The influence of optical signals in the crosstalk optical path of the coupler

The efficiency of the conversion of the conduction mode into the cladding mode in the fiber k is the condition that no radiation occurs. D is the diameter of the nth reflection of the light in the tapered fiber: where is the angle between the incident light and the fiber axis, which is the tapered fiber Angle of half cone. n and n are the refractive index of the core layer and the cladding layer, n is the number of reflections in the core when the light becomes leaking light, and l is the length of the cone. When the coupler acts as a splitter (that is, BA), the light is incident from the small end of the tapered fiber, and the incident fiber will not become leaked light; when the fiber is used as a combiner (that is, AB), the coupler is made At this time, the size parameters a and a1 of the tapered fiber at both ends are selected by calculation to meet the condition that the light does not radiate.

The index of the coupler The important indexes of the fiber coupler are additional loss, insertion loss, channel uniformity and crosstalk between channels. Additional loss and insertion loss The additional loss is mainly due to various factors at the fiber connection at both ends, including the non-parallel end faces of the two fibers, imperfect end-face processing, and incomplete collimation of the two fibers. During the tapering process, the bending deformation of the optical fiber also causes radiation loss. All these factors are closely related to the control of the process. Due to the geometry of the coupler, the incomplete matching of the light-receiving areas of the optical fibers at both ends brings basic losses. The additional loss and insertion loss are defined as, where P is the sum of the output power of each port, P is the output power of the i-th port, and P is the total input power. It is the coupling efficiency of the end reflection, the coupling efficiency of various additional loss factors at the junction of the two ends, and the coupling efficiency of the geometric structure itself, that is, caused by the mismatch of the area of ​​the two fiber end surfaces, and their values ​​are among them, n is the The refractive index of the medium, d is the diameter of the fiber at the A and B ends, respectively. Uniformity of the coupler channel The channel uniformity is defined as the optical report, where P and P are the minimum and maximum output power of each port, respectively. Coupler Crosstalk Coupler crosstalk is the effect of a certain optical path on the optical signals in other optical paths. Crosstalk is defined as a combiner where P is the input power of the i-th port and P is the output power of the j-th port.