A method of wavelength selection control is disclosed. The method includes detecting reference RF frequencies by varying the frequency of a RF signal supplied to a reference acousto-optic tunable filter with the reference RF frequencies corresponding to reference wavelengths of reference signals input to the tunable filter, performing tracking to optimize the reference RF frequencies, calculating dependent RF frequencies corresponding to wavelengths of WDM transmission signals and recording the calculated dependent RF frequencies in a first register, repeating the above when a request of wavelength selection is not received, when a request of wavelength selection is received, selecting one of the dependent RF frequencies corresponding to the requested wavelength and recording the selected dependent RF frequency in a second register for use of an acousto-optic tunable filter at a port in operation, and generating and supplying a RF signal having the selected dependent RF frequency to the acousto-optic tunable filter.