Abstract
Supercontinuum (SC) is a broadband light source first observed by Alfano and Shapiro in 1970. Due to high brightness and high coherence, SC has been applied in optical coherence tomography, frequency metrology and nonlinear spectroscopy within near-IR spectrum. Apart from near-IR, mid-IR radiation can be used for free space communication, environmental sensing, and Medicine. We propose launching an optical ultra-short pulse into a silicon rib waveguide to generate mid-IR SC. The SC generation on Si waveguides relies on the third-order nonlinear optics, such as self-phase modulation, interplaying with chromatic dispersion. Compared with silica-based optical fibers, silicon has attracted the generation of SC due to high confinement and nonlinear coefficient. Meanwhile, along with the rapid development of silicon photonic technologies, a compact nonlinear optic chip is feasible to be implemented by those silicon photonic waveguides. Most importantly, silica is very lossy in the mid-IR spectrum window but silicon is transparent from 1.3μm to 9μm. Therefore, nonlinear silicon waveguides could be a promising platform to generate mid-IR SC due to its low optical loss and strong optical nonlinearity. This study includes the analysis of nonlinear optical effects in silicon, simulation, device design, device fabrication and experiment results. The wavelength of pump mid-IR pulse in the experiment was 2.2 μm. However, the repetition rate of pump only 1 kHz, causing the chip easily damaged because of too strong peak power but weak averaged power. We then alter the light source to near-IR and observed the spectral broadening from 40 nm to 55 nm. It is demonstrated that we can use such a short silicon waveguide to generate SC.