OPTICAL FIBER DISPERSION MEASURING METHOD

摘要

PURPOSE:To measure the dispersing characteristic of an optical fiber with high accuracy, by performing sine wave modulation to continuously oscillating laser diode beam and measuring the change in the phase characteristic of the optical fiber to the change in modulation frequency while calculating the wavelength dependence of group delay time characteristic. CONSTITUTION:Measurement is performed while measuring beams from laser diodes LD1-LDN different in a light emitting wavelength are successively changed over to a fiber 2 to be measured by a change-over means 1. At first, sine wave modulation is applied to the diode LD1 by an oscillator 3 and propagated through the fiber 2. The output beam from the fiber 2 is sent to a phase difference detector 5 through APD4 to measure the change DELTAbeta(f) in the phase characteristic of the fiber 2 to the change DELTAf in modulation frequency. Subsequently, a group delay time characteristic tau(lambda) to the wavelength lambda of laser diode beam is calculated. This calculation is performed with respect to LD2- LDN and wavelength dependence of the time characteristic tau(lambda) is calculated to make it possible to measure the dispersing characteristic of the optical fiber 2 with high accuracy.