Diffraction of an ultrashort pulsed beam with arbitrary polarization state from a volume holographic grating in LiNbO3 crystals

Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.

Spectral selective fluorescence molecular imaging with volume holographic imaging system

A compact volume holographic imaging(VHI)method that can detect fluorescence objects located in diffusive medium in spectral selective imaging manner is presented.The enlargement of lateralfield of view of the VHI system is realized by using broadband illumination and demagnification optics.Each target spectrum of°uorescence emitting from a di®usive medium is probed by tuning the inclination angle of the transmission volume holographic grating(VHG).With the use of the single transmission VHG,fluorescence images with different spectrum are obtained sequentially and precise three-dimensional(3D)information of deep fluorescent objects located in a diffusive medium can be reconstructed from these images.The results of phantom experiments demonstrate that two fluorescent objects with a sub-millimeter distance can be resolved by spectral selective imaging.

Analysis of Optical Properties of Off-Axis Reflective Volume Holographic Grating

The coupled wave theory for volume holographic grating with curved interference fringes has been proposed based on the Kogelnik’s coupled wave theory with the plane interference fringes. The formula about the magnitude and directional angle of grating vector in arbitrary position of volume holographic grating with curved grating has been deduced. We found that the wavelength selectivity and angular selectivity may be different in different position of volume holographic curved stripe grating which depend on the angle between the propagation vector of reference beam and signal beam. The larger the angle, the greater the angle and wavelength selectivity, whereas the weaker.

Waveguide-based augmented reality displays:perspectives and challenges

Augmented reality(AR)displays,as the next generation platform for spatial computing and digital twins,enable users to view digital images superimposed on real-world environment,fostering a deeper level of human-digital interactions.However,as a critical element in an AR system,optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight.After decades of extensive device and material research efforts,and heavy investment in manufacturing technologies,several promising waveguide combiners have been developed.In this review paper,we focus on the perspectives and challenges of optical waveguide combiners for AR displays.We will begin by introducing the basic device structures and operation principles of different AR architectures,and then delve into different waveguide combiners,including geometric and diffractive waveguide combiners.Some commonly used in-couplers and out-couplers,such as prisms,mirrors,surface relief gratings,volume holographic gratings,polarization volume gratings,and metasurface-based couplers,will be discussed,and their properties analyzed in detail.Additionally,we will explore recent advances in waveguide combiner design and modeling,such as exit pupil expansion,wide field of view,geometric architectures of waveguide couplers,full-color propagation,and brightness and color uniformity optimization.Finally,we will discuss the bottlenecks and future development trends in waveguide combiner technologies.The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies,analyze their pros and cons,and then present the future challenges of AR displays.