Non-magnetic optical non-reciprocal devices are benefit for constructing optical information processing networks for weak signals without using an external magnetic field. This paper experimentally observed non-reciprocal transmission of electromagnetically induced transparency (EIT) in a cesium atomic gas through laser excites a Λ-type three-level atomic system.
With the help of cesium atoms, which have several advantages over other alkali atoms, including a rich and readily adjustable energy level structure, bigger ground state hyperfine energy levels, and lower saturation light intensity. 894.596nm laser as probe light excited energy level 6S_1/2(F=4) to 6P_3/2(F=5), 894.594nm laser as coupling light is divided into two beams to excite energy level 6S_1/2 (F=3) to 6P_3/2 (F=5), the coupling light entered the cesium atomic gas cell from two directions: either collinearly, in the same direction as the probe light, or in the opposite direction. The probing light that interacted with the coupling light inside the cesium atomic gas and then was detected by the detector avalanche photodiode, and the outcomes were shown and measured on an oscilloscope.
The experiment observed non-reciprocal transmission of EIT, proved optical signal isolation in a cesium atomic system. Under the experimental conditions, a series of experiments were conducted on the regulation of the optical non-reciprocal isolation ratio at room temperature by adjusting the powers of the probe and coupling lights as well as the detuning. The research analyzed the impact of adjustable parameters on the non-reciprocal isolation ratio. It has been demonstrated that moderate probe light power helps maintain the intensity of EIT in the absorption intensity curve, ensuring a high isolation ratio, which provides a reference for the performance metrics of optical isolators. The observed isolation ratio increases with the increase in coupling power, consistent with theoretical calculations. Within a certain range of coupling light power, a high-performance optical non-reciprocal system is achieved. This trend is exactly in line with the trend of EIT signal strength variation during co-directional coupling light excitation. A maximum isolation ratio 26dB was obtained when many parameters are appropriate. It revealed that in coherently prepared cesium atom systems, optically tunable parameters can provide an effective means for achieving ideal optical isolation with a high isolation ratio. Compared to existing research on high isolation ratio cavity-free non-reciprocity based on atomic coherence, our proposed experimental scheme can be conducted using a three-level system at room temperature. With the development of chip-level integrated gas cells, it becomes easier to achieve miniaturization and system integration, providing experimental support for the miniaturization and integration. This provides a certain basis for exploring high-performance non-reciprocal devices with high isolation ratios and offers new perspective for designing the next generation of optical equipment.