Barclay, Paul E.Kaviani, Hamidreza2021-01-052021-01-052020-12-22Kaviani, H. (2020). Cavity Optomechanics for Nonlinear Coupling and Torsional Sensing (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/112913In the past decade, there has been a surge in the field of nanophotonic cavity optomechanics due to the exceptional sensitivity of these systems for force and displacement detection owing to their ultra-low mass and optical mode volume. This thesis studies two topics of this field, namely nonlinear optomechanics and torsional optomechanical systems. Nonlinear optomechanics enables fundamental experiments such as quantum non-demolition measurements and non-classical light generation. Torsional optomechanics allows for ultra-precise measurement of angular momentum of physical systems such as magnetic moments, electron spins, and the orbital and spin angular momentum of photons. After a brief overview of optomechanical principles in Chapter 1 and the basics of photonic crystal cavities and their design methods in Chapter 2, we present a novel optomechanical system for torque detection in Chapter 3. This device is designed specifically for detecting torque generated by orbital angular momentum of light. However, the principles and methods developed in this Chapter can be used for sensing of other sources of torque. An optically-induced twist imparted on the device by light is detected using an integrated cavity optomechanical system based on a nanobeam slot-mode photonic crystal cavity explained in Chapter 2. This device allows measurement of the orbital angular momentum of light when photons are absorbed by the mechanical element or detection of photons’ presence when they are scattered into new orbital angular momentum states by a sub-wavelength grating patterned on the device. Such a system allows detection of an l = 1 orbital angular momentum field with an average 3.9×10^3 photons modulated at the device's mechanical resonance frequency and can be extended to higher-order orbital angular momentum states. In Chapter 4, we present an ultra-sensitive optomechanical system for detecting high-frequency vibrations that is suited for torque sensing applications, especially in the field of magnetometry. This work demonstrates an optomechanical system that can efficiently transfer torque to vibrations of a nanobeam photonic crystal cavity. We demonstrate a torque sensitivity of 9.1×10^(-22)-2.4×10^(-19) Nm/√Hz for the mechanical frequency range of 10-800 MHz. Lastly, in Chapter 5, we present nanoscale “paddle nanocavity” designed to enhance nonlinear optomechanical coupling. This device supports mechanical resonances with an effective mass of 300-600 fg, which couple nonlinearly to co-localized optical modes with a quadratic optomechanical coupling coefficient g^((2))>2π×400 MHz/nm^2, and a two phonon to single-photon optomechanical coupling rate Δω_0>2π×16 Hz. This coupling relies on strong phonon-photon interactions in a structure whose optical mode spectrum is highly non-degenerate. Simulations indicate that nonlinear optomechanical readout of thermally driven motion in these devices should be observable for T>50 mK and that measurement of phonon shot noise is achievable.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Cavity optomechanicsNonlinear optomechanicsTorsional optomechanicstorque sensingOAM detectionPhysicsdoctoral thesis10.11575/PRISM/38505