Differential Optical Spectrometer Based on Critical Angle Dispersion

We introduce and prove the concept of differential optical spectrometer based on critical angle dispersion. A long waveguide of beveled input and output interfaces is used, where the light to be detected is oriented in the vicinity of waveguide numerical aperture. The incidence angle is swept, and a single detector is used for detection from the other side. Theoretical resolution and resolving power were deduced. The concept was applied to an off-the-shelf ZnSe crystal. Validation is proven by retrieving reference wavelengths of two lasers as well as the absorption spectrum of a reference material.