Polymer-based integrated photonic devices for interconnects




Pan, Zeyu

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Integrated photonic devices based on optical waveguides have been extensively studied for various applications, especially the high-speed intra- and inter-chip interconnects. Usually, a waveguide contains a core with high refractive index and cladding with lower refractive index. Among various waveguides, silicon, polymer, and silicon-polymer hybrid devices are the most promising candidates for low cost, small size, light weight, and low power consumption (CSWaP) optical interconnect. Firstly, silicon-based optical devices can be fabricated using CMOS compatible nanofabrication technology, which is already widely used to manufacture integrated circuits. Silicon photonic devices can have very small footprint and enable high density photonic circuits, due to high refractive index contrast. However, one of the intrinsic obstacles is the absence of χ⁽²⁾-nonlinearity in unstrained silicon due to its centrosymmetric crystal structure, making modulating photons on silicon platform a great challenge. Secondly, polymer-based devices have been found very attractive, owing to the advantages of high thermo-optic (TO) or electro-optic (EO) coefficient, high transparency in the telecommunication wavelength windows, and fabrication feasibility over large areas on printed circuit board (PCB) or other kinds of substrates. The roll-to-roll (R2R) compatible imprinting and ink-jet printing for developing polymer-based devices on flexible or rigid substrates enable large-area, light-weight, low-cost optical interconnects. However, due to the low refractive index contrast, the polymer photonic devices always require large footprint. Finally, the silicon-organic hybrid (SOH) platform enables the marriage of the best of these two materials and thus has been receiving substantial attention. In this dissertation, integrated photonic devices based on silicon, polymer, or hybrid platform will be presented. First, high-efficiency quasi-vertical tapers for polymer waveguide based inter-board optical interconnects will be demonstrated. A triangular-shape tapered structure is adopted above the waveguide core to transform a fiber mode into a single mode polymer rib waveguide mode as an optical mode transformer. A coupling loss of 1.79±0.30 dB and 2.23±0.31 dB per coupler for the quasi-TM and quasi-TE mode respectively have been experimentally demonstrated, across the C and L bands (1535 nm – 1610 nm). Then, a reconfigurable thermo-optic polymer switch based true-time-delay network will be analyzed and demonstrated. Thirdly, I will show a novel subwavelength-grating waveguide ring resonator based high-speed modulators, which is the largest bandwidth and the most compact footprint that has been demonstrated for the ring resonators on the silicon-organic hybrid (SOH) platform. Finally, the on-chip time-division multiplexing and de-multiplexing system will be designed and analyzed.


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