Effects of mechanical stress on the transmission properties of optical fiber packaged in a composite structure

Optical circuit boards for system-level interconnection may be fabricated by bonding segments of optical fiber, in the configuration necessary for signal distribution, to a substrate such as a printed wiring board. To measure the effects of mechanical stress on optical transmission, a four-point bend test is applied to prototype optical circuit boards. The results show that flexing a board to a strain of approximately 0.3% leads to a decrease in loss of 0.012 ± 0.002 dB for multimode fiber. Flexing of a thin board, in two directions, around 40-in.- (101.6-cm-) bend-radius mandrels decreases fiber loss by almost 1 dB after 700 cycles. Single-mode fiber bonded to aboard, however, exhibits an increase in loss of 0.11 ± 0.05 dB under an induced strain of 0.3%, a change that is not significant relative to typical loss-per-line budgets in real systems.