Theoretical investigation of transverse mode instability in Yb-DCFs due to thermally-induced modal coupling

Abstract

This paper presents a theoretical investigation of the transverse mode instability (TMI) threshold in Yb-doped doubleclad fibers (Yb-DCFs). The analysis is based on the semi-weak guiding approximation, applied to the LP01 and LP13 modes. The thermally-induced modal coupling is modeled using coupled differential equations, and the TMI threshold is analytically estimated as a function of the fiber core diameter. Results show that, above the critical threshold, power transfer occurs between modes, highlighting the importance of thermal and modal modeling in the design of more stable fibers for high-power applications.