Photonic integrated circuit: Optimization and applications.

Abstract

Photonic integrated circuit (PIC) is a device that combines multiple optical components on a single silicon chip. It leverages the properties of silicon to enable the integration of complex optical functionalities. PIC offers several advantages, including high integration density, compatibility with CMOS fabrication process, low power consumption and potential for large-scale production. They have applications in various fields such as data communication, sensing, nonlinear optics, quantum optics, etc. This thesis proposes three novel PICs that can be applied to different fields including nonlinear optics and sensing, respectively. Firstly, an unsuspended silicon waveguide platform for enhanced stimulated Brillouin scattering is proposed. The structure is optimized by using genetic algorithm (GA). By limiting the maximum etching step to two during the GA process, a simple and fabricable unsuspended structure is obtained. The optimized platform can realize large SBS gain without suspending the Si waveguide. The best gain coefficient comes from the forward SBS of fundamental TE-like mode with the value of 2462W−1m−1. This gain value is 8 times larger than the recent result. Secondly, a novel on-chip optical frequency domain reflectometry (OFDR) system is proposed theoretically and experimentally. The experiment results show that the system achieves a spatial resolution of 7.59μm, which is, to our best knowledge, the highest value achieved on-chip. The optical components in the system are designed by traditional methods and photonic inverse design approach, respectively. It is found that the footprint of the inverse-designed-components is at least 20 times smaller than the devices designed by traditional methods, which is essential for ultra-compact PIC. In addition, to further improve the detecting scheme of the on-chip OFDR system, a modified direct-binary-search (DBS) algorithm is proposed and used to design a novel monolithically integrated polarization rotator and splitter with designed power ratio. The device can fulfil both polarization rotation (TE00 to TE00 and TM00 modes) and power splitting with a designed power ratio. The measured insertion loss is less than 1 dB and the crosstalk between TE00 and TM00 modes is less than -9.5 dB. This device iv can improve the detecting scheme of our on-chip OFDR system, where the detection complexity of the system can be reduced. Lastly, mode localization is, for the first time, established in optical system. A novel sensing mechanism based on the optical mode localization effect is applied to both optical fibre system and PIC to form ultra-sensitive sensors, respectively. The experiment results exhibit at least 3 orders of magnitudes higher sensitivity than the traditional frequency-shift, which can be applied for ultra-sensitive temperature sensing and high-speed modulation.

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Identifiers

ORCID for Jize Yan: orcid.org/0000-0002-2886-2847

ORCID for Neil White: orcid.org/0000-0003-1532-6452

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