We present a scheme to prepare an optical "quantum switch", a superposition of "open" and "closed" states. The scheme is based on the interaction of an K-type three-level atom with a single-mode of quantized cavity field and an external classical driving field, in the regime where the atom and fields are highly detuned. We show how this interaction can be used to generate coherent states of the cavity field in contrast to the usual method used in microwave cavity QED of injecting a coherent state into a cavity. A combination of switches could be used to prepare a quantum superposition of coherent field states located simultaneously in two cavities. Compared with previous proposals, our scheme is simplified due to economizes the Ramsey zone and the time equired for the state generation is short. 2006 Elsevier B.V. All rights reserved.