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Hybrid Silicon and Lithium Niobate Integrated Photonics
Chen, Li

2015, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
A hybrid silicon and lithium noibate (LiNbO3) material system is developed to combine the high index contrast of silicon and the second order susceptibility of lithium niobate. Ion-sliced single crystalline LiNbO3 thin film is bonded to silicon-on-insulator (SOI) waveguides via Benzocyclobutene (BCB) as the top cladding. The LiNbO3 thin films are patterned to achieve desired size, shape and crystal orientations. Integrated electrodes are integrated to confine electric fields to the LiNbO3 thin film. Empowered by the linear electro-optic effect of LiNbO3, compact chip-scale hybrid Si/LiNbO3 integrated photonic devices are enabled on the SOI platform, including radio-frequency electric field sensors, tunable optical filters, high speed electro-optical modulators for optical interconnects, and high linearity modulators for analog optical links.

Compact and metal-free electric field sensors based on indirect bonding of z-cut ion-sliced LiNbO3 thin film to silicon microrings are demonstrated. The demonstrated sensitivity to electric fields is 4.5 V m-1Hz-1/2 at 1.86 GHz. Tunable optical filters based on hybrid Si/LiNbO3 microring resonators with integrated electrodes are also demonstrated with a tunability of 12.5 pm/V, which is over an order of magnitude greater than electrode-free designs. By integrating metal thin film electrode and utilizing silicon as an optically transparent electrode, voltage induced electric fields in the LiNbO3 are enhanced. We also presented low power compensation of thermal drift of resonance wavelengths in hybrid Si/LiNbO3 ring resonators. A capacitive geometry and low thermal sensitivity result in the compensation of 17 oC of temperature variation using tuning powers at sub-nanowatt levels. The method establishes a route for stabilizing high quality factor resonators in chip-scale integrated photonics subject to temperature variations.

Gigahertz speed hybrid Si/LiNbO3 electro-optical microring modulators are enabled by optimizing the RC time constant of the biasing electrodes. Fabricated devices exhibit a resonance tuning of 3.3 pm/V and a small-signal electrical-to-optical 3 dB bandwidth of 5 GHz. Digital modulation with an extinction ratio greater than 3 dB is demonstrated up to 9 Gb/s. High-speed and low tuning power chip-scale modulators that exploit the high-index contrast of silicon with the second order susceptibility of lithium niobate are envisioned. An alternative design with x-cut LiNbO3 thin films on silicon racetrack resoantors enables compact highly linear integrated optical modulator for high spectral free dynamic range (SFDR) analog optical links. The measured third order intermodulation distortion SFDR is 98.1 dB·Hz2/3 at 1 GHz and 87.6 dB·Hz2/3 at 10 GHz. The demonstrated SFDR is over an order of magnitude greater than silicon ring modulators based on the plasma dispersion effect, and is comparable to commercial LiNbO3 Mach-Zehnder interferometer modulators, but with a footprint three orders of magnitude smaller.

The hybrid Si/LiNbO3 photonic platform is promising for applications in optical interconnections, microwave photonics, optical computing and sensing. More broadly, empowering silicon with second-order susceptibility opens a suite of nonlinear optic applications to the chip scale.
Ronald Reano (Advisor)
Joel Johnson (Committee Member)
Fernando Teixeira (Committee Member)
Gregory Lafyatis (Committee Member)
198 p.

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Chen, L. (2015). Hybrid Silicon and Lithium Niobate Integrated Photonics. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Chen, Li. "Hybrid Silicon and Lithium Niobate Integrated Photonics." Electronic Thesis or Dissertation. Ohio State University, 2015. OhioLINK Electronic Theses and Dissertations Center. 21 Sep 2017.

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Chen, Li "Hybrid Silicon and Lithium Niobate Integrated Photonics." Electronic Thesis or Dissertation. Ohio State University, 2015. https://etd.ohiolink.edu/

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