Time-resolved emission characteristics of Bi/Er codoped fiber for ultra-broadband applications Amirhassan Zareanborji 1 , Graham Town 2 , John Canning 3 , Jianzhong Zhang 4 , Zinat Sathi 1 , Yanhua Luo 1 and Gang-Ding Peng 1 1 School of Electrical Engineering & Telecommunications, University of New South Wales, Sydney, NSW 2052, Australia 2 Department of Engineering, Macquarie University, NSW 2109, Australia 3 interdisciplinary Photonics Laboratories, School of Chemistry, The University of Sydney, Sydney, NSW 2006 Australia 4 Key Lab of In-fiber Integrated Optics, Ministry of Education, Harbin Engineering University, Harbin 150001, China Author e-mail address: a.zareanborji@unsw.edu.au Abstract: We fabricated several Bi/Er co-doped, Al activated fibers with different doping compositions. Their luminescence and lifetime characteristics of relevant active centers pumped by 532, 815 and 1064 nm wavelengths were measured and analyzed. OCIS codes: (060.0060) Fiber optics and optical communications; (060.2290) Fiber materials; (060.2270) Fiber characterization; (060.2300) Fiber measurements; (060.2400) Fiber properties; (999.9999) Bismuth doping; (999.9999) telecommunications 1. Introduction Rapid increase in global communications and data rates is driving demand for greater transmission capacity of optical communication networks. One of the more immediate needs is the development of fiber amplifiers and lasers to cover the accessible telecommunication window from 1200 nm to 1700 nm. Different kinds of dopants such as Bi, Er, Yb, Tm and Pr are being explored in silica based fibers to increase the useable bandwidth of fiber amplifiers and lasers [1-3]. Our recent research in Bi/Er co-doped, Al activated silica optical fibers has demonstrated ultra- broadband luminescence between 1100 and 1600 nm, covering O-, E-, S-, C-, and L-bands [4-5]. However, the Bi active centers and their energy levels are still unclear and more work is required to improve the understanding of the emission properties of these codoped fibers, and to improve the quality of co-doped fiber design and fabrication. Here, we report our recent work on the luminescence spectra and lifetime of relevant active centers of Bi/Er co- doped, Al activated fibers with different doping compositions. 2. Experiments & Results Bi/Er/Al codoped fibers & experimental tests: Several Bi/Er/Al codoped fibers of varying doping concentrations, in terms of X and Y when [Bi 2 O 3 ] ~ X mol%, [Er 2 O 3 ] ~ Y mol%, [Al 2 O 3 ] ~ 0.15, [P 2 O 5 ] ~ 0.94, and [GeO 2 ] ~ 12.9 mol%, have been fabricated. We tested 3 fiber samples: Sample A (X ~ 0.02, Y ~ 0.01), Sample B (X~0.01, Y~0) and Sample C (X ~ 0.05, Y < 0.005). Sample A has the highest Er doping. Sample B has the lowest Bi and Er doping. Sample C has the highest Bi-doping. The fibers have a numerical aperture NA ~ 0.19 and the core diameters range from 3.2 to 6.0 µm. The length of fiber samples in all experiments is 55 cm. Pump: Several pump wavelengths were used to characterize the luminescence and lifetimes of the fiber samples. The laser pump (DPSS laser source 100mW) emits at three wavelengths: λ = 532 nm, 815 nm and 1064 nm. By using optical band pass filters, experimental measurements were carried out at each of the three pumping wavelengths. The emitted powers at wavelengths were: 8.3 mW at 532nm, 0.64 mW at 815nm, 76 mW at 1064nm, respectively. Luminescence spectrum: The luminescence spectrum was measured based on a lock-in amplifier - monochromator system consisting of the laser source, a chopper, micro objective lenses, optical filters, a monochromator, a photo detector and a lock-in amplifier. The measured luminescence spectra are shown in Figure 1 for three pump wavelengths 532nm (a), 815nm (b), and 1064nm (c) individually and by copumping with all three wavelengths (532nm, 815 and 1064 nm) together for comparison (d). Lifetime measurement: Similarly the lifetime, τ, of relevant emissions of the three samples is measured for the three pump wavelengths: λ = 532 nm, 815 nm, and 1064 nm, individually, as well as the three wavelengths (532, 815, 1064 nm) altogether for comparison. Table 1 summarizes the measured lifetime, τ, of the three fiber samples. It is clear that the fluorescence and lifetime characteristics thought to be associated with Bi active centers changes significantly with both Bi and Er concentrations. This confirms that the Er co-doping not only introducing its own emission ~ 1530nm, but is contributing to the emission at around 1200 nm wavelengths [5]. If this emission is attributed to Bi defect centers, then it is reasonable to assume the two species are collocated, affecting the energy levels of the Bi-defect site (more a Bi-Er center). Based