News Release

Together with Er-doped optical fiber amplification (EDFA), Raman amplification using optical fiber is one of the core technologies currently supporting optical fiber communications. The first practical application of EDFA was in the early 1990s. It uses 1.48 μm and 0.98 μm pump lasers. Furukawa Electric has led the world in the development of higher output 1.48 μm pump lasers and their practical application. The development of a high-power 1.48 μm pump laser promoted the development of Raman amplification technology and the practical application of the technology was achieved from the late 1990s to the early 2000s. In particular, Raman amplification using transmission optical fiber as the distributed amplification medium, is widely used in combination with EDFA, as a technology to improve transmission performance degradation due to optical fiber loss.
In Raman amplification, the fluctuation in the pump source can be transferred to the amplified optical signal, and this effect is maximum when the pump travels in the same direction as the signal (co-propagating) and minimum when the pump travels in the opposite direction (counter-propagating). Therefore counter-propagating Raman amplification, where the amplification is from the receiving side, is used as the standard method. In counter-propagating Raman amplification, the fluctuation of the pump light impressed on the signal light is averaged and the effect of it is reduced. However, there is a limit to the improvement of the transmission characteristics of the signal that has already propagated through the optical fiber. Co-propagating Raman amplification makes it possible to maximize the effect of Raman amplification, which further improves transmission characteristics. For this reason, it has long been hoped that new Pump Source technology would be developed to improve noise performance for co-propagating Raman amplification.

This new Pump Source technology uses Amplified Spontaneous Emission（ASE) that is emitted by a Semiconductor Optical Amplifier（SOA) as an incoherent light source. ASE is random light that does not have the fluctuations between oscillating modes that are seen in lasers with Fabry-Perot resonator structures. Even in co-propagating Raman amplification, it has no effect on the signal light.
However, optical modules for application to optical fiber communications systems must have a small size and high reliability. Furukawa Electric has SOA and advanced packaging technology that has been cultivated in the development of signal light Source for digital coherent optical transmission. By fully utilizing these technologies, we have now succeeded in the development of compact and high-output incoherent light source technology. We also promoted the development of technology for the Raman amplification of incoherent light with a pump laser and worked to expand the scope of its application to optical fiber communications systems. Because an ASE source is broadband in nature, one practical application of this technology will be as the first-order Raman pump in second-order Raman amplifiers for long or high loss spans, to reduce the cost-per-bit of transport.

Furukawa Electric has continued to lead the world in the field of pump lasers for Raman amplification and EDFA. With this new development of Pump Source technology using incoherent light, we will continue to contribute to the development of optical fiber communications systems with larger capacities and greater sophistication.

• Counter-propagating Raman amplification: Currently used as the standard method

• Co-propagating Raman amplification: Its realization was much anticipated because of its excellent improvement of transmission characteristics