Physical Optics

1. Poled glasses and optical glass waveguides with large second-order non-linearities: Fundamentals and applications

Glass, e.g. silica glass, is one of the dominant materials in information technology because of its low fabrication cost compared to crystalline materials, and its superior optical properties such as high transparency and high optical damage threshold. However inversion symmetry of the glass matrix ensures the absence of optical effects based on second-order nonlinearity such as linear electrooptic effect and parametric frequency conversion. The ability to modulate a material's refractive index with an applied field, as in the electrooptic or piezoelectric effect, is necessary for making optical switches and electric field sensors. Frequency conversion of coherent radiation through parametric processes, such as second harmonic and sum or difference frequency generation, is also desirable to produce a large range of wavelength from fibre lasers and for construction of tunable laser sources. The development of a practical second-order nonlinearity in silica and related materials would add both modulators and frequency converters to the list of active fibre components. The advantages of integrability, e.g. monolithic integration of the above devices into optical fibres, and manufacturabilty would ensure widespread use of these capabilities.

In recent years a number of groups around the world have been exploring, with some success, the use of various poling techniques to break this cento-symmetry and induce substantial second-order nonlinearity in glasses. Levels of nonlinearity of order 1 pm/V have been achieved, with some indications that even higher values may be possible. Considering that metre-long interaction length are feasible in optical fibre (compared to few cm in ferroelectric crystal), and that the dispersion of refractive index with wavelength is weak, nonlinearities of this order place glass in the unexpected position of a serious potential rival to such important crystals such as lithium niobate, potassium titanyl phosphate (KTP) and lithium triborate (LBO).

The main aims of the proposed work are the fundamental study of poled glasses with large second-order nonlinearities, the creation of new glasses and glass fibres with nonlinearity comparable with that in the best nonlinear crystals and the development (on the basis of poled glasses) practical devices such as all-fibre and waveguide frequency doublers, parametric frequency converters, electrooptic modulators, switches and electric field sensors.

2. Fibre atom waveguides and atomic integrated circuits

Optical fibres play a tremendous role in our society. The broad spectrum of applications ranges from transmitting information through telecommunications systems to delivery light for laser surgery, and the spectrum of users for optical fibres continue to grow. It has been recently demonstrated that in addition to guiding laser light, optical fibres can also guide atoms, where a hollow core fibre functions like an atom hose. In the same way that optical fibres have revolutionized the field of optics it is expected that atomic waveguides to have a huge impact on the emerging field of atom optics. The interest in fibre atomic waveguides spans from measuring fundamental atomic physics phenomena, quantum computers to industrial world applications including atom interferometry and atom lithography. The ORC, which has been pioneering fibre optics for more than 25 years, and now is the leading centre in special glass fibre fabrication and research in nonlinear fibre optics offers unique capabilities in atomic waveguide research for real-world applications.

3. Direct write of 3D photonic structures

High-power high-repetition-rate ultrafast lasers enable the new technique of femtosecond direct optical writing for patterning waveguides and gratings in three dimensions, to provide entirely new functionalities. Three-dimensional photonic structures will allow dramatic increases in the scale of integration of future optical communication and information processing. They also open tantalising possibilities in the fields of integrated optics, all-solid state lasers, optical amplifiers and switches. As yet effort in this area worldwide is small but accelerating rapidly, ensuring a window for our research to have high impact. This proposal will explore the ultrafast physics of femtosecond photosensitivity and optimise the direct write of 3D photonic structures.

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