Wavelength Shift of Cladding Mode Resonances in a Mechanically Induced LPFG by Twisting the Fiber

• Published in: Fiber and integrated optics 2007-05, Vol.26 (3), p.159-172
• Main Authors: Nair, B. Unnikrishnan, Sudeep Kumar, V. P., Mahadevan Pillai, V. P., Nayar, V. U.
• Format: Article
• Language: English
• Subjects: Applied sciences; Circuit properties; circular birefringence in twisted fibers; cladding mode resonance; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Integrated optics. Optical fibers and wave guides; long-period fiber grating; micro bends; Optical and optoelectronic circuits; photo-elasticity in fibers; shearing stress in fibers
• ISSN: 0146-8030; 1096-4681
• DOI: 10.1080/01468030701239501

The long-period fiber grating is mechanically induced over a twisted fiber and its characteristics are investigated. The amplitude as well as the wavelength shift of the resonance is studied in response to the applied twist and pressures. These resonances decrease in amplitude and shift to shorter wavelength side as the applied twist increases. The spectral responses of a grating assembly formed by two grating sections in series, one section with a twisted fiber and other with an untwisted fiber, are also investigated. Shearing stress and photo-elasticity causes the fiber to be circularly birefringent and the mechanically induced grating formed over the twisted fiber region causes the appearance of two resonances shifted away from the resonances of the untwisted grating section. At higher twist rates, resonant wavelength shift becomes insensitive to applied pressures, showing a reduction in the induced linear birefringence. The wavelength shift is almost symmetric with respect to the applied twist rate in clockwise and counterclockwise directions.