Sensing Characterization of Helical Long Period Fiber Grating Fabricated by a Double-Side CO₂ Laser in Single-Mode Fiber

Abstract

A simple and efficient manufacture method of helical long period fiber grating (HLPFG) in a single-mode fiber (SMF) is designed and verified through experiment. Different from the previous fabricating methods, the SMF is heated by a double-side CO 2 laser beam after being twisted. There are multiple transmission depletions caused by model coupling which could be observed when the period length is 500 μm. The sensing characteristics of the HLPFG have been investigated. Experimental results demonstrate axial strain sensitivities of 3.3 and 6.4 pm/με at the selected dips in the range of 0-450 με or temperature sensitivities of 35.3 and 49.5 pm/°C at the selected dips in the range of 20-70°C, respectively. Moreover, through theoretical analysis, it is found that the fabricated HLPFG can measure axial strain and temperature concurrently by monitoring the resonance wavelength shift. Therefore, the fabricated HLPFG has brilliant applications value in dual measurement.

Gold-Diaphragm Based Fabry-Perot Ultrasonic Sensor for Partial Discharge Detection and Localization

“…Based on the analysis above, the distance sensitivity S d is worked out as −1.32 dB/m. Equation 5and (6) are only suitable for the situation when the distance between discharge source and ultrasonic sensor is large than 0.25 m. When the distance is too small, the error will be relatively large. Besides the distance sensitivity, the directional property of the ultrasonic sensor is also worth researching.…”

“…Under such a circumstance, fiber-optic ultrasonic sensor shows its superiority of compact size, immune to electromagnetic interferences, internal testing capability and resistance to chemical corrosion. Moreover, it has favorable characteristics of long life, fast response and high accuracy [6]. So fiber-optic ultrasonic sensors have great potentials in the field such as power transformers and gas insulated switchgear (GIS) system for PD monitoring, as well as discharge source localization.…”

Recent Progress in Fabrications and Applications of Heating-Induced Long Period Fiber Gratings

“…Various fabrication techniques have been demonstrated and improved to fabricate high-quality SLPFGs and HLPFGs in different types of optical fibers. Compared with SLPFG, HLPFG refers to a fiber where there exists a periodical helical structure such as a screw index-modulation along the fiber axis [9,10,11,12,47]. The heating fabrication techniques, i.e., CO 2 laser, arc discharge, and hydrogen–oxygen flame as the heat source, could be used to write SLPFGs and HLPFGs in conventional glass fiber, PCF, and PBF.…”

“…Firstly, the fiber was twisted with 180° in the opposite directions by the two rotator motors. Then, the double-side CO 2 laser was employed to irradiate the fiber [47].…”

“…Among above-mentioned fabrication techniques, CO 2 laser, arc discharge, and hydrogen–oxygen flame all heat the fiber into a fused status, then the periodic refractive index modulation in the fiber is reserved due to the possible mechanisms, i.e., residual stress relaxation, physical deformation, and structural changes. Various heating-induced LPFGs in conventional fiber [12,13,22,28,35,46,47], photonic crystal fiber (PCF) [14,15,16,29,48], and photonic bandgap fiber (PBF) [27,30,31] could then be successfully written. LPFG-based devices have recently attracted great attention and found versatile applications, such as in all-fiber orbital angular momentum (OAM) mode converters [11,13,14,17,49,50,51,52,53,54,55,56], and strain [48,57,58,59,60,61,62,63,64], pressure [16,29,30,65,66], torsion [16,19,38,46] and biochemical sensors [67,68,69,70,71,72,73].…”