Optically restorable WDM ring network using simple add/dropcircuitry

An optically restorable wavelength division multiplexing (WDM) ring network carrying ATM traffic is presented. It uses a new architecture with simple add/drop circuitry allowing traffic restoration in case of a ring breakage by independent local actions at the affected nodes. Multisession video traffic at 155 Mb/s was demonstrated between stations distributed along the ring. No visible video degradation was observed during the 50 ms restoration time caused by a ring breakage     

Frequency-locked loop circuit providing large pull-in range

Presents a frequency-locking circuit that provides a larger pull-in bandwidth than that of a conventional automatic frequency control (AFC) circuit. In addition, the proposed circuit has a stable mode of operation over the full frequency response of the frequency discriminator, and locks the oscillator at exactly the centre frequency of this discriminator. The frequency offset and the unstable mode of operation presented by the conventional circuit outside its pull-in range can thus be eliminated.<>