Supermode Bragg grating inscribed in a strongly coupled seven-core fiber and its responses to temperature and curvature

A Bragg grating is successfully inscribed in a piece of strongly coupled seven-core fiber (SCF). There are two separate Bragg resonance notches observed in the transmission spectrum, corresponding to backward coupling of HE11-like and HE12-like supermodes of the SCF. The mode coupling mechanism of the Bragg grating is theoretically investigated via modeling and analyzing modal properties of the SCF. The theoretical results agree well with the experimental results. Since the SCF is spliced between two standard single mode fibers with central alignments at both ends, the transmission spectrum of the device also contains a set of interference fringe due to modal interference between the supermodes. The device's responses to temperature and curvature are experimentally measured, respectively. The obtained temperature sensitivities and curvature sensitivities of the supermode Bragg grating notches are 9.55 pm/degrees C and 9.55 pm/degrees C, -1.8 pm/m(-1) and -112.3 pm/m(-1), respectively. The obtained temperature sensitivity and curvature sensitivity of one of the interference spectrum dips are 11.8 pm/degrees C and -3909.8 pm/m(-1), respectively. This device is potentially useful for simultaneous measurement of temperature and curvature.