Temperature sensing through long period fiber gratings mechanically induced on tapered optical fibers

Abstract

In this work the feasibility of employing two well-known techniques already used on designing optical fiber sensors is explored. The first technique employed involves monomode tapered fibers, which were fabricated using a taper machine designed, built, and implemented in our laboratory. This implementation greatly reduced the costs and fabrication time allowing us to produce the desired taper length and transmission conditions. The second technique used fiber Bragg gratings, which we decided to have mechanically induced and for that reason we devised and produced our own mechanical gratings with the help of a computer numerical control tool. This grating had to be fabricated with aluminum to withstand temperatures of up to 600°C. When light traveling through an optical fiber reaches a taper it couples into the cladding layer and comes back into the core when the taper ends. In the same manner, when the light encounters gratings in the fiber, it couples to the cladding modes, and when the gratings end, the light couples back into the core. For our experimentation, the tapering machine was programmed to fabricate single-mode tapers with 3 cm length, and the mechanically induced gratings characteristics were 5 cm length, and had a period of 500 μm and depth of the period of 300 μm. For the conducting tests, the tapered fiber is positioned in between two aluminum slabs, one grooved and the other plane. These two blocks accomplish the mechanically induced long period grating (LPG); the gratings on the grooved plaque are imprinted on the taper forming the period gratings. An optical spectrum analyzer is used to observe the changes on the transmission spectrum as the temperature varies from 20°C to 600°C. The resultant attenuation peak wavelength in the transmission spectrum shifts up to 8 nm, which is a higher shift compared to what has been reported using nontapered fibers. As the temperature increases there is no longer a shift, but there is significant power loss. Such a characteristic can be used as well for sensing applications.

Mechanically Induced Long-Period Fiber Gratings and Applications

“…Both types of the structure are widely used in the transmission as band rejectors [35][36][37][38][39][40][41][42][43]. Such band rejectors are further developed to serve as transverse load, temperature, pressure, twist, and refractive index sensors [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59].…”

“…The mechanically induced LPFGs also serve as temperature sensors [48][49][50], while the model of the LPFG can be formed by using 3D printing techniques in the fabrication process [51]. In 2011, L. A. García-de-la-Rosa et al [52] reported the spectral response of a mechanically induced LPFG to the ambient temperature variation.…”

“…Potentially enhanced degree of freedom in controlling temperature sensitivity, and a short length of sensing fiber. [46,[48][49][50][51] Refractive index sensors Offering flexibility and real-time response. [52,53] Tunable bandpass filter Single-fiber configuration without insertion devices and independence between tunable range and transmission amplitude.…”

A Review of Microfiber-Based Temperature Sensors

“…Functionalization can improve the sensor sensitivity [ 81 ]: a 25-points 100 μm period MF LPG was inscribed with a UV laser on top of a PMMA coated 5.4 μm diameter MF and was used to measure temperature from 20 °C to 50 °C providing S ~ 385.11 pm/°C. LPG can be also induced mechanically in MF [ 82 ]. A 5-cm long aluminum plate with 500 μm-period and 300 μm grooves was placed under a 60 μm MF ( Figure 15 c): by applying heat to the periodic groove plate, this structure exhibited S ~ 21 pm/°C at T ~ 400 °C.…”

Graphene-assisted high-precision temperature sensing by long-period fiber gratings

“…However, this type of microfiber-attached structure is not steady, and the sensing approach is affected by various factors, including the stability of the microfiber structure, limited sensitivity and applications. Furthermore, extant studies examine temperature sensors by LPFG [34][35][36], although challenges persist, including achieving a simple structure, ease of fabrication and high precision.…”