An all-optical passive WDM upgrade of a passive optical network (PON) with an optical-fiber in-band WDM Coupler and a coarse WDM as multiplexers and demultiplexers is proposed and demonstrated. Using F-P lasers as the light source, the OLT and ONU can provide two additional wavelengths. The experiment demonstrates that the scheme can be with less optical power loss and crosstalk through selecting the proper wavelength of F-P lasers.