Modification of glasses and optical waveguides using high electric fields

Abstract

This thesis describes work done towards establishing efficient and reproducible second harmonic generation in thermally poled novel high-index bismuth-borate glass structures. According to the rectification model, glass with higher χ(3) values than silica would permit χ(2) to scale up proportionally, for a given frozen-in electric field strength. The fundamental research on poling induced nonlinearity has been extended to investigate several compositions of Bi₂O₃ZnOB₂O₃ glass systems, whose refractive index is measured to increase with the Bi₂O₃ content. Intrinsic third-order optical nonlinearity χ(3) up to thirty times higher than silica have been measured in bismuth-based compounds, and even larger values are potentially achievable.

In this thesis, a reliable procedure to induce large and stable second order nonlinear coefficient χ(2) in bismuthate glasses has been established along with the understanding towards efficient generation of second harmonic power in waveguiding layers. Characterization methods to determine the nonlinear formation dynamics and resolve nonlinear thickness and profile has been optimized to quantify the magnitude and distribution of second order nonlinearities in thermally poled bismuthate glasses. The development of a new poling procedure, where the applied voltage is varied during the cooling phase, instead of being kept constant, has allowed a record value of χ(2) = 2.3 pm/V in 12.5% Bi₂O₃ bulk samples to be achieved. The control of nonlinear region evolution gained by establishing the innovative time-varying voltage poling procedure has led to the first demonstration of second-order nonlinearity value as high as 2 pm/V induced by thermal poling in bismuthate sputtered slab waveguides.

These achievements opened new investigations towards realizing efficient monolithic structures leading to high performance active devices based on poled bismuth-based glass waveguides. In particular, an all-glass electro-optic modulator and a frequency doubler have been targeted, based on sputtering and femtosecond laser direct writing, respectively.

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Identifiers

ORCID for James Wilkinson: orcid.org/0000-0003-4712-1697

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