Numerical simulation of coupling characteristics of optical fiber with a rectangular hole

The optical fiber with a rectangular hole is proposed. The coupling characteristics of the optical fiber are analyzed and discussed using beam propagation method (BPM). Firstly, the coupling light intensity of the rectangular hole is analyzed. Secondly, the power conversion between the fiber core and the rectangular hole and the periodicity of the power conversion are discussed in detail, respectively. Finally, we study the sensing response of the optical fiber to the surrounding refractive index. The results show that the coupling efficiency are stronger in n rec > n core than in n rec ⩽ n core from the fiber core to the rectangular hole and can reach nearly 50%. The properties are benefited in realizing the surrounding sensing of a high refractive index and increasing the sensing sensitivity of the sensor. Furthermore, the research results also indicate that the compound modes are produced and transmitted in the area between the fiber core and the rectangular hole. Then, they will be converted into fiber modes when the light power is coupled from the rectangular hole to the fiber core. Therefore, The proposed optical fiber has the potential application value in high refractive index sensors and mode converters.