Experimental Demonstration of Optomechanically Induced Non-reciprocity

Abstract

Non-reciprocal devices, such as circulators and isolators, which allow light to pass in specified direction but block light in the undesired direction, are indispensable components in classical and quantum information processing in photonic integrated circuits. However, the integration of the conventional optical non-reciprocal devices, which employ the magneto-optical Faraday effect, is technically challenging because of material incompatibilities and the large footprint of such device designs. In recent years, there has been growing interest in the realization of non-reciprocal photonic devices without magnetic materials. Here, we experimentally demonstrated non-magnetic non-reciprocity using optomechanical interactions in a whispering-gallery microresonator, as proposed by Hafezi and Rabl. In this approach, the travelling wave nature of the microresonator produces a rise in the degenerate clockwise (CW) and counter-clockwise (CCW) travelling-wave optical modes. For the optomechanical interaction, the CW and CCW modes are independently coupled with the mechanical mode. Only when the optical driving and signal fields are coupled to the same optical mode, the coherent conversion between signal photon and phonon is enabled. As a result, the directional driving field breaks the time-reversal symmetry and leads to non-reciprocal transmittance for the signal light. In a fiber coupled silica microsphere system, we observed optomechanically induced non-reciprocal transparency (OMIT) and amplification (OMIA), and demonstrated a non-reciprocal phase shift of up to 40\(^{\circ }\).