# Nanobeam Cavities for Reconfigurable Photonics

 dc.contributor.advisor Loncar, Marko dc.contributor.author Deotare, Parag dc.date.accessioned 2012-11-19T16:13:55Z dash.embargo.terms 2012-12-18 en_US dash.embargo.terms 2012-12-18 dc.date.issued 2012-11-19 dc.date.submitted 2012 dc.identifier.other http://dissertations.umi.com/gsas.harvard:10414 en dc.identifier.uri http://nrs.harvard.edu/urn-3:HUL.InstRepos:9920635 dc.description.abstract 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. en_US dc.description.sponsorship Engineering and Applied Sciences en_US dc.language.iso en_US en_US dash.license LAA dc.subject electrical engineering en_US dc.subject optics en_US dc.subject nanobeam en_US dc.subject optomechanics en_US dc.subject photonic crystals en_US dc.title Nanobeam Cavities for Reconfigurable Photonics en_US dc.type Thesis or Dissertation en_US dc.date.available 2012-12-18T08:30:29Z thesis.degree.date 2012 en_US thesis.degree.discipline Engineering Sciences en_US thesis.degree.grantor Harvard University en_US thesis.degree.level doctoral en_US thesis.degree.name Ph.D. en_US dc.contributor.committeeMember Capasso, Federico en_US dc.contributor.committeeMember Hu, Evelyn en_US

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