We consider networks for interconnecting parallel computers that are p
arameterized by their degree (fan-out) of switches that are used to bu
ild the network. Electronic networks tend towards the small fan-out/la
rge diameter end of the spectrum due to limitations on the fan-out of
electronic switches. The fan-out of systems of optical switches. Thus
it has been suggested that optics can be used to build the complete ne
twork which is the most desirable of Clos's family of networks. Even o
ptics, however, has limits on the fan-out of switches in any given con
figuration. Thus in this paper, we describe an implementation of a net
work with a significantly smaller degree and slightly larger network d
iameter than the complete network. The network that we implement is ca
lled the mesh-connected bus network. We remark, however, that it is es
sentially an implementation of the second most desirable network in th
e family of networks defined by Clos, which is widely referred to as t
he Clos network. We implement the network using novel free-space optic
al interconnection techniques along with a multiple-access scheme base
d on wavelength-division multiplexing.