The invention is directed to a system and method for troubleshooting in an optical data network that has a laser transmitter/receiver unit that outputs a data signal and an OTDR unit that produces an OTDR probe signal. The data and OTDR probe signals, typically at different wavelengths, are coupled into one end of a trunk fiber which is coupled at its far end to an optical circuit that includes a number of wavelength-selective optical switches and has multiple outputs that are directed to different end users. The optical switches are configurable so as to provide the OTDR probe signal to only one of the optical circuit's outputs while maintaining the data signal at the same output, while also maintaining the data signal, without the OTDR probe signal, at other outputs.