Grating is an optical device composed of a large number of parallel slits of equal width and equal spacing. The commonly used grating is to engrave a large number of parallel lines on a glass sheet or a metal sheet. The number of slits in the precision grating can be very large, and some can reach tens or hundreds per millimeter. Gratings can be divided into two types: transmission gratings and reflection gratings: gratings that use transmitted light diffraction are called transmission gratings, and gratings that use reflected light diffraction between two notches, such as many parallel notches carved on the surface of a metal sheet , the smooth metal surface between the two notches can reflect light, and this grating becomes a reflection grating. The grating has the function of interfering and diffracting light, forming very fine bright lines, so that the wavelength of light can be measured more accurately. Gratings utilize the principle of multi-slit diffraction and can act as optical elements that disperse (decompose into spectra) light. The principle of grating refraction can also be used to convert different graphics into grating line numbers through visual software, and present different graphics at different angles.