Wavelength conversion technology boosts transmission capacity

Fujitsu Laboratories has developed an ultrahigh-capacity wavelength-division multiplexing system that considerably expands the transmission capacity of optical fibres in optical networks connecting data centres — without the deployment of new transceivers dedicated to new wavelength bands.

In recent years, the use of social networks and streaming video has contributed to exponential increases in the volumes of data handled by data centres. Moreover, many predict that data circulation will grow dramatically in the future with the spread of 5G communications and 8K video technologies. Though data centre operators have already connected multiple data centres with optical networks and use distributed storage for disaster recovery and distributed processing for high-speed processing, they need to expand transmission capacity even further to effectively prepare for the increases in data volume anticipated in the immediate future.

Expanding transmission capacities between data centres can be accomplished by increasing the number of optical fibres; however, additional fees would be assessed based on the number of optical fibres used, presenting a significant cost burden for operators. Another option is the simultaneous use of new wavelength bands outside the C-band — the wavelength band used for optical transmissions defined by ITU-T, the Telecommunication Standardization Sector of the International Telecommunication Union — however, this method would necessitate the separate development of transceivers that could support each band.

Now, Fujitsu Laboratories has developed what is claimed to be the world’s first broadband wavelength conversion technology that can batch convert C-band optical signals to new wavelength bands, including the L-band and S-band, for transmission, reconverting them back to the original C-band when received.

First, the C-band optical signal is combined with two pump lights, generating a signal with mixed wavelength. The pump lights change the signal’s refractive index of a nonlinear optical medium which the signal passes through and outputs converted signals at a different wavelength. A similar principle is used on the receiver side to return the transmitted optical signal to the C-band.

With this technology, it becomes possible to convert an optical signal to an arbitrary wavelength band efficiently by choosing the wavelengths of two pump lights, based on the chromatic dispersion characteristics of various nonlinear optical media. Additionally, the technology can reduce the noise superimposed on the signal after wavelength conversion by synchronously controlling the pump lights. This means it can simultaneously convert the signal’s wavelength efficiently while maximising the quality of the optical signal.

Fujitsu Laboratories used the technology to create a prototype system to convert an optical signal in C-band to L- and S-bands, then multiplexed them for transmission, confirming in principle that the technology could triple available wavelength without the use of transceivers for each new wavelength band. Transmissions using an even greater variety of different bands thus become possible, allowing data centre operators to use existing equipment as is to raise the efficiency of optical fibre utilisation and thereby expand transmission capacity from 2–10 times as needed.

This promises to eliminate the kind of network bottlenecks that could pose challenges for high-volume users that need to store, back up or perform parallel analysis on large volumes of data distributed between multiple data centres. This includes cases that many expect to increase dramatically in the near future, such as transfers of unstructured data including 8K video material and device log information connected through 5G networks. In addition, data centre operators can immediately make use of new C-band transceivers that will be developed going forward in wavelength bands outside the C-band.

Fujitsu Laboratories aims to incorporate this technology into a new line-up of the Fujitsu Network 1FINITY series of optical transmission systems, in fiscal 2019. In addition, the company is considering extending the technology to data centre operators, contributing to the creation of new business for its customers.

Image credit: ©stock.adobe.com/au/Maxim_Kazmin