Research - Nanophotonics

Project 2.1: CUDOS - ARC Centre of Excellence
Min Gu, Guangyong Zhou, Baohua Jia, Jiafang Li, Michael Ventura, Elisa Nicoletti

Photonic crystals (PC’s) are periodic dielectric structures that are designed to affect the propagation of light in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands. The absence of allowed propagating electromagnetic modes inside the structures, in a range of wavelengths called a photonic band gap (PBG), gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omnidirectional mirrors and low-loss-waveguiding among others. Since the basic physical phenomenon is based on diffraction, the periodicity of the photonic crystal structure has to be in the same length-scale as the wavelength of the light i.e. ~1 µm for photonic crystals operating in the near infrared part of the spectrum. This makes the synthesis cumbersome and complex. Generally, PC’s can be divided into 1D, 2D, and 3D structures depending on their dielectric function, which can be periodic in one, two or three dimensions, respectively. 3D PC’s can be used to control and guide light in three dimensions and are essential for the realization of highly integrated photonic microchips.

As a Melbourne node of CUDOS, we aim to achieve the following goals using two-photon 3-D microfabrications, photopolymerizations and microexplosions.

Some of the structures investigated by our CUDOS team are listed below.

• Polymer photonic crystals used as superprism devices

• Polymer photonic crystals with embedded planar defects

• High refractive index composite materials for photonic crystal fabrication

• 3D photonic crystals in lithium niobate

• Radiation dynamics in Quantum dot doped in crystals

Figure: (Left) White light is coupled into a 3D photonic crystal (woodpile structure) and is split into its spectral components after only a very short distance (cover taken from Adv. Mater. 18 (2), 2006). (Middle) Calculated iso-energy surface for a polymer woodpile structure. (Right) Measured directions of propagation for light inside a woodpile structure for three different wavelengths (Blue: 1000 nm, green: 1010 nm, red: 1020 nm).

Project 2.2: Multi-dimensional optical data storage systems
Min Gu, James W. M. Chon, Xiangping Li, Peter Zijlstra, Brendan Chick

In the consumer data storage market, the need for faster and high capacity optical storage systems is ever growing, and the current technology of reducing the written bit size to increase data capacity is already approaching its limit imposed by resolution limit of light. The Centre for Micro-Photonics has devoted a large research effort to overcome the problem and successfully demonstrated ~ 700 Gbytes / disc by recording data bits three-dimensionally on efficient and low-cost photorefractive polymer materials using two-photon excitation. In order to further increase the capacity beyond the multilayer, the Centre now concentrates its research focus on increasing the dimensionality of the storage system, by introducing spectrum and polarization dimensions. An ideal material candidate for realising multidimensional optical data storage system is nanoparticles (QDs and Nanorods).

The semiconductor quantum dots and metallic nanoparticles/rods are at the heart of nanotechnology revolution, due to their extraordinary optical and electronic properties caused by quantum confinement effects. The most important property of this new class of materials is that they are spectrum and polarization sensitive materials which can be a full benefit to encoding in those dimensions, providing multidimensionality.

In this ARC funded multidimensional optical storage project, we aim to demonstrate the multidimensional recording/reading on the new class of materials using various recording mechanisms, also aims to demonstrate a prototype system. The individual projects are as follows

• Multidimensional photorefractive optical storage using semiconductor nanocrystal quantum dots

• Quantum dot-dye conjugate for high density optical data storage

• Multidimensional optical data storage using metal nanoparticles/nanorods

• Photoenhancement of semiconductor nanocrystals for optical data storage applications

Figure left: Transmission electron microscope (TEM) image of aspect ratio 3 gold nanorods used for spectral encoding. The graph shows the change in absorption spectrum upon melting of gold nanorods using different laser pulse energies.
Figure right: Illustration of multilayer polarization encoding in a photorefractive polymer doped with semiconductor nanocrystals.

References

1. D. Day, M. Gu and A. Smallridge, "Rewritable 3D bit optical data storage in a PMMA-based photorefractive polymer"
   Adv. Mater., 13, 1005 (2001)

2. D. McPhail and M. Gu, "Use of polarization sensitivity for three-dimensional optical data storage in polymer dispersed liquid crystals under two-photon illumination"
   Appl. Phys. Lett., 81, 1160 (2002)

3. J. W. M. Chon, Peter Zijlstra, Min Gu, Joel van Embden, and Paul Mulvaney, "Two-photon-induced photoenhancement of densely packed CdSe/ZnSe/ZnS nanocrystal solids and its application to multilayer optical data storage"
   Appl. Phys. Lett. 85, 5514 (2004)

4. James W.M. Chon, Craig Bullen, Peter Zijlstra, and Min Gu, "Spectral Encoding on Gold Nanorods Doped in a Silica Sol-Gel Matrix and Its Application to High-Density Optical Data Storage"
   Adv. Funct. Mater. 17, 875-880 (2007)

5. Xiangping Li, James W. M. Chon, Shuhui Wu, Richard A. Evans, and Min Gu, "Rewritable polarization-encoded multilayer data storage in a 2,5-dimethyl-4-(p-nitrophenylazo)anisole doped polymer,
   Opt. Lett. 32 (3), 277-279 (2007)

Project 2.3: Multi-functional hybrid cantilever nanosensor
James W. M. Chon, and Min Gu