Optical networks based on fast optical switches (FOSes) could potentially solve the latency, bandwidth, cost and power consumption challenges in current electrical switches (ESes) based high performance computing (HPC) networks. In this work, we present a novel HPC network which employs distributed FOS interconnecting by removing ES (Firefly). In Firefly, Dragonfly topology is adopted for the inter-group connection of blades, while the intra-group connection of blades is implemented by FOS with fast optical flow control. The Firefly exploits the wavelength, space, and time switching domain with nanoseconds reconfiguration time of the FOS to achieve efficient statistical multiplexing operation. We numerically investigate the Firefly performa...