Browsing by Subject "Wave guides"

Now showing 1 - 6 of 6

Chaos in 2D electron waveguides
(2001-12) Akguc, Gursoy Bozkurt; Reichl, L.E.
The design and simulation of a broadband directional array in a cylindrical waveguide
(2002) Aldana, Guillermo Emilio; Hamilton, Mark F.; Hixson, Elmer LaVerne
Exploration of deep subterranean wells is accomplished using what is known in the oil industry as a “drill string”. A drill string is a set of long hollow steel pipe joined together by large diameter couplings; with a drill bit attached to the end. Modern oil wells reach depths of two to five miles. For over 50 years, the scientific community has been trying to develop an economical and reliable solution to the problem of acoustic telemetry using the drill string as the information carrier. Acoustic telemetry is the process by which intelligence can be transmitted from the bottom of the drilling operations to the surface, using the drill string as an (acoustic) waveguide. The drill string geometry is responsible for the dispersive and filtering properties of the structure. These two properties, make the transmission of information from one end of the drill string to the other very challenging. Two aspects of the ongoing research is the development of a repeater and a termination impedance. An acoustic repeater could be used to rebroadcast signals that have attenuated along the drill string, due to inherent attenuating mechanisms in the data carrier, and its interactions with the harsh environment. Current repeaters lack directionality and transmit information in both directions; clearly an undesirable feature. The terminating impedance concept is an “acoustic black body”. The terminating impedance absorbs all of the incoming acoustic energy at the top of the drill string, once it has been analyzed for decision making. Cancelling the echoes from the top of the structure may allow faster data telemetry, as the reflected energy does not interfere with incoming information. The focus of this dissertation in on the design and simulation of both the repeater and the terminating impedance. This work is unique in that it addresses a method to rebroadcast and cancel broadband signals, using an active, feed-forward adaptive algorithm, coupled with a properly spaced and phased array of sources (piezoelectric transducers). Both the repeater and terminating impedance are capable of reproducing complex transient wave forms. The terminating impedance and repeater designed are directional, robust to frequency content, drill string length and geometry.
Investigation of polymer waveguides for fully embedded board-level optoelectronic interconnects
(2004) Liu, Yujie; Chen, Ray T.
We proposed a fully embedded board-level optoelectronic interconnect structure utilizing polymer waveguides and 45-degree micro mirror light couplers. This structure is expected to provide high-speed, large bandwidth, low power dissipation, as well as compatibility to conventional PCB fabrication process, ease of optical alignment and packaging. High performance polymer waveguide with 45 degree micro mirror coupler is one key component to enable all these advantages. The performance analyses indicate that the polymer waveguide can provide low loss link for optical data and high channel density can be achieved without inducing significant crosstalk. Waveguide intersections and bends can be employed in the waveguide circuitry design to improve the design flexibility and interconnection density. 45 degree mirror couplers can provide high input and output surface-normal coupling efficiency. The fully embedded system features high tolerance to the linear and angular misalignments due to the possible fabrication imperfection. Ultradel 9000 series polyimides are used to form the waveguide and mirror couplers. Fabrication techniques are developed and discussed in detail. Waveguide array and mirror couplers with good quality have been fabricated and characterized. Preliminary integration of polymer waveguide array with MSM photodetector array through 45-degree micro mirror couplers is demonstrated and shows an aggregate bandwidth of 32GHz for a 1×12 channel array. Further integration is under development. An optoelectronic interconnect layer (OIL) will be developed and laminated with the other layers of PCB to improve system performance without inducing manufacturing difficulties.
Quantum chaos and electron transport properties in a quantum waveguide
(2008-05) Lee, Hoshik, 1975-; Reichl, L. E.
We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrödinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A [delta]-function model as a single impurity is very attractive, but it has been known that [delta]-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a [delta]-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also agrees with the classical predictions. We also compute the electron transmission probability through a multi-ripple electron waveguide. We find an effect analogous to the Dicke effect in the multi-ripple electron waveguide. We show that one of the S-matrix poles, that of the super-radiant resonance state, withdraws further from the real axis as each ripple is added. The lifetime of the super-radiant state, for N quantum dots, decreases as [1/N] . This behavior of the lifetime of the super-radiant state is a signature of the Dicke effect.
Quantum computation with ballistic electron waveguides
(2006) Snyder, Michael Garrett; Reichl, L. E.
We present a study of ballistic electron waveguides as used to construct simple quantum computational networks. We begin with an introduction to ballistic electron waveguides, some basic theory of quantum computers, and the possible role of electron waveguides in quantum computation. Following that, our study of various waveguide networks and the physics of the specific components of those networks. We continue with a discussion of shot noise in network elements and its possible role in helping to build good computational gates. Finally we conclude with a summary of research and possible future projects.
Suppression of radiation damping in electromagnetic waveguide, signature of quantum decoherence in the field bath
(2003) Ting, Chu Ong; Prigogine, I. (Ilya); Petrosky, Tomio Y.
Recent development of spectral analysis of the Liouville-von Neumann equation has revealed the fact that irreversibility is a rigorous dynamical property of Poincaré non-integrable systems with an infinite degrees of freedom interacting among each other through resonance coupling. In the present work we discuss this role of resonance in some examples of matter-field coupling systems for both classical and quantum mechanics: the one is a classical motion of a charged particle in electromagnetic waveguide, and the other is the decoherence problem of quantum matter-field interacting systems. In the first part of this dissertation, we study an accelerated motion of a charged classical dipole molecule with frequency ω1 inside the rectangular waveguide. If the particle is in free space, it is well known that its accelerated motion will eventually stop by radiating the field through the resonance interaction. This result is the so-called radiation damping. For the case in the waveguide, there are two possible situations, due to the existence of the cut-off frequency ωc of the waveguide. Under the cut-off frequency electromagnetic wave cannot propagate inside the waveguide. The stability of the dipole depends on the relation between ω1 and ωc. For ω1 < ωc, the dipole cannot resonate with the field. This corresponds to the Poincaré integrable system. For this case the dipole keeps its accelerated motion without emitting the radiating field. Therefore the radiation damping of the dipole molecules is suppressed inside the waveguide under the absence of resonance interaction. The motion of this steady state somewhat resembles a quantum ground state. We show that this steady state is dressed by electromagnetic field. The overlap of the dressing field leads to a force analogous to van der Waals force in quantum mechanics. The critical frequency determined by ω1 = ωc gives a critical size of the waveguide. For heavy molecules, such as HCl, this is of order 10−5m. We show that the size of the dressing field is the same order of the size of the waveguide. Hence we have a macroscopic size of the dressing in the waveguide. For ω1 > ωc, the dipole can resonate with the field, and the system becomes non-integrable in the sense of Poincaré. As a result, the accelerated motion eventually stop by emitting the resonance field. This corresponds to the problem of classical radiation damping. We show that there is non-negligible deviation of exponential decay in a short time scale of the order t ∼ 1/ω1. This corresponds to the quantum Zeno effect, well known in quantum unstable systems. After this period, the dipole decays exponentially in time by emitting the resonance field. We found by choosing ωc very close to ω1, we can increase the decay rate 105 times faster than the case where the dipole is in the free space, at the same time the emitted field travel 10−4 times slower than the speed of light. This is again a consequence of the existence of the cut-off frequency in the waveguide. Indeed, the cut-off frequency leads to a non-linear dispersion relation for the electromagnetic field. To some extent, the electromagnetic field is sticky inside the waveguide. Due to the large decay rate and slower speed of light, the size of the wavepacket emitted by the dipole is significantly small (about 10cm for HCl). This is even smaller than the quantum case in free space, where the wavepacket of the field emitted by the decay of electron in hydrogen atom is about 1m. In the second part of this dissertation, we study a quantum matter-field coupled system. We focus our attention on the problem of quantum decoherence in a system of a particle coupled with a field, the Hamiltonian of which has a similar structure to the problem of classical radiation damping mentioned above. We apply the complex spectral representation of the Liouville-von Neumann operator that gives a rigorous approach to the irreversible processes. We focus our attention on the time evolution of the field, which is commonly neglected in phenomenological approaches to the decoherence problem. We found a signature of decoherence in the field which has a characteristic time dependence proportional to t that comes from the secular effect between the particle and the field through the resonance interaction that breaks time-symmetry.