An object beam divided by a light division means (12) is caused to enter an optical fiber (23) and the object beam emitted from the optical fiber (23) is then caused to enter a photo-refractive polymer layer (6). On the other hand, a reference beam divided by the light division means (12) is irradiated on the photo-refractive polymer layer (6) from the opposite side. In this manner, the object beam is superimposed on the reference beam in the photo-refractive polymer layer (6) to form an interference pattern or fringe corresponding to the strength of light intensity. The interference pattern is recorded on the photo-refractive polymer layer (6) as a diffraction grating (4). This diffraction grating (4) exhibits a specific characteristic to emit the object beam emitted from the optical fiber (23) in the direction of the reference beam, namely parallel to an optical axis of the optical fiber (23).