WDM-PON is commonly believed to be a representative technology for the future broadband access as it enables point-to-point connection and provides each user with a pair of dedicated wavelengths.The key to WDM-PON is adopting low-cost "colorless" ONU

thus avoiding the cost increases in installation

operation and maintenance resulted from wavelength selection devices.This paper presents and briefly analyzes three approaches for colorless ONU implementation for WDM-PON and points out that colorless ONU is an ideal solution for WDM-ONU construction.