טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMizrahi Amit
SubjectElectromagnetic Forces Exerted on Neutral Bodies by Guided
Waves
DepartmentDepartment of Electrical Engineering
Supervisors Professor Moshe Horowitz
Professor Levi Schachter
Full Thesis textFull thesis text - English Version


Abstract

Electromagnetic forces on neutral bodies may prove to be the basis for a variety of future optomechanical systems. Since the first demonstration of an optical trap over 30 years ago, vast research has been devoted to the trapping and manipulation of neutral particles by scattering of light beams. Optical forces caused by guided waves, however, have received relatively little attention. In the present study, the focus is on electromagnetic forces exerted by electromagnetic eigenmodes on the guiding structure.


As a preliminary stage, a method for the design of Bragg reflection waveguides either planar, cylindrical, or coaxial is developed. These waveguides consist of a hollow core and a cladding made of alternating dielectric layers. It is shown that by adjusting the width of the layer adjacent to the core, it is possible to significantly change the properties of the waveguide, and ensure confinement of a prescribed field profile.


Optical Bragg acceleration structures are Bragg reflection waveguides designed to support a TM mode with phase velocity that equals the speed of light in order to accelerate charged particles. The optical forces on the dielectric layers due to the intense fields of both the driving laser and the fields emitted by the charged particles are investigated. It is found that although the forces developed are by no means negligible, compared for example to the gravitational forces on the structure, they are orders of magnitude below the damage threshold.


An important system that is considered is a two-mirror waveguide that consists of two parallel mirrors that guide laser light between them. A general analytic analysis of the transverse pressure exerted on each mirror is provided, showing that it may be repulsive, may vanish, and may even become attractive, according to the type of symmetry of the guided mode. Based on this analysis, two operation schemes of such a system are proposed. The first is the manipulation of a mirror by altering the light frequency, implemented with a Bragg reflection waveguide. The second is a two-slab waveguide acting as an all-optical spring, which is facilitated by the superposition of two eigenmodes.


A different configuration that is considered is a cylindrical waveguide, where the longitudinal force and the torque are the significant quantities, rather than the transverse pressure as in a two-mirror waveguide. It is shown that torque is developed on a lossy dielectric object inside the waveguide due to an incident rotating mode.