An imaging spectrometer receives a beam of light from a slit and outputs the beam of light to a focal plane. The output beam of light at the focal plane is dispersed in accordance with a spectral composition of the beam of light received from the slit. The imaging spectrometer comprises first to fourth curved reflective portions. The first to fourth curved reflective portions are arranged so that the beam of light, in its passage from the slit to the focal plane, sequentially strikes the first to fourth curved reflective portions and is reflected by the first to fourth curved reflective portions. Further, the first to fourth curved reflective portions are alternatingly concave or convex, respectively, along the passage of the beam of light. At least one of the first to fourth curved reflective portions has a reflective grating structure. Further disclosed is a method of manufacturing such imaging spectrometer.