Abstract
This paper presents the achievements and progress made on the polymer optical fiber (POF) gratings inscription in different types of Fiber Bragg Gratings (FBGs) and long period gratings (LPGs). Since the first demonstration of POFBGs in 1999, significant progress has been made where the inscription times that were higher than 1 h have been reduced to 15 ns with the application of the krypton fluoride (KrF) pulsed laser operating at 248 nm and thermal treatments such as the pre-annealing of fibers. In addition, the application of dopants such as benzyl dimethyl ketal (BDK) has provided a significant decrease of the fiber inscription time. Furthermore, such improvements lead to the possibility of inscribing POF gratings in 850 nm and 600 nm, instead of only the 1550 nm region. The progress on the inscription of different types of polymer optical fiber Bragg gratings (POFBGs) such as chirped POFBGs and phase-shifted POFBGs are also reported in this review.
Highlights
Fiber optic sensors offer key advantages over other sensing technologies, which include immunity to electromagnetic interference, electrical isolation, compactness, being lightweight, and multiplexing capability [1]
The grating type is analyzed and the refractive index modification will be discussed for uniform, chirped, and phase shifted polymer optical fiber Bragg gratings (POFBGs), as well as for the long period gratings (LPGs)
In order to obtain a POFBG without material ablation and with a lower inscription time, a low energy density with a repetition rate of 1 Hz was employed in [25]. Such pulsed laser parameters enable the inscription of POFBGs at undoped polymethyl methacrylate (PMMA) with only 30 s, which is a lot faster than the lower inscription time for the undoped PMMA fiber obtained with the 325 nm continuous laser (7 min) [24]
Summary
Fiber optic sensors offer key advantages over other sensing technologies, which include immunity to electromagnetic interference, electrical isolation, compactness, being lightweight, and multiplexing capability [1]. There may be some problems in data acquisition such as the wavelength hopping reported in [18] due to sudden changes in the wavelength peak and difficulties with the fiber handling [19], FBG sensors have been employed in applications “outside the laboratory environment” These applications include aviation fuel gauging [20], liquid level sensing in industrial plants [21], and even plantar pressure monitoring systems for biomedical applications [22]. The grating type is analyzed and the refractive index modification will be discussed for uniform, chirped, and phase shifted POFBGs, as well as for the LPGs. The setup is employed for the fabrication of FBGs in other POFs materials, revealing similar results. To provide the full advantages of the inscription system, fibers of different materials and structures will be described
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