Color filter concept
The filter working in the visible light region in the spectral range is called color glass filter. It can reflect or transmit color light within a certain wavelength range, so it will present different colors. Color filters are mostly used in color-related and monochromatic situations, such as color printing, projection display, liquid crystal display, photographic recording, color decoration, etc.
At present, the commonly used color filters are colored glass absorption filters and reflective optical thin film filters. There are also color filters designed using gratings and photonic crystals, but they are still in the experimental stage. Here are the different color filter technologies:
1、 Absorption color filter
The absorption color filter is realized by the absorption of visible light by materials. The common camera/camera filter is actually a kind of colored glass mixed with pigments, which makes use of the selective absorption of light by pigments. It can help to achieve the white balance or break the white balance, and make the color of the picture normal or biased towards a certain color. This filter can also be used in the microscope to help correct chromatic aberration or improve resolution. There are also neutral filters that uniformly weaken the light intensity and do not change the spectral composition. It relies on the metal layer with high absorption, and is generally used to attenuate the incident light intensity. Because some pigments will decompose after a long time of ultraviolet radiation, and the absorption capacity of light will be reduced, some absorption color filters are not durable. The absorption color filters used in flat panel display have 60% light loss, which reduces its light energy utilization efficiency.
2、 Optical thin film color filter
The optical thin film filter adjusts the phase or amplitude of the light propagating in it through the multi-layer thin film structure, so that the polarization state of the light in a certain band is changed or the intensity is redistributed. Optical thin film filters generally include band-pass filters, cut-off filters and other filters for special purposes, and are often used in spectral instruments, spectral correction, optical communication, laser systems and other fields. Optical thin film color filter has the following advantages:
1. Stable in nature, not easy to fade;
2. High reflection or transmittance, bright color;
3. The material is environmentally friendly and the production process is less polluted.
The optical thin film color filter used for visible light area filtering is widely used, including the filter made into detachable elements and installed in front of the light source, and the filter film inlaid on the surface of the optical lens, etc. The color separation and color combination film commonly used in the projection display system is a typical type of this filter: it uses the cut-off filter structure to decompose white light into red, green and blue light, or to synthesize white light from red, green and blue light.
