Bismuth and erbium codoped optical fiber with ultrabroadband luminescence across O-, E-, S-, C-, and L-bands Yanhua Luo, 1 Jianxiang Wen, 2 Jianzhong Zhang, 1,3 John Canning, 4 and Gang-Ding Peng 1, * 1 Photonics & Optical Communications, School of Electrical Engineering & Telecommunications, University of New South Wales, Sydney 2052, New South Wales, Australia 2 Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Shanghai University, Shanghai 200072, China 3 Department of Physics, Harbin Engineering University, Harbin 150001, China 4 Interdisciplinary Photonics Laboratories, School of Chemistry, University of Sydney, Sydney, New South Wales 2006, Australia *Corresponding author:g.peng@unsw.edu.au Received May 2, 2012; revised July 4, 2012; accepted July 4, 2012; posted July 5, 2012 (Doc. ID 167878); published August 13, 2012 We report the first (to our knowledge) development of a Bi/Er/Al/P codoped germanosilica optical fiber showing ultrabroadband luminescence between 1000 and 1570 nm, covering O-, E-, S-, C-, and L-bands, when pumped by 532, 808, or 980 nm lasers. The fluorescence profiles are found highly pump wavelength dependent, closely asso- ciated with different combinations of excitations from both Bi centers and Er ions as active centers. With a proper selection of pump wavelength(s), this Bi/Er codoped fiber could be used as an ultrabroadband gain medium for ultrabroadband amplified spontaneous emission sources, fiber lasers, or amplifiers in telecommunications and in other fields. © 2012 Optical Society of America OCIS codes: 060.2280, 060.2290, 060.2320. Water-free optical fibers have expanded the accessible telecommunications window across the entire spectrum from 1200 to 1700 nm. To date, commercial exploitation of this window has been largely limited to that enabled by erbium (Er)-doped fibers that operate over only 1520 to 1620 nm (C- and L-bands), a small portion of the available spectrum [ 1]. The O- (1260–1360 nm), E- (1360–1440 nm), S  - (1440–1460 nm), and S- (1460–1530 nm) bands are not fully utilized as yet. Recent reports show ultrabroadband (1100 to 1500 nm) gain across O-, E-, and S-bands of the telecommunica- tions window using bismuth (Bi)-doped silica glasses [ 2, 3]. Bi-doped silica fibers were also reported with lumi- nescence in the region of 1050 to 1300 nm [ 4]. Er doping in Bi-based glasses [ 5, 6] or in Bi-based glass fibers (Bi- EDFs) [ 7– 10] have been studied for improving Er emis- sion in C- and L-bands. These Bi-doped fibers and Bi- EDFs (kind of Bi/Er codoped fibers) are developed for O-, E-, and S-bands, and for C- and L-bands, separately. For ultrabroadband gain from 1100 to 1600 nm, includ- ing all the O-, E-, S-, C-, and L-bands, Bi/Er codoping in bulk glasses has been targeted [ 11, 12]. Kuwada et al. re- ported ultrabroadband fluorescence between 1160 and 1570 nm from a Bi and Er codoped bulk silica glass mix melted in a crucible [ 11]. Peng et al. reported ultra- broadband fluorescence between 1160 and 1580 nm, from Bi/Er codoped germanate glasses [ 12]. Despite these impressive achievements, it stands out that so far no Bi/Er codoped optical fiber has been developed, nor one that demonstrates ultrabroadband gain across all O-, E-, S-, C-, and L-bands. Further, the separate pumping of particular bands is not sufficient to confirm that true ul- trabroadband amplification would be possible, since it has not been confirmed that each emission band is asso- ciated with distinct defect sites. The only Bi and Er co- doping in silica fiber is reported in [ 13]. However, the codoping of the Er–Bi ions is used to supposedly alleviate clustering and improve fluorescence efficiency for high Er concentrations [ 13], although they do observe “un- usual” low emission around 1220 nm and narrow emis- sion at 1380 nm. Here, we report the first (to our knowledge) Bi/Er/Al/P codoped germanosilica fiber with ultrabroadband lumi- nescence over the 1100–1570 nm range. By introducing a multicomponent glass (Bi, Er, Al, P and Ge), we hope to increase the range and number of luminescent Bi defect sites. In addition, we report on simultaneous pumping of the fiber to confirm that the ultrawideband fluorescence obtained by selective pumping is in fact ad- ditive and that true simultaneous and ultrabroadband emission is feasible. We also explain the Er luminescence when pumped at 800 nm. The fiber is fabricated by in situ modified chemical vapor deposition (MCVD) doping [ 14] with concentra- tions of Er 2 O 3  ∼ 0.01, Al 2 O 3  ∼ 0.15, Bi 2 O 3  ∼ 0.16, P 2 O 5  ∼ 0.94, and GeO 2  ∼ 12.9 mol:%, respectively. It is noted that the compositions are similar to those reported in the melted Bi–Er bulk glass mixes: Bi 2 O 3  ∼ 1, Al 2 O 3  ∼ 7, Er 2 O 3  ∼ 0.1, GeO 2  ∼ 5, and TiO 2  ∼ 5 mol:% [ 11] and (95 − x − y) GeO 2 · 5Al 2 O 3 · xBi 2 O 3 · yEr 2 O 3 mol:% (x  0, 0.3, 0.5, 1.0; y  0, 0.5) [ 12]. The composition is modified to fit into the MCVD process—introducing P to reduce the reaction tempera- ture and increase possible defect sites, decreasing Bi to reduce the loss, and introducing Ge for core index. We selected the ratio of Al 2 O 3 :Bi 2 O 3  close to 1∶1 to allow for possible optimal formation of Bi–Al ion pairs. The fi- ber absorption spectrum, as shown in Fig. 1, was mea- sured by cutback. The inset of Fig. 1 gives an image of the cross section of the fiber. The fiber has a numerical aperture NA ∼ 0.19, a core diameter of 4.8 μm, and a cut- off wavelength λ c ∼ 1.68 μm. As shown in Fig. 1, there are distinct absorption bands at 517 (A), 717 (B), and 1090 nm (D) as well as a shoulder August 15, 2012 / Vol. 37, No. 16 / OPTICS LETTERS 3447 0146-9592/12/163447-03$15.00/0 © 2012 Optical Society of America