טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDahan Raphael
SubjectDroplet Optomechanics and Non-Reciprocal Optics
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Tal Carmon
Full Thesis textFull thesis text - English Version


Abstract

My research bridges mechanics to optics by demonstrating systems where light enables a mechanical wave excitation; or, vice versa, where a mechanical-rotation enables optical non-reciprocity.


In the first experiment, I optically excite the mechanical resonances of droplets. Despite of the fact that droplets are common in nature as well as in artificial processes; their mechanical resonances were never before investigated experimentally, nor even studied theoretically. To give an example, the acoustical resonance rates of a micro-droplet are near 30 MHz rates, where mechanical actuation methods (e.g. Piezoelectric) are challenging to implement. In contrast to electrical excitation methods, one can rapidly turn on (or off) light while it is circulating in a droplet. The centrifugal forces of light are therefore ideal for exciting the mechanical resonances of a droplet, which will be reviewed in chapter 2 of this thesis.


In the second experiment, I demonstrate optical non-reciprocity by mechanically rotating an optical resonator. This research is inspired by the Fizeau experiment, in which he measured the speed of light in moving water in 1851. The speed of light in a moving dielectric, that Fizeau measured, is related to relativistic optics and to the fact that ether does not exist. Additionally, and for reasons relating to the symmetries in nature, the Fizeau effect is a very rare optical effect that allows counter-propagating beams to experience different refractive indices.

Here, when rotating a circular resonator, its resonance frequency changes linearly with the resonator’s angular velocity, which results in asymmetrical light propagation through a fiber coupled to the resonator.  Unlike some other non-reciprocal systems, our rotating resonator is fiber coupled, allows >99% rejection ratio, has no threshold, and operates also while light is coming from both sides. Our opto-mechanical isolator will be described in the third chapter of this thesis.


In the experiments above I exploit the mechanical properties of optical modes and (via the forces that they apply) to study droplet acoustics. Inversely, I use mechanics to enable an optical “add on” by relying on the fact that the speed of light, including in a resonator, depends by the speed of the dielectric host.  Therefore, a necessary background of optical modes in a circular resonator and on the centrifugal forces that they apply is given in the first chapter. Similarly, the speed of light as a function of the speed of the dipoles it passes through is needed for understanding of the second experiment and will be reviewed in the third chapter.