We are studying and developing high-performance spectroscopy solutions in silicon technology in the framework of instrumental developments around the B-BOP bolometer arrays and in the continuation of the former developments of the Herschel space telescope instruments and in particular its photodetector array camera and spectrometer. The integration of multiwavelength spectroscopic capabilities close to the array of a cooled bolometer would make it possible to detect the interstellar medium continuum by scanning and to trace its evolution, particularly by the detection of characteristic lines such as the cooling line [CII] at 158 µm. In this paper, we present the first concept under development and the preliminary results obtained from our cryogenic optical test bench. This solution is a tunable Fabry–Perot cavity with silicon mirrors driven by a cryogenic piezoelectric mechanism with a nanometric step. Each mirror is a dielectric Bragg structure, a stack of quarter-wave layers of silicon and air providing high reflectivity without metal loss. This solution allows extremely accurate scanning around a targeted wavelength. The first prototype cannot be integrated on a focal plane as it stands, and future optimizations integrating miniaturized scanning systems will make the system much more compact.