Rare-earth ion doped TeO2 and GeO2 glasses as laser materials

Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by $\sim\!11\times$ the available bandwidth of C-band line systems and by $\sim\!5\times$ C+L-band line systems’. MBT offers a high potential for cost-efficient throughput upgrades of optical networks, even in absence of available dark-fibers, as it utilizes more efficiently the existing infrastructures. This represents the main advantage compared to approaches such as multi-mode/-core fibers or spatial division multiplexing. Furthermore, the industrial trend is clear: the first commercial C $+$ L-band systems are entering the market and research has moved toward the neighboring S-band. This article discusses the potential and challenges of MBT covering the ITU-T optical bands O  $\rightarrow$  L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and non-linear fiber propagation effects. Non-linear fiber propagation is taken into account by computing the generated non-linear interference by using the generalized Gaussian-noise (GGN) model, which takes into account the interaction of non-linear fiber propagation with stimulated Raman scattering (SRS), and in general considers wavelength-dependent fiber parameters. For linear effects, we hypothesize typical components’ figures and discussion on components’ limitations, such as transceivers,’ amplifiers’ and filters’ are not part of this work. We focus on assessing the transmission throughput that is realistic to achieve by using feasible multi-band components without specific optimizations and implementation discussion. So, results are meant to address the potential throughput scaling by turning-on excess fiber transmission bands. As transmission fiber, we focus exclusively on the ITU-T G.652.D, since it is the most widely deployed fiber type worldwide and the mostly suitable to multi-band transmission, thanks to its ultra-wide low-loss single-mode high-dispersion spectral region. Similar analyses could be carried out for other single-mode fiber types. We estimate a total single-fiber throughput of 450 Tb/s over a distance of 50 km and 220 Tb/s over regional distances of 600 km: $\sim\!10\times$ and 8× more than C-band transmission respectively and $\sim\!2.5\times$ more than full C+L.

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Assessment on the Achievable Throughput of Multi-Band ITU-T G.652.D Fiber Transmission Systems

Lanthanides in Non-Oxide Glasses

Three thulium doped tellurite glass compositions have been investigated The 1470 nm transition is radiative in these tellurite glasses and the radiative lifetimes are in the range of 350 to 470 µs The 1470 nm fluorescence is broad with a full width at half maximum of 105 nm Fibers have been drawn from these glasses with a loss of 07 dB/m at 1300 nm A fiber with an OH fundamental absorption of 200 dB/m at 299 µm has an OH first overtone absorption of 03 dB/m at 1480 nm The overlap between the thulium ion 1470 nm emission and the hydroxyl absorption depends on glass composition Tellurite glasses can accept large concentrations of Tm3+ ions and, as long as the hydroxyl level can be kept low, the effect of concentration quenching can be minimized Tm3+-doped tellurite glasses represent a viable alternative for the next generation of active components for S-band optical amplifiers It can be pumped at 795 nm with an absorption of ~38 dB/km/ppm and codoped with Ho3+ to avoid self-termination of the 1470 nm transition It can also be pumped at 1212 nm as efficiently as at 795 nm, but diodes are not yet available at this wavelength Using available pump wavelengths of 1064 nm and 1047 nm will require fiber lengths 15 times longer than pumping at 1212 nm

Spectroscopy of Tm3+-doped tellurite glasses for 1470 nm fiber amplifier

This paper describes in detail the amplification characteristics of gain-shifted thulium-doped fiber amplifiers (GS-TDFAs) operating in the 1480to 1510-nm wavelength region (1.49-/spl mu/m S-band) for use in wavelength-division-multiplexing (WDM) systems. Gain shifting of a TDFA, which normally has a gain band at 1.47 /spl mu/m (S/sup +/-band), is achieved by two types of dual-wavelength pumping: (1) 1.05 and 1.56 /spl mu/m or (2) 1.4 and 1.56 /spl mu/m. The main pump source at 1.05 or 1.4 /spl mu/m creates population inversion between /sup 3/F/sub 4/ (upper laser level) and /sup 3/H/sub 4/ (lower laser level), while the auxiliary pump source at 1.56 /spl mu/m reduces the average fractional inversion down to approximately 0.4, which is a desired level for gain shifting. We show experimentally that the former provides a low internal noise figure (<4 dB) due to high fractional inversion at the input end of a thulium fiber, while the latter provides a very high optical efficiency but a higher internal noise figure (/spl sim/5 dB) due to the lower fractional inversion at the input end. These characteristics were verified by numerical simulation based on a comprehensive rate equation modeling. We demonstrated a 1.4- and 1.56-/spl mu/m laser-diode-pumped GS-TDFA with an optical efficiency of 29.3% and high output power of +21.5 dBm. Gain flatness and tilt control were also investigated. These results strongly confirm the feasibility of using GS-TDFAs in practical ultralarge-capacity WDM networks.

1.49-/spl mu/m-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems

We describe the gain characteristics of thulium-doped fiber amplifiers (TDFA) for wavelength division multiplexing (WDM) signals. We optimized the TDF length and the ratio between the forward and backward pump power to realize efficient amplification. The TDFA achieved a gain of over 20 dB and a noise figure of less than 6 dB in the 1353-1483 nm wavelength region at a total pump power of 300 mW for WDM signals input at a total power of -7 dBm.

Tm-doped fiber amplifiers for 1470-nm-band WDM signals

Recently, attempts have been made to expand the carrier wavelength region for WDM transmission to the 1400 nm band to double or triple the total transmission capacity by multiplexing it with the conventionally-used 1550 nm band and/or the 1580 nm band [l-3].

S. Aozasa

Papers

Tm-doped fiber amplifiers for 1470-nm-band WDM signals

Gain-equalized thulium-doped fiber amplifiers for 1460 nm-band WDM signals