Single-Mode Cr-Doped Crystalline Core Fibers for Broadband Fiber Amplifiers

A single-mode Cr-doped crystalline core fiber (SMCDCCF) by cladded high-index glass is demonstrated. The SMCDCCF exhibits a core diameter of 25 μm and V-value of 2.4, which confirms the far-field measurement of the LP01 or HE11 single-mode at the wavelength of 1400 nm. A 2.7-dB gross gain of the SMCDCCF at a wavelength of 1400 nm was obtained. By subtracting the insertion loss from the gross gain, a net gain of 0.7 dB was obtained. To the best of our knowledge, this is the first experiment for single-mode Cr-doped fiber in which a net gain was achieved. The simulation result indicated that it was possible to achieve more than 10-dB gross gain in longer fibers of the SMCDCCFs. Further study on higher net gain is essential to open up the possibility of utilizing the SMCDCCF as broadband fiber amplifiers for the entire transmission bandwidths from 1300 to 1600 nm for use in the next-generation optical transmission systems.