| 摘要 |
PURPOSE:To enable measurement of relative group delay time among wavelengths accurately and quickly with no phase rotation caused, by controlling a phase shifter depending on a phase difference between measured signals of modulation frequencies and wavelengths and a reference signal. CONSTITUTION:A modulation signal generating section 3 generates modulation signals with frequencies (f1, f2, f3 and f4) sequentially to be fed to a laser diode 5 for reference while being supplied to laser diodes 71-74 to be measured which generate laser beams with difference wavelengths (lambda1, lambda2, lambda3 and lambda4) in a specified subsequence through a channel switching section 6. On the other hand, outgoing beams from a reference fiber 11 and a fiber 12 to be measured are sent to a phase measuring section 21 through opto-electric signal converting sections 13r and 13t and mixers 15r and 15t. A signal processing section 23 variably controls a phase shifter 22 to ensure a phase preset so that any phase difference will not cause a phase rotation and, then, stores a phase difference into a memory. Subsequently, phase differences are measured likewise for the wavelengths lambda2, lambda3 and lambda4 and the phase differences obtained for the wavelengths in terms of frequencies f1-f4 are used to calculate relative group delay time among the wavelengths. |
