Long period fiber grating formed by periodically structured microholes in all-solid photonic bandgap fiber.

A new type long period fiber grating is fabricated in all-solid photonic bandgap fiber by periodically drilling microholes using femtosecond laser pulse irradiation. Such a structure introduces a strong refractive index modulation in the waveguide structure and hence exhibits a compact grating dimension. Both the simulation and the experimental results confirm the existence of the light coupling from core mode to the LP(11) cladding mode. The refractive index sensing capability of the device has been investigated and the resonant wavelength shift corresponding to the refractive index change from 1.30 to 1.35 is 23.7 nm. The average refractive index sensitivity obtained is 537 nm/RIU (refractive index unit).