Acousto-optic superlattice modulator using Fibre Bragg grating

A modulator is reported in which an extensional acoustic wave is launched along a fiber Bragg grating. The acousto-optic superlattice effect causes an enhancement in reflectivity within a narrow spectral region on both sides of the Bragg wavelength. For a fixed acoustic propagation direction, the Doppler shift can be either positive or negative, depending on whether the wavelength of the incident light lies above or below the Bragg condition. The device can function as a Bragg cell and a tunable filter

Two-dimensional photonic band-gap structures as quasi-metals

By considering waves that propagate out of the transverse plane, we show that common high index materials (eg GaAs) with a 2D array of air holes can act in some ways like a 3D photonic band-gap structure. In particular, we describe a dielectric "quasi-metal" that reflects all propagating light incident from free space

Theory of forward stimulated Brillouin scattering in dual-mode single-core fibres

Recently, stimulated Brillouin scattering in a forward direction (FSBS) in a dual-mode single-core optical fiber was reported for the first time. Frequency shifts on the order of 17 MHz were seen in fiber supporting LP01 and LP11 modes at 514.5 nm. The phenomenon is examined here in more detail, and the governing differential equations of the three-wave parametric process (involving laser pump, Brillouin signal, and acoustic flexural-wave phonon) are derived and solved. FSBS is possible because although the overlap integral between a flexural fiber mode and the light is small, the phonon lifetime is much longer than in conventional SBS. FSBS may also be the first example of a nonlinear effect which is enhanced by increasing the optical mode area at constant pump power

Glass fibre poling and applications

Recent developments in the application of poled optical fibers to second harmonic generation and electrooptic light modulation are reviewed

Photonic Bloch waves and field microstructure in nonlinear gratings: An intuitive approach

Coupled wave theory is commonly used in numerical simulations of reflection from nonlinear grating structures. By contrast, the complementary photonic Bloch wave (PBW) approach has rarely been adopted, perhaps the only example being recent work on gap solitons. Bloch wave theory offers an alternative physical intuitive picture that encourages one to think in terms of field microstructure, leading to a range of simple explanations for the behaviour of light in linear gratings. In this paper the dispersion relation and field microstructure of Bloch waves are found, and used to clarify the physical mechanisms that lead to regions of bistability, instability and oscillation for incidence of a monochromatic plane wave on a nonlinear grating half-space

UV-induced refractive index changes in germanosilicate fibres

Photo-induced guided index changes approaching at both 633nm and 1.55µm, measured using a simple interferometric technique, are reported in germanosilicate single-mode optical fibres exposed to 266nm from the side

Nonlinear transmission and colour-centre dynamics in germanosilicate fibres at 420-540 nm

We report evidence in support of the view that induced loss and non-linear transmission in pure germanosilicate fibers at blue/green wavelengths are governed by the formation (via two-photon absorption), spontaneous and stimulated transformation and bleaching (via single-photon events) of Ge(1), Ge(2) and Ge(3) colour-centres. Using a tunable pulsed dye laser, the excitation spectrum of the induced absorption, its spectral attenuation and the effects of germania concentration and thermal annealing are investigated

Low power acousto-optic device in tapered single-mode fibre

We report a new acousto-optic device based on tapered single-mode fibre. Since the overlap between acoustic and optical waves is complete, very little acoustic power (less than 1 microwatt) is required

All fibre polariser using a null coupler

We report a new fibre polariser based on a twisted null taper coupler. The best extinction ratio observed so far is 15dB

High reflectivity photorefractive Bragg gratings in germania-free optical fibres

We present the first report of Bragg gratings with reflectivities exceeding 99% written in germania-fibre optical fibres by UV exposure. This result has important implications for the production of ultrashort single-frequency fibre lasers