Optical sensors based on diffraction gratings and waveguides for environmental analysis

Optical sensors are becoming increasingly widespread, and are of considerable interest for environmental applications. Among them, sensors based on diffraction gratings exploiting surface plasmon resonance (SPR) presents sometimes limits, mainly due to the signal disturbance when operating in reflection by the top of the grating. To overcome this problem, another approach is proposed here: the grating is probed from the backside, which suggests a dielectric structure comprising a thin layer of very high refractive index, transparent at the operating wavelength. Hydrogenated amorphous silicon has proved to be a suitable material regarding the manufacturing of dielectric resonant waveguide grating. The energy transfer between the reflected 0 and -1 orders diffracted by the waveguide resonant grating is of particular interest for the detection of the target species.