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104
The inverse of the slope of the dispersion curve is ∂ω ∂β , which is the group velocity.
The fact that the tapered fiber and PCWG dispersion curves have opposite slope at the
phase matching frequency means that the energy propagates in opposite directions.
Thus, contra-directional coupling, rather than co-directional coupling, is predicted.
5.3 Adiabatic Criteria and Fiber Taper Transitions
Tapered optical fibers have been used extensively in many recent applications, including
coupling to microresonators for quantum electrodynamics (QED) experiments [43], as
optical sensors [47], and as directional couplers for telecom applications. Tapering is
achieved by stretching a fiber while a small length of the fiber is heated to a temperature
above the melting point of silica. Common heat sources are microflames [21] and CO2
lasers [1]. Although heating and stretching an optical fiber are mechanically
straightforward, it is the need to maintain the near-zero (0.2dB/km) transmission loss of
the fiber that renders tapering telecom fibers an intricate process. Specifically, in order
to avoid introducing losses, the fiber must be tapered adiabatically, meaning that the
transition from the original diameter to the final diameter must be sufficiently gradual at
every point along the taper. If the taper occurs too abruptly, light couples from the
fundamental hybrid HE11 mode of the fiber to higher order modes due to the breaking of
the fiber’s cylindrical symmetry. The higher order modes propagate as cladding modes
and, while these modes are guided in the untapered region, they become unguided where
the diameter transitions to the taper waist. Power is lost when the unguided modes
propagate through the taper waist and cannot couple back to fiber core modes. This
power lost from the fundamental mode is referred to as excess loss.
Object Description
| Title | Silicon-based photonic crystal waveguides and couplers |
| Author | Farrell, Stephen G. |
| Author email | stephenf@usc.edu; sgfarrell@yahoo.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Electrical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2008-09-05 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-20 |
| Advisor (committee chair) | O'Brien, John D. |
| Advisor (committee member) |
Dapkus, P. Daniel Steier, William Haas H., Stephan |
| Abstract | Most commercial photonics-related research and development efforts currently fall into one or both of the following technological sectors: silicon photonics and photonic integrated circuits. Silicon photonics [18] is the field concerned with assimilating photonic elements into the well-established CMOS VLSI architecture and IC manufacturing. The convergence of these technologies would be mutually advantageous: photonic devices could increase bus speeds and greatly improve chip-to-chip and board-to-board data rates, whereas photonics, as a field, would benefit from mature silicon manufacturing and economies of scale. On the other hand, those in the photonic integrated circuit sector seek to continue the miniaturization of photonic devices in an effort to obtain an appreciable share of the great windfall of profits that occur when manufacturing, packaging, and testing costs are substantially reduced by shrinking photonic elements to chip-scale dimensions. Integrated photonics companies may [12] or may not [34] incorporate silicon as the platform.; In this thesis, we seek to further develop a technology that has the potential to facilitate the forging of silicon photonics and photonic integrated circuits: photonic crystals on silicon-on-insulator substrates. We will first present a brief overview of photonic crystals and their physical properties. We will then detail a finely-tuned procedure for fabricating two-dimensional photonic crystal in the silicon-on-insulator material system. We will then examine transmission properties of our fabricated devices including propagation loss, group index dispersion, and coupling efficiency of directional couplers. Finally, we will present a description of a system for adiabatically tapering optical fibers and the results of using tapered fibers for efficiently coupling light into photonic crystal devices. |
| Keyword | photonics; photonic crystal; silicon; integrated photonics; SOI; optoelectronics; waveguides; couplers; optical fiber; tapered fiber; evanescent coupling; adiabaticity; silicon photonics |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1681 |
| Contributing entity | University of Southern California |
| Rights | Farrell, Stephen G. |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Farrell-2433 |
| Archival file | uscthesesreloadpub_Volume32/etd-Farrell-2433.pdf |
Description
| Title | Page 115 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 104 The inverse of the slope of the dispersion curve is ∂ω ∂β , which is the group velocity. The fact that the tapered fiber and PCWG dispersion curves have opposite slope at the phase matching frequency means that the energy propagates in opposite directions. Thus, contra-directional coupling, rather than co-directional coupling, is predicted. 5.3 Adiabatic Criteria and Fiber Taper Transitions Tapered optical fibers have been used extensively in many recent applications, including coupling to microresonators for quantum electrodynamics (QED) experiments [43], as optical sensors [47], and as directional couplers for telecom applications. Tapering is achieved by stretching a fiber while a small length of the fiber is heated to a temperature above the melting point of silica. Common heat sources are microflames [21] and CO2 lasers [1]. Although heating and stretching an optical fiber are mechanically straightforward, it is the need to maintain the near-zero (0.2dB/km) transmission loss of the fiber that renders tapering telecom fibers an intricate process. Specifically, in order to avoid introducing losses, the fiber must be tapered adiabatically, meaning that the transition from the original diameter to the final diameter must be sufficiently gradual at every point along the taper. If the taper occurs too abruptly, light couples from the fundamental hybrid HE11 mode of the fiber to higher order modes due to the breaking of the fiber’s cylindrical symmetry. The higher order modes propagate as cladding modes and, while these modes are guided in the untapered region, they become unguided where the diameter transitions to the taper waist. Power is lost when the unguided modes propagate through the taper waist and cannot couple back to fiber core modes. This power lost from the fundamental mode is referred to as excess loss. |
