# Effect of Fiber Optic Plate on Centroid Locating Accuracy of Monocentric Imager
## 1 Introduction  
The fiber optic plate (FOP) is a large-area array rigid passive fiber optic image transmission element composed of millions of fibers arranged in a hexagonal shape, with a compact and stable structure. In theory, each fiber optic transmits light independently as a unit without interfering with the others. The output end face of FOP is aligned with the input end face. The FOP thickness is thin; that is, fiber optic transmission channels are short. Therefore, the FOP has lower transmission signal loss, higher transmittance and better image transmission performance. The most important advantage of FOP is that it can achieve one-to-one signal transmission between the input and output end faces of different shapes. According to actual requirements of image surface characteristics, we can prepare the input-output end surface of a FOP as a spherical-planar surface, a planar-spherical surface, a curved-curved surface, a planar-planar surface and other forms.  
Engineering practice shows that monocentric imagers have the characteristics of light weight, miniaturization and larger fields of view for imaging than traditional imaging systems under the same circumstances [1, 2]. There is no need to correct the curvature of field when the image quality of the monocentric imager needs be optimized, because the symmetry in a monocentric lens cancels out most of the geometrical aberrations [3]. However, current large-area array image sensors are basically flat and cannot be fully coupled with the spherical focal surface. FOP can solve this problem well. We can prepare the input-output end surface of an FOP as a spherical-planar surface according to the actual needs of monocentric imager, which not only realizes the coupling between the spherical focal surface and image sensor, but also realizes the large-format imaging of hundreds of millions or even billions of pixels by splicing multiple FOPs through a specific spatial layout. [PERSON]'s team at the University of California used the structure of fiber-coupled monocentric lens imaging to develop an ultra-wide-angle 30 Mpixel panoramic imager with a 126\({}^{\circ}\) \"letterbox\" format field of view [2, 3, 4, 5]. The research and applicationsof monocentric imagers are currently mainly aimed at the ground-based field, and the research in the space-based field for space target imaging has not been reported yet. In the field of the space-based space target surveillance, the monocentric imagers with FOPs as relay image transmission elements can realize the detection of space targets in a large field of view, and the FOP has the characteristics of miniaturization, reliability, etc., in line with the requirements of the aerospace environment. However, the addition of FOPs will inevitably increase the error of the centroid positioning of the spatial point target. It is of great significance to analyze the influence of FOP on the centroid locating accuracy (CLA) and to reduce the loss of CLA caused by the addition of FOPs by choosing a suitable FOP scheme.  
In this paper, according to FOP structural characteristics, we construct a two-stage discrete coupling model of the spherical, focal surface (FOP) image sensor and analyze the influences of FOP parameters, including the fill factor and the fiber diameter, and FOP in-plane displacements, including rotation and translation on CLA. Finally, we get the FOP scheme that can achieve the best CLA.