Fiber Bragg grating with a waveguide fabricated in no-core fiber and multimode fiber

Abstract

A new, to the best of our knowledge, method of fabricating a fiber Bragg grating (FBG) in no-core fiber (NCF) and multimode fiber (MMF) is proposed and demonstrated, achieved by writing an in-fiber waveguide before the grating inscription. This approach makes it possible to fabricate the FBG in NCF and can improve the quality of the existing FBG in MMF. The reflection peak of the FBG with a waveguide fabricated in NCF has a very good side-mode-suppression ratio of 15 dB and a narrow 3 dB bandwidth of 0.44 nm. For the FBG written in MMF, the 3 dB bandwidth of the reflection peak achieved is 0.71 nm, which is highly improved compared with that without a waveguide, which is in the order of a few nanometers. This approach opens new prospects for the applications involving the use of an FBG in various types of optical fibers.