Detrimental Fluctuation of Frequency Spacing Between the Two High-Quality Resonant Modes in a Raman Silicon Nanocavity Laser

To understand how we can maximize the fabrication yield, we study the fluctuations of the cavity parameters of an ultralow-threshold Raman Si laser that employs two high-quality resonant modes of a photonic crystal heterostructure nanocavity. We measure the quality (Q) factors, the resonant wavelengths (lambda), and the frequency spacing between the resonant modes (Delta f) for 40 nanocavity-based Raman Si lasers with the same design. The Q, lambda, and Delta f fluctuate due to random variations of the cavity geometry and we find that 12 out of 40 devices provide laser emission. While the fluctuations of Q and lambda in these 12 cavities are basically the same as those in the other 28 cavities, the detuning between Delta f and the Raman shift of Si for the 12 cavities is less than 0.024 THz, which is strictly smaller than the detuning for the other 28 cavities. A large fluctuation of Delta f is, thus, detrimental for the yield of Raman Si lasers. Numerical simulations reveal that a decrease in the random variations of the air hole positions and radii is important for high yields.