Hi corners,Avanex does have two dispersion compensation technologies. The first is the VIPA based product and the second is this "12 etalons" thing you readabout on the Gilder site. You can make something called an all-pass filter using special etalons.An etalon is simply 2 parallel mirrors spaced closely. In this case, onemirror is 100% and the other is not. These are called Gires-Tournois (G-T) etalons.G-T cavities have a certain chromatic dispersion characteristic. It'ssort of a sine wave over wavelength. One cavity by itself is not particularly helpful since the chromatic dispersion from optical fiberis not periodic, but basically flat over wavelength. However, if you cascade a whole bunch of different G-T cavities, the composite chromaticdispersion can correct optical fiber dispersion. The compensation by this cascaded set of G-T etalons will be periodic. Itwill only work for some passband centered on the ITU grid. In the space between channels, you'll get the wrong compensation. Fortunately, thereshouldn't be any signal in the space between channels. Using this approach, you can not only correct fixed dispersion for allchannels, you can also correct dispersion slope over a set of channels. This approach is mathematically identical to cascaded ring resonators inplanar lightwave circuits. Christi Madsen at Lucent (I think she's still there) has published a number of papers and even a book on desiging general filters using all-pass filters. Her empirical work has focused on the ring resonators, but the theory works for G-T etalons as well.-chris
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