, the University of Texas at Austin (2013)
  • CST University Publication Award, CST-Computer Simulation Technology (2012)
  • First Place, the 11th Annual Nano Night Poster Competition, the University of Texas at Austin (2012)
  • Honorable Mention, IEEE AP-S/URSI Student Paper Competition, IEEE International Symposium on Antennas and Propagation (2012)
  • Nanoscience Portfolio Best Presentation Award, the University of Texas at Austin (2012)
  • The AP-S/URSI Travel Grant Award, IEEE International Symposium on Antennas and Propagation (2012)
  • First Place, IEEE AP-S/URSI Student Paper Competition, IEEE International Symposium on Antennas and Propagation (2011)
  • Professional Development Award, the University of Texas at Austin (2011)
  • The AP-S/URSI Travel Grant Award, IEEE International Symposium on Antennas and Propagation (2011)

Professional Education

  • Master of Philosophy, Chinese University of Hong Kong, Automation and Computer Eng. (2004)
  • PhD, University of Texas at Austin, Electrical and Computer Engineering (2013)
  • MS, CREOL-College of Optics and Photonics, University of Central Florida, Optics (2008)

Stanford Advisors

All Publications

  • Chirality detection of enantiomers using twisted optical metamaterials NATURE COMMUNICATIONS Zhao, Y., Askarpour, A. N., Sun, L., Shi, J., Li, X., Alu, A. 2017; 8


    Many naturally occurring biomolecules, such as amino acids, sugars and nucleotides, are inherently chiral. Enantiomers, a pair of chiral isomers with opposite handedness, often exhibit similar physical and chemical properties due to their identical functional groups and composition, yet show different toxicity to cells. Detecting enantiomers in small quantities has an essential role in drug development to eliminate their unwanted side effects. Here we exploit strong chiral interactions with plasmonic metamaterials with specifically designed optical response to sense chiral molecules down to zeptomole levels, several orders of magnitude smaller than what is typically detectable with conventional circular dichroism spectroscopy. In particular, the measured spectra reveal opposite signs in the spectral regime directly associated with different chiral responses, providing a way to univocally assess molecular chirality. Our work introduces an ultrathin, planarized nanophotonic interface to sense chiral molecules with inherently weak circular dichroism at visible and near-infrared frequencies.

    View details for DOI 10.1038/ncomms14180

    View details for Web of Science ID 000392650700001

    View details for PubMedID 28120825

    View details for PubMedCentralID PMC5288493

  • Nanoscopic control and quantification of enantioselective optical forces Nature Nanotechnology Zhao, Y., Saleh, A., van de Haar, M., Baum, B., Briggs, J. A., Lay, A., Reyes-Becerra, O. A., Dionne, J. A. 2017: 1055–59


    Circularly polarized light (CPL) exerts a force of different magnitude on left- and right-handed enantiomers, an effect that could be exploited for chiral resolution of chemical compounds as well as controlled assembly of chiral nanostructures. However, enantioselective optical forces are challenging to control and quantify because their magnitude is extremely small (sub-piconewton) and varies in space with sub-micrometre resolution. Here, we report a technique to both strengthen and visualize these forces, using a chiral atomic force microscope probe coupled to a plasmonic optical tweezer. Illumination of the plasmonic tweezer with CPL exerts a force on the microscope tip that depends on the handedness of the light and the tip. In particular, for a left-handed chiral tip, transverse forces are attractive with left-CPL and repulsive with right-CPL. Additionally, total force differences between opposite-handed specimens exceed 10 pN. The microscope tip can map chiral forces with 2 nm lateral resolution, revealing a distinct spatial distribution of forces for each handedness.

    View details for DOI 10.1038/nnano.2017.180

    View details for PubMedCentralID PMC5679370

  • Enantioselective Optical Trapping of Chiral Nanoparticles with Plasmonic Tweezers ACS PHOTONICS Zhao, Y., Saleh, A. A., Dionne, J. A. 2016; 3 (3): 304-309
  • Twisted optical metamaterials for planarized ultrathin broadband circular polarizers NATURE COMMUNICATIONS Zhao, Y., Belkin, M. A., Alu, A. 2012; 3


    Optical metamaterials are usually based on planarized, complex-shaped, resonant nano-inclusions. Three-dimensional geometries may provide a wider set of functionalities, including broadband chirality to manipulate circular polarization at the nanoscale, but their fabrication becomes challenging as their dimensions get smaller. Here we introduce a new paradigm for the realization of optical metamaterials, showing that three-dimensional effects may be obtained without complicated inclusions, but instead by tailoring the relative orientation within the lattice. We apply this concept to realize planarized, broadband bianisotropic metamaterials as stacked nanorod arrays with a tailored rotational twist. Because of the coupling among closely spaced twisted plasmonic metasurfaces, metamaterials realized with conventional lithography may effectively operate as three-dimensional helical structures with broadband bianisotropic optical response. The proposed concept is also shown to relax alignment requirements common in three-dimensional metamaterial designs. The realized sample constitutes an ultrathin, broadband circular polarizer that may be directly integrated within nanophotonic systems.

    View details for DOI 10.1038/ncomms1877

    View details for Web of Science ID 000304611400065

    View details for PubMedID 22643897

  • Temperature-dependent optical properties of titanium nitride APPLIED PHYSICS LETTERS Briggs, J. A., Naik, G. V., Zhao, Y., Petach, T. A., Sahasrabuddhe, K., Goldhaber-Gordon, D., Melosh, N. A., Dionne, J. A. 2017; 110 (10)

    View details for DOI 10.1063/1.4977840

    View details for Web of Science ID 000397871800011

  • Enhancing Enantioselective Absorption Using Dielectric Nanospheres ACS PHOTONICS Ho, C., Garcia-Etxarri, A., Zhao, Y., Dionne, J. 2017; 4 (2): 197-203
  • Controlling the Polarization State of Light with Plasmonic Metal Oxide Metasurface ACS NANO Kim, J., Choudbury, S., Devault, C., Zhao, Y., Kildishev, A. V., Shalaev, V. M., Alu, A., Boltasseva, A. 2016; 10 (10): 9326-9333
  • Polarizability Tensor Retrieval for Subwavelength Particles of Arbitrary Shape IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION Liu, X., Zhao, Y., Alu, A. 2016; 64 (6): 2301-2310
  • Localized fields, global impact: Industrial applications of resonant plasmonic materials MRS BULLETIN Dionne, J. A., Baldi, A., Baum, B., Ho, C., Jankovic, V., Naik, G. V., Narayan, T., Scholl, J. A., Zhao, Y. 2015; 40 (12): 1138-1145
  • Recent advances on optical metasurfaces JOURNAL OF OPTICS Zhao, Y., Liu, X., Alu, A. 2014; 16 (12)
  • Intrinsic Optical Properties and Enhanced Plasmonic Response of Epitaxial Silver ADVANCED MATERIALS Wu, Y., Zhang, C., Estakhri, N. M., Zhao, Y., Kim, J., Zhang, M., Liu, X., Pribil, G. K., Alu, A., Shih, C., Li, X. 2014; 26 (35): 6106-?


    Using atomically smooth epitaxial silver films, new optical permittivity highlighting significant loss reduction in the visible frequency range is extracted. Largely enhanced propagation distances of surface plasmon polaritons are measured, confirming the low intrinsic loss in silver. The new permittivity is free of extrinsic spectral features associated with grain boundaries and localized plasmons inevitably present in thermally deposited films.

    View details for DOI 10.1002/adma.201401474

    View details for Web of Science ID 000342148600008

    View details for PubMedID 24923858

  • Wave propagation in twisted metamaterials PHYSICAL REVIEW B Askarpour, A. N., Zhao, Y., Alu, A. 2014; 90 (5)
  • Alignment-Free Three-Dimensional Optical Metamaterials ADVANCED MATERIALS Zhao, Y., Shi, J., Sun, L., Li, X., Alu, A. 2014; 26 (9): 1439-1445


    Three-dimensional optical metamaterials based on multilayers typically rely on critical vertical alignment to achieve the desired functionality. Here the conditions under which three-dimensional metamaterials with different functionalities may be realized without constraints on alignment are analyzed and demonstrated experimentally. This study demonstrates that the release of alignment constraints for multilayered metamaterials is allowed, while their anomalous interaction with light is preserved.

    View details for DOI 10.1002/adma.201304379

    View details for Web of Science ID 000332330400006

    View details for PubMedID 24307266

  • Tailoring the Dispersion of Plasmonic Nanorods To Realize Broadband Optical Meta-Waveplates NANO LETTERS Zhao, Y., Alu, A. 2013; 13 (3): 1086-1091


    The response of optical metasurfaces is usually narrowband, and mechanisms to increase their bandwidth often clash with causality and passivity constraints of materials. Here we are able to theoretically and experimentally demonstrate that broadband, strong polarization conversion and quarter-wave plate functionality may be achieved using a single, ultrathin planar metasurface in the visible regime. Our realized sample is based on interleaved silver nanorods with properly tailored frequency dispersion that introduce an abrupt flat 90° phase shift for orthogonal polarizations over a thickness of few tens of nanometers, achieving achromatic quarter-wave plate behavior covering a good portion of the visible spectrum. Analogous design principles are extended to cover the entire visible spectrum and beyond.

    View details for DOI 10.1021/nl304392b

    View details for Web of Science ID 000316243800035

    View details for PubMedID 23384327

  • Individual Nanoantennas Loaded with Three-Dimensional Optical Nanocircuits NANO LETTERS Liu, N., Wen, F., Zhao, Y., Wang, Y., Nordlander, P., Halas, N. J., Alu, A. 2013; 13 (1): 142-147


    Nanoantennas are key optical components that bridge nanometer-scale optical signals to far-field, free-space radiation. In analogy to radio frequency antennas where tuning and impedance-matching are accomplished with lumped circuit elements, one could envision nanoantenna properties controlled by nanoscale, optical frequency circuit elements in which circuit operations are based on photons rather than electrons. A recent investigation of the infrared nanocircuits has demonstrated the filtering functionality using dielectric gratings. However, these two-dimensional prototypes have limited applicability in real-life devices. Here we experimentally demonstrate the first optical nanoscale circuits with fully three-dimensional lumped elements, which we use to tune and impedance-match a single optical dimer nanoantenna. We control the antenna resonance and impedance bandwidth using suitably designed loads with combinations of basic circuit elements: nanoscale capacitors, inductors, and resistors. Our results pave the way toward extending conventional circuit concepts into the visible domain for applications in data storage, wireless optical links, and related venues.

    View details for DOI 10.1021/nl303689c

    View details for Web of Science ID 000313142300026

    View details for PubMedID 23215034

  • Experimental realization and modeling of a subwavelength frequency-selective plasmonic metasurface APPLIED PHYSICS LETTERS Li, P., Zhao, Y., Alu, A., Yu, E. T. 2011; 99 (22)

    View details for DOI 10.1063/1.3664634

    View details for Web of Science ID 000298244500006

  • Manipulating light polarization with ultrathin plasmonic metasurfaces PHYSICAL REVIEW B Zhao, Y., Alu, A. 2011; 84 (20)
  • Optical metasurfaces with robust angular response on flexible substrates APPLIED PHYSICS LETTERS Di Falco, A., Zhao, Y., Alu, A. 2011; 99 (16)

    View details for DOI 10.1063/1.3655332

    View details for Web of Science ID 000296517600070

  • Effects of shape and loading of optical nanoantennas on their sensitivity and radiation properties JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS Zhao, Y., Engheta, N., Alu, A. 2011; 28 (5): 1266-1274
  • Homogenization of plasmonic metasurfaces as transmission-line loads Metamaterials Zhao, Y., Engheta , N., Alu, A. 2011; 5: 90
  • Laser wakefield electron acceleration on Texas petawatt facility: Towards multi-GeV electron energy in a single self-guided stage 2nd International Conference on High Energy Density Physics Kalmykov, S. Y., Reed, S. A., Yi, S. A., Beck, A., Lifschitz, A. F., Davoine, X., Lefebvre, E., Khudik, V., Shvets, G., Dong, P., Wang, X., Du, D., Bedacht, S., Zhao, Y., Henderson, W., Bernstein, A., Dyer, G., Martinez, M., Gaul, E., Ditmire, T., Downer, M. C. ELSEVIER SCIENCE BV. 2010: 200–206
  • High figure-of-merit laterally fluorinated biphenyltolane-isothiocyanates MOLECULAR CRYSTALS AND LIQUID CRYSTALS Gauza, S., Zhao, Y., Le Cor, T., Wu, S., Ziolek, A., Dabrowski, R., Catanescu, O., Chien, L., Hsu, C. 2007; 479: 1207-?
  • Enhancing Birefringence by Doping Fluorinated Phenyltolanes JOURNAL OF DISPLAY TECHNOLOGY Gauza, S., Zhao, Y., Le Cor, T., Wu, S., Dziaduszek, J., Sasnouski, G., Dabrowski, R., Chien, L. 2006; 2 (4): 327-332
  • Isothiocyanato-tolanes based high birefringence and fast response time mixtures for photonic applications MOLECULAR CRYSTALS AND LIQUID CRYSTALS Gauza, S., Wen, C., Zhao, Y., Wu, S., Ziolek, A., Dabrowski, R. 2006; 453: 215-226