The invention discloses a 
spectrometer coaxial optical 
system adopting a combination of two volume holographic gratings and a 
prism for light splitting, relates to the field of 
spectrometer light splitting systems and solves the problem that an existing off-axis-type 
grating dispersion spectrum 
system is large in size, difficult to 
mount and adjust and low in stability. The 
spectrometer coaxial optical 
system comprises an 
imaging lens, a slit, a collimating lens, a light splitting element, a converging lens and a CCD (
charge coupled device) 
detector, the slit is positioned at an image focal point of the 
imaging lens, the light splitting element comprises the volume holographic gratings which are completely identical and the 
prism, the volume holographic gratings are glued on two sides of the 
prism respectively, the 
imaging lens images object light in the slit, the collimating lens collimates the object light to be parallel light, and the parallel light is refracted at an interface of the first volume 
holographic grating and the prism to enter the prism after 
diffraction light splitting through the first volume 
holographic grating, totally reflected on the undersurface of the prism to reach an interface of the prism and the second volume 
holographic grating and converged on the 
CCD detector through the converging lens after 
diffraction light splitting through the second volume holographic 
grating. The spectrometer coaxial optical system is compact in structure, simple to 
mount and adjust and high in 
light energy utilization rate.