Optical Filters are a class of optical elements that selectively select spectral wavelengths for transmission, reflection, cutoff, and attenuation. There are two kinds of filters, one is a colored glass sheet, and the other is achieved by coating on the optical substrate. 

According to its function, it can be divided into band pass Filter, long wave pass filter, short wave pass filter, dichroic filter, neutral density filter (ND Filter), notch filter, cold mirror, thermal mirror, color filter and so on. According to the processing technology, it is divided into interference filter and color absorption filter. These filters are widely used in spectral analysis, biomedicine, machine vision, fluorescence microscopy, industrial automation and other industries and product fields. 

The bandpass filter selectively allows and prevents the transmission of a spectral wavelength in its spectral range. The neutral density Filter (ND Filter) reduces the light flux by reducing the transmittance of the specified spectral wavelength range, which is conducive to the protection of sensors/electronic components, and it is widely used in the field of laser optics/optoelectronics; Cold/thermal mirrors can be targeted to reflect and transmit longer wavelengths of light in the spectral range, and are widely used in lighting systems, which is conducive to removing heat generated in lighting systems.