  Construction of an optical quantum computer (OQC) is finished by implementing
all necessary ingredients with light (photon). There is, however, one more
hurdle to clear. It is scalability, which is easily lost when accommodating
many qubits by densely nesting quantum circuits. Any of the reported OQC
schemes is not neces-sarily best placed in this regard. Here we demonstrate the
power of "frequency" de-gree of freedom of light, which outperforms others with
its potentially infinite basis states: as multiple qubits share the same
"one-photon" superposition state all along, a realistic OQC design in frequency
basis adopts only one port each for input and out-put. As such quantum logic
gates are configurable in a cascade of compact in-line modules, which ensures
scalable computing. Finally, our implementation of Deutsch-Jozsa's algorithm
using standard laboratory laser demonstrates that fre-quency-basis OQC is
ideally suited for such tasks even without help of nonclassicality of light.
