Achromatic Polarization Rotator

Achromatic polarization rotator is an important optical element,which can realize the change of polarized light direction in a wide wavelength range,and has been widely used in liquid crystal display,optical communication,polarization spectrum imaging and other widely aspects,so it is of great significance for the research of achromatic polarization rotator.In this paper,two kinds of polarization rotators are proposed.One is composed of wave plates,the other consists of liquid crystal cells.The wave plate polarization rotator consists of several wave plates superimposed at an angle of the optical axis.When the transmission axis of the two polarizers is parallel,the polarization direction of the incident linearly polarized light turn 90° through several wave plates,so it can't transmit the analyzer,and the ideal transmittance is 0.When the polarizers are orthogonal,the linearly polarized light can transmit through the analyzer,and the ideal transmittance is 1.In this paper,the achromatic polarization rotator composed of four,five and six wave plates are proposed in the firstly step,and their achromatic performances are simulated and calculated by Techwiz LCD 1D software,the results show that this polarization rotator has good achromatic profile in the visible light range.Then,the achromatic polarization rotator composed of liquid crystal cells is proposed.This liquid crystal achromatic polarization rotator can be controlled by voltage,which can control the distribution of liquid crystal molecules by applying voltage,so as to control the polarization state of polarized light.The achromatic polarization rotator composed of parallel liquid crystal cells operates similarly to the wave plate polarization rotator when no voltage is applied.The azimuth angle of the liquid crystal cell is at a certain angle to the polarized light coming from the polarizer.After applying voltage,the liquid crystal molecules are arranged along the perpendicular direction to the substrate of the liquid crystal cell.At this time,the phase retardation of the liquid crystal is 0,and the polarization state of the light does not change,so the light transmit the parallel polarizers.Thirdly,we put forward a kind of twisted nematic liquid crystal polarization rotator which consists of three low twisted nematic liquid crystal cells,the total distortion angle is 90°,when the polarizer is placed in parallel and no voltage is applied,the polarization state of light through three TN cells rotate 90°,however the light can't through analyzer,when voltage is applied on each liquid crystal cell,liquid crystal molecules are driven to perpendicular to the plane of the liquid crystal cell substrate,birefringence of liquid crystal is 0,the light transmit,so the change of polarized light in the orthogonal direction is realized.Finally,the achromatic polarization rotator composed of two tandem TN liquid crystal cells with same parameters is simulated.The rubbing direction of the bottom substrate of the upper liquid crystal cell is perpendicular to the rubbing direction of the upper substrate of the bottom liquid crystal cell.This polarization rotator can realize the transformation of polarized light in any direction and has good achromatic performance.