Mid-infrared planar silver halide waveguides with integrated grating couplers

Grating couplers for planar silver halide waveguides were designed and fabricated by using focused ion beam (FIB) milling technology, facilitating coupling of mid-infrared radiation from quantum cascade lasers into thinfilm waveguide structures. An optimized rectangular grating structure for an emitted wavelength of 10.4 μm, with a grating constant of 16.4 lm was integrated into a silver halide waveguide substrate via an optimized FIB fabrication procedure. Efficient incoupling and radiation propagation through the waveguide was confirmed by analyzing droplets of acetic acid at different concentrations, deposited at the waveguide surface via evanescent field absorption spectroscopy.