BENDING EFFECTS IN BICONICALLY TAPERED SINGLE-MODE FIBERS

Biconically tapered single-mode fibers are fabricated and their characteristics are studied experimentally. The optical throughput is measured as the fiber is being pulled to produce the required radial profile. The tapered single-mode fiber is then bent in a simple fixture and the optical throughput is measured as a function of the bending angle. It is seen that the bending results in very strong oscillations of the optical power as the bend angle is varied; the optical throughput goes nearly to zero at about 3.5° before increasing afterward. At the point when the light in the core is minimum, the cladding region is bright indicating that the light has moved to the cladding. These fluctuations are much stronger than the fluctuations usually seen in tapered fibers as the fiber is being pulled. The propagation characteristics of the tapered single-mode fiber subjected to bending are analyzed using a stepwise approximation. The theoretical results agree very well with the experimental results. A simple sensor based on this principle is discussed. © 1990 IEEE