Few-Mode Cr-Doped Fibers by Cladded High Index Glass for Broadband Fiber Amplifiers

A few-mode Cr-doped crystalline core fiber (FMCDCCF) with high-index glass as a cladding is demonstrated. The FMCDCCF exhibits a core diameter of 34 μm and a V-value of 3.4, which could guide about two linear modes in theory, namely the LP
₀₁
and LP
₁₁
modes in fiber. A 4.1-dB gross gain of the FMCDCCF at wavelength of 1400-nm was obtained. Further study on higher gain is essential to open the possibility of utilizing the FMCDCCF as broadband fiber amplifiers for use in the next-generation optical transmission systems.