Transformation and amplification of light modulated by a traveling wave with a relatively low frequency

Abstract

The behavior of electromagnetic waves in a medium modulated in time and space, largely investigated decades ago, has recently attracted renewed interest. Here, we address an intriguing problem of this research: can light with an initial frequency ω0 be amplified solely pumped by a traveling wave with a much lower frequency ωp≪ω0? Generally, the bandwidth of the modulation-induced optical frequency comb spectrum can be substantially broadened when the phase velocity of the traveling wave, vp, approaches the phase velocity of light, v0. However, in realistic photonic waveguides, the amplification effect remains small due to the unfeasible modulation and waveguide parameters required. In contrast, we demonstrate that modulating an optical resonator by a traveling wave having the frequency ωp and phase velocity vp much smaller than the frequency ω0 and phase velocity v0 of light can result in large light amplification accompanied by conversion to multiple comb lines within a relatively small frequency band.