Novel chirped-fiber Bragg grating based filters

Chirped-fiber Bragg grating (CFBG) is a type of excellent wavelength selective and dispersion variable device that has been widely studied and employed in various optical fiber systems. To meet different requirement of bandwidth and/or dispersion, chirp rate tunable CFBGs have been demonstrated and realized by using various techniques, which employ thermal, mechanical, electrical, or magnetic methods. Among these methods, however, few can maintain center wavelength of the CFBG's reflection band fixed during the tuning process. It is a serious drawback since shift of the center wavelength may cause the signal wavelength being located outside or at the edge of the effective band of the CFBG. In this chapter, a novel chirp tuning method is introduced which allows, to date, the largest tuning bandwidth range and nearly fixed center wavelength in CFBGs. Based on this chirp tuning method, several optical fiber filters, based on CFBGs written in various fibers (e.g. single-mode fiber and highly-birefringent fiber) with various grating structures (e.g. sampled or superimposed structures), are demonstrated and characterized. Several filters with tunable bandwidth and/or tunable wavelength spacing (for multi-channel filters) are achieved. Their applications in tunable chromatic dispersion compensation, differential group delay generation and spacing-tunable multiwavelength fiber laser are also reported.