Compact Long-Period Fiber Gratings Based on Periodic Microchannels

A novel formation method of long-period fiber gratings (LPFGs) based on periodic microchannels, which are fabricated by femtosecond laser micromachining and selective chemical etching in conventional single-mode fibers, is proposed and experimentally demonstrated. This kind of grating may be as short as only 3 mm and exhibits low-temperature sensitivity of 9.95 pm/
^°
C from 30
^°
C to 120
^°
C. The strain sensitivities of the resonant wavelength and peak loss are -2.4 nm/mε and -3.5 dB/mε, respectively. High refractive-index (RI) sensitivity with one order of magnitude larger than that of the conventional LPFGs near RI=1.33 is achieved in general single-mode fibers.