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

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

Low power all-fibre intensity modulator at 2.7MHz

A monolithic single-mode fibre acousto-optic amplitude modulator is reported. Nearly 100% modulation is achieved at a modulation frequency of 2.7MHz for an electrical drive power of 2mW

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

3x3 all-fibre routing switch

An all-fibre acousto-optic switch has been constructed from a 3x3 null fused coupler. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB. The switch shares the advantages of an earlier 2x2 switch but with more fibre ports. and should permit the design of compound routing arrays with fewer switching elements per channel

All-fibre 3 x 3 acousto-optic switch

We report an all-fibre 3 x 3 acousto-optic switch. The maximum drive power required is 4 mW, the switching time is 100µs and the insertion loss is less than 0.5 dB

Behaviour of asymmetric fused-tapered single-mode fibre couplers

Fused-tapered single-mode fibre couplers are available which have a flattened wavelength response and which are therefore useful in applications requiring a near-constant power-splitting ratio over a range of wavelengths. They are made by inducing an asymmetry in the constituent fibres, for example by pre-tapering or pre-etching one or both fibres prior to coupler fabrication, or by using two dissimilar fibres. The maximum coupled power in these couplers has been shown to decrease with increasing asymmetry. Couplers made from dissimilar fibres could also be useful for integrating systems made from different fibres, and it may be necessary for such a coupler to exhibit complete power transfer despite the asymmetry in fibre type. Complete power transfer has only previously been shown to be possible in dissimilar fibre couplers by differentially etching the fibres used to make the coupler, in order to adjust the extent of cladding diameter asymmetry. It would be advantageous to be able to adjust the splitting ratio of these couplers without requiring close control over the cladding diameter asymmetry of the constituent fibres. We demonstrate that the maximum coupled power of an asymmetric coupler is strongly dependent on the degree-of-fusion in the coupler, and that it is possible to obtain near-total power transfer (or indeed any level of power transfer) for a given cladding diameter asymmetry by controlling the degree-of-fusion of the coupler. We therefore remove the requirement for a controllable differential etching process prior to coupler fabrication

40-MHz all-fiber acoustooptic frequency shifter

We report the development of a 40 MHz four-port all-fibre frequency shifter operating at a wavelength of 1.55 µm. The device has a high conversion efficiency, low drive power requirement and is manufactured from standard telecommunications fibre

All fibre 2x2 polarisation insensitive switch

We report the development of a polarisation insensitive, low loss, broad band all fibre 2×2 acousto-optic switch based on twisting the waist of a null taper coupler. The best polarisation insensitivity observed so far is 0.2dB

Surface modes of multilayer stacks

A parallel interface between a periodic multilayer structure and a uniform external medium can support surface electromagnetic waves. The energy in such a wave is localised about the boundary, and is excluded from the bulk of the multilayer structure by a Bragg condition. The possibility of quasi-single-mode behaviour, together with the freedom to make k as low as the plane-wave value in the external medium, and the great sensitivity of k to the detailed properties of the edge layer, gives these surface waves many potential applications in optical sensors, modulators, and other device