Physical insights into inverse-scattering profiles and symmetric dispersionless FBG designs

We revisit representative and widely used inverse-scattering fiber Bragg grating designs and shed physical insight into their characteristics. We first demonstrate numerically and experimentally that dispersionless square filters are actually dispersion compensated devices and we physically identify the spatially separated main (dispersive) reflector and dispersion compensator sections. We also look into the features of pure 2nd-order dispersion and 3rd-order dispersion compensator designs and discuss their physical importance. Finally, we use the gained physical insight to design strong symmetric gratings with dispersionless response from both sides. Using this knowledge we design and fabricate strong (>30dB) bidirectional dispersionless filters.