Due to its comb filter characteristics, Sampled optical Fiber Bragg Grating (SFBG) has attracted wide-spread attention and become a new focus in the research of optical fiber grating technology. The research work on designing optical filters with high channel numbers, flat tops, and narrow pass bands is of great importance in practical situation. Consequently, an Multi-Phase Shift Interpolated Sampling optical Fiber Grating (MPS-ISFBG) filter is proposed.

ISFBG has a large number of reflection channels and can introduce multiple flat top narrow transmission channels by inserting multi-phase shift. By optimizing the location of the two π phase-shift distributions of the inserted ISFBGs, an optical filters with 41 transmission channels was designed which covers the C-band with a channel interval of 100 GHz. Each channel has a flat-top response, a narrow 3 dB bandwidth (<1 GHz) and a small shape factor (<3.2). With structure parameters unchanged, three π phase shifts are inserted, which can further reduce the shape factor, thus improving the rectangular shape of the transmission channel. Finally, doubling the number of channels with half of the channel interval is achieved by introducing the MPS technique and inserting three π phase shifts into the ISFBG.

The filter with 81 channels flat-top narrow bandwidth covering the C-bands with 50 GHz channel spacing is demonstrated. The 3-dB bandwidths of the multiple channels are 900.5 MHz and the shape factors are close to 2.17. Meanwhile, the effect of the magnitude of the multiphase shift, the location and the equivalent length of the fiber on the actual fabrication is discussed.

The designed filter has a large number of channels. Each channel has a flat-top response and narrow bandwidth, in line with the design purpose. Such filters have potential applications in multi-wavelength lasers and multi-wave microwave signal processing systems.