Includes bibliographical references (p. 74-79).

We investigate the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities, with theoretical quality factors of \(1.4 × 10^7\) in silicon, operating at ~1550 nm. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a quality factor of nearly \(7.5 × 10^5\). We show on-chip integration of the cavities using waveguides and an inverse taper geometry based mode size converters, and also demonstrate tuning of the optical resonance using thermo-optic effect. We also study coupled cavities and show that the single nanobeam cavity modes are coupled into even and odd superposition modes. Using electrostatic force and taking advantage of the highly dispersive nature of the even mode to the nanobeam separation, we demonstrate dynamically reconfigurable optical filters tunable continuously and reversibly over a 9.5 nm wavelength range. The electrostatic force, obtained by applying bias voltages directly to the nanobeams, is used to control the spacing between the nanobeams, which in turn results in tuning of the cavity resonance. The observed tuning trends were confirmed through simulations that modeled the electrostatic actuation as well as the optical resonances in our reconfigurable geometries. Finally we demonstrate reconfiguration of coupled cavities by using optical gradient force induced mechanical actuation. Propagating waveguide modes that exist over wide wavelength range are used to actuate the structures and in that way control the resonance of a localized cavity mode. Using this all-optical approach, more than 18 linewidths of tuning range is demonstrated. Using an on-chip temperature self-referencing method that we developed, we determined that 20% of the total tuning was due to optomechanical reconfiguration and the rest due to thermo-optic effects. By operating the device at frequencies higher than the thermal cut-off, we show high speed operation dominated by just optomechanical effects. Independent control of mechanical and optical resonances of our structures, by means of optical stiffening, is also demonstrated. / Engineering and Applied Sciences

The mid-infrared wavelength region (2-20 µm) is of great utility for a number of applications, including chemical bond spectroscopy, trace gas sensing, and medical diagnostics. Despite this wealth of applications, the on-chip mid-IR photonics platform needed to access them is relatively undeveloped. Silicon is an attractive material of choice for the mid-IR, as it exhibits low loss through much of the mid-IR. Using silicon allows us to take advantage of well-developed fabrication techniques and CMOS compatibility, making the realization of on-chip integrated mid-IR devices more realistic. The mid-IR wavelengths also afford the opportunity to exploit Si's high third-order optical nonlinearity for nonlinear frequency generation applications. In this work, we present a Si-based platform for mid-IR photonics, with a special focus on micro-resonators for strong on-chip light confinement in the 4-5 μm range. Additionally, we develop experimental optical characterization techniques to overcome the inherent difficulties of working in this wavelength regime. First, we demonstrate the design, fabrication, and characterization of photonic crystal cavities in a silicon membrane platform, operational at 4.4 μm (Chapter 2). By transferring the technique known as resonant scattering to the mid-IR, we measure quality (Q) factors of up to 13,600 in these photonic crystal cavities. We also develop a technique known as scanning resonant scattering microscopy to image our cavity modes and optimize alignment to our devices. Next, we demonstrate the electro-optic tuning of these mid-IR Si photonic crystal cavities using gated graphene (Chapter 3). We demonstrate a tuning of about 4 nm, and demonstrate the principle of on-chip mid-IR modulation using these devices. We then investigate the phenomenon of optical bistability seen in our photonic crystal cavities (Chapter 4). We discover that our bistability is thermal in origin and use post-processing techniques to mitigate bistability and increase Q-factors. We then demonstrate the design, fabrication, and characterization grating-coupled ring resonators in a silicon-on-sapphire (SOS) platform at 4.4 μm, achieving intrinsic Q-factors as high as 278,000 in these devices (Chapter 5). Finally, we provide a quantitative analysis of the potential of our SOS devices for nonlinear frequency generation and describe ongoing experiments in this regard (Chapter 6). / Engineering and Applied Sciences

In this paper we outline a new direction in the area of photonic crystals, or photonic band gap materials,one-, two-, or three-dimensional superstructures with periods that are comparable with the wavelengths of electromagnetic radiation. The main characteristic of this new class of PCs is the presence of magnetically ordered components. The linear and nonlinear optical properties of such magnetic PCs are discussed.

Two dimensional photonic crystal slabs are studied theoretically and experimentally for the application of refractive index sensing with a focus on increasing both quality factor and sensitivity simultaneously. An overview of simulation and experimental techniques, along with fabrication protocols used is given. Through the use of new wafer architectures which allow for an air substrate, sensitivity is enhanced in some cases by more than a factor of 2 from our previous studies. Combining this with a novel lattice proposed which greatly reduces fabrication tolerances, experimental quality factors above 10,500 are achieved while maintaining an experimental sensitivity of above 800 nm/RIU. The effects of a finite photonic crystal slab are studied through the group velocity of guided mode resonances, with an emphasis on zero-group velocity. Future applications of the designs proposed are discussed.

Two dimensional photonic crystal slabs are studied theoretically and experimentally for the application of refractive index sensing with a focus on increasing both quality factor and sensitivity simultaneously. An overview of simulation and experimental techniques, along with fabrication protocols used is given. Through the use of new wafer architectures which allow for an air substrate, sensitivity is enhanced in some cases by more than a factor of 2 from our previous studies. Combining this with a novel lattice proposed which greatly reduces fabrication tolerances, experimental quality factors above 10,500 are achieved while maintaining an experimental sensitivity of above 800 nm/RIU. The effects of a finite photonic crystal slab are studied through the group velocity of guided mode resonances, with an emphasis on zero-group velocity. Future applications of the designs proposed are discussed.

No description available.

Holographic lithography is a new technique developed for the fabrication of threedimensional photonic crystals in polymer. Four coherent laser beams are interfered to generate a three-dimensionally periodic interference pattern in a film of photoresist. Subsequent processing steps render a three-dimensional photonic crystal, whose structure is commensurate with the original interference pattern. Two interference patterns are discussed in detail: a face-centred cubic pattern with a conventional lattice constant of 922nm in air and a face-centred cubic pattern with a conventional cube side of 397nm in air (interference wavelength 355nm). Three types of basis are presented for the interference pattern with a 922nm lattice constant: a righthanded, a left-handed and a non-chiral basis. Photonic crystals have been fabricated with both a chiral and a non-chiral basis and evaluated by scanning electron microscopy. Optical transmission measurements are presented for the non-chiral photonic crystals and are interpreted in both a Bragg scattering model and a photonic bandstructure model. A 'GaAs' and a 'diamond' basis are presented for the interference pattern with a 397nm lattice constant. Photonic crystals have been fabricated with the 'GaAs' basis and evaluated by scanning electron microscopy.

No description available.

No description available.