Fujitsu Laboratories (Kawasaki, Japan) and the Fraunhofer Heinrich Hertz Institute HHI (Berlin, Germany) have developed a new method to simultaneously convert the wavelengths of wavelength-division-multiplexed (WDM) signals necessary for optical communication relay nodes in future WDM-based optical networks, and have successfully tested the method using high-bandwidth signal transmission in the range of 1 Tbps.
In conventional methods, each individual optical wavelength is converted into an electrical signal and re-transmitted at a new wavelength, which is impractical for terabit-class processing as each wavelength requires its own O/E/O circuit. Using the new technology, the optical wavelength conversion and the polarization state are controlled at the same time, so simultaneous wavelength conversion of wide-band optical signals can be achieved without restrictions on the wavelengths of the optical input signal or the modulation formats.
As a result, processing can be achieved with a single wavelength converter, regardless of the number of wavelengths multiplexed. Therefore, considering optical signals in excess of 1 Tbps multiplexed from ten wavelengths, for example, the new method can process them using just one-tenth of the power or less compared to previous technologies that required a separate circuit to convert each wavelength into an electrical signal and back.
It is known that by combining an optical signal comprised of multiple wavelengths with pump light when inputting into a nonlinear optical medium, it is possible to generate a wavelength converted light that is still mixed with the input optical signal. Fujitsu Laboratories and Fraunhofer HHI developed a new simultaneous wavelength conversion technology that, in accordance with the wavelength conversion, alters the polarization state of the optical signal, and, using a polarization filter instead of the wavelength filter used in previous technologies, removes the optical signal prior to the wavelength conversion. It then extracts just the optical signal after the wavelength conversion. By controlling the spacing of the pump light's wavelength, the wavelength after conversion can be controlled at the user's discretion.
The companies say thatthis represents the world's first successful implementation of a simultaneous wavelength conversion capability that functions without any restrictions on the wavelength of the optical signal input or the modulation format.