Differential delays due to fiber dispersion represent the ultimate limitation on achievable guard-times and packet durations for WDMA/TDMA "switchless" optical transport networks. A delay compensator based on fiber gratings is proposed to decrease such delays Keywords-"Switchless" Optical Network, Delay Compensation I. WDMA/TDMA "SWITCHLESS" OPTICAL NETWORK The European Union ACTS project SONATA has shown the feasibility of a PON-based (passive optical network), 200 Tbit/s "switchless" optical

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... etwork transport architecture on a national scale [1] serving up to 20 million terminals, capable of transporting and switching multiple client layers (eg ATM, PSTN) within a single optical technology layer, with common control for all client layers. No electronic switches or cross-connects are required within the national-scale network. A WDMA/TDMA, burst-mode optical packet format is employed, using time-slots within frames on each wavelength. A time-slot of 10 ms and a frame duration of 10 ms are envisaged, i.e. 1,000 time-slots per frame. For a national-scale network, up to 800 wavelength channels are employed with 0.05 nm channel spacing within each PON, using heterodyne detection. Signalling is required between end terminals and a network controller, to request and allocate time-slots (optical packets) on appropriate wavelength channels to prevent packet collisions and output contentions at the receiving terminals. The "switchless" optical network [1] is intended to perform the concentration/distribution, switching and routeing functions within a single network layer by providing end-to-end optical connections between a large number of terminals, over a large geographical area extending to 1,000 km from terminal to terminal. The structure is shown in figure 1 . The fast tunable terminals are attached to amplified passive optical network (PON) infrastructures directly connected to a single passive wavelength router with N input and N output ports, i.e. an N´N wavelength multiplexer. Any terminal wishing to communicate with another terminal simply tunes its transmitter and receiver, in the allocated time slots, to a wavelength channel carrying multiplexed traffic through the wavelength router between the pair of PONs to which the transmitting and receiving terminals are attached.