UEC e-Bulletin
June 2014 Issue
Research Highlights

Optical signal processing: Neater networks

The demand for fast access to data through optical networks requires technology that can handle ever more complex and high-bandwidth signals. However, the signal processing usually requires conversions from optical to electronic and back again, which can be power-hungry and expensive.

To move towards cheaper, more environmentally-friendly photonics, researchers are working on optical signal processing devices that require no signal conversions. A central aim for such devices is 'wavelength division multiplexing' (WDM), whereby one device can operate on many signals at the same time, if each signal has a different wavelength.

Now, Hung Nguyen Tan, Motoharu Matsuura and Naoto Kishi at the University of Electro-Communications in Tokyo have built an optical switching device that not only performs WDM, but also processes signals with different data formats, and convert signals between formats1.

Their device is based on a conventional photonic design called a Sagnac interferometric switch, and has selectable windows for collecting and processing signals of different wavelengths. It can receive and convert signal formats from so-called non-return-to-zero (NRZ) to return-to-zero (RZ) formats.

Most impressively, the tests performed by Tan, Matsuura and Kishi showed that their device could regenerate signals that have degraded due to dispersion or spontaneous emission in the optic fibres of a network. In a network with mixed NRZ and RZ signals, it demonstrated excellent signal transmission on all wavelengths.

The researchers suggest that their device has potential for other processing tasks, especially for multicasting - the delivery of information such as clock pulses to many computers simultaneously.

  1. Tan, H.N., Matsuura, M. & Kishi, N. Parallel WDM signal processing in mixed NRZ and RZ transmission networks using a single optical gate with multiple switching windows. IEEE Journal of Selected Topics in Quantum Electronics 18(2), 926-934 (2012) doi: 10.1109/JSTQE.2011.2151832
Neater networks
A device developed at the University of Electro-Communications, Tokyo, can process signals of several different wavelengths and data formats at once, and repair degradation caused by defects in optical fiber networks.