N.G.R. Broderick

Holey optical fibers: an efficient modal model

A new model for light propagation in holey optical fibers is developed in which the transverse index profile and the modal field are decomposed using different orthogonal functions. It is an efficient and accurate alternative to previous techniques, and is an invaluable tool to aid fabrication efforts. Using this model, a number of regimes of interest in these fibers are explored.

Nonlinearity in holey optical fibers: measurement and future opportunities.

Holey fibers combine two-dimensional microstructuring with one-dimensional longitudinal propagation, resulting in fibers with tailorable dispersive and nonlinear properties. We measure the effective nonlinearity of a typical holey fiber. The small effective area that is possible in this type of fiber significantly enhances its effective nonlinearity relative to standard fiber.

Holey fibers with random cladding distributions

We provide what is to our knowledge the first direct confirmation that light can be guided in a holey fiber with randomly distributed air holes in the cladding. We also show that many of the features previously attributed to periodic holey fibers, in particular, single-mode guidance at all wavelengths, can also be obtained with random holey fibers. We provide insight into exactly how sensitive a holey fibers optical properties are to the details of the cladding profile.

Inverse design and fabrication tolerances of ultra-flattened dispersion holey fibers

We employ a Genetic Algorithm for the dispersion optimization of a range of holey fibers (HF) with a small number of air holes but good confinement loss. We demonstrate that a dispersion of 0 +/- 0.1 ps/nm/km in the wavelength range between 1.5 and 1.6 microm is achievable for HFs with a range of different transversal structures, and discuss some of the trade-offs in terms of dispersion slope, nonlinearity and confinement loss. We then analyze the sensitivity of the total dispersion to small variations from the optimal value of specific structural parameters, and estimate the fabrication accuracy required for the reliable fabrication of such fibers.

Modeling large air fraction holey optical fibers

We develop a modal decomposition approach to solve the full vector wave equation for holey optical fibers (HF). This model can be used to explore the modal properties of a wide range of HFs, including those with large air holes. The optical properties of HF can be tailored via the arrangement of the air holes, and this flexibility leads to a wide range of practical applications.

High-energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode-area erbium-doped fiber.

We demonstrate that appropriately designed doped multimode fibers provide robust single-mode output when used within a fiber laser cavity. Using a novel large-mode-area fiber, we demonstrate what we believe to be record single-mode (M(2) <1.2) pulse energies of >0.5 mJ from a Q -switched fiber laser and even higher pulse energies (as high as 0.85 mJ) with slightly compromised spatial-mode quality (M(2)<2.0) . This approach offers significant scope for extending the range of single-mode output powers and energies that are achievable from fiber-laser-amplifier systems.

Nonlinear self-switching and multiple gap-soliton formation in a fiber Bragg grating.

We report, for the first time to our knowledge, the experimental observation of quasi-cw nonlinear switching and multiple gap-soliton formation within the bandgap of a fiber Bragg grating. As many as five gap solitons with 100-500-ps durations were generated from a 2-ns pulse at a launched peak intensity of approximately 27 GW/cm(2). A corresponding increase in the grating transmission from 3% to 40% of the incident pulse energy was observed.

Greater than 20%-efficient frequency doubling of 1532-nm nanosecond pulses in quasi-phase-matched germanosilicate optical fibers

We fabricated second-order nonlinear gratings in D-shaped germanosilicate fibers, using thermal poling and periodic electrodes defined by standard photolithography. These gratings, which are up to 75 mm long, were used for efficient quasi-phase-matched frequency doubling of 1.532-mum nanosecond pulses from a high-power erbium-doped fiber amplifier. Average second-harmonic powers as high as 6.8 mW and peak powers greater than 1.2 kW at 766 nm were generated, with average and peak conversion efficiencies as high as 21% and 30%, respectively.

Control of surface modes in low loss hollow-core photonic bandgap fibers

We report low-loss hollow-core photonic bandgap fibers free from surface modes. They have low attenuation over the full spectral width of the bandgap, and approximately halved dispersion and dispersion slope compared to previous fibers.

Supercontinuum generation at 1.06µm in holey fibers with dispersion flattened profiles

We report the results of a systematic experimental and theoretical study of 1.06 mum pumped supercontinuum generation in a range of holey fibers with different flattened dispersion profiles. Clear differences in terms of the underpinning mechanisms emerge depending on the spacing between the two fiber zero-dispersion wavelengths. By examining the phase matched wavelength range of the corresponding fiber dispersions, one can predict the maximum achievable supercontinuum bandwidth.