Liu C.-NLi J.-WTung Y.-HYang C.-CCheng W.-CHuang S.-LCheng W.-H.SHENG-LUNG HUANG2021-09-022021-09-02202019430655https://www.scopus.com/inward/record.uri?eid=2-s2.0-85082174720&doi=10.1109%2fJPHOT.2020.2974802&partnerID=40&md5=3230cb7204e88e585a7ae9e6bcff91afhttps://scholars.lib.ntu.edu.tw/handle/123456789/581119Tetrahedral chromium (Cr4+)-ions is the main contributor to gain in the broadband single-mode Cr-doped crystalline core fibers (SCCFs). We have demonstrated a gross gain of 8-dB on a length of 27-cm for a 300-nm broadband SCCF using a thermal annealing technique. Gross gain and fiber length are the highest yet reported for the SCCF. The record gain is mainly due to both the longer fiber by aligned molten-zone growth and Cr4+-ions enhancement by thermal annealing. The enhancement mechanism of the Cr4+-ions in the SCCF is experimentally verified by the means of superconducting quantum interference device (SQUID) and electron probe X-ray micro-analysis (EPMA). As a practical application of the proposed 8-dB gain in the SCCFs in fiber transmissions, a 25-Gb/s error-floor free link is successfully demonstrated. ? 2009-2012 IEEE.Annealing; Chromium; Chromium compounds; Fibers; Ions; Optical fiber fabrication; Quantum interference devices; SQUIDs; Cr-doped; Crystalline core; Electron probe; Enhancement mechanism; Fiber length; Molten zones; Single mode; Thermal-annealing; Fiber amplifiersjournal article10.1109/JPHOT.2020.29748022-s2.0-85082174720