Richard Michael Jenkins

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.

Laser resonators with self-imaging waveguides

Novel laser resonator concepts based on the self-imaging properties of multimode waveguides are proposed. These resonators have widely applicable designs and are predicted to produce TEM00 output with low round-trip loss and excellent mode discrimination.

Effects of curved mirrors in waveguide resonators

Waveguide gas lasers (CO(2) ones especially) continue to be widely used. We have previously studied simple resonator designs with plane mirrors close to each end of the waveguide. Here we examine theoretical predictions concerning hybrid waveguide/free-space resonators with square-bore guides and curved mirrors. We show how resonator mode losses vary as functions of guide length and width, guide-to-mirror distance, mirror radius of curvature, and mirror tilt. We have tested a 7-W cw rf-excited CO(2) laser with unusually good near-TEM(00) transverse-mode quality; it is one of many promising resonator geometries not covered by earlier published research. The common case 3 reflector, sometimes viewed as guaranteeing near-TEM(00) mode performance, is shown to be alarmingly sensitive to small misalignments for certain guide geometries.