Real-time all-optical quality of service monitoring by use of correlation and a network protocol to exploit it

Abstract

We propose to use optical correlation to measure the quality of an optical link in real time, staying completely within the optical domain. We transmit a test signal of 010 and correlate the received (degraded) signal with 010. The strength and shape of the output measure dispersion and attenuation in just 3 bit periods (75 ps at 40 Gb/s) compared with minutes by traditional methods. Correlation becomes feasible owing to the recent development of tapped delay lines with very large numbers of taps. We present simulations showing that this technique can detect attenuation, dispersion, noise, and jitter. With this instantaneous quality-of-service information available to all nodes in a network, new protocols will enable the network to select paths based on quality, allowing service providers to take into account the system's physical impairments when selecting new light paths or when restoring existing ones and to guarantee varying levels of service. We present one such protocol.

Real-time all-optical performance monitoring using optical bit-shape correlation

“…Figure 11(a) shows the effect on the correlator output as the attenuation is varied. Figure 11(b), the theoretical case for an ideal square pulse, is repeated here from [8]. The amplitude of the correlation function reduces in a linear fashion, as expected.…”

“…Thus if a test stream 010 is sent, the quality is measured in three bit periods, which could be tens of picoseconds, compared to many seconds or minutes for techniques that use BER or eye diagrams. In earlier work [8], we showed in simulation that the correlation pulse shape relates well to eye-diagram opening. The optical correlator we used is a novel type based on a passive, White cell-based TDL.…”

“…In [8] it was shown that the area above the threshold related very well to eye-diagram measurements of attenuation, dispersion, noise, and jitter and to combinations of these effects. It is not the intent here to diagnose what is wrong with the link, but rather to monitor whether it currently meets some minimum standard due to combined impairments.…”

“…We propose a quality-of-signal measurement method that is all optical and provides results in real time [8]. The approach is based on correlating the shape of each received data bit with a standard bit representing the ideal shape of a sent bit.…”

Hardware Demonstration of Extremely Compact Optical True Time Delay Device for Wideband Electronically Steered Antennas

“…Recently the White cell has been adapted to a variety of optical signal processing applications including optical switching [29], optical correlation and quality-of-signal monitoring [30], and optical true time delays for phased array antennas. The detailed operation of these devices is reviewed, for example, in [24], so we will only summarize here.…”