A novel lensed fiber for side-coupling of a single-mode fiber

Abstract

A novel lensed fiber for side-coupling of a single-mode(SM) optical fiber and the corresponding fabrication method were proposed, which makes the coupling assembly more compact and easy to integrate and package. The novel lensed fiber mainly composes of a portion of SM optical fiber and a portion of coreless optical fiber. The two fibers are jointed by fusing splicing. The end of the coreless fiber is shaped to have a 45 degree angled end face and polished to form a contoured curved surface. Then the contoured surface is coated so it acts as a curved reflective surface. Besides, the cylindrical surface of the coreless fiber acts as a second curved surface. The two curved surfaces compose a pair of equivalent cylindrical lens. After being focused by the equivalent cylindrical lens pair, the output spot size is comparable to the mode field radius of the SM optical fiber. Matrix optics was used to analyze the output beam parameters of the proposed lensed fiber structure. Simulation results showed that the proposed lensed fiber can bend the beam with 90 degree and make a focused spot on its side with a small spot size close to 6µm, which is suitable for fiber to photodetector chip side-coupling applications.