Analyzing Optics' Pivotal Role in Augmented and Mixed Reality Displays

In designing a successful, engaging AR/MR display, optics knowledge is key. Useful and well-designed display technologies require careful consideration of both the hardware intended application. For example, in case augmented mixed reality (AR/MR) products, it's important to get correct design for optics, but also critical that final suitably matches use cases so user has wholly satisfactory experience. This requires expertise several technical disciplines, including optics. When must work seamlessly with application, there are many potential pitfalls. To help avoid these, this article discusses used headsets looks at specific examples analyses. Fig. 1 shows most common forms currently headsets. Each type its advantages disadvantages, as detailed following sections. Common optical design. Many companies have made diffraction-grating waveguides (Fig. 2). They thin, light, typically support field view (FoV) from 25 60 degrees. normally two or three be sandwiched together full color. Because they by total internal reflection, each waveguide an air gap between sandwich. The often reasonably high transparency 80 90 percent, frequently covered light-blocking make virtual images more visible. Typical diffractive waveguide. Diffraction drawbacks, such mediocre poor color uniformity worsens FoV increases. Optical efficiency quite low, it difficult couple light into While supposed relatively inexpensive produce, been theory than practice. Historically, diffraction known “front projecting” 3), which seen socially unacceptable even dangerous some cases. Some newer gratings designed reduce projecting forward. Another trend try replace fragile glass substrate plastic, date, results further loss image. Front projection (glowing eyes). Diffractive designs historically Texas Instruments digital processing (DLP) liquid crystal on silicon (LCoS) devices. Almost all LCoS microdisplays because cost, smaller pixels, higher resolution, lower power. A notable exception using Hololens 2, uses laser-scanning display. Lumus developed reflection-based 4). Until recently, only supported one-dimensional (1D) pupil expansion, resulting their engines being much larger 2D expanding waveguides. recently 2) engines. Reflective generally better approximately 3 7 times efficient advantage translates them supporting brightness given FoV. can deliver 3,000 4,000 nits over 50-degree one watt LED illuminating device. reflective (multimirror) perception market expensive claims addressing issue new partnership Schott (https://www.schott.com/en-us/news-and-media/media-releases/2020/lumus-and-schott-enter-into-strategic-partnership). development waveguides, were larger. thicker diffractive, since single colors, net difference thickness weight small. Birdbath (shown 1) common, dozen market. main consist lens spherical curved 50/50 mirror, polarizing beam splitter. simple, inexpensive, and—if well decent materials—provide good image quality. Most birdbath micro-OLED displays various quality small light. part order inch (∼25 mm). block 75 percent real-world making effectively dark sunglasses. lose 85 display's first polarized then bounce off through elements. starting 1,000-nit OLED, about 120 eye. level restricts indoors shade. pretty same similar size (thickness), efficiency, blocking. little thinner smaller, would result very large These constraints inherent improved minorly components. Ant Reality demonstrated variants considerably while wider FoVs combining reflection (TIR) birdbath-like TIR structures produce >100-degree 5). variants. Using off-axis combiner least way show AR 1). single-cell, phone-sized flat panel (VR) LCDs Two somewhat lenses molded coated inside semi-reflective mirror coating, forming semi-transparent mirror. An feature gives great deal eye relief, glasses sizes worn. magnifies moves focus (typically 2 meters) focus. low angular resolution magnified. “off axis,” distorted somewhat. varies top bottom, not cannot adjust. was popularized startup Meta (now defunct confused Meta-Facebook). startup, Campfire, original electronic business-oriented product. famous today Universal Studios Mario Kart attractions Osaka, Japan, Hollywood, California. Several companies, notably North (later acquired Google), tried direct laser scanning bouncing holographic Although compact design, small, disappointing, eyebox tiny. Additionally, anyone older 30 experienced floaters cause shadows retina. Laser addresses issues tiny eyebox, FoV, floaters. With poor, deficient uniformity. See later section Beam Scanning comparison Maximus 2D. wave products Meta, Apple (expected 2023), Lynx supports “passthrough AR/MR” VR device camera feeds There disadvantages passthrough AR. MR Fresnel lenses, aspherical lenses. pancake inefficient, drive need displays, 5 10 brighter prior Generating up battery life generates heat. Except adjunct games few business uses, massive problems everyday use. Even best systems come close matching what see. person needs safe environment, indoors, room where unlikely walk move hand arms something could seriously hurt them. It advantageous suggest (with passthrough) applications computer monitors. moderately high-end 20 pixels per degree. contrast, sitting front monitor gets 40 degree, depending proximity user. monitor, text blown factor two, meaning one-fourth content area user's vision. eventually will degree (a accomplished this), human factors always remain issue, things won't behave do real world. include following: follows: objective near-to-eye plus around Unlike desirable viewable wide range angles, want concentrated narrow angle. Unfortunately, emit nearly Lambertian wasted displays. All see-through fraction 15 usually worst 0.1 6 major sources issues. million may needed less 1,000 entrance area, helps coupling-in 3.5 lightweight, correspondingly Typically, means built semiconductor Micro-OLED without any microdisplay terms color, Usually, frame rates Hz. high-volume output ∼1,000 nits. Adding MLAs other improvements enhance higher-end commercial micro-OLEDs ∼3,000 volume optic applications, Companies eMagin Kopin shown OLED expected enable ∼30,000 High-performance tend military head-up applications. tens thousands level, bright enough orders magnitude MicroLEDs crystalline inorganic LEDs. significantly electricity driven harder (using power). emitted (than micro-OLED) collimation LED's roughly emission. Combining these factors, microLED (in green). extremely fast switching speeds, nanoseconds. As technology, microLEDs fairly immature far control. Often rate dead weak pixels; Jade Bird Display devices production gray-scale depth. assembly process control backplane difficult. Supporting full-color serious problem, trying different techniques; nobody production-worthy Full-color seem years away best. proposed approach monolithic spatial side-by-side red, green, blue (RGB) Producing native LEDs side challenge. number quantum dot (QD) conversion UV diodes RGB direct-view manufacturing QDs when applied microdisplays. Porotech publicly ability diode emitter, still early stages development. Both MIT Ostendo stacking But stacked issues, having pass circuitry above Small, low-resolution (640 × 480 less) monochromatic green successfully coupled nearing glasses-like form products. prototype demonstrations, (and TCL CES separate combined X-Cube highly accurately aligned makes complicated. power consumed tends proportional content, if mostly transparent (pixels near off), lower. problem occurs higher-resolution If pixel grow due collimate reduced. grow, smaller. worse etendue coupling until someone develops inherently emits collimated rather Overall, future potential. exploited uses. Beyond rates, speed “pixel shifting” address increase resolution. Other leverage light-field concepts. Field-sequential dominant technology designs. DLP reasons size, choice aspect ratios, chips. works conjunction polarizers change amount reflected transmitted pixel-by-pixel basis. whole illuminated every component imperfect, contrast micro-OLED. take no matter whereas darker. LEDs’ collimated, percentage configurations field-sequential process, downside field-switching enough, see breakup colors head. reduced tracking head motion warping subframes headset requiring re-rendered central graphics unit (CPU GPU). surface practice, ideal Microsoft's degrees Hz below flicker. Fundamentally, mirror(s) moved quickly high-resolution laser's complex, compensate varying sweep speed. Resolution affected resample onto sweeping pattern. backward compared LCoS. 1: versus Theoretically, near-zero optically couples efficiently interference coherent problems. 8 engine engine. eight brightest lens. 9 maps commonly AR/MR. Mapping headword mapping primarily either ultra-small green-only (from Display) Extremely low-cost, theme parks “bug-eye” challenge meet expectations placed Tens billions dollars spent, showing modest success. appears Apple, others backed pursuing pass-through AR, solution drawbacks application environment. longer-term seems toward achieve desired. Of available technologies, types. garnered attention investment last five average value, (usually promise, long go volume. likely continue LCD panels Karl Guttag president KGOnTech, blogging consulting company. He earned MS electrical engineering University Michigan. electronics industry experience devices, projector accelerators, video game His blog, comments designs, www.kguttag.com. reached [email protected].