Ultra short long-period gratings (LPGs) fabricated using the electric arc discharge method are demonstrated with regular single-mode fibers. The gratings were as short as two periods, which were the shortest LPGs ever reported. The evolution of this short gratings and their characteristics are investigated in this paper. The excellent bending insensitivity and high temperature robustness demonstrated by this unique LPG make it particularly suitable for harsh environment sensing and communication.

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In this paper, a unique all-fiber tunable filter based on the combination ofsingle resonant band long period grating (LPG) and harsh environment electro-optic polymer second cladding layer is presented. The single resonant band LPG is used to select the resonant wavelength and the tuning of resonant wavelength is realized by changing the refractive index of electro-optic polymer cladding layer via external electric field. Although the basic operational principle and implementation of this unique tunable filter have been previously reported by authors, this paper is focused on athermal operation design and synthesis of harsh environment electro-optic polymer, which enhances the practicability of proposed tunable filter.

In this paper, we will provide a brief review on the progress of a unique all-fiber tunable filter based on the combination of single resonant band long period grating (LPG) and harsh environment electro-optic polymer second cladding layer recently developed at Penn State University. The single resonant band LPG is used to select the resonant wavelength and the tuning of resonant wavelength is realized by changing the refractive index of electro-optic polymer cladding layer via external electric field. Although the basic operational principle and implementation of this unique tunable filter have been previously reported by authors, this paper is focused on recent progress in this project.

A unique all-fiber tunable filter is based on the combination of a single resonant band long period grating (LPG) and an electro-optic polymer second cladding layer. The single resonant band LPG is fabricated by etching the cladding of a standard 125 µm thick fiber and using either ultraviolet (UV) illumination or electric arc discharge to write the grating. Once a single resonant band has been achieved, a polymer second cladding layer is applied to the LPG. The refractive index of the polymer cladding determines the resonant wavelength of the filter and is tuned by applying an external electric field. The grating fabrication method and type of polymer used for the second cladding affect filter performance, and both must be considered when designing an application specific all-fiber filter.