Liquid crystal on silicon achieves the corresponding gray scale by outputting the corresponding voltage value. The gamma 2.2 curve is just complementary to the human eye's color sensitivity, that means, the human eye has the best viewing effect on the display device with gamma 2.2 curve. On the one hand, in order to fit the response curve of the display device better to the gamma 2.2 curve to improve the viewing effect, gamma value with analog correction can not meet the fitting requirements;on the other hand,under the condition of ensuring the low power consumption,it is more difficult for designers to redesign a higher precision DAC.Improving the display accuracy of silicon-based liquid crystal has become an important research direction.In this paper, the frame ratio control algorithm to improve the display accuracy of silicon-based liquid crystal is proposed. The experimental results show that, the display accuracy is 7 bit without processing,there will be a "ladder" curve segment in the gamma curve of silicon-based liquid crystal. After using the frame ratio control algorithm, the display accuracy is increased to 10 bit,the measured gamma curve eliminates the "ladder". Moreover, because the more frames are divided, the smoother curvature of measured gamma curve is, the higher display accuracy is. This conclusion proves that the frame ratio control algorithm can improve the display accuracy in silicon-based liquid crystal display, and make the image display effect finer and smoother, which has a wide range of application scenarios and value。
High resolution and accuracy phase modulation could help to improve the diffraction efficiency of spatial light modulator. For spatial light modulator with analog driving pixels, the phase accuracy is mainly decided by the DAC design. The conventional circuit design method to improve the DAC accuracy is using a large chip area or using expensive advanced manufacturing technology. In this paper, a calibration method with both analog and digital algorithm is presented. By adding digital calibration and improving the frame frequency, the liquid crystal response characteristic is improved without changing the on chip DAC design. An 8 bit DAC LCoS panel is used for verification. The experiment result shows, the phase error is reduced from 1.49% to 0.44%, and the diffraction efficiency is improved from 72% to 75%. And a holography picture is projected to verify the effect.
Freeform surfaces are optical surfaces without linear or rotational symmetry. Their high degrees of design freedom liberate designers and engineers from restrictions on optical surface geometry, yielding compact and lightweight imaging systems with excellent optical performance. Freeform optics have become a competitive tool in the design of optical seethrough head-mounted display (OST-HMD) systems. In this paper, we present two different OST-HMD systems which have different optical different configurations and both employ freeform optics to correct and balance optical aberrations. In the optimization design of the two OST-HMD systems, we start from a spherical imaging system with an on-axis configuration, and then tilt and decenter each optical surface to find a starting point. In the final state of optimization, the order of each XY polynomial used to represent the freeform surface is gradually increased. The modulation transfer functions of the two OST-HMD systems are evaluated and the three-dimensional models of the two systems are also presented.
Spectral confocal technology is an important three-dimensional measurement technology with high accuracy and non-contact; however, traditional spectral confocal system usually consists of prisons and several lens whose volume and weight is enormous and heavy, besides, due to the chromatic aberration characteristics of ordinary optical lenses, it is difficult to perfectly focus light in a wide bandwidth. Meta-surfaces are expected to realize the miniaturization of conventional optical element due to its superb abilities of controlling phase and amplitude of wavefront of incident at subwavelength scale, and in this paper, an efficient spectral confocal meta-lens (ESCM) working in the near infrared spectrum (1300nm-2000nm) is proposed and numerically demonstrated. ESCM can focus incident light at different focal lengths from 16.7 to 24.5μm along a perpendicular off-axis focal plane with NA varying from 0.385 to 0.530. The meta-lens consists of a group of Si nanofins providing high polarization conversion efficiency lager than 50%, and the phase required for focusing incident light is well rebuilt by the resonant phase which is proportional to the frequency and the wavelength-independent geometric phase, PB phase. Such dispersive components can also be used in implements requiring dispersive device such as spectrometers.