Adiabatic Frequency Conversion

Changing the frequency of light outside the laser cavity is essential for an integrated photonics platform, especially when the optical frequency of the on-chip light source is fixed or challenging to be tuned precisely. To achieve continuous on-chip optical frequency conversion, we apply adiabatic frequency conversion to a lithium niobate ring resonator. To be specific, we fabricate Lithium niobate ring resonator with a pair of electrodes on the side of the waveguide, which can apply electric field to change the refractive index of the waveguide based on Pockels effect, resulting in resonance shift. The light trapped inside the cavity will also shift its frequency together with the resonance. Just like tuning the frequency of sound on a vibrating guitar string by changing the string length! To achieve continuous frequency tunning, we only need to adjust the voltage applied. In this work, frequency shifts of up to 14.3 GHz are achieved by adjusting the voltage of an RF control. With this technique, we can dynamically control light in a cavity within its photon lifetime by tuning the refractive index of the ring resonator electrically, which will have potential application in Frequency Modulated Continuous Wave (FMCW) Lidar.