In-fiber Bragg grating tap

TLDR: In this paper, the authors describe a method for the noninvasive production of wavelength selective taps in germanosilicate optical fiber. But this method is based on the assumption that Bragg gratings can be formed in the core of a fiber by exposing it through the side of the cladding to a coherent UV interference pattern at a wavelength which lies in the oxygen vacancy defect band of germania.

Abstract: In many network and sensor applications, small amounts of light need to be coupled out at many points from a transmission bus fiber. In-line devices with some wavelength selectivity are particularly desirable, especially if light radiated from the fiber can be efficiently coupled into another fiber. This paper describes a new method developed for the noninvasive production of wavelength selective taps in germanosilicate optical fiber. The technique is based on a recent discovery that Bragg gratings can be formed in the core of a fiber by exposing it through the side of the cladding to a coherent UV interference pattern at a wavelength which lies in the oxygen vacancy defect band of germania.1-3 The grating period and tilt of the Bragg planes are selected to couple coherently a guided mode into a narrow radiated beam which propagates through the side of the cladding. The same arrangement is also useful for coupling light into the fiber.