The optical propulsion of mammalian eukaryotic cells along the surface of an integrated channel waveguide is
demonstrated. 10μm diameter polymethylmethacrylate (PMMA) spherical particles and similarly sized mammalian
eukaryotic cells in aqueous medium are deposited in a reservoir over a caesium ion-exchanged channel waveguide. Light
from a fibre laser at 1064nm was coupled into the waveguide, causing the polymer particles or cells to be propelled
along the waveguide at a velocity which is dependent upon the laser power. A theoretical model was used to predict the
propulsion velocity as a function of the refractive index of the particle. The experimental results obtained for the PMMA
particles and the mammalian cells show that for input powers greater than 50mW the propulsion velocity is
approximately that obtained by the theoretical model. For input powers of less than ~50mW neither particles nor cells
were propelled; this is considered to be a result of surface forces (which are not considered in the theoretical model).
The results are discussed in light of the potential application of optical channel waveguides for bioanalytical
applications, namely in the identification and sorting of mammalian cells from mixed populations without the need for
fluorescence or antibody labels.
Design, fabrication and optimization of high refractive index (2.1 @ 1070 nm), sub-micron thickness (200 nm) Tantalum
Pentoxide waveguides is reported. Optimization of fabrication parameters reduces the propagation loss to ~ 1 dB/cm @
1070 nm for Ta2O5 waveguides. Ta2O5 waveguides were found to be stable for high power application with no significant
absorption peaks over a large range of wavelengths (600-1700 nm). Ta2O5 waveguides provide high intensity in the
evanescent field, which is useful for efficient optical propelling of micro-particles. We have employed Ta2O5 waveguide
to propel polystyrene micro-particles with 50 μm/s velocity.
A new class of Surface-Enhanced Raman Scattering (SERS) substrates have been engineered by exploiting both Photonic Crystal (PC) and semiconductor technologies. Gold coated inverted pyramids nanotextured substrates allow reproducibility <10% and enhancement factors > 106 over large areas. Modelling and optical characterization of the engineered structures is demonstrated. Examples of applications to amino acids and illicit drug detection are given. Concentrations as low as ppm-ppb (mg/mL to ng/mL) have been measured depending on the adsorbed analytes. Information on structure and conformation of the molecule is inferred due to the richer nature of SERS spectra.
In this paper we demonstrate ultra-low loss transmission across a photonic crystal super-prism device consisting of 600 lattice periods etched into a slab waveguide at wavelengths both above and below the primary band-gap. By modifying the refractive index of the holes we have reduced overall insertion loss to 4.5 dB across the entire visible region of the spectrum, greatly enhancing transmission and extinction in higher order stop-bands. In addition we show that the remaining loss is predominantly due to impedance mismatch at the boundary between patterned/unpatterned slab waveguide regions and so is no longer proportional to the length of the photonic crystal or the number of lattice periods. This is an important step forward for the realization of functional photonic crystal time delay elements, dispersion compensators and super-prism spectrometer devices. Experimental loss measurements compare extremely well with Finite difference time domain simulations which were used to investigate the effect of etch depth on scattering loss. We find that partial penetration into the underlying buffer region causes massive scattering loss to substrate modes due to loss of waveguiding in the holes.
We demonstrate the fabrication, characterization and simulation of visible wavelength superprism devices in photonic crystal waveguides. We studied the super refraction dependence on lattice symmetry orientation and for propagation angles close to the main symmetry orientation. A variety of rectangular lattices devices with various pitches and hole diameters as well as number of rows have been fabricated. We used our previously developed automated broadband spectral and angular measurement to map the chromatic refractivity. We found the refraction angles and sign to be dependent on the lattice orientation and bandgap. As the lattice was rotated away from the main symmetry direction the magnitude of the angular dispersion increased indicating enhanced super-refractive properties away from symmetry direction. We found the chromatic refraction to be up to 1°/nm close to the band edge of the principal bandgaps, 10x more than equivalent gratings, and 100x more than equivalent prisms [[xiv]]. Dispersion curve obtained from plane wave simulation allowed us to model the Bloch mode propagation directions in the periodic structure. We found these simple models to be in excellent agreement with the experimental results, allowing us to design a range of effective superprism devices.
Ultra-high bandwidth continua generated by ultrashort fs pulses have
been attracting enormous interest for applications such as general
spectroscopy, Optical Coherence Tomography and metrology. Dispersion
engineering is one of the key aspects of optimised continuum generation in optical waveguides. However in addition, the dispersion
of the pump pulse can be continuously adapted to control bandwidth and spectral characteristics of the generated continua. In this work we report on a systematic investigation of how 2nd, and 3rd order dispersion affects the continuum generated in strongly nonlinear planar waveguides. A ~30 fs Ti:Sapphire tuned to 800 nm was used as a pump source delivering ~3 nJ pulses. The chirp of the pulses was controlled completely-arbitrarily by an acousto-optic programmable dispersive filter (Dazzler). The power launched into the structures was kept constant to compare the generated continua as the pulse dispersion is varied. High refractive index tantalum pentoxide (Ta2O5) waveguides grown by standard silicon processing techniques were used. The devices investigated were specially designed tapered ridges with ~5 mm2 input modal volume and zero group velocity dispersion
at ~l - 3.7 mm. Self-phase modulation, which is responsible for
the spectral broadening of the continua, is tracked by finely tuning the both 2nd and 3rd order dispersions. The nonlinear propagation is dramatically influenced by the simultaneous presence of these dispersive effects resulting in a change of bandwidth and spectral shape. Pulse widths of up to Dl > 100 nm for launched powers as low as 300 pJ. Spectral peak intensity can also be systematically modulated by simply scanning the 2nd and 3rd order dispersion around their relative zeros. Specific combinations of high order dispersion contribution are currently targeted as a route to control and optimise the continua bandwidths and to control dispersion lengths in specifically engineered waveguides.