the present invention provides for an apparatus and method to manufacture optical fiber in a way that produces controlled and patterned diffusion of optical radiation along its length . the novelty of the described invention is that the patterns of diffusion are produced at the time the optical fiber is manufactured . the “ in - line ” manufacturing method avoids the need for post - production treatment of the fiber , which makes the process highly efficient and economical . light diffusing optical fibers of significant length can be produced . several manufacturing configurations to achieve the desired effects and their inclusion in the fiber production process are described . the processes can be configured to process optical fibers constructed from a wide variety of known glass , polymeric or other materials . the partially diffusing optical fibers of this invention have applications ranging from illuminated fabrics and toys and to lighting systems and medical instruments . a distributed sensor comprising a light detector coupled to a partially diffusing fiber is also disclosed .