17-dB Net Gain of Broadband Single-Mode Cr-Doped Crystalline Core Fiber Fabricated by Small Core

A record net gain of 17-dB has been demonstrated in a 300-nm broadband single-mode Cr-doped crystalline core fiber (CCF) with a 19-μm core diameter and 18-cm fiber length. The gain-per-unit-length of the CCF, which is an impressive 94 dB/m, is significantly higher than that currently achieved in other rare-earth doped fiber amplifiers, such as Er and Bi-doped fibers. This high gain was achieved by matching the transmission mode between CCF and single mode fiber for improving the coupling efficiency. We controlled precisely the conical molten-zone in the growth process, as well as the optimization of the Cr⁴⁺ concentration through thermal annealing and polarization pumping techniques. We also measured the noise figures of several core diameters, finding that the 19-μm core diameter CCF exhibited a noise figure 4.2 dB lower than the previous 25-μm core diameter CCF. This result is important because it indicates that the smaller diameter CCF is capable of providing even better signal-to-noise ratios. And the error-floor free data transmission of the CCF was successfully demonstrated at a rate of 10 Gb/s. This is an important achievement because it shows that the CCF has the potential to be used in high-speed communication applications.