<title>Novel OADM structure for two-fiber unidirectional optical path protection switching ring networks</title>

Abstract

SWavelength Division Multiplexing (WDM) optical ring network is becoming more and more attractive due to its high capacity and survivability against fiber breaks. At the same time wavelength routing simplifies the node structure by using optical add/drop multiplexer (OADM) and optical cross-connect (OXC) in the network. In the two-fiber unidirectional optical path-protection switching ring (TUPSR) network, two separate OADM equipments are required to add/drop channels from the two fiber-rings simultaneously. Due to this high price, the cost benefit introduced by the WDM systems is reduced. In this paper, a novel OADM structure is proposed and demonstrated for two-fiber unidirectional optical path protection switching ring network. The OADM is designed with only one arrayed-waveguide grating (AWG) multiplexer in a loop-back configuration. Being used in bidirectional mode, the proposed OADM can add and drop any channel to and from both fiber-rings of the TUPSR simultaneously with only one module. As a result it is cost effective. Experimental results show that the degradation observed in the receiver sensitivity is very limit when the proposed OADM module is used in the two-fiber unidirectional optical protection switching ring network to add/drop multiple channels. The restoration time is less than 7 ms, which satisfies the requirement of ITU-T recommendations. Performance of the TUPSR against the two-fiber unidirectional optical line protection switching ring (TULSR) is also analyzed. It can be derived that the TUPSR has better performance compared to the TULSR not only on the transparent-ring circumference but also on the reliability and the simplicity of control.keywords optical add/drop multiplexer (OADM), wavelength division multiplexing (WDM), two-fiber unidirectional optical path protection switching ring (TUPSR), two-fiber unidirectional optical line protection switching ring(TUPSR), . INTRODUCTIONWavelength Division Multiplexing (WDM) optical ring network is becoming more and more attractive due to its high capacity and survivability against fiber breaks. At the same time wavelength routing simplifies the node structure by using optical add/drop multiplexers (OADMs) and optical cross-connects (OXCs) in the network [1].The WDM optical ring networks can be divided into two catagories according to the object being protected -optical path protection switching ring network and the optical line protection switching ring [2,3] network. In an optical line protection switching ring, the multplexed section is protected by the collaboration ofthe nodes before and after the fiber cut. APS (automatic protection switching) protocol is required during the protection procedure. As a result the protection is slow and complicated. Whereas in an optical path protection switching ring network, each of the opitcal signal is transmitted via two different physical paths that are call working path and protection path respectively. At the destination node the two signals are monitored and only the one with better quality ...