1,721,234 research outputs found
Eternal 5D storage in quartz glass
No full textFemtosecond laser writing in transparent materials has attracted considerable interest due to new science and a wide range of applications from laser surgery, 30 integrated optics and optofluidics to optical data storage. A decade ago it has been discovered that under certain irradiation conditions self-organized subwavelength structures with record small features of 20 nm, can be created in the volume of fused quartz, which is renowned for its high chemical stability. On the macroscopic scale the self-assembled nanostructure behaves as a uniaxial optical crystal with negative birefringence. The optical anisotropy, which results from the alignment of nano-platelets, referred to as form birefringence, is of the same order of magnitude as positive birefringence in crystalline quartz. The two independent parameters describing birefringence, the slow axis orientation (4th dimension) and the strength of retardance (5th dimension), are explored for the optical encoding of information in addition to three spatial coordinates. The slow axis orientation and the retardance are independently manipulated by the polarization and intensity of the femtosecond laser beam. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity and thermal stability up to 1000°. Even at elevated temperatures of 160 °C, the extrapolated decay time of nanogratings is comparable with the age of the Universe - 13.8 billion years. The demonstrated recording of the first digital document, which will survive the human race, is a vital step towards an eternal archive
Quantum interference and poling in optical glass waveguides
No full textOptical glass-fibres and waveguides dominate optical communications. The development of linear electrooptic modulators/switches and parametric frequency converters directly integrated into optical glass waveguide structures technologically is very attractive. However such components require a second-order nonlinearity - a χ(2), which is normally absent in glass owing to its inversion symmetry. Thus, when self-organised frequency doubling was first discovered wide-ranging studies ensued into the mechanism and properties of this unexpected phenomenon. The mystery of photoinduced χ(2) gratings was finally solved on the basis of a new physical phenomenon - the coherent photogalvanic effect, consisting in quantum interference, which excites a phase dependent current (coherent photocurrent). Coherent photocurrent induces quasi-phase matching χ(2) gratings. More recently the value of nonlinearity has been increased to a level, comparable to the best nonlinear crystals by new poling techniques. Moreover in the experiments on fibre electric field poling the first evidence of phase dependent modulation of a total cross-section of ionization due to quantum interference (coherent photoconductivity) in solid state materials has been obtained
Light craft: creating unusual properties in glass with light
No full textGlass dominates modern optical technologies. Nonlinear optical processes, such as second-harmonic generation and parametric frequency conversion, are technological very attractive and require a second-order optical nonlinearity - a χ(2), which is normally absent in glass owing to its inversion symmetry. Thus, when light-induced frequency doubling was first discovered wide-ranging studies ensued into the mechanism and properties of this unexpected phenomenon. The mystery of self-organized χ(2) gratings was finally solved on the basis of a new physical phenomenon - the coherent photogalvanic effect, consisting in quantum interference between light fields at two different frequencies, ω and 2ω, which excites a phase dependent current (coherent photocurrent). Coherent photocurrent creates quasi-phase matching χ(2) gratings. Moreover in the experiments on electric-field second harmonic generation in optical fibres the first evidence of phase dependent modulation of a total cross-section of ionization due to quantum interference (coherent photoconductivity) in solid state materials has been obtained
Unusual structuring of glass: from periodic poling to femtosecond laser-induced nanostructures
No full textGlass and waveguide poling
No full textGlass, 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. Until fairly recently, second harmonic generation in specially treated glasses and glass fibres has been of more scientific than practical interest, owing to small levels of nonlinearity (several orders of magnitude less than in lithium niobate) that could be induced. A recent breakthrough is the observation of high second-order nonlinearities of the order of 1 pm/V in glasses and 0.2 pm/V in optical fibres using a variety of different techniques similar to those which are used for making polymer electrets: thermal poling, corona poling and electron implantation. These values of nonlinearity are large enough to be useful for parametric frequency conversion. The nonlinear coefficients, especially for the electrooptic effect, are still small, and so require long interaction lengths. This is not a significant problem in fibre applications where the issues are cost, integrability and packaging, not length. It is worth also noting one more important advantage of poled glass in comparison with nonlinear crystals, namely that the bandwidth of phase-matched second harmonic conversion in poled silica (0.78 nm.cm) is an one order of magnitude larger than in an equal length of periodically poled lithium niobate (0.06 nm.cm). Moreover the group velocity mismatches are about 130 fs/mm and 1.8 ps/mm respectively. This may be of great importance in short pulse work where large acceptance bandwidths and long interaction lengths are required. A better understanding of the physical mechanisms of glass poling may lead to even higher values of nonlinearity, perhaps competitive with the best nonlinear crystals. In the talk we review recent progress in glass and waveguide poling
Femtosecond laser induced vortex anisotropy
No full textAnisotropic bubble chain structures are produced by ultrashort pulse laser irradiation in silica glass. Vortex anisotropy is observed in the irradiated volume
Electric field poling of quasi-phase-matched optical fibers
No full textElectric field poling of silica glass provides the prospect of efficient second-order nonlinear interactions in optical fibres. Recent advances in quasi-phase-matched second harmonic generation in electric field poled silica fibres are reviewed
Electrically stimulated light-induced second-harmonic generation in glass: evidence of coherent photoconductivity
Full text linkA strong electrostatic field applied to glass is spatially modulated by intense light at frequencies ω and 2ω. The phenomenon is explained in terms of photoconductivity being dependent on the relative phase of the light fields at different frequencies
Quasi-phase-matching in ferroelectric crystals and in glass: principle, fabrication and efficient nonlinear optical processes
No full textPeriodic patterning of the second-order nonlinearity χ microstructures in lithium niobate, in glass and in glass fibre
Frequency doubling of picosecond pulses in periodically poled D-shape silica fibre
No full textD-shape silica fibres have been periodically poled at elevated temperature by applying high voltage via a patterned electrode deposited on the plane side. The resulting nonlinear grating of 25µm period, uniform over the whole 1.8cm length, has been used for quasi-phase-matched second harmonic generation. With a mode-locked laser as fundamental source blue powers up to ~76µW have been generated at ~422nm with an average conversion efficiency of ~0.22%
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