In this scheme, some of the already deployed and active
ONUs would be assigned, in a static manner, to a distinct wavelength domain for both
upstream and downstream transmission lanes. While the effective data rate on each
wavelength would remain the same, there would simply be fewer ONUs to share that
raw bandwidth capacity, increasing the bandwidth available per subscriber. The extreme
example of this approach would be a WDM PON system wherein each subscriber
is allocated unique wavelengths for upstream and downstream transmission. It is still
not clear when WDM components will be available at the appropriate prices to make
this solution commercially viable. The price of the tuneable laser sources applicable for
the ONUs is continuously dropping, allowing for development of colourless subscriber
units, though the necessary control electronics, wavelength tracking systems and the
need to employ the DWDM channel allocation to assure sufficient number of subscribers
are still cost-prohibitive. The complexity of the OLT unit connected with the need
for a dedicated receiver per subscriber port as well as highly complicated wavelength
allocation plan and the requirement for a special wavelength allocation protocol make
the management of WDM PON a real nightmare from the logistic point of view.
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