The use of wavelength-division multiplexing (WDM) technique has significantly advanced in various fields including telecommunications and fiber-optic communications among others. WDM systems are capable of multiplexing or demultiplexing carrier signals over different sets of wavelengths. Intensive technological advancement witnessed every day has however increased the demand for various new applications in the optical networks and signal processing. As a result, the demand for high transmission capacity without compromising the quality of the signals, signal components and time-resolved measurements at large bandwidths has increased recently. The need for signals and waveforms characterization over a single channel has been considered as an excellent move to enhance the efficiency and operations of the WDM signals.
Researchers from the Department of Electronic Engineering at Shanghai Jiao Tong University in China led by Professor Zuyuan He and Professor Xinyu Fan proposed and demonstrated the application of a modified linear optical sampling (LOS) technique for WDM signals characterization. A multiheterodyne detection-based approach was employed. The method also represented a simplified model for the same as it only focused on using a single receiving channel for the characterization and monitoring of the signals. This research work has henceforth been published in the journal, Optics Express.
The authors evaluated the workability of the modified LOS system by experimenting to measure a pseudo-random bit sequence (PRBS) signal. In the experiment, the optical carrier signal was produced by a fiber laser with a narrow linewidth and modulated using a Mach-Zehnder modulator. Included was also a Menlo Systems mode-locked laser for source sampling at the desired frequencies and modulations. The experiment involved validation of both multi-channel and single-channel WDM signals.
The research team observed a positive result in the performance of the LOS technique attributed to the importance of using multiheterodyne detection concept. For instance, only one sampling channel was required to observe 40 WDM channels successfully for a bandwidth of 1 THz and a data flow rate of 800 Gbits/s.
Indeed, the study significantly contributed towards improving the performance of the LOS techniques that have been used previously. Unlike in traditional LOS systems that relied on the optical gate effect theory which experienced a challenge in establishing the mutual relationship between the sampling pulses and data signals, the newly proposed technique uses the concept of multiheterodyne detection. It has the capability of monitoring a range of WDM signal channels over a broader bandwidth as compared to the earlier systems due to its constant sensitivity. Another advantage of LOS is that apart from the pulsed laser, other methods such as the well-defined spectrum-sources can be used for its implementation. On the other hand, LOS technique requires simplified hardware hence a simplified system for monitoring WDM channels especially the multi-channels.
Following their success, the authors are very optimistic that their proposed technique will help advance the available LOS techniques for characterization WDM channels thus solving challenges as well as introducing new applications in their relevant fields.
Wang, S., Xu, B., Fan, X., & He, Z. (2018). Linear optical sampling technique for simultaneously characterizing WDM signals with a single receiving channel. Optics Express, 26(2), 2089.
Go To Optics Express