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Lasers & Sources

Amplification with 200nm bandwidth using Tm- and Er-doped fibers

By pumping short tellurium-oxide fibers doped with erbium and thulium oxides with a high-power source, we can produce gain blocks for amplification in the S-, C- and L-bands.
6 April 2006, SPIE Newsroom. DOI: 10.1117/2.1200602.0110

In our recent research on Er-doped short fibers for amplification, funded by the Engineering and Physical Research Council (UK), we have demonstrated that the Er-Ce-co-doped tellurite fibers can have twice as large a signal gain as Er-doped fibers (see Figure 1) using a 980nm excitation source.1 In this fiber, co-doping with cerium oxide (Ce2O3) enhances the pump-inversion efficiency, allowing rapid inversion of ions to the desired 4I13/2 Er-ion energy level. This causes amplification from 1530-1580nm: the entire C-band and a part of the L-band. By controlling the doping of ions (Er and Ce), fiber length, and pumping scheme, the amplification bandwidth can be extended up to 1615nm into the L-band.

Figure 1. Amplification in Ce-Er-doped fibers in C- and L-bands using a 980nm pump.1

The improvement in pump-inversion efficiency is noticeable by recording the diminution of green up-conversion in the fibers. However, the Tm-doped fibers cannot be pumped to achieve sufficient inversion for amplification from 1420–1520nm (see Figure 2), which covers the S-band and the shorter wavelengths of S+-band. By sensitizing Tm-ions with Yb-ions, the 980nm excitation source can be used effectively.2 This, surprisingly, also significantly reduces the blue up-conversion emission at 480nm and allows the favorable 800nm amplified spontaneous emissions to build up and contribute to amplification in the 1420–1520nm bandwidth.2 This scheme thus allows self-utilization of energy at 800nm for the inversion process and can be engineered to achieve larger gain than current (see Figure 2).

Figure 2. Gain versus wavlength for Tm-doped tellurite fibers for amplification in the S-band.2

The tellurium-oxide fibers can also be co-doped with Tm and Er oxides for designing a single-pump-source-driven broadband source with 210nm bandwidth in the S-, C-, and L-bands.3

The tellurite fibers have loss in the range of 2–5dB/m in the telecommunication window due to residual OH-ions, and the gain media are typically 5–15cm long, depending upon the amplification wavelengths. The new fibers thus open up opportunities for on-chip integration of coarse WDM technology for metro-networks. Modularization of gain blocks with transceivers may be a way forward for capturing this future market.

Animesh Jha
Photonic Materials Group, University of Leeds
Leeds, UK