Sub-milliwatt optical frequency combs in dual-pumped high-Q multimode silicon resonators

Abstract

We experimentally study the generation of optical frequency combs (OFCs) in dual-pumped high-quality factor (>106) multimode silicon racetrack resonators and show that sub-milliwatt (0.3 mW) input pump powers were sufficient to produce six-order OFC generation with eleven peaks, even in waveguides with normal dispersion. The low pump power and enhanced efficiency of the OFC generation can be attributed to mode coupling between two mode families of the multimode resonator, which acts to change the effective magnitude and the sign of the local dispersion of the resonator. We experimentally observed that the OFC generation had 3.6 times more peaks and 12.1 dB higher conversion efficiency than that without any bias. We compared the efficiencies of the OFC generation at different pump wavelengths within and beyond the mode coupling region. At low pump powers circulating in the resonator, pump wavelengths in the mode coupling regime produced 1.3 times more peaks and 8 dB enhancement in conversion efficiency than pumping beyond the mode coupling regime. The experimental results were consistent with the theoretical simulations by solving the modified Lugiato–Lefever equation.

Near-infrared frequency comb generation from a silicon microresonator

“…Theoretically, based on a modified Lugiato-Lefever equation, recent simulation work using a nanoscale silicon microresonator with a diameter of 230 µm and a p-i-n diode structure along the microresonator to reduce the effective lifetime to picosecond level exhibits the broadband comb spectrum with further increased pump power to several tens of milliwatts [39]. Our recent work also demonstrated the efficiency of the reverse bias to enhance the performance of the KCG in silicon resonators [40]. Therefore, a reverse-bias-based configuration in the resonator to mitigate the free carriers may further increase the comb output powers by 10 dB [33,40].…”

“…Our recent work also demonstrated the efficiency of the reverse bias to enhance the performance of the KCG in silicon resonators [40]. Therefore, a reverse-bias-based configuration in the resonator to mitigate the free carriers may further increase the comb output powers by 10 dB [33,40]. And further increasing the diameter of the microresonator is necessary to get the broadband comb spectrum [39].…”

“…Recent numerical work predicts the possibility of the KCG in the silicon microresonators with nanoscale dimensions at near-infrared wavelengths, and they propose to use a reversebiased p-i-n junction to reduce the carrier lifetime to several tens of picoseconds to minimize the impact from the FCA [39]. Until now, in the telecom band, few experimental demonstrations on the KCG in the silicon microresonators except for our initial demonstration of the near-infrared KCG in the silicon microresonators with dual pumps and different reverse bias voltages recently [40]. Another recent work using silicon photonic crystals achieved the OFCs with a pump wavelength around 1538 nm and input power of 5 dBm [41].…”

Broadband high-Q multimode silicon concentric racetrack resonators for widely tunable Raman lasers

“…Conventional multimode racetrack resonators consist of one multimode bus waveguide and one multimode racetrack. In such multimode racetrack resonators, the fundamental mode can couple to the higher-order mode in the multimode bends, leading to the reduction in Q factors of the fundamental mode-based resonances 44 – 46 . This is a well-known problem and has been previously tackled by using single-mode bends 47 , 48 , Euler bends 42 , 43 , 49 , and Bezier bends 50 to suppress the higher-order modes at the bends and maintain a high Q factor for the fundamental mode.…”

Investigation of low-power comb generation in silicon microresonators from dual pumps

“…Therefore, silicon-chip-based comb generation has been investigated and demonstrated in the midinfrared region with a reverse-biased p-i-n junction structure to help with the removal of free carriers from three-photon absorption [28][29][30][31][32]. At telecom wavelengths, early attempts on silicon comb generation have just been reported in recent work using microresonators with reverse-biased p-i-n diodes: one theoretical work using nanoscale resonators [33] and our preliminarily experimental demonstration in multimode resonators [34].…”