In large quantum systems multipartite entanglement can be found in many
inequivalent classes under local operations and classical communication.
Preparing states of arbitrary size in different classes is important for
performing a wide range of quantum protocols. W states, in particular,
constitute a class with a variety of quantum networking protocols. However, all
known schemes for preparing W states are probabilistic, with resource
requirements increasing at least sub-exponentially. We propose a deterministic
scheme for preparing W states that requires no prior entanglement and can be
performed locally. We introduce an all-optical setup that can efficiently
prepare W states of arbitrary size. Our scheme advances the use of W states in
real-world quantum networks and could be extended to other physical systems.