Arc-Induced Long Period Gratings from Standard to Polarization-Maintaining and Photonic Crystal Fibers

Abstract

In this work, we report about our recent results concerning the fabrication of Long Period Grating (LPG) sensors in several optical fibers, through the Electric Arc Discharge (EAD) technique. In particular, the following silica fibers with both different dopants and geometrical structures are considered: standard Ge-doped, photosensitive B/Ge codoped, P-doped, pure-silica core with F-doped cladding, Panda type Polarization-maintaining, and Hollow core Photonic crystal fiber. An adaptive platform was developed and the appropriate “recipe” was identified for each fiber, in terms of both arc discharge parameters and setup arrangement, for manufacturing LPGs with strong and narrow attenuation bands, low insertion losses, and short length. As the fabricated devices have appealing features from the application point of view, the sensitivity characteristics towards changes in different external perturbations (i.e., surrounding refractive index, temperature, and strain) are investigated and compared, highlighting the effects of different fiber composition and structure.

Sensing Features of Arc-induced Long Period Gratings

“…For the purpose of the work, we selected a standard Ge-doped core SMF28 optical fiber provided by OZ Optics (DCO = 8.2 µm, DCL = 125.0 µm, MFD = 10.4 ± 0.8 µm at 1550 nm, NA = 0.14). The gratings were achieved by using the setup reported in [2] and the following optimized fabrication parameters: arc power in range 15-20 step (proprietary unit), arc duration of 650-700 ms, weight of 12.0 g and 0.8 mm electrodes gap. LPGs were fabricated at different period in the range Λ = 330-630 µm, resulting in total lengths within 15-30 mm as consequence of maximum power coupling with the highest order cladding mode in the range 1100-1700 nm.…”

“…The response of the LPGs to surrounding refractive index, temperature and strain was experimentally investigated using the setups from [2] and by focusing the attention on the higher order band for each sample. It is the first time to our knowledge that a such systematic investigation is conducted on this kind of gratings.…”

“…As a result, the transmission spectrum of the fiber shows attenuation bands centered at discrete wavelengths, each one corresponding to the coupling between the core mode and a different cladding mode. First demonstrations of gratings were through UV irradiation, nowadays alternative and simpler approaches, based on CO2 lasers and Electric Arc Discharge (EAD) are also proposed, since they enable the inscription in not photosensitive and unconventional fibers as well [1,2]. In the EAD procedure the perturbation is created by applying an electric arc to the fiber with a certain periodicity.…”

Liquefied Petroleum Gas Monitoring System Based on Polystyrene Coated Long Period Grating

“…The design and characterization of such a sensor has been presented and discussed in our previous paper [ 31 ]. Briefly, we focused the attention on LPG technology, since it has been employed in several physical, chemical, and biological applications [ 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. It consists of a periodic perturbation, with period of hundreds of μm, in the refractive index and/or the geometry of the optical fiber [ 39 , 40 , 41 ].…”

Temperature Stability of a Hybrid Polarization-Maintaining Photonic Crystal Fiber Resonator and Its Application in a Resonant Fiber Optic Gyro

“…In contrast, a photonic crystal fiber (PCF) exhibits much better temperature stability [ 33 , 34 , 35 , 36 ], which can effectively solve the problem of thermal instability [ 31 ]. This is because the cladding in PCF contains multiple air holes that confine light within the core and because the thermal constant of air is much lower than that of silica.…”