Continuously Tunable Bi-Doped Germanosilicate Fiber Laser From 1400nm to 1479nm

Recently, tunable bismuth (Bi)-doped fiber lasers (BDFLs) have been demonstrated in phosphosilicate fiber (BPSF) for the O+E band [1]–[3] and germanosilicate fiber (BGSF) for the E+S band [4]. However, the current generation of tunable BDFLs is constrained by requiring relatively long fiber lengths, due to the low Bi concentration. A 200m of BPSF was utilized to achieve a 165mW laser output power, tunable from 1320-1370nm by applying a mechanically tunable fiber Bragg grating (FBG) [1]. A 70m of BPSF provided a 57mW of output power, which was further scaled to 144mW by employing a Bi-doped fiber amplifier (BDFA) [2]. For watt-level output, a tunable BDFL covering 1283-1460nm was reported using 80m of BPSF, achieving a 1.705W output power under a 5.18 W pump power [3]. BGSF-based tunable BDFLs remain underexplored. In the E+S band, a 65m of BGSF has been reported to provide BDFL tuning from 1366-1507nm using a plane diffraction grating, while the output power is limited to 25-50mW [4]. Here we experimentally demonstrate an all-fiber continuously tunable CW E+S band BDFL within a compact ring cavity utilizing a 23m of BGSF fabricated in-house. A 163.4mW output power with 19.1% slope efficiency at 1445nm represents, to the best of our knowledge, the highest output power for tunable BDFLs in the E+S band and in BGSFs.