APPARATUS FOR THE MEASUREMENT OF THE TRANSFER FUNCTION MODULES OF AN OPTICAL FIBER AND ITS USE

摘要

The transfer modulation measuring system is made up of an adjustable multifrequency generator, a laser emission circuit, an optical detector and a spectrum analyzer. The generator includes oscillators at predetermined frequencies belonging to a discrete frequency distribution. Component signals at selected predetermined frequencies may be time-division multiplexed or frequency-division multiplexed into an electrical composite signal which modulates the laser emission. The system comprises also two optical fiber connectors and a so-called priming optical fiber which excits uniformly the propagation modes at the entrance end of the optical fiber to be measured. During a calibration phase, the connectors are joined end-to-end and aligned optically. The spectral lines at predetermined frequencies are successively adjusted to a same predetermined level on the screen of the spectrum analyzer by means of potentiometers adjusting the amplitudes of the component signals. These adjustments contribute the transfer function of the optical fiber to be displayed directly on the screen of the spectrum analyzer during the measurement phase for which the optical fiber to be measured is connected between the two connectors. The modulated light signal crossing the optical fiber arises from the modulation of the selected time-multiplexed or simultaneously mixed frequencies.