We are interested in understanding the fundamental physics and material science by studying, engineering, and characterizing nano-optical materials and metasurfaces.

Applications include advanced optical imaging, sensing, communication, dense, energy optimization and beyond. 

I) Active Plasmonics and Metasurfaces 

(via electrical, nonlinear-optical, and magneto-optical interaction)

Nanoscale plasmonic, metasurface, zero-index optical structures offer unique optical features such as sub-wavelength field confinement, unusual optical constants, and advanced wavefront shaping. Particularly, recent studies on Epsilon-Near-Zero (ENZ) materials (material with near-zero permittivity) have shown an abnormally large intrinsic ENZ nonlinearity, enhanced non-reciprocal magneto-optical (MO) response, and enhanced quantum emission, showing significant breakthrough for developing ultrafast and ultracompact nanophotonic applications. While ENZ/metasurface optics have been extensively investigated in the last few years, the previous studies suffer on several limitations, for instance, (i) lack of efficient tunability due to the fixed conductivity of noble metal/semiconductor, (ii) lack of precise control of carrier distribution and efficient excitation methods, and (iii) weak optical responses (e.g. nonlinear/magneto-optical) due to the limited light-matter interaction length in planar structures or meta-surfaces. Our group is working on developing novel ENZ/metasuface excitation platforms and materials to enhance, to tune, to integrate the zero-index and metasurface optical properties, and to overcome several limitations described above. 

Specifically, we are working projects on studying the interesting physics of the light properties in plasmonic and metasurface nanostructures and 2D materials for instance, field-effect tunable phase and amplitude modulation, spin-orbit interaction of light, optical nonlinearity and harmonic generation, and non-reciprocal magneto-optical Faraday rotation.

A. Anopchenko, L. Tao, C. Arndt, H. W. Lee, “Field-effect tunable and broadband Epsilon-near-zero perfect absorbers with deep subwavelength thickness,” ACS Photonics 5, 2631 (2018). (Highlighted in Photonics Spectra and Laser Focused World)

A. Ciattoni, C. Rizza , H. W. Lee, C. Conti, and A. Marini, “Plasmon-enhanced spin-orbit interaction of light in graphene”, Laser & Photonics Reviews 12, 1800140 (2018).

Y. W. Huang*, H. W. Lee*, R. Sokhoyan, R. Pala, K. Thyagarajan, S. Han, D. P. Tsai, and H. A. Atwater, “Gate-tunable conducting oxide metasurfaces,” Nano Lett. 16, 5319-5325 (2016).

H. W. Lee, G. Papadakis, S. P. Burgos, K. Chander, A. Kriesch, R. Pala, U. Peschel and H. A. Atwater, “Nanoscale conducting oxide plasMOStor,” Nano Lett. 14, 6463-6468 (2014).

A. Marini, M. Conforti, G. D. Valle, H. W. Lee, T. X. Tran, W. Chang, M. A. Schmidt, P. St.J. Russell and F. Biancalana, “Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals,” New Journal of Phys. 15, 013033 (2013).

J. Zhang, L. Tao, A. Anopchenko, H. W. Lee, “Gate-tunable conducting oxide metasurface color filter,” submitted (2018).

II) Active Zero-Index Optics with Linear, Nonlinear, Quantum, and Non-reciprocal Responses

The optical response of epsilon-near-zero (ENZ) materials has been a topic of significant interest in the last few years as the electromagnetic field inside media with near-zero permittivity has been shown to exhibit unique optical properties, including strong electromagnetic wave confinement, non-reciprocal magneto-optical effects, and abnormal nonlinearity. We are currently studying the ENZ materials and heterostructures in the linear, nonlinear, and quantum regimes. For instance, we are working on projects on investigating the enhanced ultrafast ENZ nonlinearity in ENZ materials and metasurfaces, enhancing of optical emission for optical sensing and absorption/emittivity for energy harvesting, and investigating the spin-orbit interaction of light in ENZ/2D medium. 

A. Anopchenko, L. Tao, C. Arndt, H. W. Lee, “Field-effect tunable and broadband Epsilon-near-zero perfect absorbers with deep subwavelength thickness,” ACS Photonics 5, 2631 (2018). (Highlighted in Photonics Spectra and Laser Focused World)

A. Anopchenko and H. W. Lee, “Broadband and Tunable Perfect Optical Absorption in Conducting Oxide Epsilon-Near-Zero Nano-Films,” Laser Focus World, September issue (2018) (invited article).

A. Anopchenko, S. Gurung, L. Tao, C. Arndt, H. W. Lee, “Atomic Layer Deposition of Ultra-thin and smooth Al-doped ZnO for Zero-Index Photonics”, Materials Research Express, 5, 014012 (2018).

A. Ciattoni, C. Rizza , H. W. Lee, C. Conti, and A. Marini, “Plasmon-enhanced spin-orbit interaction of light in graphene”, Laser & Photonics Reviews 12, 1800140 (2018).

K. Minn, A. Anopchenko, J. Yang, H. W. Lee, “Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber,” Nature Scientific Reports 8, 2342(2018).

Y. W. Huang*, H. W. Lee*, R. Sokhoyan, R. Pala, K. Thyagarajan, S. Han, D. P. Tsai, and H. A. Atwater, “Gate-tunable conducting oxide metasurfaces,” Nano Lett. 16, 5319-5325 (2016).

III) "Meta"-Optical Fibers 

Optical fiber is well-known example of a way to guide and manipulate light. It has been used extensively in various applications including long distance optical communication, light generation using fiber lasers, remote and optical sensing, fiber imaging in endoscopes, and fiber laser surgery. Although a dielectric optical waveguide is very efficient in transmitting light, its functionality is somewhat limited by the dielectric material of the core, which has poor electronic, magneto-optical, and nonlinear-optical responses and has the dielectric diffraction limit. As a result, the optical properties of the optical fiber waveguide such as phase, amplitude, polarization state, and mode profile cannot be altered after the fiber drawing fabrication, thus limiting the development of novel in-fiber optical devices. Therefore, there is a need to integrate new materials and nanostructures into fiber components for enhanced processing and transmission capabilities and novel functionalities.

We are advancing the functionality of optical fibers by introducing optical metasurfaces and plasmonic/ENZ materials into optical fibers. We are developing efficient tunable “meta”-optical fibers with reconfigurable phase profile, controllable light emission, and magneto-optical effects by merging the advantages of three remarkable sciences, i) tunable transparent conducting oxide (TCO)/transition metallic nitride ENZ materials, ii) optical metasurfaces, and iii) nanostructured optical fiber waveguides. Our study will open the path to revolutionary in-fiber optical devices such as an ultrathin tunable fiber lens for high power lasers, in-fiber optical imaging and sensing devices and efficient, compact optical modulator and light emitter for optical communication.

J. Yang, I Ghirmire, P. C. Wu, S. Gurung, C. Arndt, A. D. P. Tsai, H. W. Lee, “Photonic crystal fiber metalens”, submitted (2018).

I. Ghimire*, J. Yang*, S. Gurung, S. K. Mishra, H. W. Lee, “Polarization dependent metasurface color filter in highly birefringence photonic crystal fiber,” submitted (2018).

K. Minn, A. Anopchenko, J. Yang, H. W. Lee, “Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber,” Nature Scientific Reports 8, 2342(2018).

H. W. Lee, M. A. Schmidt and P. St.J. Russell, “Excitation of a nanowire "molecule" in gold-filled photonic crystal fiber,” Opt. Lett. 37, 2946-2948 (2012) (Highlighted in vol. 6, p.501 Nature Photonics “Metal-filled fibres”).

G. K. L. Wong, M. S. Kang, H. W. Lee, F. Biancalana, C. Conti, T. Weiss and P. St.J. Russell, “Excitation of orbital angular momentum resonances in helically twisted photonic crystal fiber,” Science 337, 446-449 (2012) (Highlighted in Laser Focus World, Photonics.com and Phys.org). 

P. Uebel, M. A. Schmidt, H. W. Lee and P. St.J. Russell, “Polarization-resolved near-field mapping of a coupled plasmonic waveguide array,” Opt. Express 20, 28409-28417 (2012) (Highlighted in Vol. 8, Iss. 1 Virtual Journal for Biomedical Optics).

H. W. Lee, M. A. Schmidt, R. F. Russell, N. Y. Joly, H. K. Tyagi, P. Uebel and P. St.J. Russell, “Pressure-assisted melt-filling and optical characterisation of Au nano-wires in microstructured fibres,” Opt. Express 19, 12180-12189 (2011).

H. W. Lee, M. A. Schmidt, H. K. Tyagi, L. P. Sempere and P. St.J. Russell, “Polarization-dependent coupling to plasmon modes on submicron gold wire in photonic crystal fiber,” Appl. Phys. Lett. 93, 111102 (2008) (Highlighted in Vol. 18, Iss. 13 Virtual Journal for Nanoscale Science and Technology).

IV) Quantum Biophotonics and Raman Sensing with Meta-structures

One of the major hurdles of probing light-matter interaction in nano-scale regime is the efficient delivery and collection of electromagnetic energy to and fro the miniscule region of interest. For studies of molecular interaction with light such as tip-enchanced Raman spectroscopy (TERS), it is imperative that light be confined to a small space in the order of nanometers which can be achieved by means of localized surface plasmons. In conventional TERS, surface plasmons are excited on the metallic probe by directly focusing the laser beam in the vicinity of tip apex. Although such excitation scheme can improve the resolution of the spectroscopic device, it suffers from low efficiency in converting far-field light energy into localized field at the tip apex. In addition, directing the laser beam to the nanoscale tip proves to be a daunting task. Moreover, such devices require a separate mechanism for collecting the scattered field for analysis.

Our group is working toward developing optical fiber-incorporated plasmonic devices as a platform for transporting electromagnetic energy in nanoscale with high efficiency. For example, the waveguide mode excited in the optical fiber can be coupled to plasmons on the surface of gold layer coated on the tapered end of fiber. The coupled plasmonic mode then propagates down the conical waveguide to the narrow apex where it gets localized and strongly focused, exhibiting immense longitudinal field enhancement which enables intense interaction with the sample placed near the apex. Such confinement provides the fine spatial resolution that we need in near-field imaging such as TERS. These efficient and compact photonic-plasmonic structures will find many applications in near-field spectroscopy and biosensing. 

B. Birmingham, Z. Liege, N. Larson, W. Lu, H. W. Lee, D. V. Voronine, M. O. Scully, Z. Zhang, “Probing charge transfer between individual submonolayer nanoislands and bulk MoS2 using ambient TERS,” Journal of Physical Chemistry C 122, 2753 (2018).

B. A. Ko, A. Sokolov, Z. Zhang, M. O. Scully, H. W. Lee, “Degenerate Four-Wave Mixing near the Excitonic Resonances of Bulk MoS2”, Photonic Research accepted (2018).

J. N. Kunz, D. V. Voronine, H. W. Lee, A. V. Sokolov, and M. O. Scully, “Rapid Detection of Drought Stress in Plants using Femtosecond Laser-Induced Breakdown Spectroscopy,” Opt. Express 25, 7251-7262 (2017).

J. N. Kunz, D. V. Voronine, W. Lu, Z. Liege, H. W. Lee, Z. Zhang, and M. O. Scully, “Aluminum plasmonic nano-shielding in ultraviolet inactivation of E. coli bacteria”, Nature Scientific Reports 7, 9026 (2017).

C. Rizal, B. Niraula, and H. W. Lee, “Bio-Magnetoplasmonics, Emerging Biomedical Technologies and Beyond,” J Nanomed Res 3, 00059 (2016).

V) Hybrid Photonic-Plasmonic Materials and Components

Plasmonic active components can provide a capability for active modulation of lightwave signals in interconnects between future electronic and photonic networks co-located on a chip since plasmonic structures can guide light in small modal volumes while maintaining high optical bandwidth. We are working projects on developing a versatile architecture based on conducting oxide active plasmonic resonant guide wave networks (RGWNs). RGWNs, acting as a new class of artificial optical material, are structures that show multiple resonances formed from coherent interference of plasmon waves inside the network. This structure provides unique way to tune optical dispersion according to the network layout and can function as a compact optical logic device at telecommunication wavelengths, routing different wavelengths via different on/off combinations to separate transmission ports. This gate-tunable method would benefit to broad range of nano-optical components, such as compact modulators, active resonators, couplers, and so on. These studies enable facile integration of active conducting oxide materials and plasmonic structures, allowing realization of efficient active optical components for novel nano-device applications and next-generation ultra-compact and high speed integrated nanophotonic circuits.

L. Tao, A. Anopchenko, J. Zhang, S. Gurung, H. W. Lee, “Gate-tunable plasmon-induced transparency waveguide modulator,” submitted (2018).

A. Ciattoni, C. Rizza , H. W. Lee, C. Conti, and A. Marini, “Plasmon-enhanced spin-orbit interaction of light in graphene”, Laser & Photonics Reviews 12, 1800140 (2018).

H. W. Lee, G. Papadakis, S. P. Burgos, K. Chander, A. Kriesch, R. Pala, U. Peschel and H. A. Atwater, “Nanoscale conducting oxide plasMOStor,” Nano Lett. 14, 6463-6468 (2014).

S. P. Burgos*, H. W. Lee*, E. Feigenbaum, R. M. Briggs and H. A. Atwater, “Synthesis and characterization of plasmonic resonant guided wave networks,” Nano Lett. 14, 3284-3292 (2014).