Nonreciprocal and Nonlinear Nanoplasmonic Devices

• Author / Creator

  Firby, Curtis J.

• This thesis explores the incorporation of nonreciprocal magneto-optic effects, as well as nonlinear phenomena into integrated nanoplasmonic devices, and encompasses a wide spectrum of theoretical, numerical, fabrication, and characterization methodologies.

  Incorporating magnetic dielectrics into conventional nanoplasmonic waveguide geometries produces unique magnetoplasmonic architectures capable of fulfilling novel nonreciprocal functions. Application of a transverse magnetization across such devices leads to a nonreciprocal phase shift of the propagating mode, while a longitudinal magnetization can induce nonreciprocal polarization rotation via the Faraday effect. Additionally, the magnetization within the material exhibits highly nonlinear temporal dynamics when stimulated by external magnetic fields. These dynamics can be mapped onto the polarization or phase of the guided mode, or in an interferometer configuration, onto the output intensity.

  These concepts are employed to demonstrate several novel magnetoplasmonic devices including:

  • A high-speed phase shifter capable of up to 0.33rad of phase modulation and encoding data onto the phase of the mode.
  • An optical isolator exhibiting 2.51dB insertion loss and a 22.82dB isolation ratio.
  • A nanoplasmonic analog to an electrical clock multiplier, with modulation depths up to 16.26dB, a tunable output frequency between 280MHz and 5.6GHz, and multiplication factors of up to 2.5×10^3.
  • A nonlinear frequency mixer, which can generate harmonics, frequency splitting, and frequency down-conversion of a driving signal, as well as frequency mixing when two driving signals are present.
  • A dynamic plasmonic polarization modulator providing 99.4% mode conversion within only 830µm and operable in either a pulsed-output mode, or a continuous-output mode at up to 10GHz. This is the first demonstration of the Faraday effect within a plasmonic waveguide.
  • A versatile, broadband, and polarization-independent Faraday effect optical circulator.

  Furthermore, extensive fabrication process development was undertaken to construct a unique silicon-on-insulator waveguide characterization platform, which simultaneously incorporates micromachining of a bulk substrate and nanopatterning of Si-based metal-encapsulated plasmonic waveguides. This process allows nanoplasmonic waveguides only a few microns in length to be directly excited by ultrafast laser pulses via end-fire excitation.

  Experimental characterization of these waveguides depicts a complex interplay between the numerous nonlinear processes occurring within silicon. Notably, the infrared exciting pulses are converted into bright green visible light via third-harmonic generation. The conversion efficiency is measured to be 4.9×10^-4, which is over an order of magnitude higher than any previously reported result in a silicon-based waveguide structure, and was achieved within a device 100nm wide, 340nm tall, and 2.4µm long, yielding a compact on-chip footprint of only 0.24µm^2.

  Further examination of the measured spectra and their power scaling trends, as well as comparison to simulated results, suggests that an additional electric field enhancement of up to 2.2 times is present, due to the granular nature of the Au film. This leads to consequential nonlinear absorption via mechanisms such as two-photon absorption and free-carrier absorption within the silicon. Moreover, evidence of the onset of self-phase modulation is present. All measured results are found to be in good agreement with theoretical predictions.

  The findings presented in this thesis open new pathways for development of nonreciprocal and nonlinear nanoplasmonic devices, which are of fundamental importance to the future development of chip-scale integrated nanoplasmonic networks.

• Subjects / Keywords

  • integrated optics
  • nanofabrication
  • magneto-optics
  • waveguides
  • nonlinear plasmonics
  • magnetoplasmonics
  • plasmonics
  • nonlinear optics

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-z2cn-2f70

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.