Gain-shifted thulium-amplifier efficiency rivals that of EDFAs

July 1, 2001

Tadashi Kasamatsu and others at NEC Corp. (Nakahara-ku, Kawasaki, Japan) developed a fiber amplifier for the 1480- to 1510-nm band with efficiency of 29%, which rivals that of erbium-doped fiber amplifiers (EDFAs) in the C- and L-bands.1 This increase in efficiency may allow the gain-shifted thulium-doped fiber amplifier to be used in practical WDM networks.

Other gain-shifted thulium amplifiers have been reported, but in addition to having low optical-to-optical conversion efficiencies of around 9%, they also require a solid-state pump laser emitting at 1.05 µm. These pump lasers, typically Yb:YLF or Yb fiber, are larger and less efficient than laser diodes.

The thulium amplifier is a laser-diode (LD) pumped system using an optimized two-stage configuration. Instead of pumping the material at 1.05 µm, it is pumped by laser diodes at 1.4 and 1.56 µm.

This pumping scheme changes the way a population inversion is created in such a way that less energy is lost,and the overall efficiency increases. In a conventional upconversion pumping process, two 1.05-µm photons are needed to push a thulium ion into the excited state, from which it can release a coherent photon; in both cases there is energy loss because the exciting photons push the ion slightly above the necessary energy level. In the new design, the 1.56-µm light pumps the thulium ions to the lower state with less energy loss. The 1.4-µm light populates the upper state and creates a population inversion (necessary for lasing) between the upper and lower states.

The researchers constructed a two-stage, LD-pumped, gain-shifted thulium-doped fiber amplifier using a 40-m fiber (see figure). The first stage is forward-pumped by dual wavelengths to obtain low noise, while the second stage is bidirectionally pumped at 1.4 µm and forward-pumped at 1.56 µm to obtain high efficiency and high output power. In this case, the 1.56-µm pump source was a distributed-feedback (DFB) laser diode, with output power amplified by an EDFA; however, the maximum power was less than 60 mW for all the experiments, leading the researchers to believe that the DFB/EDFA system can be replaced with a simple laser diode.

The output power is 21.5 dBm with a total pump power of 480 mW, gain of more than 20 dB, and a noise figure of less than 7 dB.

For more information, contact Tadashi Kasamatsu at [email protected].

Yvonne Carts-Powell

REFERENCE

  1. T. Kasamatsu, Y. Yano, and T. Ono, IEEE Phot. Tech. Lett. 13, 433 (May 2001).

Yvonne Carts-Powell is a science and technology writer based in Belmont, MA.

Sponsored Recommendations

April 10, 2025
The value of pluggable optics in open-line systems is also becoming more apparent. This webinar describes this trend and explores how such modules can best be employed. Register...
Nov. 25, 2024
Join us as we explore the technological advancements, features, and applications of 800G coherent modules, which will enable network growth and deployment in the future. During...
May 30, 2024
Discover the revolution of pluggable transceivers in our upcoming webinar, where we delve into the advancements propelling 400G and 800G coherent optics. Learn how these innovations...
April 11, 2025
Taking a comprehensive approach to developing electronic products is the key to successful outcomes.