Axial hyperchromatic spectrometers: compact solutions for spectral analysis in the NIR range

This paper presents the design and implementation of compact, fully axial wavelength-scanning systems for infrared spectroscopy. The proposed systems are based on an optical design that employs a hyperchromatic approach and a simple on-axis structure with a point detector. Two implementations are investigated: a purely refractive system combining highly and weakly dispersive elements and a hybrid system incorporating both diffractive optical elements (DOEs) and refractive components. Wavelength scanning is achieved by axially shifting an optical element, with the required displacement being significantly smaller than the corresponding axial spectral range. The hybrid spectrometer exceeds the performance of the purely refractive system, achieving a nearly constant resolution of up to 30 nm over the 1000-2200 nm wavelength range. A minimum equivalent Abbe number of 0.22 and a corresponding axial chromatic spread of 90 mm enables this characteristic. These results are achieved in a compact design, requiring an adjustment range of only 4.3 mm for the tunable optical component-approximately 1/20 of the axial chromatic spread. The findings underscore the feasibility of this axial wavelength-scanning system for NIR spectrometry, providing a compact and cost-effective alternative to existing technologies with potential applications across various scientific and industrial fields.