Dear Wenjie Jiang , the best way to couple a image to a fiber is focusing the image on the surface of the fiber end. To do so a convergent lens is placed after the image and before the fiber, the distance between the lens and the fiber must be equal to the focal distance of the lens.

Hope it helps.

How to get maximum coupling efficiency of the light, comming out of the image area ? In any case you must produce reimaging of your image on the fiber end by the lens. The required lens power and the distances from image to the lens and from the lens to the fiber end one can calculate using lens formula and considering the required magnification and numerical aperture of the fiber. But coupling efficiency will depend on light source - natural or coherent, collimated or not. In the case of coherent light efficiency can be 100%, minimum efficiency we get with diffuse noncoherent light from the image. In the last case to increase efficiency we must use lens and fiber with maximum available numerical aperture.

to couple a image to a fiber is focusing the image on the surface of the fiber end by convergent lens is placed after the image and before the fiber