Abstract
Society’s reliance on high speed communication continually drives industry approaches towards communication technologies with higher speed, larger bandwidth, and better power efficiency. Optical signal processing, which manipulates the optical signal without the optical-electrical-optical conversion, is considered a practical solution. To achieve high efficiency optical signal processing, Silicon-on-Insulator has been naturally considered as the best platform, due to its high Kerr nonlinearity, large refractive index, and compatibility with complementary metal oxide semiconductor technology. However, it has been assessed by numerous groups to be disadvantageous for high speeds and energy efficiency, because of its nonlinear loss induced by two-photon absorption at telecommunications wavelengths. This phenomenon results from Silicon’s small energy band gap, despite its success in photonic integrated chips integrated with electronics, aimed at replacing the copper wire for data transmission at short distances. To overcome the limitation, two-photon absorption free platforms with high nonlinear refractive index and CMOS-compatibility are sought after for integrated nonlinear photonics. In this dissertation, two platforms, silicon carbide and ultra-silicon-rich nitride, are presented. Amorphous silicon carbide deposited on insulator, using plasma enhanced chemical vapor deposition at 300°C, is evaluated as a nonlinear optical material. Possessing a band gap of 2.3 eV, the films do not exhibit two-photon absorption at wavelength of 1550 nm. The Kerr nonlinearity around 1550 nm is measured to be 4.8 ×10-14 cm2/W – one order of magnitude higher than previous results. Wavelength conversion with -32 dB conversion efficiency exploiting four wave mixing is achieved on the waveguides, and more than 25 dB conversion efficiency enhancement is demonstrated using ring resonator. Deposited by inductively coupled plasma chemical vapor deposition at 250°C, ultra-silicon-rich nitride film with large band gap (2.1 eV) which eliminates two-photon absorption and large Kerr nonlinearity (2.8 × 10-17 m2/W) is achieved. Racetrack resonator with intrinsic quality factor of 170,000 is demonstrated. Comparing with 4.5 mm long waveguide, conversion efficiency of four wave mixing is enhanced by more than 15 dB using racetrack resonator. The high quality factor combining with high Kerr nonlinearit of ultra-silicon-rich nitride, with further tuning the dispersion of the waveguides, lead to the future realization of optical parametric oscillator on the CMOS-compatible silicon nitride platform for the first time. In addition, graphene-on-silicon waveguide mode filters are proposed and studied to suppress the propagation of spurious waveguide modes, which function as auxiliary components to enhance the performance of existing mode-division multiplexing systems. Our design of graphene-on-silicon waveguide mode filters can achieve high selection and extinction ratios for a broadband spectrum around the telecommunications wavelength, hence providing low insertion losses and high signal contrasts for relatively small device footprints. They are also easier to fabricate and their performance has higher tolerance to fabrication imperfections compared to the current crop of resonant mode filters. Graphene-on-silicon waveguide mode filters demonstrated here show promise towards improving the performance of mode-division multiplexing systems, paving the way for their eventual market adoption.