This invention relates to the process of correcting for phase errors during the fabrication of Bragg gratings.
Bragg gratings in optical waveguides (fiber and planar) are used for a variety of optical processing functions. The most common application is simple wavelength filtering in dense wavelength-division multiplexing (DWDM) systems.
In such applications, the ideal Bragg grating filter has a spectral response that is rectangular in shape, with sharp edges and a flat top. In general, any phase or amplitude errors in the fabrication process lead to a non-ideal spectral response.
Moreover, as the DWDM channel spacing becomes smaller, the filter bandwidth must also be reduced by the same amount. The reduced bandwidth requires the Bragg grating lengths to increase. These requirements lead to a significantly increased sensitivity in the spectral quality of the filter to any errors in the fabrication process. One common source of such errors is the imperfection of the phase masks used in the fabrication process.
More generally, any filter response will be negatively affected by the presence of errors in the fabrication process. In general, the longer the grating, the more sensitive it will be to errors.
A process that can eliminate or reduce the effect of these errors is desirable and will become more valuable as more complex optical processing functionality is required.