Efficient Synthesis of Room Acoustics via Scattering Delay Networks

An acoustic reverberator consisting of a network of delay lines connected via scattering junctions is proposed. All parameters of the reverberator are derived from physical properties of the enclosure it simulates. It allows for simulation of unequal and frequency-dependent wall absorption, as well as directional sources and microphones. The reverberator renders the first-order reflections exactly, while making progressively coarser approximations of higher-order reflections. The rate of energy decay is close to that obtained with the image method (IM) and consistent with the predictions of Sabine and Eyring equations. The time evolution of the normalized echo density, which was previously shown to be correlated with the perceived texture of reverberation, is also close to that of IM. However, its computational complexity is one to two orders of magnitude lower, comparable to the computational complexity of a feedback delay network (FDN), and its memory requirements are negligible

Phase-driven optomechanics in exotic photonic media

Integrated photonics provide unique advantages in tailoring and enhancing optical forces. Recent advancements in integrated photonics have introduced many novel phenomena and exotic photonic media, such as photonic topological insulator, negative index material, photonic crystals, 2D material, and strongly-modulated time-dynamic systems. In my dissertation, I theoretically and numerically explore the novel properties and applications of optical forces in these systems. We propose guided-wave photonic pulling forces in photonic crystal waveguides. Photonic crystal waveguides offer great capability to define the mode properties, and can incorporate complex trajectories, leading to unprecedented flexibility and robustness compared to previous works in free space or in longitudinally uniform waveguides. With response theory, a virtual work approach, we establish general rules to tailor optical forces in periodic structures involved with photonic crystals: pulling forces arise from negative gradients in the phase responses of the outgoing modes, which corresponds to forward scattering on the Bloch band diagram with unit cell function corrections. We devise robust forward scattering, first, using topologically protected nonreciprocal chiral edge states, second, using backward (i.e. negative index) waves in a reciprocal system. The structures are tailored to accommodate only the necessary modes, which largely benefits the robustness. With these, we numerically demonstrate long range pulling forces on arbitrary particles through sharp corners. Our work paves the way towards sophisticated optical manipulation with single laser beam. We next explore the implication and applicability of momentum conservation in periodic media, which has been unclear due to the inhomogeneity and strong near field. We first quantify the linear momentum flux of Bloch modes under discrete translational symmetry, which is further understood from their plane wave composition. We then demonstrate through varies examples that the change in momentum flux predicts a total force distributed to both the scatterer and the media. However, one still need response theory to predict the forces on individual objects. Using response theory, we can predict more general forms of optical forces. We numerically demonstrate optical motoring effect due to singularity in the phase responses, and strong optical forces between graphene sheets due to large gradients in the phase responses. In particular, by combining the strong forces in graphene guided-wave system and the exceptional elastic properties of graphene, we can get an SBS gain that is four orders of magnitude stronger than in a silicon step-index waveguide, which may lead to smaller devices for RF signal processing.Physic

Instrument Design and Radiation Pattern Testing for Terahertz Astronomical Instruments

abstract: The Milky Way galaxy is a powerful dynamic system that is highly efficient at recycling material. Stars are born out of intergalactic gas and dust, fuse light elements into heavier elements in their cores, then upon stellar death spread material throughout the galaxy, either by diffusion of planetary nebula or by explosive events for high mass stars, and that gas must cool and condense to form stellar nurseries. Though the stellar lifecycle has been studied in detail, relatively little is known about the processes by which hot, diffuse gas ejected by dying stars cools and conglomerates in the interstellar medium (ISM). Much of this mystery arises because only recently have instruments with sufficient spatial and spectral resolution, sensitivity, and bandwidth become available in the terahertz (THz) frequency spectrum where these clouds peak in either thermal or line emission. In this dissertation, I will demonstrate technology advancement of instruments in this frequency regime with new characterization techniques, machining strategies, and scientific models of the spectral behavior of gas species targeted by these instruments. I begin this work with a description of radiation pattern measurements and their use in astronomical instrument characterization. I will introduce a novel technique to measure complex (phase-sensitive) field patterns using direct detectors. I successfully demonstrate the technique with a single pixel microwave inductance detectors (MKID) experiment. I expand that work by measuring the APEX MKID (A-MKID) focal plane array of 880 pixel detectors centered at 350 GHz. In both chapters I discuss the development of an analysis pipeline to take advantage of all information provided by complex field mapping. I then discuss the design, simulation, fabrication processes, and characterization of a circular-to-rectangular waveguide transformer module integrated into a circularly symmetric feedhorn block. I conclude with a summary of this work and how to advance these technologies for future ISM studies.Dissertation/ThesisDoctoral Dissertation Exploration Systems Design 201