We report on the inscription of a long period grating (LPG) in a multimode cyclic transparent optical polymer (CYTOP) fibre using the plane-by-plane femtosecond laser inscription method. The LPG was inscribed in the centre of the fibre core and tailored for operation at C-band wavelength range. The CYTOP-LPG sensitivity was characterised in transmission for relative humidity and temperature. The humidity measurements performed are the first for a POF-LPG, whereas the temperature sensitivity is significantly higher than reported in other works. In addition, dynamic mechanical measurements were performed comparing the mechanical characteristics of the laser exposed sections of the polymer fibre, where the LPG was inscribed, with the unexposed regions.
FBG in polymer optical fibers (POFs) is a promising technology for a wide range of sensing applications due to a lower Young’s modulus and a large range of applying strain. Furthermore, POFs have several properties which make them attractive for biosensing applications such as nonbrittle nature, flexibility in bending and biocompatibility. Chirped Fiber Bragg gratings (CFBGs), which are characterized by a nonuniform modulation of the refractive index show a broad reflection spectrum, enabling shortlength distributed sensing. The combining benefits of POF and CFBGs is attractive for biomedical applications. Here, we present a novel method to obtain CFBG in POF with a postprocess uniform POF FBG by using resin.
We demonstrate a long period grating (LPG) inscription in microstructured polymer optical fibers (mPOFs) using a single 248 nm UV laser pulse of 15 ns duration for every inscription point using a point by point technique with total length of 25 mm. The fabrication time indicates shortening for a single coupling point (15 ns against 42 s reported in literature). A grating with 20 dB transmission dip has been fabrication by using two UV pulses for each coupling point. The device has been fabricated in mPOF with a core that has been doped with benzyl dimethyl ketal (BDK) for photosensitivity increase. The strain and temperature responses of the fabricated gratings under different conditions have been characterized in order to assess the viability for sensing applications. Better performance was achieved with suitable post annealing process of the gratings.
In this contribution we report on the fabrication of novel bandpass transmission filters based on PS-FBGs in microstructured polymer fibers at telecom wavelengths. The phase mask technique is employed to fabricate several superimposed gratings with slight different periods in order to form Moiré structures with a single or various π phase shifts along the device. Simulations and experimental results are included in order to demonstrate very narrowband transmission filters. Experimental characterization under strain and temperature variations is provided in a non-annealed fiber and time stability of the fabricated devices has been also measured under different pre-strain conditions.