Mode coupling characteristics investigation on a tapered seven-core fiber sensor.

In this work, we analytically derive the transmission spectra of the seven-core fiber (SCF) with a phase mismatch between the center core and outer cores based on the mode coupling theory. We also establish the wavelength shift as a function of temperature and ambient refractive index (RI) using approximations and differentiation techniques. Our results reveal the opposite effects of temperature and ambient RI on the wavelength shift of the SCF transmission spectrum. The theoretical conclusions are confirmed by our experiments on the behavior of SCF transmission spectra under various temperature and ambient RI conditions.