In this paper, the coupling between self-focusing lens and optical fiber and the coupling between optical fiber collimators are discussed, the loss of optical fiber collimators is calculated and measured, and the improvement method is put forward. The application research, latest progress and existing problems of self-focusing lens in coupling system, collimation system, imaging system, speculum system, measurement system and interference system are discussed.

Self-focusing lens, also known as gradient index lens, is a very key technology. This kind of lens is amazing: we generally know that lenses are spherical or curved, such as magnifying glasses, and the glasses we wear are curved, while self-focusing lenses do not need curved surfaces, and the effect of spherical lenses can be achieved through two planes. Its principle is to bend the light by gradually changing the refractive index inside the lens. The size of self-focusing lens can be much smaller than that of conventional spherical lens, which is suitable for optical fiber coupling and beam control.