Coupling between propagated modes in optical fibers with periodical structures

Abstract

Theoretical analysis was conducted with the purpose for further development of spectral-sensitive elements for fiber optic devices including sensors of physical magnitudes. Forecasting performances of such elements is conducted. Analysis has shown that coupling coefficient between propagating modes (incident and reflected) of fiber cladding grating is sufficient for sensitive elements manufacturing because on fiber cladding it is possible to achieve significant equivalent periodic modification of refraction index not taking into consideration that wave amplitude in the cladding is significantly less than in the core. Such gratings can be created by holographic method using photopolymeric media and lasers working in blue-green area of spectrum. The case of the corrugated or sinusoidal boundary between fiber core and cladding is also possible, and between cladding and external medium under investigation, for example with water, where various substances are dissolved, influencing on refraction and absorption of light waves propagating in the fiber. The results of theoretical researches can be used for developing devices with periodic structures on optical fibers.