Near-infrared frequency comb generation from a silicon microresonator

Abstract

Optical frequency combs (OFCs) have been widely explored in the silica and silicon nitride platforms, from visible light to mid-infrared wavelength. Although silicon has a larger nonlinear coefficient, it suffers from larger two-photon absorption and consequent free-carrier absorption. Therefore, microresonator-based OFCs have not been experimentally demonstrated in the silicon platform with a single pump in the near-infrared region. Here, we experimentally demonstrated the Kerr comb generation (KCG) in a high-quality-factor silicon microresonator using sub-milliwatt pump power without any reverse bias for removing the free carriers. We experimentally investigated the effects of pump powers and quality factors (Qs) on the comb output power and number of comb lines. Under low pump power, either larger pump power or larger Q can yield higher comb output power and more comb lines. However, at higher pump powers, the comb output power is limited by nonlinear absorptions. The KCG was well established by using pump wavelengths in the range from 1340 nm to 1650 nm. The further combination of this microresonator with a p-i-n diode is possible to obtain considerable comb output powers. This work shows the possibility of microresonator-based OFCs in silicon chips at telecom wavelengths.