Multimode‐fiber‐type optical directional coupler for otdr using acoustooptical deflector

The optical directional coupler is one of the key devices for an optical time domain reflectometer (OTDR). In this paper, an optical directional coupler employing an acoustooptical deflector was used to investigate the backscattered light from a multimode fiber. First, the fundamental characteristics of an acoustooptical deflector, diffraction efficiency, and rise time were evaluated. For this evaluation, the theoretical value of the diffraction efficiency was obtained by the ray tracing method. The length and height of the transducer in an acoustooptical deflector were optimized. The relationship between the rise time of the acoustooptical deflector and the focusing distance of a lens in the collimator was also obtained. Using the results, an optical directional coupler was designed and fabricated. Finally, the optical directional coupler was built in an OTDR and excellent performance was confirmed.