Residual-stress-induced helical long period fiber gratings for sensing applications

Abstract

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

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

“…Using this HLPFG inscription method, small numbers of HLPFGs could be obtained by twisting the fiber once. Moreover, various types of HLPFGs in conventional glass fiber [13,17,22] and solid-core PCF [14,15,16] could be fabricated.…”

“…Vengsarkar et al wrote the first standard LPFG (SLPFG) with periodic refractive index change in the conventional glass fiber core using an ultraviolet (UV) laser radiation in 1996 [8]. Compared with SLPFG, helical LPFG (HLPFG) refers to a fiber where there exists a periodical helical structure such as a screw index-modulation along the fiber axis [9,10,11,12,13,14,15,16,17,18,19,20,21,22]. A HLPFG with double helix symmetry was firstly produced by twisting glass optical fiber with a noncircular core cross section as it passed through a miniature oven [9].…”

“…Following this, the fabrications and applications of LPFGs, including SLPFGs and HLPGs, were rapidly developed. Various methods to fabricate the LPFG, such as CO 2 laser [23,24,25,26,27,28,29,30,31,32], arc discharge [33,34,35,36,37,38], hydrogen–oxygen flame heating [13,14,15,16,17,22], femtosecond laser [39,40], mechanical micro-bend [41,42], etched corrugations [43,44], and ion beam implantation [45], have been proposed and demonstrated. One of the key steps of fabricating the LPFG is to introduce periodic refractive index modulation in the fiber.…”

“…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].…”

Braided Fabrication of a Fiber Bragg Grating Sensor

“…Helical gratings can open new avenues for applications of orbital angular momentum in the nanoworld. Helical shapes often result from the competition between bending and stretching energies as well as due to a variety of driving forces [ 1 , 2 , 3 ].…”