M.Sc Thesis

M.Sc StudentShlomi Keren
SubjectSynchronization in On-Fiber Optomechanical Devices
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Eyal Buks


Optomechanical cavities have raised much interest in the past few decades. Coupling between mechanical elements, which serve as resonators, to optical or electronic devices, allows actuation or detection of the mechanical element. Recent advances in the intertwined fields, such as micro-electro-mechanical devices (MEMs), optics, microwave devices and superconducting enable the mechanical elements to show distinct quantum mechanical effects, such as ground state cooling, asymmetry in power spectral density, Rabi oscillations and quantum back-action induced noise. These exciting technological innovations allow, from the applicative aspect, to fabricate and operate devices at the quantum mechanical regime with extremely low noise, and from the theoretical aspect, to better understand the measurement problem and the quantum to classical transition. Other theoretical motivations include detection of gravitational waves, which requires the lowest measurement noise possible, and mechanical devices, which may function as memory elements in a quantum computer, or as transducers of quantum states from microwave to optical frequencies.

Micro and nano optomechanical systems exhibit many interesting and useful phenomena, such as self-excited oscillations (SEO), bi-stability and chaotic dynamics. In this work we investigate several aspects of some of these phenomena both theoretically and experimentally, with the objective of deducing how they could be used to enhance desired effects in optomechanical devices or reduce other undesired effects, such as noise.

The research presented here is divided into three main parts. The first investigates the case where self- oscillations are synchronized by adding modulation to the CW laser light. This investigation includes theoretical derivation of the phase space distribution (PSD) based on the Fokker- Planck equation followed by a state tomography technique for extracting PSD from the measured data and comparing it to theory. The different cases include synchronization by activation of modulation amplitude, and by enlarging it for both the effective mechanical resonance frequency and twice the former frequency, and dephasing by switching off the modulation amplitude. A bifurcation analysis leads to the theoretical and experimental synchronization region.

The second part discusses the fabrication of an on- fiber optomechanical cavity. The main obstacles that were overcome and fabrication tips for creating an on- fiber optomechanical cavity are elaborated.

The third part of this work elaborates on the applicative aspect of the optomechanical cavity- a hydrocarbon contamination detector. This detector is operated using an optical actuation scheme, and the contamination is detected by the change in frequency response measured by a network analyzer.