Mini-LED,Micro-LED and OLED displays:present status and future perspectives

Presently,liquid crystal displays(LCDs)and organic light-emitting diode(OLED)displays are two dominant flat panel display technologies.Recently,inorganic mini-LEDs(mLEDs)and micro-LEDs(μLEDs)have emerged by significantly enhancing the dynamic range of LCDs or as sunlight readable emissive displays.“mLED,OLED,orμLED:who wins?”is a heated debatable question.In this review,we conduct a comprehensive analysis on the material properties,device structures,and performance of mLED/μLED/OLED emissive displays and mLED backlit LCDs.We evaluate the power consumption and ambient contrast ratio of each display in depth and systematically compare the motion picture response time,dynamic range,and adaptability to flexible/transparent displays.The pros and cons of mLED,OLED,andμLED displays are analysed,and their future perspectives are discussed.

Augmented reality and virtual reality displays:emerging technologies and future perspectives

With rapid advances in high-speed communication and computation,augmented reality(AR)and virtual reality(VR)are emerging as next-generation display platforms for deeper human-digital interactions.Nonetheless,to simultaneously match the exceptional performance of human vision and keep the near-eye display module compact and lightweight imposes unprecedented challenges on optical engineering.Fortunately,recent progress in holographic optical elements(HOEs)and lithography-enabled devices provide innovative ways to tackle these obstacles in AR and VR that are otherwise difficult with traditional optics.In this review,we begin with introducing the basic structures of AR and VR headsets,and then describing the operation principles of various HOEs and lithography-enabled devices.Their properties are analyzed in detail,including strong selectivity on wavelength and incident angle,and multiplexing ability of volume HOEs,polarization dependency and active switching of liquid crystal HOEs,device fabrication,and properties of micro-LEDs(light-emitting diodes),and large design freedoms of metasurfaces.Afterwards,we discuss how these devices help enhance the AR and VR performance,with detailed description and analysis of some state-of-the-art architectures.Finally,we cast a perspective on potential developments and research directions of these photonic devices for future AR and VR displays.

Advanced liquid crystal devices for augmented reality and virtual reality displays:principles and applications

Liquid crystal displays(LCDs)and photonic devices play a pivotal role to augmented reality(AR)and virtual reality(VR).The recently emerging high-dynamic-range(HDR)mini-LED backlit LCDs significantly boost the image quality and brightness and reduce the power consumption for VR displays.Such a light engine is particularly attractive for compensating the optical loss of pancake structure to achieve compact and lightweight VR headsets.On the other hand,high-resolution-density,and high-brightness liquid-crystal-on-siilicon(LCoS)is a promising image source for the see-through AR displays,especially under high ambient lighting conditions.Meanwhile,the high-speed LCoS spatial light modulators open a new door for holographic displays and focal surface displays.Finally,the ultrathin planar diffractive LC optical elements,such as geometric phase LC grating and lens,have found useful applications in AR and VR for enhancing resolution,widening fiield-of-view,suppressing chromatic aberrations,creating multiplanes to overcome the vergence-accommodation conflict,and dynamic pupil steering to achieve gaze-matched Maxwellian displays,just to name a few.The operation principles,potential applications,and future challenges of these advanced LC devices will be discussed.

Novel developments in computational spectropolarimeter

Compared to conventional bulky spectropolarimeters,computational spectropolarimeters which reconstruct light-field information such as polarization and spectrum in a compact form factor,are critical equipment enabling new applications.The key component of a computational spectropolarimeter is a tunable light-field modulator,in which liquid crystal-based device is a promising candidate.By varying the applied voltage,the tunable liquid crystal metasurface can modulate the phase and spectral information of the incident light,and after a few trials,this important information can be decoded mathematically.Such a novel approach paves the foundation for developing compact and low-cost spectropolarimetric imaging devices with widespread applications in biomedical imaging,remote sensing,and optical communications.