Microstructured polymer optical fiber for long period gratings fabrication using an ultraviolet laser beam

Abstract

We present a microstructured polymer fiber dedicated to long period grating (LPGs) inscription using a focused UV laser beam. The core and the microstructured cladding of the developed fiber are made of pure poly(methyl methacrylate) (PMMA). The external layer of the solid part of the cladding has increased UV absorption due to doping with trans-4-stilbenemethanol, which shows an absorption band at around 310 nm related to trans-cis photoisomerization. We present transmission characteristics of LPGs fabricated in this fiber using the point-by-point inscription technique with a He-Cd laser beam of 325 nm wavelength. We also demonstrate that in the proposed fiber, the fabrication process is shortened six times compared to pure PMMA fibers. Moreover, we report on temperature response and long-term stability of the fabricated gratings.

Multifunctional Smart Optical Fibers: Materials, Fabrication, and Sensing Applications

“…The key to the fabrication process is to tune the refractive index difference between the fiber core and cladding and to control the diameter of the fiber core so that the produced fiber supports only single-mode transmission. In addition, PMMA is used to make micro-structured POFs, which are normally fabricated by drilling holes in a designed pattern into the preform and then thermal drawing [36], or by stacking PMMA rods/tubes to form a preform and then thermal drawing [37]. In addition to PMMA, thermoplastic cyclic olefin copolymer (TOPAS ® ) has been used to make micro-structured POFs in the past few years [4,38].…”

Latest Achievements in Polymer Optical Fiber Gratings: Fabrication and Applications

“…However, both non-annealed and annealed TS-doped polymer optical fibers were studied in terms of FBG stability, and the post-inscription thermal annealing process was necessary to produce stable gratings [83]. POF grating fabrication has been reported using different lasers, such as an 800 nm Ti:sapphire fs laser system [74,86], a 532 nm Nd:YVO4 laser system [77,87], a 387 nm Ti:sapphire fs laser system [88], a 355 nm Nd:YAG laser [89], a 325 nm optical parametric oscillator (OPO) pulsed laser, a dye laser, an He-Cd laser [81,[90][91][92][93][94][95], and a 248 nm KrF excimer laser system [73,96]. Although 325 nm was the first irradiation wavelength reported by Peng's group [45], and initially 248 nm wavelength was not considered suitable for polymer fiber Bragg grating writing, due to high absorption, the first successful Bragg grating inscription in 30 seconds using low flow and a repetition rate at 248 nm UV light opened a new field of interest for grating irradiation [96].…”

“…The simplicity of this method is one of its main advantages, since no special phase mask or additional etching are needed, and it enables easy control tuning of the central wavelength and chirp characteristics. Finally, regarding long period gratings in POF, the extensive literature during the last years shows different mechanisms and methods to be used for fabricating them in POF [47,75,76,87,95,112]. Recently, Min et al [113] demonstrated a -20 dB transmission LPG in mPOF (see Figure 9a) using the point-by-point method, with an slit width of 0.2 mm; the beam was shifted 1 mm for inscribing every point, and 25 steps were completed to obtain an LPG total length of 25 mm.…”

“…Recently, Min et al [113] demonstrated a -20 dB transmission LPG in mPOF (see Figure 9a) using the point-by-point method, with an slit width of 0.2 mm; the beam was shifted 1 mm for inscribing every point, and 25 steps were completed to obtain an LPG total length of 25 mm. Each inscription point was irradiated by two 15 ns pulses emitted by the UV laser at 1 Hz frequency repetition rate, and therefore, a 2 s irradiation time means a significant reduction from the 42 s per point writing time Finally, regarding long period gratings in POF, the extensive literature during the last years shows different mechanisms and methods to be used for fabricating them in POF [47,75,76,87,95,112]. Recently, Min et al [113] demonstrated a −20 dB transmission LPG in mPOF (see Figure 9a) using the point-by-point method, with an slit width of 0.2 mm; the beam was shifted 1 mm for inscribing every point, and 25 steps were completed to obtain an LPG total length of 25 mm.…”

Fabrication of Polymer Optical Fibre (POF) Gratings

“…So far, based on different kinds of mechanisms and writing methods, many LPGs have been fabricated in SM and MM POF, SI and GI POF, as well as mPOFs as listed in Table 4 [48,67,71,72,73,75,76,78,79,82,84,87,109,110,123,135,136,138,142,147]. The point-by-point technique is the most used method used for POF LPG fabrication.…”