Baseband Response Characteristics Measurement Method and Measuring Equipment for Multimode Fiber.

Problems and solutions for the far end measurement of frequency characteristics of the baseband response of a multimode fiber due to dispersion are presented. Also described is a configuration of the measuring equipment of the baseband response. For the latter, the following are important: (i) removal of the effect of the material dispersion; (ii) stabilization and leveling of the modulation level; (iii) stabilization of the optical output level; (iv) removal of the effect of the reflected light from the output end and the input end of the fiber. Solutions for these problems are: (i) single-mode oscillation of the semiconductor laser by reduction of the modulation index; (ii) stabilization and leveling of the modulation level by a negative feedback loop that monitors the modulation level of the backward light of the laser; (iii) stabilization of the optical output by a negative feedback loop that monitors the output level of the backward light of the laser; and (iv) removal of the effect of the reflected light by means of oblique incidence and small input aperture angle. When the baseband characteristic of a fiber a few kilometers long is measured, irregular variations are observed. A solution to this problem is also included. [ABSTRACT FROM AUTHOR]