Using the quantum fast Fourier transform in linear optics the input mode annihilation operators ͕â 0 , â 1 ,. .. ,â s−1 ͖ are transformed into output mode annihilation operators ͕b 0 , b 1 ,. .. ,b s−1 ͖. We show how to implement experimentally such transformations based on the Cooley-Tukey algorithm, by the use of beam splitters and phase shifters in a linear optical system. Optical systems implementing 1,2, and 3 qubits discrete Fourier transform (DFT) are described, and a general method for implementing the n-qubit DFT is analyzed. These transformations are used on various input radiation states by which phase estimation and order finding can be computed.