H. Kasai, M. Abe and S. Komatsu: Multidimensional Photonic Key Consisting of Phase-Shifted FBGs, Collected Post-Deadline Papers (Optics and Photonics Japan 2006) (2006) 6-7.

We propose a multidimensional photonic key consisting of several phase-shifted FBGs, each of which has a small region of constant index of refraction within the grating structure. The center wavelength and maximum transmittance of each FBGﾕs resonance peak can be controlled by changing the amount of phase shift introduced by the region with constant index. In addition to Bragg wavelength, these properties can be used to increase the security level of the photonic key for personal identification.