Enhancement Of Optical Nonlinear Effects Based On Silicon Plasmonic Waveguides

Silicon photonics is the most promising platform to overcome the intrinsic bandwidth and power density bottlenecks of integrated electronics. It has been one of the most active disciplines within the field of integrated photonics. However, in the process of further development, new stumbling blocks emerge. The sizes of photonic devices are restricted by the diffraction limit and thus result in a strong mismatch between photonic and electronic components in their co-integration. In addition, lack of second-order nonlinearity and existence of free carrier effects in silicon tend to limit the versatility and operating speed of nonlinear optical signal processing, which plays a key role in multiple photonic functionalities.Plasmonics is a good candidate to overcome the first obstacle due to its ability to confine the optical field into nanoscale beyond the diffraction limit. Moreover, the localized strong field enhancement in plasmonic structures enhances interaction of light and matter, which is promising for enhancing the efficiency and reducing the power consumption in nonlinear applications. For the second limit, organic materials with large nonlinear susceptibility and free of carrier effects have attracted a growing attention in the last years and their integration on silicon have been proposed to be an efficient silicon organic hybrid platform.In this dissertation, we combine the plasmonic and organic technologies onto the silicon photonics platform to investigate silicon plasmonic organic structures and explore the nonlinear effects induced in them. Silicon plasmonic organic structures, which combine the advantages of silicon with the ultra-compact and strong-field performance of plasmonics and the ultrafast and large-nonlinearity property of organic materials, enable highly efficient nonlinear effects within short lengths and with low pump powers and thus have great potentials for nonlinear integrated optics. This dissertation addresses the use of two kinds of plasmonic waveguides:plasmonic slot waveguides (PSW) and hybrid plasmonic waveguides (HPW). Detailed research contents are as follows:(1) A full-vectorial nonlinear coupled-wave equation model which is valid for lossy waveguides is proposed and then used to analyze various nonlinear effects in silicon plasmonic waveguides.(2) In the PSW, we firstly proposed an enhanced second harmonic generation (SHG) process. A normalized efficiency up to 105 W-1cm-2 is predicted, which is four orders of magnitude higher than those previously reported. Then, by applying two electrodes onto the two sides of PSW, the SHG process can be controlled by the voltage, which is proposed to be a new mechanism for high-speed electro-optic modulation. Another nonlinear effect investigated in PSW is the optical rectification (OR) effect, through which an electrical signal is generated between the two metal slabs when an intensity modulated optical signal is injected into the PSW. This efficient OR process supports flat response for a wide range of wavelength, which can be applied for the realization of high-speed broadband optical detection and demodulation.(3) Besed on HPW, an enhanced mid-to-near-infrared SHG is also explored. The SHG yield is as large as 8.8% for a pumping power of 100 mW and a short length of 120?m. Then, by utilizing the resonant effect in a microring, the efficiency is further enhanced by two orders of magnitude. This provides a potential route for realizing efficient frequency conversion between mid-infrared and near-infrared wavebands on a chip. Besides, efficient optical parameter amplification (OPA) is also studied in a symmetric HPW. Based on the OPA, phase regeneration of phase-shift keying signals is then theoretically proposed.(4) Finally, the design, fabrication and characterization of PSWs are also described for the demonstration of OR effect. The fabricated PSW have good performance in terms of linear loss. The measure losses are very near to the theoretical values. By spin-coating the commercial available second order nonlinear polymer, the nonlinear response of the PSW is under testing at the present writing time.