Temperature insensitive long-period fiber grating devices

Applicants have determined that the temperature sensitivity of long-period grating devices is due to differential variation with temperature of the refractive indices of the core and cladding. They have further determined that the cladding profile and fiber composition can be redesigned to substantially reduce this differential variation, thereby reducing the temperature sensitivity of long-period gratings of less than 4 nm per 100 DEG C and preferably less than 2 nm per 100 DEG C. This design permits the use of long-period grating devices without temperature control or compensation.