Observation of strong mode coupling in multimode step index silica optical fibers with fluorinated thermoplastic polymer cladding

Using the power flow equation, the state of mode coupling in step index multimode silica optical fiber with fluorinated thermoplastic polymer cladding is investigated in this work. Coupling coefficient is determined by employing our previously reported calculation method. The silica optical fiber with fluorinated thermoplastic polymer cladding shows much stronger mode coupling than the all plastic-clad silica fibers investigated in earlier works. Consequently, it takes much shorter fiber length for the equilibrium mode distribution or steady state distribution to develop (faster launch beam narrowing), which is of great interest in employing silica optical fiber with fluorinated thermoplastic polymer as a part of telecommunication, medical and sensory system.