Ultra-Broadband Optical Filter Based on Chirped Long-Period Fiber Grating and PMTP

We propose an ultra-broadband apodized chirped long period fiber grating (CLPFG) filter based on phase matching turning point. An ultra-broadband with efficiency of ~100% can be obtained under a small grating period change, which overcomes the conflict between chirp coefficient and grating length. The spectrum of this CLPFG filter is symmetrical, which is hard to achieve for traditional CLPFG filters. The CLPFG filter operates at a single cladding mode, so it will not interfered by any other cladding modes. For reducing the fluctuations on the attenuation band of the filter, it is apodized by use of the Tanh and Gaussian functions, and a perfect attenuation band is obtained. Furthermore, the center wavelength and bandwidth of the filter is adjustable. In future, this filter is expected to be widely applied in communication and other fields.