Liquid Crystal Blazed Grating, A Realization Of The Scan

As a kind of gratings, blazed gratings can focus most of the energy of diffraction light on a certain diffraction order. Because of this property, blazed gratings have very high spectrum resolution and diffraction efficiency, and have become an important optical device. They can be used in many fields, such as high-precision optics test system, array illumination, optical interconnection, spectrograph and so on.A new-style liquid crystal blazed grating is presented in this paper. The theoretical principles, which are called continuous elastic body theory and electrically controlled birefringence (ECB), are given. The distribution of liquid crystal director can be calculated by difference iterative method, and the relationship between the refractive index of extraordinary light and the position is illuminated. According to the phase characteristic, the liquid crystal blazed grating has an equivalent transformation which is called echelon blazed grating made of glass with a constant refractive index for a certain wavelength. The diffractive efficiency and the condition to realize blaze and scan are derived by Fourier transform and binary optics. Here are also some parameters relating to the diffractive efficiency, and finally the electrodes arrangement is given.The liquid crystal blazed gratings have many advantages compared with conventional blazed gratings. The parameters like grating constant, blazing angle and the refractive index for one certain wavelength of the conventional blazed gratings can not be changed when they have been made. As a result, there is a limitation for them to be used. All of these parameters of the liquid crystal blazed gratings can be changed easily by modulating the external electric field. The best advantage of the liquid crystal blazed gratings is that they can realize scan and can be used for every wavelength. Besides the properties to realize blaze and scan, the liquid crystal blazed gratings can also be used in many other fields, such as beam splitter. They also have smaller volume and weight.