Properties of Specialist Fibres and Bragg Gratings for Optical Fiber Sensors

Figure 11

Transmission spectrum of a two-photon written Bragg gratings within a two-mode 4-ring photonic crystal fibre. (1)—fundamental mode; (2)—higher-order mode and the dip in the centre is some cross coupling between the two arises from some asymmetry in transverse profile of the induced index change [80].