Abstract

Wavelength-routing [1] in the access network offers the prospect of high security and Gbit/s capacity to the end user. However, for large numbers of wavelengths (e.g. >32) issues of stability and precision become important. In this paper, we present a novel 3-stage switched ATM access architecture, shown in fig. 1, which (while maintaining the above benefits) can route to large numbers of customers using a minimal set of wavelengths, and also allows an evolutionary path from current passive optical networks (PONs). We exploit the functionality of cascaded programmable and passive arrayed-waveguide gratings (AWGs) [2], to provide a multi-dimensional bi-directional addressing strategy, based on spatial, wavelength and temporal multiplexing. The same network can be used for independent upstream routing by utilising the reciprocal input and output AWG ports, and taking advantage of their cyclic-shifting properties to avoid potential collisions. Stage 1 in the proposed architecture is a P-way splitter with semiconductor optical amplifiers (SOAs), stage 2 is an active coarse AWG with Q output ports, and stage 3, located at the distribution point (DP) near the end users, is a passive coarse AWG with R output ports. To upgrade from existing PONs, the 3^rd stage can also equally consist of an R-way optical splitter, with coarse wavelength-filters at the customer end. At the DP, the coarse AWGs (insensitive to temperature changes > 70°C) each have R=24 output ports, which allows the architecture to map onto 99% of the current UK network topology. The parameter R also defines the number of wavelengths to be 24. The total number of customers served is the product PQR=6912, where P=12, Q=R=24. Since only coarse demultiplexing is performed, the need for stable and accurately defined wavelength sources at the exchange and end user is obviated.

© 1998 IEEE