Block diagram of FIOS concept adapted from Ben-Ami et al. (2018). Light enters the system at the top left via an optical fiber. Each chain in the array consists of a collimator, an FPI and a focusing lens. Part of the light reflects from each FPI and is redirected by the central reflective surface into the next chain. The chained spectral profiles are created and fed into the external spectrograph using optical fibers. The red dashed box in the block diagram shown in this figure is equivalent to the red dashed box of the FIOS demonstrator in Fig. 2.