Design of a compact spectrometer with large field of view based on freeform surface

A compact multichannel grating imaging spectrometer that includes the ultraviolet (UV), visible-near-infrared (VNIR), and shortwave-infrared (SWIR) spectrum is proposed. A filter set and two reflectors are added near the detectors allowing a wide spectral band to be divided into three independent channels. These three channels share the same telescope and spectrometer. A freeform mirror is introduced to suppress the off-axis senior aberrations caused by widening the spectrum and increasing the field of view. This unique design method covers a wide spectrum from UV to SWIR using only one imaging spectrometer without splicing systems or researching wide-spectrum detector, which allows for a compact size and reduced cost. A spectrometer with a slit of 48 mm and a measured spectrum from 240 nm to 2500 nm, is designed. Simulation results demonstrate that the total length is 316 mm, the image performance is superior and is a potential for airborne and satellite applications.