Abstract
High-resolution spectrometers hold irreplaceable value in cutting-edge fields such as deep-space exploration, Earth remote sensing, and meteorological observation, serving as a core payload for detailed astrophysical studies and global environmental monitoring. In a spectrometer system, the diffraction grating is the key component that determines spectral resolution. However, constrained by the current state of manufacturing technology, the development of large-area, high-density ruled gratings still faces significant process limitations. To further enhance spectral resolution, coherent dispersion techniques have been recognized as a critical technological pathway to surpass conventional resolution limits in infrared astronomical spectroscopy. This technique employs an interferometer placed in front of the spectrometer to modulate the incident light interferometrically, which is then dispersed and detected by the downstream optical system. By precisely retrieving spectral shifts from the phase variations of interference fringes, this method enables high-sensitivity detection of faint, distant targets, thereby establishing a crucial foundation for next-generation astronomical spectrographs. This study focuses on the Coherent Dispersive Exoplanet Detection System (CODES) and concentrates on the optimal design of a trapezoidal Sagnac interferometer. A fixed-delay structure is introduced into one interference arm, enabling phase encoding of the interference signal and effectively enhancing system stability. Meanwhile, by increasing the optical path difference (OPD) of the interferometer, the spectral resolving power of the CODES system is further improved. In terms of engineering implementation, the optomechanical structure and mechanical support design of the fixed OPD module are optimized to suppress OPD drift induced by temperature fluctuations. Furthermore, ultra-low-expansion materials are adopted, combined with both active and passive temperature control strategies, to ensure that the axial displacement variation of the optical elements within the fixed-delay module remains within ±0.1 mm. By systematically comparing various optical material combinations and integrating finite element analysis with experimental measurements, this study significantly enhances the system's force-thermal stability during prolonged continuous operation. These results provide robust engineering support and important technical references for high-precision detection of faint targets using coherent dispersion techniques.