Deep-notch, ultracompact long-period grating in a large-mode-area photonic crystal fiber

An extremely short long-period grating (LPG) with strong resonance has been developed in a large-mode-area photonic crystal fiber (PCF) by use of the heat source of a CO2laser. We believe that such a LPG in pure silica PCF is the first example to be obtained with the point-by-point technique. The fabrication method is simple and repeatable. The resulting LPG has 8 periods, written by a CO2laser, within a 2.8-mm length of fiber, which yields a deep notch of core-cladding mode coupling of -31.5 dB at the telecommunication wavelength of 1529.2 nm, with a FWHM of ∼0.7 nm. The principal advantages of this LPG are that it is practical, cost effective, and compact.