Higher Gain of Single-Mode Cr-Doped Fibers Employing Optimized Molten-Zone Growth

Higher gain of single-mode Cr-doped crystalline core fibers (SMCDCCFs) with longer fiber length employing an optimized molten-zone in laser-heated pedestal growth (LHPG) technique is demonstrated. The optimized molten zone in the LHPG is determined by an empirical formula. The SMCDCCFs exhibit a length of 24-cm, a core diameter of 25-μm, and a V-value of 2.40 which confirms the LP ₀₁ single-mode operation. A 6.44-dB gross gain and a 4.44-dB net gain with 24-cm fiber length of the SMCDCCF at wavelength of 1.4-μm were obtained. Further studies on higher gain of more than 10-dB gross gain of the SMCDCCFs including a longer length of 30-cm, a lower loss fiber, and a suitable annealing technique are essential to develop the SMCDCCFs as broadband fiber amplifiers for practical use in the next-generation fiber transmission systems and are currently under investigation.