On the number of fiber connections and star couplers in multi-star single-hop networks

The single-star optical network is limited in size b y the available power budget. When the network size exceeds the number of connections a star coupler can support, it becomes necessary to use multiple passive star couplers to implement the network. The cost of a multi-star optical network is determined by the number of fiber connections per station and the number of star couplers in the network. To reduce the cost of the network, it’s desirable to use as less fiber connect ions per station and star couplers as possible. I n this paper, we consider two multi-star implementations of of single-hop networks, and discuss how t o implement them with least cost. Emerging lightwave networks are expected to provide end users with the integrated services at ultrahigh speed. However, the maximum data rate a t which a user can access the network is limited by the electronic interfaces. The key to improve the aggregate network bandwidth is to introduce concurrence among the users. Wavelength Division Multiplexing is a scheme in which light is modulated into different wavelengths each running at a speed compatible with electronic devices. This scheme has been recognized as one of the most promising and effective ways to remedy the performance bottleneck of the relatively slow electronic interface devices. A bundle of wavelengths, with enough spacing in between wavelength channels to avoid interference, are able to be used for transmission in the same fiber simultaneously. Fig. 1 shows a typical WDM network in which N stations connect to a common optical passive star eoupler[9, 131, each via a pair of unidirectional fibers. Each station has a set of transmitters and receivers. Each transmitter (receiver) is tuned to a specific wavelength from which it transmits (receives) light signals into (from) an optical fiber. A passive star coupler of dimension N can be viewed as an N x N switch where any incoming light signals is evenly split into N weaker signals, one for each output port. A transmission from one station to another station is accomplished by tuning a transmitter of the sending station and a receiver of the receiving station to the same wavelength. Note that several transmissions can be carried out simultaneously as long as those transmitters are using different wavelengths.