## 2 Special Issue Papers  
This special issue provides a collection of papers demonstrating the impact of LCoS microdisplays in current and future spatial light modulation applications. State-of-the-art in LCoS device technology, LC materials, modeling and characterization techniques are presented. A complete review of LCoS origins, evolution, and applications is given by [PERSON] et al. [7]. They cover both the interest in display applications and their developments as spatial light modulators (SLM), with special focus on phase-only spatial light modulation capabilities in digital holography or holographic video projection. The authors explain that the origin of LCoS backplane dates back to 1973, and the development of LCoS has been beneficial for full high definition displays and spatial light modulation. They start summarizing state-of-the-art developments of high-resolution panels, followed by addressing issues related to the driving frequency (i.e., liquid crystal response time and hardware interface), taking into account phase linearity control, phase precision, phase stability, and phase accuracy. A good complement to the previous paper is given by [PERSON] and [PERSON] [8]. The authors focus their review on the available characterization techniques to obtain the grayscale-phase response of LCoS devices. They demonstrate that precise calibrations are necessary since they greatly influence the results when applied in phase-only applications, including the majority of interesting cases such as holographic display, optical tweezers, lithography, etc. Due to limitations in the manufacturing process, the grayscale-phase response could be different for every single SLM device, even varying on sections of an SLM panel due to the screen or electrical addressing spatial inhomogeneities. They divide the numerous calibration methods into two categories: the interferometric phase calibration methods and the diffractive phase calibration methods. The main phase calibration methods are discussed and reviewed, comparing their possible advantages in different applications. Regarding the analysis of LC materials enabled for LCoS devices, we consider the review paper by [PERSON] et al. [9]. They investigate ferroelectric liquid crystals (FLCs) of a new type developed for fast low-voltage displays and light modulators. They are helix-free FLCs, characterized by spatially periodic deformation of smectic layers and a small value of spontaneous polarization. Both theoretical models and experimental results are presented for modulation of light transmission, scattering, and phase delay with a high rate. Alternative optically addressable spatial-light modulators (OASLM) are investigated by [PERSON] et al. [10], which are very interesting for phase-only modulation applications. They focus on the influence of driving conditions on their phase-modulation ability. To this end, they use an equivalent circuit method and a system for measuring wave-front modulation that uses a phase-unwrapping data-processing method, and is constructed with a charge-coupled device and wave-front sensor. They demonstrate that wave-front on-line modulation with feedback control is possible with the OASLM and the corresponding monitoring system. In previous years, there has been considerable interest in augmented reality (AR) displays. [PERSON] et al. [11] review LCoS technology capabilities' new application in emerging AR displays. They start by reviewing the LCoS working principles of three commonly adopted LC modes. Then, the fringing field effect is analyzed, which is very important in very high resolution LCoS microdisplays. The novel pretilt angle patterning method for suppressing the effect is presented. They also show how to integrate the LCoS panel in an AR display system. Authors show that the application of LCoS in AR head-mounted displays and head-up displays is foreseeable. In dealing with holographic projection and application of phase-only holography with SLMs for display applications, we consider the paper by [PERSON] and [PERSON] [12].