Optical time domain reflectometry measurements on a multi-branch optical network

Apparatus and a method are disclosed for detecting and evaluating optical subcircuits created by optical splitters (203) in an optical circuit. One or more optical wavelengths are utilized for the transmission of data, whereas other optical wavelengths are utilized to perform optical time domain reflectometry measurements on each optical subcircuit. Following an optical splitter, each optical path from the optical splitter has inserted into it an optical filter (204, 209) which allows the transmission of the optical wavelengths utilized for data transmission and one of the optical wavelengths utilized to perform the optical time domain reflectometry measurements. An optical time domain reflectometry instrument (201) transmits each of the optical wavelengths, utilized for testing, individually into the optical circuit and analyses the returned optical pulse. Since only one optical subcircuit allows the passage of any given optical wavelength for testing, each optical subcircuit can be fully analysed.