14 August 2003 All-optical quality-of-signal monitoring in real time
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An new optical correlator containing a tapped delay line with thousands of taps is described. This enables ultra-high resolution correlation. We apply this to monitoring quality-of-signal by correlating the received, degraded bits with and un-degraded signal. The strength of the correlation signal, which is all optical, is proportional to the quality. Dispersion and attenuation can be evaluated in less than 100 ps at 40Gb/s, and jitter and noise in less than 100 ns. This is a significant improvement over minutes or even hours for bit-error-rate measurements. Simulations show good correspondence to eye-diagram measurements, the conventional (but slow) way to measure signal quality. If a network node can know the quality of all its links in real-time, it can re-route signals around poor links, and provide restoration and protection as well. The key to all this is an optical correlator with a very large number of taps in its internal tapped delay line. Our device uses a White cell and a fixed micro-mirror array. In a White cell, light bounces back and forth between three spherical mirrors. Multiple beams circulate in the same cell without interfering and are each refocused to a unique pattern of spots. We make the spots land on the micro-mirror array to switch between cells of slightly different lengths. Our current design provides 6550 possible delays for thousands of light beams, using only ten mirrors, a lens, and the micro-mirror array. We have developed two routing and protection protocols to exploit having this real-time information available to the network.
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Betty Lise Anderson, Betty Lise Anderson, Feras Abou-Galala, Feras Abou-Galala, David Rabb, David Rabb, Arjan Durresi, Arjan Durresi, } "All-optical quality-of-signal monitoring in real time", Proc. SPIE 5246, Active and Passive Optical Components for WDM Communications III, (14 August 2003); doi: 10.1117/12.511250; https://doi.org/10.1117/12.511250


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