We develop a design method for creating a large-scale optical switch consisting of two sub-switch parts, i.e., delivery-and-coupling switches and wavelength-routing switches based on cyclic arrayed-waveguide gratings, where the available optical-power budget is optimally allocated to the two sub-switches to maximize the entire switch scale. The power budget necessary for each sub-switch is quantitatively evaluated via extensive computer simulations. The simulation results show that a 1000 × 1000 switch scale can be realized when the available optical-power budget is 23 dB. The simulation results are verified via proof-of-concept experiments.