Single-Channel Bandpass Filter Based on Vernier-Aligned Long-Period Fiber Gratings

We present an all-fiber bandpass filter that produces a single passband in the telecommunication spectral range. This filter employs two concatenated long-period fiber gratings that have mutually different grating periods, and an absorptive core-mode blocker fabricated in the center of the two gratings. Transmission spectrum of the bandpass filter exhibits the passband at a center wavelength of 1545 nm with a 17-nm bandwidth over a wavelength range of 1200-1700 nm.