A novel bidirectional ultra-wideband over-fiber (UWBoF) system compatible with the wavelength-division-multiplexing (WDM) architecture is presented. In the proposed scheme, a 6th order Gaussian derivative is generated for UWB transmission in a downstream (DS) scenario, based on the directly modulated laser, accumulative chromatic dispersion in the transmission fiber and delay-line-interferometer (DLI). While the UWB signal is received from one of the DLI outputs, the other output is utilized to reuse the wavelength by injection locking a colorless Fabry-Perot laser diode (FP-LD). Due to the filtering effect of the FP-LD, a clear optical carrier without intensity modulation is then generated which can be used for upstream (US) baseband (BB) transmission by directly modulating the FP-LD. In order to eliminate the unwanted Rayleigh scattering induced noise in the bidirectional transmission, a dual - fiber transmission architecture is used. The principle of operation is explained. A symmetric transmission of 1.25 Gbps UWB over 60 km single mode fiber (SMF) is performed. Bit-error-rate (BER) measurements and eye diagrams for both down and upstream transmissions are presented.