Session Chair: Jianfang Wang, The Chinese University of Hong Kong Session Chair: Masanobu Iwanaga, National Institute for Material Science
4:00pm - 4:30pm Invited
3D Gradient Refractive Index Porous Silicon and Porous Silica Micro-Optics
Paul V. BRAUN
University of Illinois at Urbana-Champaign, United States
Via electrochemical etching of silicon, followed by materials conversion, 3D gradient refractive index micro-optics including flat lenses, Bragg mirrors, polarization sensitive optical splitters and structures with nearly arbitrary refractive index distributions were formed with a particular focus on micro-optics important for solar energy harvesting. The conversion from silicon to silica and titania enabled the optics to operate in the visible with minimal loss, something particularly important for solar energy harvesting applications. A detailed model was developed which enabled tight control over optical properties based only on the electrochemical etch conditions.
4:30pm - 5:00pm Invited
Nanophotonics for Enhancing Light Detection and Light-Vapor Interactions
Uriel LEVY, Liron STERN, Meir GRAJOWER, Roy ZEKTZER, Alex NAIMAN, Eliran TALKER
Hebrew University of Jerusalem, Israel
In this talk we will present our recent results related to the plasmonic enhancement of light detection in the mid IR. Furthermore, we will discuss and demonstrate the interaction of plasmonic resonances with atomic and molecular narrow lines. Finally, we will also discuss the interactions of light and vapor in advanced nanoscale photonic waveguides and resonators
5:00pm - 5:30pm Invited
Sieving Photons for Optical Holography
Kun HUANG, Hong LIU, Qian WANG, Jinghua TENG
Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
Holography is of great interests to both scientific research and industry application. Recently, metasurface holograms have enriched the holography community in terms of powerful and efficient manipulation of wavelength and polarization of light. As one member, nanosieve holograms with random holes in a opaque screen have played an important role in demonstrating high-quality and high-tollerence functionalities. Here, we will introduce such a nanosieve hologram in echieving an high-uniformity and high-signal-to-noise image. In addition, based on the concept of photon nanosieve, we propose a novel holography mechanism by elaborately choosing discrete point sources (PSs) to reconsctuct an image and realize it experimentally by mimicking the radiated fields of these PSs through carefully designed nanosieves. Removing the modulation dispersion usually existing in traditional and metasurface holograms, our hologram as the first prototype empowers the simultaneous operation throughout the ultra-violet, entire-visible and near-infrared wavelengths without polarization dependence. Due to the deep-subwavelength dimension of nanosieves, this robust hologram offers a remarkable angle-of-view of 40º×40º and possesses a unique lensing effect under a spherical-wave illumination, which can work as a high-resolution, lens-less and distortion-free micro-projector that displays an impressive 260x magnified image. It might open an avenue to high-tolerance holographic technique for electromagnetic and acoustic waves.
5:30pm - 5:45pm Oral
Resonant Mode Coupling for Targeted Light Trapping in Low Mode Density Colloidal Quantum Dot Absorbers
Fiona Jean BECK
The Australian National University, Australia
Lead based colloidal quantum dots (CQDs) are an interesting optoelectronic material system as the excitonic peak can be tuned from the visible to the near infra-red, covering a wide spectrum, with potential applications in solar energy harvesting, photo detection, and night vision. These materials can be manufactured in the solution phase and spin-cast to form dense, cross-linked, semiconductor films on a variety of substrates, reducing the cost of device fabrication. However, like other non-crystalline based semiconductors, these films exhibit short carrier lifetimes and diffusion lengths. Active layers must be kept very thin to ensure efficient extraction of the photo-generated carriers, and device efficiencies will ultimately be limited by absorption. Additionally, because of the composite nature of the material the refractive index of these materials is relatively low. This means that typical absorber film thicknesses support few guided modes in the bandwidth of interest.These characteristics make CQD based absorbers ideal candidates for the implementation of nano-photonic light trapping.
In this work we revisit the problem of light trapping in low mode density absorbers, and show that insights gained from an intuitive understanding of the system can be leveraged to provide tuneable light trapping and dramatically increase the absorption enhancement. We present a conceptual model of light trapping by resonant mode coupling, and show that targeting certain guided modes results in larger overall absorption, resulting in two key insights: 1) that a large spatial overlap of the mode profile with the grating is important; and 2) CQD materials have favourable material constants to benefit from absorption in the near-field of plasmonic resonances.
We demonstrate, both theoretically and experimentally, absorption enhancements up to 250% at the exciton peak for optimized resonant mode coupling employing our conceptual model, compared with an increase of 25% in the same wavelength region for the non-optimized case.
5:45pm - 6:00pm Oral
Wave Functions and Phase Shifts of Amplified Modes within A Vibrating Metallic Photonic Crystal
The Jikei University School of Medicine, Japan
We have so far investigated the optical properties within a one-dimensional photonic crystal whose stacked metallic plates are artificially driven by using actuators. A simple model was proposed and numerically analyzed, and the following novel phenomena were found out: The lattice vibration generates the light of frequency which added the integral multiple of the vibration frequency to that of the incident wave and also amplifies the incident wave resonantly. On a resonance, the amplification factor increases very rapidly with the number of layers. Resonance frequencies vary with the phases of lattice vibration. The amplification phenomenon was analytically discussed for low frequency of the lattice vibration and is confirmed by numerical works.
The conditions of the resonance, however, have not been discovered yet. The lattice vibration is different from the usual phonon, since the photonic crystal is vibrated artificially, so that the dispersion relation of the lattice vibration does not exit. This fact is one of the causes which complicate the problem.
In the present study, we compute the wave functions and phase shifts between the transmission and reflection coefficients around the amplifying resonance, and approach and discuss the resonance conditions with the photonic band structures and the Friedel sum rule in one dimension.
We also would refer to a disordered photonic crystal case, which is metal plates of random thickness arranged in parallel with equi-intervals.