Geometrical Waveguide Research Articles

Additive 3D printed optical waveguide for augmented reality

The mass production of augmented reality (AR) waveguides has been challenging due to the intricate nature of the fabrication technique and the high precision required for their optical characteristics. In this paper, we have presented a novel and low-cost approach for fabricating geometric optical waveguides designed for AR applications utilizing 3D printing techniques. To strike a balance between optical performance and fabrication feasibility, we have optimized the conventional geometric waveguide design to facilitate easier fabrication. It is worth noting that our proposed method does not require molding, dicing, or post-surface polishing after printing. A prototype based on this method has been successfully fabricated, showing the immersion between the virtual image and the real-world scene. The proposed method has great potential for adaptation to mass production in various AR applications.

Design method of an ultra-thin two-dimensional geometrical waveguide near-eye display based on forward-ray-tracing and maximum FOV analysis.

A two-dimensional geometrical waveguide enables ultra-thin augmented reality (AR) near-eye display (NED) with wide field of view (FOV) and large exit-pupil diameter (EPD). A conventional design method can efficiently design waveguides that meet the requirements, but is unable to fully utilize the potential display performance of the waveguide. A forward-ray-tracing waveguide design method with maximum FOV analysis is proposed, enabling two-dimensional geometrical waveguides to achieve their maximum FOV while maintaining minimum dimensions. Finally, the designed stray-light-suppressed waveguide NED has a thickness of 1.7 mm, a FOV of 50.00°H × 29.92°V, and an eye-box of 12mm × 12 mm at an eye-relief of 18 mm.

Depth error correction for plenoptic cameras based on an innovative AR system combining geometrical waveguide and micro-lens array

Plenoptic cameras have been increasingly applied in three-dimensional (3D) optical imaging and measurements. Micro-lens array is the key component to capture the images at different depths simultaneously to realize the 3D reconstruction of the scenery. However, only a part of the captured information will be used eventually when focusing on specific objects, which implies a waste of time and resources that are incompetent for fast-response tasks like gesture recognition. Furthermore, it is still quite challenging to accurately calibrate the depths under complex circumstances, even sometimes losing a part of the target information due to the low signal-to-noise ratio. In this paper, a new hybrid optical system is developed combining a geometrical waveguide and micro-lens array to project a virtual scale network for quantitative depth calibration and fast-tracking of targets. Such a methodology based on the augmented reality (AR) mechanism helps to rapidly scope the targeted objects/features without reconstructing the full range model, significantly saving the processing time for a low-latency response. By establishing a geometrical model to quantitatively correlate the images in the auxiliary coordinate system and the virtual scale coordinate system, the depth error caused by the plenoptic camera can be calibrated and corrected. The coefficient of determination R2is used to evaluate the depth accuracy of 3D images and acts as the threshold to control the depth correction iterations. The closer the value of R2 is to 1, the more accurate the depth information is. Experiments proved that even under complex backgrounds or insufficient light, in virtue of the virtual coordinate networks, backgrounds could be rapidly filtered, and targets were effectively identified with accurate depth information. The algorithm flow chart for the correction of depth error is given. In such a way, the system can achieve faster and more accurate capturing of 3D objects in a real-time manner than conventional plenoptic cameras.

Method for parallelism measurement of geometrical waveguides based on the combination of an autocollimator and a testing telescope.

Augmented reality (AR) is desperately needed in the Metaverse. The geometrical waveguide receives increased attention in AR technology as achieving high resolution, full-color display, etc. However, the stray light and ghost image problems resulting from the parallelism errors severely deteriorate the imaging quality. According to the light propagation of the waveguide, a measuring system based on the combination of the autocollimator and the testing telescope (CAT) method was proposed to measure the parallelism errors of the partially reflective mirror array (PRMA). The results indicated that this method could measure the parallelism errors precisely with the maximum repeatability of 0.63 ' ' . The method could decouple the coupling of the parallelism errors of the PRMA and the substrate surfaces to imaging quality effectively. The precise parallelism measuring is expected to contribute to mass production and low cost by promoting the waveguide design and fabrication.

Objective measurement technique for mitigating the augmented-reality geometric waveguide double-image problem

In this paper, we propose a method for using angle offset measurements of an augmented-reality (AR) geometric waveguide partially reflective mirrors array (PRMA), to inform the design and manufacture of future iterations. These offsets are the main cause of display defects such as the formation of double-images. Our design provides a method for quantitative measurement to support the solution of the AR geometric waveguide double-image problem. Our study is based on the principle of optical lever amplification, and PRMA high accuracy measurement is achieved. We also provide an analysis that determines the maximum permissible offset limit of the PRMA geometric waveguide module, without affecting the display quality. The technique is validated on virtual models made in SolidWorks that are synchronized with optical components whose parameters are changed in LightTools. This provides a powerful technique for speeding up the design and manufacturing cycle where until now this has been based on subjective innacurate and unreliable human observation. This paper provides the theoretical basis for the development of a rigorous and reliable measurement technique.

Design of a dual-focal geometrical waveguide near-eye see-through display

Vergence-accommodation conflict (VAC) is an obstacle in approaching the natural visual perception in near-eye see-through display. Conventional stereoscopic displays provide virtual images in a single focal plane, which are unable to satisfy the accommodative perception of the human eyes. The geometrical waveguide can be employed to achieve a larger field of view (FOV), larger exit pupil area, lower thickness and lighter weight, thus providing the possibility to offer multiple focal planes in a compact design. In this paper, we propose a wide-FOV dual-focal geometrical waveguide see-through display with a relatively thin structure. The causes of stray light in the dual-focal model are systematically analyzed based on the non-sequential ray tracing. Correspondingly, a solution is presented to eliminate the stray light and reach uniform illumination at the entire exit pupil area. The achieved illumination uniformity of the dual-depth system reaches 0.83 and the intensity uniformity is over 0.7. The depth cues of the optimized design are infinity and 100 mm with 35° FOV, 38.46 mm eye box and 20 mm eye relief, which greatly improves the optical performance and reduces the dizziness caused by the VAC problem. The total internal reflection (TIR) collimator greatly improves the uniformity of the virtual images from the projector.

Design method of a wide-angle AR display with a single-layer two-dimensional pupil expansion geometrical waveguide.

Waveguide near-eye displays (NEDs) consist of a planar waveguide combiner and a coupling-in projection system. A two-dimensional geometrical waveguide (TDGW) can achieve an ultra-thin, large exit pupil diameter (XPD), wide-angle NED. The design method of a single-layer TDGW is presented and discussed in detail in this paper. A high-precision processing technology that can effectively guarantee the parallelism accuracy is also presented. A miniature coupling-in projection optics is designed with a catadioptric structure and integrated with the waveguide accordingly. Finally, a TDGW with a thickness of 1.75 mm is designed and analyzed. The results show that the stray light over the normal light is less than 0.5%, and the illuminance uniformity is well optimized. The field of view is up to 55°, and the XPD exceeds 12mm×10mm at an eye relief (ERF) of 18 mm. A proof-of-concept prototype was fabricated and demonstrated.

Design of a large field-of-view two-dimensional geometrical waveguide

Geometrical waveguide has great advantages over conventional imaging systems, like larger field of view, larger exit pupil area, lower thickness and lighter weight. Two-dimensional (2D) geometrical waveguide can expand the vertical and horizontal pupil simultaneously, thus becoming a mainstream solution for commercial applications. The transmission path of two-dimensional optical system is more complicated and therefore the stray light in two-dimensional geometrical waveguide is more complex compared with one-dimensional waveguide. In this paper, the causes of stray light in 2D geometrical waveguide are discussed based on the non-sequential ray-tracing with detailed numerical analysis and the targeted solutions are developed to effectively improve the imaging quality. Consequently, a stray-light-free design of geometrical waveguide is proposed having the field of view reaching 49° × 56° with 22.6 mm × 26 mm eye box at 20 mm eye relief.

56.5: Pupil Swim Suppression in Augmented Reality (AR) Waveguide Combiner

Pupil Swim refers to change in extent of distortion when human eye moves in exit pupil of near eye display. Though this artifact is rarely discussed in normal metrics of augmented combiner, it deteriorates the long‐time viewing experience of AR headsets. Previously, this phenomenon was noticeable to public in virtual reality (VR) optics with large field of view.[3] We recently take a survey and find similar occurrence in AR products, especially in geometric waveguide with large FOV and small F/#. In this work, we first give a phenomenal description of this issue and research on the optical aberrations creating this artifact. To address pupil swim, a practical design methodology was proposed based on a comprehensive discussion inclusive of the interaction of human vision and project virtual image. Future directions like using catoptric design were proposed to further suppress the pupil swim and improve the visual comfort of near eye display.

P‐47: A Geometric Waveguide with Two‐Dimensional Pupil Expansion for Near‐Eye Displays

We have designed and simulated a geometric waveguide for near‐eye displays. The image source is a DLP projector with a 4mm pupil. The waveguide consists of two pupil expanders for the horizontal and vertical directions. Simple optical coating and inject molding process could reduce the cost. A near‐eye display with field‐of‐view 40 degrees in diagonal is achieved. The luminance efficiency is 0.5% and the total weight is only 6.1g.

Stray light analysis and design optimization of geometrical waveguide

Abstract Waveguide technology has great prospects of development in optical see-through near-eye displays with larger field of view, lower thickness and lighter weight than other conventional optical technologies. However, the stray light is usually inevitable in current optical design and manufacturing, causing a poor imaging quality. In this paper, the principle and structures of stray light generation are analyzed, and the causes are discussed by non-sequential ray-tracing with mass precision calculation. From the ray-tracing, the suppression of stray light by optimizing design and manufacturing are achieved. A 2 mm-thickness geometrical waveguide with partially reflective mirror array is designed. The field of view of the optimized geometrical waveguide reaches 47° with 10 mm at exit pupil diameter and 20 mm at eye relief.

Design of an ultra-thin, wide-angle, stray-light-free near-eye display with a dual-layer geometrical waveguide.

The field of view (FOV) of a geometrical waveguide display is limited by the total internal reflection (TIR) condition (related with the index of glass) and the stray light generated inside the waveguide. A novel concept of an ultra-thin, wide-angle, stray-light-free, optical see-through near-eye display (NED) with a dual-layer geometrical waveguide is proposed in this paper. In the dual-layer waveguide, the two waveguides have different structures and are responsible for two different FOVs which are spliced together to form the entire FOV. The stray light of the dual-layer waveguide is analyzed and an optimized structure to suppress the stray light is designed. An optimized coupling-in structure is designed and a progressive optimization method is proposed for optimizing the illuminance uniformity of the entire FOV across the exit pupil. A dual-layer waveguide with a total thickness of 3.0 mm and stray light of less than 1% is designed. The FOV is 62° in the pupil-expanding direction, and the diameter of the exit pupil (EPD) is 10 mm at an eye relief (ER) of 18 mm. A compact projection optic is designed and finally is integrated with the dual-layer waveguide.

Parallelism measurement of geometric waveguide array based on autocollimation

Parallelism measurement of geometric waveguide array based on autocollimation

Design of a uniform-illumination two-dimensional waveguide head-up display with thin plate compensator.

Nonuniform illumination is one of the factors in degrading image performance of geometrical waveguide-based head-up display. The two-dimensional (2-D) waveguide expanding the exit pupil along two orthogonal directions makes illumination uniformization more intractable. To solve this problem, the reasons for nonuniform illumination in 2-D geometrical waveguide were probed and a novel waveguide structure incorporating illumination compensator was proposed. A bilayer illumination compensator was first presented to change the period of rays propagating in waveguide to improve the inter-pupil illumination uniformity and inter-field illumination uniformity. Then optimized coating design for different partially reflective mirrors in horizontal waveguide and the vertical one allowed further improvement of these two kinds of illumination uniformity, raising both up to 70%. A matched catadioptric projection optics using freeform surface was designed and integrated with the resultant 2-D geometrical waveguide, achieving a head-up display with an eye relief of 400 mm, an eyebox of 80 mm × 80 mm and a field of 24° × 15°. A prototype of the proposed 2-D geometrical waveguide display was developed and demonstrated.

Design of a two-dimensional stray-light-free geometrical waveguide head-up display.

Stray light is one of the factors exerting negative influences on the image quality of the head-up display based on the geometrical waveguide. Particularly, compared with the architecture used to expand a one-dimensional pupil, the geometrical waveguide expanding the two-dimensional pupil makes it difficult to remove the stray light due to the combined effect from two orthogonal directions. To overcome it, causes of stray light in the two-dimensional geometrical waveguide are analyzed based on the detailed calculation of the parameters that determine the geometry; the corresponding approach is put forward to decrease the percentage of the stray light across the eye box to below 0.1%. The relationship between the resultant combined waveguide and the projection optics is also clarified to obtain the pupil matching. The head-up display integrating the combined waveguide and the designed projection optics achieves the field of 24°×15° and the eye box of 80 mm×80 mm.

Design of an ultra-thin near-eye display with geometrical waveguide and freeform optics

Small thickness and light weight are two important requirements for a see-through near-eye display which are achieved in this paper by using two advanced technologies: geometrical waveguide and freeform optics. A major problem associated with the geometrical waveguide is the stray light which can severely degrade the display quality. The causes and solutions to this problem are thoroughly studied. A mathematical model of the waveguide is established and a non-sequential ray tracing algorithm is developed, which enable us to carefully examine the stray light of the planar waveguide and explore a global searching method to find an optimum design with the least amount of stray light. A projection optics using freeform surfaces on a wedge shaped prism is also designed. The near-eye display integrating the projection optics and the waveguide has a field of view of 28°, an exit pupil diameter of 9.6mm and an exit pupil distance of 20mm. In our final design, the proportion of the stray light energy over the image output energy of the waveguide is reduced to 2%, the modulation transfer function values across the entire field of the eyepiece are above 0.5 at 30 line pairs/mm (lps/mm). A proof-of-concept prototype of the proposed geometrical waveguide near-eye display is developed and demonstrated.

Tailoring the dispersion behavior of silicon nanophotonic slot waveguides

We investigate the chromatic dispersion properties of silicon channel slot waveguides in a broad spectral region centered at ~1.5 μm. The variation of the dispersion profile as a function of the slot fill factor, i.e., the ratio between the slot and waveguide widths, is analyzed. Symmetric as well as asymmetric geometries are considered. In general, two different dispersion regimes are identified. Furthermore, our analysis shows that the zero and/or the peak dispersion wavelengths can be tailored by a careful control of the geometrical waveguide parameters including the cross-sectional area, the slot fill factor, and the slot asymmetry degree.

Gyrotropic band gap optical sensors

Faraday-effect-active photonic band gap structures fabricated in iron garnet films are shown to provide a platform for optical sensing based on refractive index detection. Strong near-band gap-edge polarization rotations serve as a sensitive probe to cover-index changes in birefringent magneto-optic waveguides. A wide index range from air to n=1.6 is explored. Device sensitivity is found to improve with cover index increase. Theoretical analysis of Bloch modes polarization state shows large near stop-band edge rotations and strong sensitivity to cover index. The combined effects of geometrical waveguide birefringence and Faraday rotation contribute to the strength of the sensor response.

The waveguide effect of metastable olivine in slabs

We use a finite difference algorithm to compute P‐SV synthetic seismograms for deep earthquakes recorded at regional seismic stations located above a subducting slab. We calculate synthetics for 2‐D slab models in which the 410 km‐discontinuity is uplifted, owing to the exothermic nature of the α → β transition (the equilibrium model), and models in which the 410 km‐discontinuity is depressed, owing to inhibited kinetics of the α → β olivine transition (the metastable model). In the latter case the existence of the low‐velocity wedge of metastable olivine has a profound influence on the waveforms of deep‐focus earthquakes. The wedge acts as a geometrical waveguide, with the energy‐focusing effect apparent even after the wavefront has traveled the several hundred kilometers from the wedge boundary to the Earth's surface. The guided energy is most pronounced for receivers located near the surface projection of the deep slab but is observable over a range of 300 km and so may provide a valuable diagnostic for discriminating between equilibrium and metastable models of subduction. A recent search for such guided energy, using regionally recorded P and S waves from deep events in Tonga, yielded negative results.

Guided-wave Mach-Zehnder Modulators fabricated on LiNbO3 via Ti-indiffusion and Proton Exchange

Two types of Mach-Zehnder modulators in LiNbO 3 fabricated via Ti-indiffusion and annealed proton exchange (APE) are presented. Their geometrical configuration and waveguide structure, as well as the modulation characteristics are discussed. A considerable reduction of r 33 electro-optic coefficient in the protonated LiNbO 3 based modulator is registered.