Measurement of attenuation of an optical fiber using bidirectional transmission of information via the fiber

摘要

Attenuation of an optical fiber is measured by transmitting an optical signal having a predetermined wavelength to the fiber, and FSK modulating the optical signal with information identifying the wavelength and transmitted power of the optical signal. At a receiver, the optical signal is detected and the information is recovered by demodulation. Wavelength-dependent sensitivity information for the detector is read from a store in dependence upon the wavelength information and used to control the gain of an amplifier for amplifying a subsequently transmitted continuous wave optical signal used for attenuation measurement. The received power level of this optical signal is converted into a digital value and used with the transmitted power information to determine the fiber attenuation at the predetermined wavelength. Reference power levels are determined by connecting a jumper between a port and an external detector. Measurement of attenuation and communication data over the fiber under test may be effected using two transceiver units, one at each end of the fiber. In addition to the external detector, each unit has an internal detector and sources connected to a port which is connected to the fiber under test by a jumper. Determination of the attenuation of the fiber then takes account of the loss of each fiber using reference power levels determined by initial calibration measurements.