Dual resonant peaks of LP015 cladding mode in long-period gratings

It is found that the coupling of the guided core mode to a higher order cladding mode may lead to dual resonant wavelengths in long-period gratings (LPGs). The dual peaks of the LP,,, cladding mode have been observed to shift towards each other during the second exposure of a 100 mu m period grating. It is also shown that the resonant wavelengths of LPGs can be tuned over a wide range by the post-exposure technique.