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Analysis and development of a tunable Fiber Bragg grating filter based on axial tension/compression



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Fiber Bragg gratings (FBGs) are key elements in modern telecommunication and sensing applications. In optical communication, with the advancement of the Erbium doped fiber amplifier (EDFA), there is a great demand for devices with wavelength tunability over the Erbium gain bandwidth (in particular, for wavelength division multiplexing (WDM) networks). The center wavelength of a FBG can be shifted by means of change of temperature, pressure or mechanical axial strain. The axial strain approach is the best method among all other techniques because it allows relatively large wavelength shifts with high speed. Axial strain of up to 4% will be required to cover the whole EDFA region (more than 40 nm of central wavelength shift). The formation of Bragg grating results in significant reduction in mechanical strength of optical fibers especially in tension. As a result, axial strain of only about 1% can be achieved by mechanical stretching of FBGs. In order to achieve the remaining 3% strain compression of FBGs has to be applied. In this thesis, the design and analysis of a novel device for achieving central wavelength shift are presented. In particular, the device has achieved, for a fiber with 12 mm FBG, a shifting of 46 nm in compression and 10.5 nm in tension with a reflection power loss of less than 0.25 dB and a FWHM bandwidth variation of approximately 0.1 nm. Both variations are well below the Bellcore standards requirement of 0.5 dB for peak reflectivity variation and 0.1 nm for bandwidth variation. The device consists of two fixed and one guiding ferrules. The difficulties associated with compressing the FBG were handled by carefully selecting tolerances and adjustment procedures. The device allows both tension and compression of FBGs, and the use of different FBG lengths and actuators. The effects of glue deformation and bending of the FBG during compression were analyzed in detail. Further, using the piezoelectric transducer (PZT) actuator as a driver, tuning speed of around 1.5nm/ms was achieved.



filters, optical fibers, buckling, bending shortening, WDM systems, Tunable, Fiber Bragg gratings



Master of Science (M.Sc.)


Mechanical Engineering


Mechanical Engineering


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