Optical structure writing system

Abstract

The present invention relates to a system for writing an optical structure in a waveguide. The system including, means for splitting a light beam into two coherent writing beams, an optical circuit for directing the writing beams along substantially the same optical path in opposite directions such that they produce an interference pattern in an interference region substantially within the waveguide to write the optical structure, said optical circuit including at least two acousto-optic modulators (AOMs) configured to enable a controllable phase shift to be applied to a light beam propagating therethrough, the two AOMs being arranged such that, in use, each AOM shifts the phase of only one of the writing beams, to thereby provide a controllable phase difference between the writing beams.

Description

FIELD OF THE INVENTION [0001] The present invention relates broadly to a system for writing an optical structure in a waveguide, to a method of writing an optical structure in a waveguide, and to an interferometer. BACKGROUND OF THE INVENTION [0002] Typically, the writing of optical structures such as Bragg gratings into a photosensitive material involves an interferometer in which two coherent light beams (typically in the UV wavelength range) are directed along separate optical paths and brought to interference substantially within the photosensitive material. Within the photosensitive material, refractive index changes are induced through the interaction between the light beams and the photosensitive material, with the refractive index profile being determined by the interference patterns. [0003] In order to write complex optical gratings, e.g. in an optical fibre, a high contrast, phase stable and arbitrarily chirpable UV interference pattern is typically required. The design pr...

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Benefits of technology

[0023] In some implementations the method can include detuning the extent of velocity balance between the variations in the interference pattern and the movement of the waveguide, by controlling the relative phase shift between the writing beams.

[0032] Accordingly, in certain embodiments the system may exhibit a strong common mode rejection, improving the quality of the written grating while providing the flexibility of electrical phase control.

Problems solved by technology

The design problem associated with the creation of such a UV interference pattern for the writing of optical gratings is multi-dimensional and it has been found to be non-trivial to design an optical system that can satisfy all criteria simultaneously while minimising errors in each dimension due to the non-ideal nature of optical and mechanical components.

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