Supercontinua generated in microstructured optical fibre are now used widely. The detailed spectral and temporal behaviour arising from the processes causing the extreme spectral broadening remains of interest particularly where users require temporal stability for specific visible wavelengths generated by a supercontinuum source. The theoretical gravity-like potential model requires NIR Raman self-frequency shifted solitons in the anomalous dispersion region of the fibre to be phase matched with short wavelength dispersive waves travelling in the normal dispersion region of the fibre. This is difficult to probe in the fundamental EM mode of the host fibre as competing wavelength generating and spreading non-linear processes obscure results. Here, specific high order EM modes excited in the fibre generate a spectrally sparse supercontinuum which was investigated using polarization and spatio-spectral mapping to provide unequivocal phase matching evidence supporting the gravity-like trapping model. Further, polarization measurements reveal that the input polarization state is scrambled due to non-linear effects within the fibre during supercontinuum generation, having implications for interferometry using supercontinua.
The optical performance of a volume scanner is analyzed using modelling software. The
existence of an embedded scattering volume with a 2.5% difference in scattering coefficient from the
host media may be detected.
Non-invasive optical screening mammography has a significant barrier in the extreme scatter of human tissue at optical wavelengths. A volume scanner suited for high numerical aperture capture of scattered light from diffuse media has been designed, modelled using Trace Pro software and experimentally constructed. Modelling results indicate the presence of an embedded volume with different scatter properties from the bulk yields a measurable difference in the overall scatter pattern and intensity recorded. Work towards a full tomographic reconstruction from scattered light recorded on the two dimensional array detector is currently underway.
Optical imaging through complex biological media remains a very challenging task due to the extremely high scattering
experienced. A new design scanner is proposed and modelled which images scatter spatio-temporally. Modeling
confirms the performance of the design. The inversion algorithm to reconstruct the scattering object remains as future
This article describes two- and three-dimensional optical simulations for determining optimal conditions for near-field scanning optical lithography. It was found that a combination of 30-nm thick photoresist and 50-nm thick anti-reflective coating will yield optimal results with 405 nm incident light and a hollow-cantilever probe with 100-nm aperture width. In addition to identifying the optimal conditions, the sensitivity of the resolution with respect to each parameter is explored and plotted. The mechanisms behind each trend are described with supporting simulation data.
A comparison is made between unpackaged and packaged distributed feedback (DFB) fibre lasers
using the Michelson interferometer configuration for delayed self-heterodyne interferometery (MIDSHI)
to ascertain the improvements to the external environmental noise, quantified by reductions in
the Gaussian linewidth. Voigt fitting is used to extract and separate out the Lorentzian and Gaussian
linewidth contributions and therefore the associated sources of noise. Significant improvements in the
Gaussian linewidth were achieved as a result of significant reductions in the sensitivity of the DFB
laser to external perturbations using packaging. However, a broadening of the laser Lorentzian
linewidth was observed.
Soliton behaviour in higher order electromagnetic (EM) modes in commercial highly nonlinear photonic crystal fibre
(PCF) was investigated by mapping spatial and spectral emission. A femtosecond mode-locked Titanium:Sapphire laser
was used to generate supercontinua within a set of higher-order electromagnetic modes by piezoelectric control of the
spatial field input to the PCF. Coupling pump wavelengths within the normal dispersion regime for the fundamental EM
mode into higher EM modes resulted in the emission of blue light, characteristic of higher order soliton fission, in higher
order EM modes. Detailed spectral measurements across the spatial mode field output from the PCF, showed different
spectral components of the generated continua occupying different spatial electromagnetic modes. In particular, the blue
emission was found to be structured with spectral wavelengths at 440 nm and 450 nm associated with different spatial
These new measurements are the first to detail high order solitonic interactions in higher order electromagnetic modes
and to record different spectral emission wavelengths associated with different higher order spatial modes. These results
are not well matched to current theoretical models for supercontinuum generation developed for the fundamental EM
mode. The lower zero dispersion wavelengths associated with higher EM modes in PCF enable previously undetected
engagement of these modes in supercontinuum generation and propagation.
Off-axis parabolic elements have found application in Tera-Hertz imaging and new application in two-photon microscopy scan engines. Both these applications demand spatial and temporal precision in photon location. This modelling work examines how close off-axis parabolic elements are to the perfect image relay by calculating the geometrical performance metrics of spot diagrams, point spread functions and wavefront distortion for different arrangements of off-axis parabolas and a parabolic torus when compared to a close-coupled two mirror scan engine. Results identify the off-axis parabolic elements as a superior scan engine particularly in wide-field scan instruments. When within the optimum beam size versus parabola focus length ratio, the imaging of these systems is superb.
We report some of our recent progress in the area of Bragg grating writing in photonic crystal fibres (PCFs). The various
challenges that PCFs present are discussed and the methods used to overcome these challenges are presented. The
fabrication of highly-durable type-IIa gratings in highly nonlinear photonic crystal fibre is demonstrated, the rotational
variance of grating inscription is also investigated through both experiments and numerical modeling. In other
experiments we fabricate a narrow-linewidth distributed feedback (DFB) laser in erbium-doped PCF, achieving stable,
single-mode and CW operation. The potential of such a DFB PCF in sensing applications is assessed by accurately
measuring an absorption line of acetylene gas.
We investigate the fluorescence of an Er-doped aluminosilicate stepped index core with surrounding structured lattice
when pumped transversely with the collimated output of a 980nm diode. A small rotational dependence is observed
indicating the importance of cladding structure alignment during experiments that involve processing the core from the
side, including Bragg grating writing.
A distributed feedback laser was fabricated in Er3+-doped photonic crystal fibre. Single mode lasing is obtained with
<10kHz linewidth. The output was amplified to 12mW using a commercial erbium doped fibre amplifier (EDFA).
The first polarization lidar was developed in Manila in early 1997 and it has been operating regularly to the present time. The regular observations aim to monitor and characterize the urban air ofManila and to study tropical clouds as well. The fixed, vertically pointing lidar transmits l5OmJ, 532 nm polarized pulses at 20Hz. The backscatter that is collected by the 27.9 cm, 0.358 nirad telescope is transmitted through a narrow bandpass filter and polarizing beamsplitter, to a two-channel receiver with PMTs operated in analog mode. Lidar signals are averaged for 2 minutes by an 8-bit digitizing storage oscilloscope and transferred to a PC. In this paper, combined measurements on suspended aerosols and boundary layer with lidar and filter-sampling of particles will be presented. These measurements, together with the meteorological data from radiosonde soundings of the weather bureau, on particular cold and hot months will be analyzed and compared. Measurements on an episodic event such as New Year's celebrations will also be discussed. The discussions in this paper will focus on the following: a) characterization of suspended aerosols and boundary layer by lidar depolarization ratio and extinction coefficient measurements and by filter-sampling method, and b) seasonal and diurnal changes ofthe above items.