Breaking the limits in glass: From quantum interference to fs nanostructuring

Abstract

Optical 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 optical nonlinearity - a χ(2) which is normally absent in glass owing to its inversion symmetry. Thus, when self-organized 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 [1]. Another interesting field demonstrating unusual light-matter interactions and properties of materials is modification of index of refraction and direct writing of photonic structures by ultrashort light pulses in glass.

A critical advantage of using femtosecond pulses relative to longer pulses for optical writing and data storage is that such pulses can rapidly and precisely deposit energy in solids. This is the principle of femtosecond photosensitivity and 3D direct writing of photonic structures ranging from 3D waveguides to embedded Fresnel zone plates. This research has led to demonstration of new phenomena - anomalous anisotropic light scattering and form birefringence in glass [2]. The anisotropic phenomena have been interpreted in terms of self-induced index nano-gratings in glass and self-organized form birefringence, which is a new manifestation of self-organization under intense irradiation.

The observed self-organized periodic structures are the smallest (20 nm width) and the strongest (-0.2 index change) ever created by light in transparent materials. Moreover these are the first gratings created by light-matter (electron plasma) interference [3]. In the talk I review properties and potential applications of glass and optical fibres modified by strong fields and related new phenomena.

More information

Identifiers

Catalogue record

Export record