Optical fiber couplers generally have the following characteristics: First, the device is composed of optical fiber, which is an all-fiber device; second, the demultiplexing and combining of the optical field are mainly realized by mode coupling; third, the optical signal. Optical fiber couplers generally have the following characteristics: First, the device is composed of optical fiber, which is an all-fiber device; second, the demultiplexing and combining of the optical field are mainly realized by mode coupling; third, the optical signal. When using fiber optics, one often needs to use fiber couplers for various purposes. Some examples: A coupler can be used as a splitter to couple out some portion of the light circulating in the resonator of fiber laser, for example. Directional 2 × 2 couplers (see Figure 1) are usually used for. Optical fiber coupler is a kind of optical fiber passive device used for transmitting and distributing optical signal. Longitudinal misalignment Longitudinal misalignment occurs when fibers have same axes but their end faces are separated by distance ‗S'. It is like an invisible "traffic command", silently completing the distribution and combination of optical signals in scenarios such as 5G base stations, data centers, and optical fiber sensing, supporting.