R. W. J. Devereux

Waveguide beam splitters and recombiners based on multimode propagation phenomena

Novel waveguide beam splitters and recombiners based on multimode propagation phenomena in hollow step-index waveguides are predicted and demonstrated. The splitter designs are based on symmetrically feeding the fundamental-mode field from a square cross-section waveguide, 2a × 2a, into a multimode rectangular guide, 2a × 2b (b > a). As a result of multimode superposition phenomena, unique transverse-field patterns representing different-order multiway splitting of the input field occur at predictable positions along the rectangular-guide axis. The predictions are verified experimentally at 10.6 μm with hollow dielectric waveguides but are considered to be more widely applicable.

A novel waveguide Mach-Zehnder interferometer based on multimode interference phenomena

Abstract A novel form of Mach-Zehnder interferometer based on multimode interference (MMI) phenomena in multimode waveguides is predicted and demonstrated. The interferometer is based on symmetrically feeding fundamental mode fields from two square waveguides, 2a×2a, in cross section, into a multimode rectangular guide, 2a×2b, (b >a). As a result of multimode interference phenomena, depending on whether the input fields are “in” or “out of” phase, two completely different forms of resultant field pattern are produced at a distance of 2b2/λc, along the multimode guide. The predictions are verified experimentally at 10.6 μm with hollow dielectric guides, but the underlying design concepts are considered to be much more broadly applicable.

Effect of field regeneration on the TEM(00) transmission characteristics of a circular-section waveguide.

The transmission of a 10.6-microm TEM(00) beam through a hollow circular-cross-section waveguide is modeled in terms of the excitation and propagation of the two lowest-order circularly symmetric EH(1n) modes. At points along the guide axis where the are in phase the TEM(00) input field is shown to be regenerated, but midway between these points, transverse-mode profiles that have a doughnut shape are produced. It is proposed that these dramatic field variations should cause variations in the effective attenuation coefficient along the length of the waveguide. The first direct experimental measurements to our knowledge of the guide-length-dependent attenuation characteristics of a 1.0-mm-bore hollow silica waveguide support this hypothesis by revealing a strong periodic component in addition to the anticipated exponential decay.

Hollow-waveguide integrated optic system with an integrated laser source

The paper describes recent work on the development of hollow waveguide integrated optic systems with integrated laser sources. Both monolithic and hybrid laser integration concepts have been considered. The hybrid approach has been carried through into the design, manufacture and demonstration of a homodyne system. Details of design, manufacturing and assessment issues, and the demonstration of the system as a Doppler anemometer, will be discussed.