WDM(Wavelength Division Multiplexing) based-on fixed wavelengths is a new means of utilizing the bandwidth of optical fibers. In this Paper, an improved virtual topology called "(a, $eta$,${gamma}$) ShuffleNet " is introdced for designing large-scale WDM switches. The proposed one is an architecture created by vertically stacking x planes of a ($eta$,${gamma}$) ShuffleNet in parallel via $eta$r nodes called "bridge nodes" so that N-by-N(N=(x*$eta$${gamma}$*${gamma}$) switching is achieved based on the self-routing algorithm for each ($eta$,${gamma}$) ShuffleNet. With the topological parallelism, in contrast to the conventional virtual topologies, the diameter of 2${gamma}$ hops can be fixed and high utilization and performance are provided while N increases. Such a scalability characteristic allows to design a growable broadband switch. As for the delay, we show that the traffic locality, due to the topological feature. result in low delay characteristics.lay characteristics.