Abstract
We have proposed and demonstrated experimentally a novel and simple tunable optical filter based on mechanically induced and cascaded long period optical fiber gratings. In this filter variable FWHM and center wavelength is provided by cascading long period and ultralong period optical fiber gratings with different periods in a novel fiber structure. We report here for the first time to our knowledge the characterization of mechanically induced long period fiber gratings with periods up to several millimeters in novel multimode-single-mode-multimode fiber structure. We have obtained maximum loss peak of around 20 dB.
Highlights
Long period fiber grating (LPFG) is the special case of fiber Bragg grating (FBG)
Light is launched from a broadband superluminescent LED source to the lead in MMF, through the device (MLPFG) to the lead-out MMF and spectrally resolved using an optical spectrum analyzer (OSA) (Prolite60)
The Mechanically induced long period fiber gratings (MLPFGs) in MSM structure with Λ = 600 μm and length = 70 mm can be used as a band reject filter
Summary
Long period fiber grating (LPFG) is the special case of fiber Bragg grating (FBG). It was first suggested by Vengsarkar and coworkers in 1996 [1]. In contrast to the Bragg grating, LPFG does not produce reflected light and can serve as spectrally selective absorber Their spectral properties, that is, resonance wavelength, bandwidth, and so forth, can be varied in a wide range. LPFGs formed by a mechanically induced technique have generated great interest due to their versatility in the process of fabrication In these gratings, the fiber is subject to periodical stress, which results in alternated regions under compression and stretching that modulate the refractive index via the photoelastic effect. Induced long period fiber gratings (MLPFGs) induced by pressure need neither a special fiber nor an expensive writing device for fabrication These gratings offer advantages of being simple, inexpensive, erasable, and reconfigurable and give flexible control of transmission spectrum
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