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Fiber Gratings' Applications In Microwave Optical Filtering, Wavelength Switching And Fiber Lasers

Posted on:2009-12-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z W YuFull Text:PDF
GTID:1118360272478708Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Fiber gratings are key components for a vast number of applications in optical communication systems, microwave photonics systems, optical signal processing and optical sensors, etc. The main topic of this thesis is fiber gratings' fabrication and their applications in direct microwave optical filtering, high speed wavelength switching and switchable dual-wavelength fiber lasers.First, a brief overview is given about the basic techniques for fabricating fiber gratings, the popular coupled-mode theory for describing fundamental characteristics of fiber gratings and the Transfer Matrix method for numerically simulating complex-structured fiber gratings.An advanced fiber grating fabrication system based on the technique of multiple printing in fiber (with a continuous-wave source) has been used to write complex fiber gratings incorporating phase shifts, apodization and chirp.Direct detection combined with direct microwave optical filtering technique has been proposed. A single double-peaked superimposed grating working in reflection can be employed as a direct optical filter for millimetre-wave signals. Bit error rate measurements confirm that the filter exhibited nearly on-off behaviour in the passband with a 3-dB bandwidth of 2 GHz for a central frequency of 20 GHz. The presented technique can be used in radio-over-fiber systems.This thesis focuses mostly on the research of gratings written in twin-hole fibers with internal electrodes. The temperature dependence measurements show that the birefringence of the component increases with the temperature. Dynamic measurements have shown nanosecond full off-on and on-off switching. During the electrical pulse excitation, the grating wavelength is blue-shifted for the x-polarization and red-shifted for the y-polarization due to the mechanical stress. Both grating wavelengths of x- and y-polarization subsequently experience a red-shift due to the relaxation of mechanical stress and the increasing core temperature in many microseconds. All the wavelength shifts of the two polarizations depend quadratically on the electrical pulse voltage and linearly on the pulse duration. Numerical simulations give accurate description of the experimental results and are useful to understand the physics behind the wavelength switching.Finally, two switchable dual-wavelength erbium-doped fiber lasers based on fiber grating feedback are proposed. In one method, an overlapping cavity for the two lasing wavelengths and hybrid gain medium in the fiber laser are introduced. Dual-wavelength switching are achieved by controlling the Raman pump power. The other method employs an injection technique and the dual-wavelength switching is controlled by the power of the injection laser. The switching time is measured to be~50μs. Detailed characteristics of the dual-wavelength switching in the two fiber lasers are experimentally studied and corresponding principles are physically explained.
Keywords/Search Tags:fiber grating, direct optical filtering, direct detection, twin-hole fiber, switching, birefringence, dual-wavelength, fiber laser
PDF Full Text Request
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