Phase-Inserted Fiber Gratings and Their Applications to Optical Filtering, Optical Signal Processing, and Optical Sensing: Review

Phase-inserted fiber gratings (PI-FGs) refer to those where there exist a number of the phase-shifts (spatial spacing) among different sections (or local periods) themselves. All PI-FGs developed date can mainly be divided into three categories: phase-shifted gratings, phase-only sampled and phase-modulated which utilized could either Bragg ones (FBGs) or long-period (LPGs). As results proposed numbers, quantities, positions inserted phases along direction are optimally selected, have already been designed used as various complex filters such ultra-narrow filters, triangular (edge) high channel-count flat-top band-pass/band-stop which, however, extremely difficult even impossible realized by using ordinary gratings. In this paper, we briefly but fully reviewed past recent advances on PI-FGs, in principles design methods, corresponding fabrication techniques, applications fields optical filtering, signal processing, sensing, etc., highlighted.