Large refractive index modulation based on BDK-doped step-index PMMA optical fiber for highly reflective Bragg grating inscription

Xuehao Hu, Xiaoyu Yue, Xin Cheng, Shixin Gao, Rui Min, Heng Wang, Hang Qu, Hwayaw Tam

Research output: Journal article publicationJournal articleAcademic researchpeer-review


We experimentally report high reflectivity on the poly(methyl methacrylate) (PMMA)-based polymer optical fiber Bragg gratings by means of a 266 nm pulsed laser and phase mask technique. In the first recipe, fiber Bragg gratings (FBGs) were manufactured with a single pulse up to 3.7 mJ. After post-annealing, a stable refractive index change up to 4.2×10−4 was obtained. In the second recipe, FBGs were inscribed by 22 pulses with a lower pulse energy of 1.4 mJ, showing a stable refractive index change of 6.2×10−4. Both behaviors may mainly be attributed to the movement of initiating radicals arising from benzyl dimethyl ketal (BDK) under UV irradiation. The high refractive index change in step-index fibers paves the way to tilted FBG manufacturing with large tilt angles potentially for biomedical applications.

© 2021 Optical Society of America

Fiber Bragg grating (FBG)-based sensors in polymer optical fibers (POFs) have been developed for more than two decades [1]. Because of their unique properties compared to silica fibers, such as a smaller Young’s modulus, larger thermo-optic coefficient, and better biocompatibility, etc., polymer optical fiber Bragg grating (POFBG) sensors are highly attractive in temperature [2], strain [3], humidity [4], and saline solution [5] sensing. Since the first manufacturing of the FBG in the step-index POF in 1999 [1], the FBG inscription technology has been improved step-by-step to pursue high-quality gratings in POFs made from different materials, such as cyclic olefin copolymers TOPAS [6], cyclic transparent amorphous fluoropolymers CYTOP [7], cyclic-olefin polymer ZEONEX [8,9], polycarbonate [10], and different structures, such as microstructured POFs (mPOFs) [11].

In 2005, the first FBGs in poly(methyl methacrylate) (PMMA) mPOFs were inscribed using a
Original languageEnglish
Pages (from-to)2864-2867
JournalOptics Letters
Issue number12
Publication statusPublished - 11 Jun 2021

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