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Sensitivity evaluation of baseband carrier-sense circuit for optical CSMA/CA packet networks

The ability to detect the presence or absence of optical signals on specific channels is used to prevent packet collisions in networks implementing the optical carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. This optical carrier-sense capability can be provided by a baseband carrier-sense circuit (BCSC), which directly detects the envelope of optical packets propagating in the network. A fraction of the optical power of packets passing through a node is tapped off for detection at the BCSC. It is therefore desirable to minimize the amount of optical power required at the circuit to perform reliable packet detection such that the additional insertion loss encountered by the in-transit packets is minimal. However, the performance of the BCSC is limited at low levels of received optical power. For a given topology and size of a practical optical CSMA/CA packet network, knowledge of this sensitivity limit is essential for determining the power budget while ensuring that collision avoidance and minimal insertion loss are achieved. This paper identifies the factors that contribute to the sensitivity of the BCSC. A theoretical description of a practical implementation of the BCSC is derived and an efficient method to evaluate the sensitivity is presented. The theory is validated using experiments, with results showing that the model presented in this paper is a useful tool for the design and performance analysis of highly sensitive BCSCs in future optical CSMA/CA networks.