Process and apparatus for manufacturing blown optical fibre units

A process for manufacturing an optical fibre unit for air-blown installations comprising:

• providing a deposition chamber for applying particulate material, the deposition chamber having an inlet end and an outlet end, a longitudinal axis, a frusto-conical section at the inlet end, and a chamber pipe with a central part having a longitudinally changing cross section, wherein the longitudinally changing cross section of the central part of the chamber pipe has the form of a sinusoid;
• passing through the chamber pipe an optical fibre assembly comprising at least one optical fibre embedded in an inner layer of cured resin material, and having an outer layer around the inner layer, the outer layer comprising uncured resin material;
• injecting a flow of fluid and particle material in the deposition chamber in a direction substantially parallel to the chamber longitudinal axis, at an injection speed of below 4 m/s;
• perturbing the flow when in the chamber pipe, thus causing the particle material to impact and partially embed into the outer layer of the optical fibre assembly;
• and
• curing the outer layer.