Color gamut characteristics of diffractive-light guides of near-eye augmented reality glasses.

We delve into the distinctive color gamut characteristics resulting from color dispersion of surface relief grating (SRG) and wavelength degeneracy of volume holographic optical element (VHOE) in a diffractive light guide. While a laser-like spectrum achieves an impressive 194% sRGB color gamut for both cases, it proves unsuitable for VHOE light guides due to limitations in breaking the field of view (FOV) of the display. Conversely, a broad-band light source, such as LEDs, offers continuous FOV but reduces the common color gamut to 50% sRGB. We then present a newly designed VHOE light guide capable of achieving the common color gamut of 130% sRGB using two multiplexed holograms of each color, closely matching the 133% sRGB achieved by an SRG light guide. This article presents the first theoretical methodology to elucidate color performance of diffractive light guides utilizing VHOEs with holographic multiplexing, affirming their suitability for crafting high-quality near-eye display.

Aberration analysis of a projection-type CGH display with an expanded FOV based on the HOE screen.

This paper proposed a holographic optical element as a see-through screen for the computer-generated hologram projection system with 3D images. The proposed holographic screen consisted of a linear grating and a lens phase. The linear grating is used to redirect the information light and guide information into the observer's eye and achieve the see-through function. The lens phase is used to magnify the field of view of the holographic projection system. The aberration caused by the screen was analyzed in this paper and the aberration can be pre-corrected in the hologram calculation algorithm. Finally, the proposed system achieved 20.3 by 14.3 degrees field of view at 532 nm laser based on the spatial light modulator with 6.4 µm pixels.

Tunable focal waveguide-based see-through display with negative liquid crystal lens.

A see-through display based on a planar holographic waveguide with a tunable focal plane is presented. A negative liquid crystal lens is attached on the outcoupling location of the waveguide to manipulate the image distance. The continuous tunable range for the focal length is from negative infinity to -65 cm. The demonstrated prototype system provides 10.5° field-of-view (FOV) for the images not locating at infinity. The FOV for the images not locating at infinity is limited by the diameter of the liquid crystal lens. The lens function of the liquid crystal lens is polarization dependent. By controlling the polarization states of the real scene and the input information image, the liquid crystal lens keeps the see-through function for a real scene and simultaneously plays the role of a negative lens for the input information image. Compared to the see-through display system with a single focal plane, the presented system offers a more comfortable augmented reality (AR) experience.

Curved Planar Reformation: A Useful Method for Screening Dental Pathologies in Chronic Rhinosinusitis via Paranasal Sinus Computed Tomography.

(1) Background: Curved planar reformation (CPR) is a multiplanar reformatting technique of computed tomography (CT) commonly used during dental cone-beam CT (CBCT) to generate panorex-like images for dental evaluation. Here, we evaluated the utility of an additional CPR sequence in detecting dental pathologies in patients with chronic rhinosinusitis (CRS). (2) Methods: CRS patients who underwent paranasal sinus CT were enrolled retrospectively. The CT images featured three orthogonal sequences and a reconstructed CPR sequence. Additional dental CBCT was performed in patients with pathologies with a strongly suspected odontogenic origin. Dental pathologies detected by CT, CPR, and CBCT were analyzed. (3) Results: A total of 82 CRS patients (37 females and 45 males; mean age 47.3 ± 13.7 years) were included, of whom 23 underwent dental CBCT. In total, 1058 maxillary teeth were evaluated. Compared with paranasal sinus CT, CPR identified greater frequencies of dental pathologies, particularly caries (p < 0.001), periapical lesions (p < 0.001), and fistulae (p = 0.014). CBCT identified greater frequencies of periodontal dental pathologies (p = 0.046) and premolar caries (p = 0.002) compared with CPR. CBCT and CPR detected molar dental pathologies at similar frequencies. (4) Conclusions: CPR could increase the diagnostic rate of odontogenic pathologies compared with standard CT orthogonal views, especially when the sinusitis is caused by caries, periapical lesions, or fistulae. The addition of a CPR sequence allows for simple screening of dental pathologies in CRS patients without a need for additional radiation.

Rapid prototyping-assisted tooth autotransplantation is associated with a reduced root canal treatment rate: a retrospective cohort study.

BACKGROUND: Autotransplantation is a beneficial treatment with a high success rate for young patients. However, most adult patients require root canal treatment (RCT) of the donor teeth after the autotransplantation procedure, which causes a prolonged treatment time and additional expenses and increases the rate of future tooth fracture. Rapid prototyping (RP)-assisted autotransplantation shortens the extra-alveolar time and enables a superior clinical outcome. However, no cohort studies of the application of this method on adult populations have been reported. METHODS: This study is a retrospective cohort study. All patients underwent autotransplantation from 2012 to 2020 in the Kaohsiung and Chia-Yi branches of Chang Gung Memorial Hospital, and the procedure and clinical outcomes were analysed. Differences in clinical outcomes, age, sex, extra-alveolar time, fixation method, and RCT rate were compared between the two groups. RESULTS: We enrolled 21 patients, 13 treated using the conventional method and 8 treated using the RP-based technique. The RCT rates of the conventional group and RP group were 92.3% and 59%, respectively. The mean age of the two groups was significantly different (28.8 ± 10 vs. 21.6 ± 2.1); after performing subgroup analysis by excluding all of the patients aged > 40 years, we found that the RCT rates were still significantly different (91.0% vs. 50%). The mean extra-alveolar time was 43 s in the RP group, and the autotransplantation survival rate in both groups was 100%. CONCLUSIONS: Rapid prototyping-assisted autotransplantation was successfully adopted for all patients in our study population. By shortening the extra-alveolar time, only 50% of the patients required a root canal treatment with a 100% autotransplantation survival rate. TRIAL REGISTRATION: Retrospectively registered.

Binocular dynamic holographic floating image display.

This paper proposes a binocular holographic floating display. The device consists of two phase-modulation spatial light modulators (SLM) and a dihedral corner reflector array (DCRA) element. The conjugate images of the SLMs generated by the DCRA become the system's exit pupils. Exit pupils that are larger than the pupils of human eyes are arranged to locate at the position of observer's eyes. Therefore, the dimension of the SLM will not limit the viewing angle, although the pixel pitch of the SLM still limits the maximum field of view. For the laser light source, the resolution of the images can achieve 3 arc minutes when the distance between images and DCRA is less than 20 cm. The full-color display function is also performed in the proposed device.

Astigmatism correction and quality optimization of computer-generated holograms for holographic waveguide displays.

In this manuscript, the astigmatism of the waveguide combiner with a pair of symmetry HOEs was analyzed. The light field can be predicted by the modified convolution formulation of Fresnel diffraction when the information of light passes through the astigmatism causing element. Then the astigmatism can be corrected. The theory was experimentally proved by the system with a phase-only SLM and a diffraction planar waveguide. Furthermore, the image quality of astigmatism corrected phase-type CGHs can be improved via the iteration process. Since the coherence of light source was employed, the temporal averaging method was utilized to avoid speckle noise.

Astigmatism and deformation correction for a holographic head-mounted display with a wedge-shaped holographic waveguide.

In this study, a head-mounted display (HMD) system based on a wedge-shaped holographic waveguide that can present holographic virtual images with tunable distance is achieved. The compact computer-generated-hologram system using a spatial light modulator was employed to offer the dynamic image, where the probe beam for the hologram reconstruction is a convergent wave, and the DC term of the diffraction wave can be blocked by a barrier. The wedge-shaped holographic waveguide element was used as the combiner of the HMD system to generate a compact structure. A wedge with a polished surface was designed for in-coupling the image into the waveguide, and a reflection-type holographic optical element (HOE) was used for out-coupling the image from the waveguide. The astigmatism aberration and deformation of the diffraction images at various distances are analyzed and then are compensated. Finally, the virtual image can be obtained without aberration with experimental verification.

All-on-4 concept implantation for mandibular rehabilitation of an edentulous patient with Parkinson disease: A clinical report.

Parkinson disease (PD) is a progressive neurologic disorder. Compromised voluntary and involuntary muscle control of the orofacial-pharyngeal muscles of patients with PD may lead to difficulty in mastication, dysphagia, and tremor of the mouth and chin. All of these problems represent major challenges for the clinician with respect to the oral rehabilitation. This clinical report describes the use of the All-on-4 concept implantation for mandibular rehabilitation with a fixed detachable dental prosthesis in an edentulous patient with PD. The treatment steps, outcome, and limitations are discussed.

Polarization-independent distortion corrector fabricated using polymer-dispersed liquid crystals.

We demonstrate a polarization-independent distortion corrector fabricated using a polymer-dispersed liquid crystal (PDLC) cell placed on the intermediate image plane of an optical system. At low voltage, a hazy PDLC cell scatters the incident rays and redirects the off-axis propagated chief ray. The chief ray approaches the principal point of the lens element, thereby decreasing image distortion. At high voltage, the PDLC cell becomes transparent, thereby restoring the image distortion. The PDLC-based distortion corrector is an easy-to-fabricate universal device that can be applied to various optical systems. With a large lens diameter, the distortion of a PDLC-corrected image is approximately 1/5 of that of an uncorrected image.

Switchable holographic image splitter fabricated with dye-doped liquid crystals.

Two electrically controllable holographic polarization gratings are spatially multiplexed to serve as an image splitter for further stereogram application. An external AC voltage is used to modulate the diffraction efficiency of the fabricated holographic image splitter for the switching of a 3D stereogram and a 2D plane image. The polarization grating was generated by two writing beams with orthogonal circular-polarization state in dye-doped liquid crystal films. With proper experimental arrangements, a quasi single order diffraction was obtained and the other non-zero order diffractions were suppressed in this presented polarization grating. This characteristic leads to a good image contrast ratio for a stereogram. Finally, a switchable stereogram system using circular-polarization beam as backlighting was demonstrated successfully.

Distortion aberration correction device fabricated with liquid crystal lens array.

A distortion aberration (DA) correction device is fabricated using a liquid crystal lens array (LCLA), which is placed at the intermediate image plane of the optical system. Without voltage, the LCLA does not work, the image is distorted due to the aberration from the optical system; with voltage, the incident light is focused by the LCLA and then the distorted image is corrected. The correction of distorted image by LCLA is attributed to the redirection of the off-axis propagated chief ray approaches the principal point of the lens element.

Security optical data storage in Fourier holograms.

We have proposed and demonstrated a holographic security storage system that is implemented with a shift multiplexing technique. The security function of this storage system is achieved by using a microdiffuser (MD) for random phase encoding of the reference beams. The apparatus of random phase encoding in this system offers an additional and flexible function during the recording processes. The system can generate holographic security memory or nonsecurity holographic memory via using the MD or not. The storage capacity and the average signal-to-noise value of the security storage system are 16 bits/µm(2) and 3.5, respectively. Lateral shifting selectivity in this holographic security storage system is theoretically analyzed and experimentally investigated.

Stereogram implemented with a holographic image splitter.

A special holographic optical element (HOE) which is used as an image splitter is developed to generate a stereogram on a 2.2-in. liquid crystal display panel. The special designed holographic optical element can be attached on the conventional panel directly to replace the traditional image splitter in a stereoscopic display panel. Experimental results show that two images corresponding to slightly different viewing angles displayed on a panel can be separated effectively and can be delivered to the right eye and left eye of an observer individually. The diffraction efficiency for individual right and left image in this developed holographic optical element is about 43%, and the contrast ratio of the diffracted images induced by cross talk is larger than 60%. Theoretical analyses show the proposed technique generates good contrast ratio and brightness performance for stereogram application.

Projected fringe profilometry using a liquid-crystal spatial light modulator to extend the depth measuring range.

An approach using a liquid-crystal spatial light modulator (LC-SLM) to enlarge the depth measuring range of the projected fringe profilometry is presented. This approach is especially applicable to detect dynamic objects with micro-scale sizes. Compared with a typical 2D image system, the LC-SLM provides a better performance for a 3D shape sensing system. The main advantages include (1) a much higher allowance to increase in the depth measuring range, (2) easiness to compensate perspective distortion and geometric distortion, (3) very high accuracy (in the micron-range) and (4) only one phase measurement needed for operation.

Effect of recording-beam ratio on diffraction efficiency of polarization holographic gratings in dye-doped liquid-crystal films.

The +1 order diffraction of polarization holographic gratings generated by two linear orthogonally polarized writing beams in dye-doped liquid-crystal films were increased by using two recording beams with unequal intensity. The maximum diffraction efficiency of the polarization holograms in our experimental sample can reach 23% when the intensity ratio of two recording beams is 7:1, and this value is almost triple that when the intensity ratio of two recording beams is 1:1.

Orthogonal polarization simultaneous readout for volume holograms with hybrid angle and polarization multiplexing in LiNbO(3).

The orthogonal polarization simultaneous readout technique in a hybrid-multiplexed memory using angular multiplexing and polarization multiplexing is presented. Twenty holograms were hybrid multiplexed in a single LiNbO(3) crystal with ten angular positions for angular multiplexing. In each angular position of the holographic memory, two images with orthogonal polarization are multiplexed in the same spatial location inside the LiNbO(3) via polarization multiplexing. These two orthogonally polarized images can be reconstructed simultaneously with a linear polarization reading beam, but they can be separated with a polarization beam splitter, and accordingly each can be viewed independently. The exposure schedule for holographic storage using the proposed hybrid-multiplexing technique is derived.

Enhancement of the angular selectivity in encrypted holographic memory.

Enhancement of the angular selectivity in a double random-phase encoded holographic memory by use of reference plane waves is presented. In the storage algorithm, the angular selectivity is improved with the effect of random-phase masks. We show that the angular selectivity achieved by this scheme is more sensitive than that for Bragg angle detuning in a 90 degrees geometry. Both theoretical and experimental results are presented and analyzed.

Duplication of phase key for random-phase-encrypted volume holograms.

Holographic memory encrypted by an optical random-phase key and decrypted by either the original phase key or a duplicate key is proposed and demonstrated. The duplicate key is made by recording the encryption wave front with angle multiplexing during writing of the hologram. The amount of three-dimensional shifting that is tolerable in the duplicate key is analyzed.