Narrow Results

The pulse evolution of mid-infrared optical parametric oscillator based on silicon-on-insulator (SOI) waveguides is numerically investigated. The properties of pulse evolution in the process of optical parametric oscillation have been described. The numerical results show that the threshold of the optical parametric oscillation cavity can be lowered due to the high nonlinearity of the waveguide. The parametric signals initiate to oscillate when the circle trip number is 5 with the appropriate length of the SOI waveguide 7 mm. Meanwhile the peak power of the output signal pulse can be reached to 400 W at the stable situation when the circle trip number is over 10 with the conversion efficiency as high as 5%. This research can supply a kind of way to generate the mid-infrared femtosecond pulse at the highly stable on-chip integration level.

The femtosecond pulse propagation and free carriers’ evolution in the silicon-on-insulator (SOI) waveguides have been numerically investigated considering the carrier’s lifetime and the pulse width of the input pulse at 1.5 $\mu$m regime. Numerical results show that the free carriers’ density profile becomes gentle between the leading edge and trailing edge of the pulse in time domain due to the decreasing of the pulse intensity caused by the nonlinear absorption, which becomes more remarkable when the pulse width expands. It can be found that lifetime ranging from 5 ns to 100 ns does not affect the free carriers’ evolution clearly in femtosecond regime. In addition, the refractive index modulation can be appeared in the process of pulse propagation and free carriers evolution with lower peak power of 200 W. This research can supply some contribution to the insight of free carriers evolution in SOI waveguides.

Raman scattering in air-covered and SiO₂-covered Silicon-on-insulator waveguides of 1.25 cm length, 220 nm height and two widths of 2 μm or 0.45 μm was investigated. A continuous wave (CW) Raman fiber laser at 1454.8 nm with linewidth of <0.1 nm was used as a pump source. The coupling efficiency was estimated to be around 10% for one end facet. Spontaneous Raman shift of 521 cm^-1 (1574.2 THz) scattering was observed at 1573.8 nm for SOI waveguides in air and 1574.2 nm for waveguides covered with SiO₂ at pump power of <1.5 mW inside both waveguides of 2 and 0.45 μm. Anti-Stokes scattering was observed at 1352.8 nm with pump power of 16 mW. The stimulated Raman gain was calculated from spontaneous Raman efficiency. Total Raman on-off gain was determined to be 0.6 dB for waveguide with width of 2 μm and 1 dB for waveguide with width of 0.45 μm.