Design And Fabrication Of All-Fiber Add/Drop Filter

Optical add/drop filters are key components of wavelength-division multiplexing (WDM) systems, and are going to break through the main obstacle to extend fiber-to-the-home (FTTH) by reducing the cost. Under the supporting of national natural science foundation and national 863 high technology program, this thesis is mainly devoted to design and fabricate all-fiber optical add/drop filters. Based on the detailed theoretical analyses, structural optimum and experimental researches, the main achievements of this thesis are listed as follows:A. Design and fabricate a high-precise fiber side-polished machine and controllable fused taper equipment.B. The unified coupled-mode equations for three types of optical add/drop filter based on"Two-Fiber-Bragg-Gratings (FBGs) reflecting coupler","FBG-frustrated coupler"and"FBG-assisted coupler"are deduced. By investigating the influences of grating position and coupler waist's uniformity, a novel Two-FBGs reflecting coupler with symmetric configuration is designed and fabricated, which can simultaneously optimize add and drop filter characteristics. And the slow varying, adiabatic, asymmetric fused taper technology is presented to improve the fabrication program of FBG-assisted coupler. Experimental results show that add/drop filter made by this method not only meets the rigorous requirements of DWDM system, but also exhibits lower insertion loss and higher stability.C. The characteristics of Long-Period-Grating (LPG) are analyzed when gain/loss effect is added to refractive index modulation. And a novel unidirectional complex grating-assisted coupler, which exhibits a strong amplification to the dropped signal at resonance wavelength is proposed. The structure of Two-Parallel-LPGs coupler is optimized. Both the numerical and experimental results show the add/drop efficiency can be enhanced by choosing proper surrounding and refractive modulation depth. And the spectral characteristics of add/drop filter can be improved if LPG's cladding thickness isn't reduced. Four-layer waveguide model is founded and precise all-vector method is introduced so as to the spectral responses of LPG with nm-thickness polymer thin-film can be analyzed. Compared with liquid, both polymer's material and its deposited thickness play very important role on LPG's resonance wavelengths. And widely tunable range (>120nm) can be obtained by optimizing device's structural parameters.D. The amplitudes and phase delays of two types of single-ring resonator ('all-pass'...