Methods and systems for using modulation frequencies for optical channel monitoring with periodic optical filtering may allocate modulation frequencies based on bandwidth slices of an optical spectrum. The bandwidth slices may have an equal spectral band that is associated with a respectively unique modulation frequency. An optical carrier aligning with a bandwidth slice may be modulated using the modulation frequency assigned to that bandwidth slice. Additionally, the bandwidth slices may be used to determine a maximum frequency error of an optical carrier when received, such as from frequency drift during transmission.