Sampled Gratings in Planar Ge-Doped Waveguides

We have UV-induced sampled gratings with a reflectivity up to 99.9% in planar Ge-doped waveguides. Sampled gratings are formed by modulating the amplitude of a conventional grating with an amplitude mask.
The transmission spectrum of a sampled grating structure can be obtained from coupled mode theory. The result is a series of equally spaced peaks centered around a wavelength close to that of the unsampled grating. The spacing between the peaks is given by where c is the speed of light, nave the average refractive index in the sampled grating and Z0 is the sampling period. This spacing is controlled very accurately by the amplitude mask which determines Z0. The shape of the convolution curve below the peaks can also be controlled in a simple way by the duty cycle of the amplitude mask (ratio between grating and no grating.
The experimental transmission spectrum of a sampled grating is shown above. Sampled gratings with multiple reflection peaks are interesting candidates for wavelength selective elements in integrated optical devices. Particularly in WDM-networks which are based on simultaneous transmission of several equally spaced wavelengths.