Optical Isolation In Chip-based High-Q Silica Miacrocavities

Optical isolator is vital in optical communication,signal processing,laser protection and logic computation and it will be an indispensable optical element for all-optical integration in the future.The miniaturization and chip integration of the optical isolator have become a hotspot in optical research field.So far,the optical isolators have been achieved in the types of waveguides or whispering gallery mode(WGM)micro-cavities.The waveguide-type optical isolators require long-range interaction,which make it challenging for the integration.However,the size of micro-cavity is in order of microscale,and could be scaled down to several hundred nanometers in some special structures,which can greatly enhance the miniaturization of the optical isolators.Here,we employ high-Q silica optical micro-cavities as a platform for the realization of chip-based optical isolation.This thesis mainly consists of two optical isolation experiments.One of them is implemented based on gain saturation of doped rare earth ions,and the other one is based on optical parametric amplification.In the first experiruent,we realize optical isolation based on the gain saturation effects in the erbium-doped silica micro-cavities.The gain of the signal light is determined by the distribution of erbium ions at different energy levels.Moreover,the stimulated emission and stimulated absorption caused by the pump or signal lights,can also change the distribution of the erbium ions.So,the gain of the signal light is related with its own intensity.Based on this effect,we design an erbium-doped high-Q micro-toroid cavity coupled with two tapered optical fibers under different coupling efficiencies.We have verified the feasibility of this mechanism and realized the chip-based optical isolation using one active optical micro-cavity.In the second experiment,we achieve a chip-based optical isolator in a high-Q silica micro-toroid resonator by exploiting phase-matched parametric amplification in four-wave mixing.Due to the condition of momentum conservation,the signal light is affected only when its transmission direction same with the pump light,while the signal light incident from the opposite direction stays intact.This isolation mechanism can work when the forward and backward signal light incident at the same time.We studied the effect of pump or signal light on isolation effectiveness under different operation conditions,and proved that it was a "true" optieal isolator experimentally.