All-Optical Modulation in Si Quantum Dot-Doped SiO Micro-Ring Waveguide Resonator

Abstract

The Si quantum dot-doped SiO $_x$ rib waveguide-based free-carrier absorption (FCA) modulator with enhanced all-optical modulation depth is demonstrated by integrating with a micro-ring waveguide resonator. The micro-ring waveguide resonator with a Q-factor of 6×103 induces a throughput transfer function in wavelength domain, such a transmittance notch can be blue-shifted by varying the excited free-carrier density of Si-QD. When injecting the continuous-wave probe at central wavelength of the transmittance notch, the probe signal can be inversely modulated by optically pumping the micro-ring waveguide resonator to blue-shift the notch away from its original wavelength. By optimizing the pump wavelengths, the largest FCA loss and highest free-carrier density can be enhanced to 2.9 cm−1 and $7.83\times 10^{16}$ cm−3, respectively. With the excited free-carrier density of $\sim 1.3\times 10^{16}$ cm−3 inside the micro-ring waveguide, the maximal wavelength of the transmittance notch can be blue-shifted by 0.033 nm. The optical pumping also induces the broadened linewidth of transmittance notch from 0.25 to 0.27 nm. With the integrated micro-ring waveguide resonator, the all-optical modulation depth can be further enhanced from 52.5% to 63.5% by shifting the notched transmission spectrum of the micro-ring waveguide with the excited free-carrier density of Si-QD at probe wavelength of 1563.5 nm.