Arc-Induced Long-Period Fiber Gratings in the Dispersion Turning Points

Abstract

We demonstrated the possibility to inscribe longperiod fiber gratings (LPFGs) in a B/Ge codoped fiber by using grating periods shorter than 150 μm. We also have arc-induced in the SMF 28 fiber an LPFG in the dispersion turning points by using a grating period of 197 μm. In previous works, the shortest periods were, respectively, of the order of 190 and 320 μm for the same fibers. To achieve such a considerable reduction in the grating periods which enables access to the higher order cladding modes (higher sensitivity), we have developed a high-voltage power supply that allows for a constant and stable electric current ranging from 10.5 up to 21 mA. Computer simulations were used to identify the cladding mode resonances for each grating inscribed in the different fibers. The fabricated LPFGs were characterized as a function of the external refractive index from 1.33 up to 1.42, and an average refractive index sensitivity of -720 nm/RIU in the 1.33-1.41 range was obtained for a 192-μm LPFG without further optimization, such as the use of etching or thin films deposition.

Sensing Features of Arc-induced Long Period Gratings

“…A final comment should be made about the grating with Λ = 330 µm, since despite its period is close to the limit of the technique in standard fiber it presents high quality spectral features, in terms of attenuation band depth. In fact, even if there is evidence of arc-induced LPGs in the dispersion turning point (with Λ = 197 µm) [11], these results are still not satisfactory from the practical point of view, since as declared by the authors, a weak grating was obtained (depth of 1-2 dB) even after 400 arc discharges.…”

Manufacturing and Spectral Features of Different Types of Long Period Fiber Gratings: Phase-Shifted, Turn-Around Point, Internally Tilted, and Pseudo-Random

“…Figure 4a shows the front panel of the software used to manufacture LPFGs with a fixed value of Λ, like standard LPFGs and turn-around point (TAP) gratings. For the sake of completeness, TAP LPFGs are a special class of standard gratings where, by decreasing the value of Λ down to 200 μm, the coupled cladding mode (high order) exhibits a dual-band feature in the transmission spectrum [32][33][34]. When those bands merge into a broader one, the TAP in the PMC of the mode is reached.…”

Optical Fibre Long-Period Grating Sensors Operating at and around the Phase Matching Turning Point

“…The refractive index can be altered using a number of different methods. Some of these include local exposure of the fibre to a UV laser [28,32,33,34], CO 2 laser [35,36], femtosecond laser [23,37] or by electrical arc discharge [30,38]. PMTPs have been written in conventional single mode and doped fibres [12,11,33,34,36,39], and have been theoretically investigated using photonic crystal fibres [23].…”