Linear gradient filter (LVF) is an optical device whose spectral characteristics change linearly with position. It is formed by plating multi-layer film systems with varying thickness on the substrate surface by ion assisted method or ion beam sputtering method.
Compared with the traditional narrow-band filter, the linear gradient filter has a nearly continuous spectral channel, so the linear gradient filter can obtain higher spectral resolution. Wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) in optical communication is to couple the linear gradient filter to the optical fiber transmission port, and expand the communication transmission volume dozens or even hundreds of times without increasing the number of optical fibers.
Another application field of linear gradient filter is spectral imaging technology. Compared with prism and grating spectral imagers, the spectral imager based on linear gradient filter has the characteristics of high integration, high stability and high resolution. Its whole machine has compact structure, small volume and light weight, low R & D and manufacturing cost, and has a good application prospect. The linear gradient filter can also be used in portable spectrometer, grating secondary light separation / cut-off, laser mirror design and other fields.
Due to the limitation of the coating process, various errors will be introduced in the plating process of the linear gradient filter, resulting in the deviation between the finished filter and the design characteristics, and the change of the use environment, such as temperature, humidity and pressure, will cause the change of the filter characteristics. In order to apply it to the design of related aspects, its actual characteristics must be tested for pre calibration.