Multi-Channel Optical 3R Regeneration and Buffering for Networking Applications

Northwestern University, Evanston IL

Investigators

Abstract

0401251 KUMAR One of the critical features that are likely to hinder massive deployment of optical networks using already existing technologies is their inability to perform optical IP routing functions. Optical buffering is one of the key techniques for efficiently implementing optical/photonic packet switchers or IP routers. Buffers are needed for queuing packets at the access nodes in order to bridge the photonic-electric speed gap, for enabling receivers to handle data at rates faster than can be processed, and for rate conversion in conjunction with optical switches. A preliminary analysis shows that the loop-type dynamic storage techniques are the most efficient for practical implementation of optical buffering, although the issue of integrability of such devices still needs to be addressed. It is desirable to have a long storage time, extending to tens of seconds, if possible. Given the fact that in fiber storage loops the signals are stored dynamically, it is equivalent of several million kilometers of distance traveled by the stored signals. For this reason optical 3R regeneration (retiming, reshaping, and retransmitting) is a key enabling technology. It is needed to prevent distortion of the data signals that get impaired by the amplified spontaneous emission noise, chromatic and polarization-mode dispersion, and optical nonlinearity in the buffer components. Furthermore, the existing optical buffering technologies allow data storage only at a single channel. On the other hand, it is clear that the next generation optical networks will use massive wavelength-division-multiplexing. From this standpoint it is highly desirable to have a buffer that is capable of storing multi-channel data in a single device versus the conventional approach in which a separate buffer has to be dedicated to each channel. The multi-channel buffering approach provides more efficient and economic solution in terms of smaller footprint, lower power consumption, and smaller number of components needed for handling the same number of packets. In addition, for networking applications it is important to have optical add-drop multiplexer (OADM) functionality in the buffer. To the best of the PI's knowledge, thus far, OADM functionality has not been demonstrated in existing and proposed optical buffers. In this project a 4-channel optical buffer using a nonlinear asymmetric loop mirror (NALM) and a synchronous electro-absorption modulator (EAM) operating at 20 Gb/s data rate per channel is proposed. The OADM functionality will be demonstrated, i.e., adding additional packets (at additional wavelengths) to the buffer without affecting the packets already stored and dropping from the buffer stored packets leaving the packets at other channels intact. The multi-channel optical buffer will have simultaneous 3R regeneration feature for all channels, allowing tens of seconds of storage time. Detailed and accurate numerical simulation and parameter studies of the proposed multi-channel buffering system will be performed. The goals of the modeling include: 1) maximum packet storage time and its limiting factors, 2) degradation of the signal-to-noise ratio versus storage time, 3) limits to system scalability in terms of data rate per channel and the number of channels. Intellectual merit of the proposed activity: The proposed activity will address two of the fundamental roadblocks to widespread deployment of packet-switched optical networking, namely, 3R regeneration and optical buffering. Theory and practice will need to go hand-in-hand for a successful outcome. The PI and co-PI bring a unique combination of theoretical and experimental expertise and skills to bear upon the problem. Broader impacts of the proposed activity: The students will get involved in cross-disciplinary work. They will be trained in the network engineering concepts in addition to the usual curriculum in electro-physics and photonics. The ECE department at Northwestern University has a strong group in communications networks. Consequently, a full menu of courses is available to the students for formal learning and a diverse student body exists for peer-to-peer learning. Outreach activities through the Center for Photonic Communication and Computing at Northwestern will be undertaken to have a much wider impact on the community at large. Full scale efforts will be made through all resources available at the University to engage underrepresented students in this project. See the Project Description for further details.