Dichroic filters are used to transmit wavelengths that longer than the cut-on wavelength or shorter than the cut-off wavelength. Depending on the wavelength range of reflection or transmission, they are divided into long pass filter and short pass filter. Dichroic filters are ideal for applications of fluorescence excitation spectrum measurement, beam splitting or beam combination. Compared with the traditional design of long pass filter and short pass filter (0° angle of incidence) , Dichroic filters are designed for a 45° angle of incidence, which separate the reflection and transmission bands in space, and make it widely used in various optical systems and laboratory optical path.