We demonstrate a simple approach to generating optical wideband chaos and verify that it can be used to locate simultaneously and precisely the faults among all branches in a wavelength-division-multiplexing (WDM) passive optical network (PON). The chaotic light source consists of a semiconductor optical amplifier ring structure with an output optical 3 dB bandwidth of above 60 nm covering the whole C-band. This kind of optical wideband chaos can be naturally filtered by the WDM devices in the PON. Each filtering light signal along the corresponding branch retains good chaotic characteristics We demonstrate a proof-of-concept experiment for the detection of three International Telecommunication Union channels. The experimental measurements show that a much higher spatial resolution of 1.66 cm and a dynamic range of about 10.1 dB are achieved.