This study introduces a microspectrometer with a solid immersion grating for compact design and improved spectral resolution. The size is over 1,000 times smaller than conventional spectrometers while maintaining high resolution and sensitivity, which  spectroscopic applications demonstrated in handheld fruit maturity verification.

The spectrometer is actively used in various fields for non-destructive sample analysis, allowing the analysis of spectral components through the distribution of reflected or absorbed light. While conventional spectrometers provide real-time analysis, their large size limits their portability and on-site diagnostic applications. Recently, the advancement of micro/nano-fabrication technologies has led to the development of small spectrometers for applications such as quality control, environmental monitoring, anti-counterfeit, and healthcare monitoring. However, current small spectrometers undergo a simplification of internal optical components, leading to a significant degradation in optical performance and a reduction in the accuracy of sample analysis. Overcoming the challenge of maintaining optical performance while reducing size remains difficult.

In this study, the research team proposes a microspectrometer with a solid immersion grating structure, having high angular dispersion, within a few millimeters of the thickness. In  the structure, a reflective grating and a convex lens with a similar refractive index are combined to focus dispersed light onto an image sensor, achieving uniform and improved spectral resolution on the entire visible spectrum. The microspectrometer module has compact dimensions of 8 mm × 12.5 mm × 15 mm, demonstrating a size reduction of over 1,000 times compared to conventional commercial spectrometers. Furthermore, it exhibits a high spectral resolution of approximately 5.8 nm, similar to that of commercial spectrometers, and a sensitivity of over 76% within the operating wavelength range.