Novel Optical Fiber Installation by Use of Spiral Airflow

Abstract

A high performance apparatus for installing optical fiber has been developed. With this apparatus, a 2 mm-diameter optical fiber was blown through a 6 mm-diameter rolled tube over a distance of 1200 meters, which is longer than the 700 meters achieved by the best conventional techniques. The heart of the apparatus is a novel nozzle with an annular slit and a conical cylinder to create a spiral airflow. In the spiral flow, the back flow of air is prevented due to the Coanda effect and the fiber scraping along the tube wall is minimized, owing to the ordered flow structure, leading to effective fiber installation. To obtain a spiral flow, pressurized air is forced into the buffer area of a nozzle and then through the angled annular slit into the tube entrance. Due to the Coanda effect of the annular jet from the slit attaching to the nozzle walls and the conical cylinder, the downstream flow in the tube develops a highly stable spiral structure with a steep axial velocity distribution that is more ordered than typical turbulent tube flows at the same mass-flow rate.