Two-photon photochemical long-period grating fabrication in hydrogenated photonic crystal fiber

We report on the photochemical fabrication of a long-period grating in photonic crystal fiber. The characteristic fluence value for inscription is an order of magnitude less than that for standard telecom fiber

Photonic band gaps

Dielectric crystals that act on photons as semiconductors do on electrons — forbidding certain wavelengths to propagate — promise highly efficient lasers and novel photonic materials

Fibre gratings

Information highways, fibre lasers and amplifiers, and a whole range of optical-based sensors have all been waiting for a simple grating that can be written directly into the fibre

Excimer laser production of fibre Bragg gratings

Using a KrF excimer laser operating at 248 nm. we have demonstrated that fibre gratings having essentially 100% reflectivity can be manufactured using a single 20 ns pulse. In the course of studying the dynamics of the grating formation process. it was found that transient optical gains of as much as 8 dB/cm could be obtained in germanosilicate fibre. The first distributed feedback (DFB) fibre laser has been made using this mechanism

Photonic Bloch waves and photonic band gaps

Photonic band gap materials are dielectrics with a synthetic, three dimensional, multiply periodic microstructure (lattice constant of order the optical wavelength) whose distinguishing feature is a very large modulation depth of refractive index. When appropriately designed, these "photonic crystals" exhibit ranges of optical frequency where light cannot exist - the photonic band gaps. The current interest in these materials has led us to re-appraise propagation in structures that, while not exhibiting a complete photonic band gap (PBG), nevertheless display anomalous and intriguing propagation effects in the vicinity of their Bragg condition. In most cases, around each Bragg condition appear incomplete momentum and energy gaps (i.e., ranges of, respectively, wavevector and frequency where propagation is forbidden) with widths that are given approximately by the product of the index difference with, respectively, the vacuum wavevector and h times the optical frequency. With the exception of the multi-layer dielectric stack, most conventional electromagnetic gratings, such as those encountered in holography, waveguides, distributed feedback lasers, acousto-optic and x-ray diffraction, consist of weak periodic perturbations about a mean refractive index. In these gratings, while strong spatial and temporal dispersion are present around each Bragg condition, the ranges of angles and frequencies over which this occurs are very narrow; and although PBG's do appear, they are incomplete and mostly very weak. ..

Frequency doubling, absorption and grating deformation in glass fibres: effective defects or defective effects?

The present understanding of colour centres in germanosilicate glass fibres and the diverse effects attributed to colour centre activity are reviewed. Drawing on a wide range of up-to-date research results, an attempt is made to piece together as far as possible a unified picture of the defect processes behind second harmonic generation, nonlinear transmission and photorefractive grating formation in optical fibres

Optically induced creation, transformation and organisation of defects and color centers in optical fibres

Over the past five years, a colour-centre model for the dynamics of the absorption induced in germanosilicate fibres upon exposure to blue/green light has been under development at Southampton. This model is introduced and its predictions used for the first time to test our proposed Kramers-Kronig mechanism for the concurrent refractive index changes induced in the visible and the infra-red. It is found that the predicted colour-centre population changes in the UV are to explain these refractive index changes. A possible alternative model, based on density changes in the glass triggered by colour-centre formation, is assessed experimentally and analytically. The implications of this result to photonically driven self-organisation in fibres is briefly assessed, and reference made to recent experimental results

Effects of squeezed-film damping on the optomechanical nonlinearity in dual-nanoweb fiber

The freely-suspended glass membranes in a dual-nanoweb fiber, driven at resonance by intensity-modulated light, exhibit a giant optomechanical nonlinearity. We experimentally investigate the effect of squeezed-film damping by exploring the pressure dependence of resonant frequency and mechanical quality factor. As a consequence of the unusually narrow slot between the nanowebs (22 μm by 550 nm), the gas-spring effect causes a pressure-dependent frequency shift that is ∼15 times greater than typically measured in micro-electro-mechanical devices. When evacuated, the dual-nanoweb fiber yields a quality factor of ∼3 600 and a resonant optomechanical nonlinear coefficient that is ∼60 000 times larger than the Kerr effect

Fibre acousto-optic frequency shifter based on a null coupler

A prototype all-fibre acousto-optic frequency shifter, based on a four-port coupler with a null maximum splitting ratio, is reported. Near 100% conversion with 30 dB sideband and carrier suppression is achieved for 1 mW of electrical drive power