Tapered silicon core fibres for optical parametric amplification and wavelength conversion in the telecom band

Abstract

Silicon waveguides have been investigated widely for nonlinear photonics because they have high nonlinear coefficients and can be fabricated with low cost. Among the different platforms for silicon waveguides, silicon core fibres show excellent nonlinear behaviour and also offer potential for seamless integration with other fibre-based devices. In this thesis, silicon fibres with polycrystalline core materials were fabricated via a conventional molten core drawing method. To obtain high nonlinearity, the polysilicon core fibres were subsequently tapered down to have small sub-micron metre core diameters (800 nm to 1.5 µm) and low transmission losses less than 3 dB/cm. After optimisation of the twostep tapering method, several polysilicon core fibres were characterised. Firstly, two submicron sized silicon core fibres with different waist lengths were tapered using the optimized method. Broad-band wavelength conversion using a continuous wave pump in the telecom band was realized, with a bandwidth covering from the S- to L- band, and conversion efficiencies of -30 dB. Then, another silicon core fibre with its dispersion engineered for optical parametric amplification based on four wave mixing was obtained. An optical on-off parametric gain of up to 9 dB was demonstrated, which we believe is the largest parametric gain observed in any crystalline silicon waveguide when using a telecom pulsed pump source. Moreover, 20Gb/s QPSK signals at both the C- and L- band have been successfully converted with the power penalties at a BER of 3.8 ×10⁻³ less than 1 dB. These results highlight the potential of silicon core fibres for use in nonlinear signal processing within future telecommunication system

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ORCID for Anna Peacock: orcid.org/0000-0002-1940-7172

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