AnAugmentedRealityHead-UpDisplaySystemwitha Wide-ViewEyeboxdownloads.hindawi.com/journals/ijo/2020/4719268.pdf · ResearchArticle AnAugmentedRealityHead-UpDisplaySystemwitha Wide-ViewEyebox

Research ArticleAn Augmented Reality Head-Up Display System with aWide-View Eyebox

Pei-Jung Wu1 Chih-Hao Chuang2 Chien-Yu Chen 3 Jeng-HanWu4 and Bor-Shyh Lin5

1College of Information and Distribution Science National Taichung University of Science and TechnologyTaichung 40401 Taiwan2Graduate Institute of Photonics and Optoelectronics National Taiwan University Taipei 106 Taiwan3Graduate Institute of Color and Illumination Technology National Taiwan University of Science amp TechnologyTaipei 10607 Taiwan4Department of Electronic Engineering National Yunlin University of Science amp Technology Yunlin 64002 Taiwan5Institute of Imaging and Biomedical Photonics National Chiao Tung University Tainan 71150 Taiwan

Correspondence should be addressed to Chien-Yu Chen chencyuemailntustedutw

Received 5 October 2019 Revised 12 May 2020 Accepted 10 June 2020 Published 30 June 2020

Academic Editor Paramasivam Senthilkumaran

Copyright copy 2020 Pei-JungWu et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

is study proposes to apply the combination of two 90-degree prisms and a holographic optical element to an image-dividingelement divide an image into three through the virtual image projection system and accurately project the images to 160 cmbehind the windshield In order to distinguish the left image middle image and right image at the horizontal direction the 90-degree prism is first utilized for horizontally deflecting the light a holographic optical element is then used for presenting thevertical deflection of the image and finally the images are horizontally arranged as a real image on the diffuser An image-dividingelement is eventually integrated to the virtual image projection systemen the divided images are made as a virtual image whichis projected to 160 cm behind the windshield to combine with the street scene e horizontal angle of view of an eyebox isincreased from 251deg to 722deg and the size of the eyebox is 3168 cmtimes 1248 cm allowing a wide-view laser-based head-up displaywith the large-angle beam-splitting function being successfully designed It would not affect the field of view on the road and thissystem could reduce the space and be arranged easily in a vehicle erefore this proposed system is suitable for the aftermarket

1 Introduction

Head-up displays are normally applied to airplanes [1]Nevertheless the rapid development of science and tech-nology has such a technique be gradually introduced toautomobile display systems Driving a vehicle is not ascomplicated as flying an airplane and the surroundinglandscape presents few changes However when drivers aredistracted by watching the information from the dashboardit is hard for them to keep focusing on the road en thetraffic accidents are likely to be enhanced [2] e devel-opment of head-up displays therefore could solve suchinconvenience for drivers and ensure the safety on streets Inregard to the development of automobile displays displayshave evolved from traditional CRT to liquid-crystal displays

(LCDs) [3] liquid crystal on silicon (LCoS) and digitalmicromirror devices (DMD) because of the advance ofdigital technology e advance of MEMS process in pastyears further allows the application of laser-based picoprojectors [4]

Based on distinct imaging principles head-up displayscould be divided into direct projection HUD and virtualimage HUD [5] e former utilizes optical projection fordirectly projecting an image to the reflecting coating on thewindshield [6] (Figure 1(a)) so as to actually image the trafficinformation on the reflecting coating in front of the driverNonetheless the transmittance is also reduced to generatevisual blind angle Besides the imaging position of such adirect projection HUD is close that the visual accommo-dation is necessary for a driver viewing the image

HindawiInternational Journal of OpticsVolume 2020 Article ID 4719268 9 pageshttpsdoiorg10115520204719268

information e latter merely requires an optical lens tocontrol the imaging distance of a virtual image without areflector on the windshield that the system cost could bereduced [7] As shown in Figure 1(b) the lens imagingprinciple is used for controlling the imaging position behindthe windshield and combining with the street scene beyond3m In this case eye-accommodation is not necessary forhuman eyes that the road safety could be largely enhancede construction of this system is huge among the currentliterature and patents that it is not easily equipped in a vehicleBesides the horizontal angle of view of the eyebox is the anglebetween an image width and human eyes under the premiseof not affecting the image quality that a narrow angle couldeasily result in inconvenient viewing for a driver Accordingto some previous studies [8 9] the HUD systems based on theprinciples of total internal reflections and holographicwaveguides have some advantages such as decreasing the totalvolume and increasing the eyebox However there are someproblems or limitations from the holographic waveguideHUD systems by using many HOEs First the dispersioncould be caused when the light passing through the HOEen the aberration could be also caused by the flatness of theholographic materials ird both the wavelength and theangle of the incident light need to satisfy with the require-ments of HOE and the total internal reflection condition ofthe waveguide In addition the volume of the optic systemwith many HOEs can be decreased but the structure of theHOE system is too difficult to be built for mass productiondue to the very low tolerance of the HOE system Besides it ishard to correct the image after the system completed

By combining an image-dividing element and the virtualimage projection system a wide-view laser-based head-updisplay is produced in this study e high illumination andhigh power of the laser beam source are used for replacingthe LCD image module and eyebox for automobile head-updisplays is designed and expanded e eyebox of a generalvirtual image HUD is not wide enough because of the limitedimage projection size and lens imaging size and the

projected image information is also crowded resulting inviewing difficulty for drivers Two 90-degree prisms and aholographic optical element are therefore combined todivide images with the characteristics of laser wavelengthselectivity and diffraction of the holographic optical elementNot only this system could divide the image projected by thelaser-based pico projector into three horizontal images butalso a virtual image projection lens is designed to projectsuch three images to 160 cm behind the windshield which isused as a combiner e volume of this system is not hugeForevermore this system can be installed and adjusted fordifferent types of cars easily It could prevent a driver fromlooking away from the street and expand the angle of view ofthe eyebox for a driver

2 Materials and Methods

A laser-based pico projector (PicoPreg display) is used for anautomobile head-up display outputting the traffic infor-mation [10] Nevertheless both the vertical and horizontalprojection angles of the laser projector are narrow that theimage can hardly be enlarged in the limited space through aprojection lens For this reason an image dividing element isdesigned to clip and project an original image so as toexpand the eyebox of the head-up display allowing thedriver to view more traffic information

e laser-based pico projector used in this study showsthe resolution 848times 480 and the focus range 200mmndash2500mm In this study the designed original images are threepieces of vertical traffic information side by side includingspeed direction indication and warning light and the in-termediate image reveals the size 1 cmtimes 1 cmWhen an imagegoes through the image dividing element designed in thisstudy the upper middle and lower parts of the original imagewould be divided into three horizontal images side by sideSuch an image dividing element could increase the horizontalfield of view and provide more comfortable and secureviewing images for the driver

Driver eyes

Displaymodule

Windshield

Real image

120kmh

(a)

Driver eyes

Displaymodule

Windshield

Lens

Virtual image

120kmh

(b)

Figure 1 (a) Direct projection HUD (b) virtual image HUD

2 International Journal of Optics

Figure 2 presents the system architecture covering animage-dividing element and a virtual image projectionsystem e image-dividing element is designed with thecombination of two 90-degree prisms and a holographicoptical element e 90-degree prisms are first used fordeflecting the upper-layer image and the lower-layer imageto the left and the right and such two images are deflected tothe required positions with the holographic optical elementFurthermore a diffuser is placed at the intermediate imageto make the divided images become an intermediate realimage [11] With the convex lens in the virtual imageprojection system the traffic information is virtually pro-jected to 160 cm behind the windshield e design andproduction of the image-dividing element and the holo-graphic optical element are described in the section ldquoImage-Dividing Elementrdquo and the design and production of thevirtual image projection system is demonstrated in thesection ldquoVirtual Image Projection Systemrdquo

21 Image-DividingElement In this study an original imagecan be divided into horizontal images with two 90-degreeprisms and the subimages can be vertically moved with aholographic optical element In Figure 2 a laser-based picoprojector is used for projecting an original image and aprism is used for moving the upper subimage rightward andthe lower subimage leftward (Figure 3(a)) e holographicoptical element is further used for generating the verticalfirst-order diffraction of the image to vertically move thesubimages on the right top and the left bottom so as todisplay the three subimages on the same horizontal planeside by side (Figure 3(b)) In addition to assisting twosubimages in diffracting to the required positions the ho-lographic optical element presents the advantages of smallsize and light weight and the diffracted image would not bedistorted because of refraction [12]

First of all the relationship between the incident angleand the deviation is utilized for estimating the requiredparameters of the 90-degree prismse laser beam source isused as the incident light in this study However the laser-based pico projector has a stable divergence angle e threedivided images might be overlapping partially after theincident light passing through the prism us the rela-tionship between projection distances and the system set-tings needs to be optimized On the other hand therelationship between the prism base angle and distortion aswell as the match with the back-end virtual image projectionsystem should be taken into account As shown in Figure 4the incident angle is preset the minimum θ1 and themaximum θ2 the minimum refraction angle empty1 and themaximum refraction angle empty2 through the prism and thematerial refractive index n Equation (1) is applied to cal-culate the required minimum prism base angle α

θi sinminus1 sin α

n2 minus sin2 φi

1113969

minus cos α sinφi1113874 1113875 i 1 2

(1)

According to the parameters provided by the projectorthe maximum projection emission angle appears about 34deg

and the required minimum prism base angle about 55deg afterthe calculation BK7 (n 1516) is used as the material for theproduction and the produced prism with the dimension10mmtimes 7mmtimes 5mm is shown in Figure 5 Using such aprism for image dividing the horizontal angle of view of theeyebox in the laser-based pico projector is enhanced from251deg up to 722deg that the driver could easily view the pro-jected image An image going through the prism hasachieved the wide-view projection while the images are nothorizontally arranged e diffraction of a holographicoptical element therefore is needed to make the images sideby side horizontally

en the diffraction angle of the holographic opticalelement (HOE) needs to be evaluated As the higher orderof diffraction would reveal lower efficiency the first-orderdiffraction is designed in this study so as to ensure thebetter diffraction efficiency As shown in Figure 6 thecrow-flight distance between the projection light sourceand the diffuser after going through the prism is assumed sand the vertical distance between the projected image andthe central point h is assumed In other words the upper-layer and lower-layer images need to be vertically displacedby h to parallel the middle image side by side In thissystem the distance between the projector and Image 2 isset 3 cm the required displacement height h on the diffuseris 055 cm and the angle β between Image 1 and Image 2 is15dege distance d between the projector and Image 1 couldbe acquired with the trigonometric relationship and thefirst-order diffraction angle is about 10deg according toθ tanminus1 dh e three images could be horizontally dis-played side by side through the diffraction with such anangle In the production process the VRP-M hologramsensitized by green light wavelength is applied to record theholographic optical element and according to the energycurve provided by Slavich the hologram presents thehighest diffraction efficiency at the exposure energy75 μJcm2 with which the required recording time is cal-culated [13] Finally the shot holographic optical elementwith the length and width of 7mm and 5mm respectivelythe grating period of 3157 μm and the diffraction angleabout 97deg is shown in Figure 7

22 Virtual Image Projection System e three parallelimages divided by the image-dividing element are imaged onthe diffuser at the intermediate image in the virtual imageprojection system a convex lens as a projection lens isplaced at the back of the system Before designing the virtualimage projection system the intermediate image on thediffuser is first analyzed by the resolution e 1951 USAFresolution test chart is utilized for measuring the imageresolution in this study and the required 1951 USAF res-olution test chart is established with equations (2) and (3)e result is shown in Figure 8 from which the projectionlimit of the projector is about the 4th element in the 1stgroup e minimum resolution allowed for the projector iscalculated about 0707l pmm which is regarded as theminimum optimization of the projection lens for theanalysis

International Journal of Optics 3

line length(mm) 25mm

2group+(elementminus1)6(2)

linewidth(mm) 25mm

2group+1+(elementminus1)6(3)

In the projection system design the object distance of thesystem is set l and the image distance lprime the parameter of theinitial order lens is calculated with the lensmakerrsquos equation[14] In this system the object height is set 50mm which isthe imaging width of the divided image After the design thevirtual image projection system presents the imaging at 1600behind the combiner the image amplification about 85x theimage distortion less than 5 through the lens optimizationand the enlarged image height up to 425mm

3 Simulation

In this study LightTools the nonimaging simulation soft-ware is applied to simulate the beam splitting and Zemaxthe imaging simulation software is used for simulating thevirtual image projection lens e simulation and design ispreceded with the following three steps (1) module con-struction of the laser-based projector e angle of emer-gence of the projector and the working principle of eachpixel reflected from the laser going through the scanninglens are followed e point light source is utilized forconstructing the optical system of the laser-based projectorand simulating the beam characteristics of the laser(wavelength 532 nm) reflecting through MEMS the hori-zontal projection angle of the system is 34deg (2) Design of the

Virtual image projection system

160cm

Virtualimage

Windshieldscreen

Virtualprojection lens

DiffuserLaser projector

Original image

Prism 2

Prism 1HOE

HOE

Image-dividing element

Figure 2 System architecture

Diffuser

Laserprojector

Prism 2 Prism 1

30kmh

(a)

Diffuser

Laserprojector

HOE

Prism 2 Prism 1

30kmh

(b)

Figure 3 Application of the image-dividing element to the system (a) 90-degree prisms (b) a holographic optical element


image-dividing element containing two 90-degree prisms anda holographic optical element Figure 9(a) shows the simulationof optical path without adding the element e simulationresult reveals the original image size about 1 cmtimes 1 cm beingdivided into 3 images through the image-dividing system as in

Figure 9(b) From Figure 10 the horizontal projection angle ofthe system is about 100deg after the optical path being split by thebeam Such a result proves that the combination of a prism anda holographic optical element could largely increase the imagewidth (3) Zemax utilized for designing and evaluating theprojection lens in the virtual image projection system Aprojection lens is designed in this study with the focus distanceof 200mm and the diffuser distancing the intermediate imageof 149mm e image information would be enlarged as avirtual image at 1600mm behind the windshield the lensamplification appears 85x and the virtual image sizes272 cmtimes 68 cm From this structure when human eyes viewthe traffic image information at 45 cm in front of the wind-shield the horizontal angle of view of the eyebox is about 722degFigure 11 shows the relationship between field curvature of theprojection structure and distortion Figure 12 shows the Griddistortion on the virtual image projection lens Apparently theimage distortion is controlled below 1 Human eyes generallyappear about 5 sensitivity to distortion [15] In this case whendistortion is controlled in the value it could be accepted byhuman eyes

4 Results and Discussion

From Figure 9 the image after the beam splitting appearssome trapezium distortion because of the emission angle ofthe 90-degree prism and the laser projector [16] In the real

7mm

5mm

Figure 7 Photograph of designed holographic elements

Figure 8 Evaluation of the 1951 USAF resolution test chartprojected on the diffuser by the miniaturized projector

θ1

θ2

Oslash2Oslash1

α

Laserprojector

Diffuser

Figure 4 Incident angle and angle of emergence of a prism

10mm

55deg

7mm

5mm

Figure 5 Photograph of the designed prisms

sd

h

θ

β

Laserprojector

Image 1

Image 2

Image 3

120kmh

Figure 6 Evaluation of the diffraction angle


system the divided images would appear slight trapeziumdistortion because of the prism refraction the originalhorizontal image width 1 cm becomes 115 cm for the upper-and lower-layer image width after the deflection showingthe distortion about +15 As a result the horizontal widthof upper- and lower-layer images needs to be reduced 15 inorder to present the consistent width of the three images aswell as to eliminate the distortion

According to the simulation result the real optical pathis set up in this study as in Figure 13 e laser-based picoprojector in the simulation is regarded as an image forcombining with the entire system including the image-di-viding system and the virtual image projection system and areflection mirror with OS-50 reflecting coating is set up inthe system Ti3O5 is used as the OS-50 reflecting coatingmaterial with the reflectivity and the transmittance ratio of

10

0

ndash10

3020100X (mm)

Y (m

m)

ndash10ndash20ndash30

(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)

Figure 9 Imaging simulation of the image-dividing element (a) without an element and (b) with elements

100deg

x

z

Figure 10 Optical path through the image-dividing element

ndash05ndash10000 0000 0510000PercentMillimeters

+Y+YDistortionField Curvature

T S

Figure 11 Field curvature and distortion of the virtual image projection lens


4 6 A screen is placed at 160 cm behind the windshield anda camera is used for recording the imaging Figure 14 showsthe real optical path e projecting images are shot atdaytime and in the evening

In Figure 14 a screen is place at the image plane and acamera focuses on the image plane in order to acquire the clearimage information and prove the correct imaging at 1600mme virtual image size of this system is about 26 cmtimes 68 cmwhich is slightly smaller than the result of the simulation withthe error about 5 Such an error might be resulted from theplusmn2deg tolerance of the prism base angle causing the deviation ofthe horizontal image On the other hand the production of aholographic optical element is comparatively complex but thequality of chemicals or the surrounding environments couldresult in slight errors of holographic optical elements in theproduction Such considerations have been controlled asmuchas possible for the consistence

Reviewing the current head-up displays in the marketmost of them directly display on a screen that the small angleof view cannot provide sufficient information for the usersCurrently a lot of research increases the image size withlenslet arrays or the amplification of projection lens [17 18]

Such methods could enhance the enlargement of the imageand the image height that the field of view of the driver couldbe obstructed On the other hand the three divided imagescan be projected by three head-up projectors but the volumeof the systemmight become lager and the cost might becomehigher [19] In this Densorsquos system four reflectors were usedfor dividing an image into two images and large-areaoverlapping technology was used for displaying the completeimage e optical components were more and the volumeof Densorsquos system was also large [20] us the image-di-viding element produced by combining two 90-degreeprisms and a holographic optical element is thereforeproposed in this study As a holographic optical element islight and thin the entire system size is miniaturized smallerthan the systems with reflective elements or refractive ele-ments appears no distortion and presents the fixed de-flective angle both the image quality and the installationconvenience are significantly promoted

e automobile head-up display proposed in this studycould improve the projection angle of the current laser-basedpico projectors from 34deg to 100deg In addition to increase theinformation coverage the field of view obstruction would not

Figure 12 Grid distortion of the virtual image projection lens

Virtual imageprojection system

Spectral imagingdevice

Figure 13 Photograph of the laboratory setup of the proposed system


occur in this system Besides it could be combined with othertypes of head-up displays providing drivers with largerhorizontal field of view Moreover the projection distance isat 1600mm behind the windshield that the augmented realityof the street scene is compatible with the projected imagewhen a driver views the projected information e eyestherefore do not need to focus on the changing view to causeeye fatigue

5 Conclusions

In this study an image-dividing element is produced bycombining two 90-degree prisms and a holographic opticalelement and integrated with a virtual image projectionsystem to produce a wide-view laser-based head-up displaye prism is used for horizontally deflecting the beam andthe holographic optical element is utilized for verticallydeflecting the imagee images are eventually arranged as areal image horizontally on a diffuser to distinguish the leftimage middle image and right image e divided imagescould be imaged at 1600mm behind the windshield throughthe virtual image projection system Such a virtual imagingsystem increases the horizontal projection angle from 34deg to100deg the image size is enlarged into 85x and the finalimaging size appears 26 cmtimes 68 cm When human eyesview from 45 cm in front of the windshield the horizontalangle of view of the eyebox increases from 251deg to 722deg andthe size of the eyebox is 3168 cmtimes 1248 cm With such asystem a driver could reduce the situation of not payingattention to or distracting from the street to view the trafficinformation that the accident could be relatively reducedMeanwhile a driver could acquire more vehicle conditionsand real-time traffic conditions with the laser-based head-updisplay Because the miniaturized system could reduce thespace and be arranged easily in a vehicle this proposedsystem could be suitable for the aftermarket

Data Availability

e data of the optical design used to support the findings ofthis study are included within the article and the data of thesimulation used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

is research was partially supported by the Ministry ofScience and Technology (MOST) Taiwan under contractnumbers MOST 107-2221-E-011-086 and MOST 107-2622-E-011-007-CC3

References

[1] M H Kalmanash ldquoDigital HUDs for tactical aircraftrdquo inProceedings of the Defense Security COCKPIT and FutureDisplays II vol 6225 Kissimmee Florida USA April 2006

[2] Y-C Liu ldquoEffects of using head-up display in automobilecontext on attention demand and driving performancerdquoDisplays vol 24 no 4-5 pp 157ndash165 2003

[3] R D Brown D H Modro andM R Greer ldquoHigh-resolutionLCD projection based color head-up displayrdquo in Proceedingsof the International Society for Optical Engineering vol 4362pp 183ndash193 New York NY USA September 2001

[4] M K Hedili M O Freeman and H Urey ldquoMicrolens array-based high-gain screen design for direct projection head-updisplaysrdquo Applied Optics vol 52 no 6 pp 1351ndash1357 2013

[5] M K Hedili M O Freeman and H Urey ldquoTransmission char-acteristics of a bidirectional transparent screen based on reflectivemicrolensesrdquoOptics Express vol 21 no 21 pp 24636ndash24646 2013

[6] I-H Shao W-W Yang C-H Chen and K-T Luo ldquo403high efficiency dual mode head up display system for vehicleapplicationrdquo SID Symposium Digest of Technical Papersvol 44 no 1 pp 559ndash562 2013

[7] T P Pearsall andMWanninger ldquoLED light sources for head-up displaysrdquo in Proceedings of the Photonics in the Auto-mobile vol 5663 pp 225ndash229 Geneva Switzerland 2005

[8] C T Draper C M Bigler M S Mann K Sarma andP A Blanche ldquoHolographic waveguide head-up display with2-D pupil expansion and longitudinal image magnificationrdquoApplied Optics vol 58 no 5 pp 251ndash257 2019

[9] C M Bigler M Mann C Draper A Bablumyan andP A Blanche ldquoImproving head-up display with waveguidesand holographic optical elementsrdquo in Proceedings of thePractical Holography XXXIII Displays Materials and Ap-plications vol 10944 International Society for Optics andPhotonics San Francisco CA USA February 2019

[10] H Urey ldquoTorsional MEMS scanner design for high-resolutiondisplay systemsrdquo in Proceedings of the Optical Scanning IIvol 4773 pp 27ndash37 Washington DC USA July 2002

[11] W-C Su C-Y Chen Y-F Wang Y-W Chen and S S YangldquoEffect of a diffuser on distortion reduction for a virtual imageprojectorrdquo Journal of Optics vol 13 no 10 pp 105401ndash1054062011

[12] S Sinzinger and J Jahns Microoptics VCH VancouverCanada 1991

100mm

(a)

100mm

(b)

Figure 14 (a) Real shot simulated at daytime and (b) real shot simulated in the evening


[13] D Psaltis and F Mok ldquoHolographic memoriesrdquo ScientificAmerican vol 273 no 5 pp 70ndash76 1995

[14] V N Mahajan Optical Imaging and Aberration Part I RayGeometrical Optics SPIE Press Washington DC USA 1998

[15] D Brown ldquoDecentering distortion of lensesrdquo Photogram-metric Engineering vol 32 pp 362ndash444 1966

[16] X Ning Y Wang and X Zhang ldquoObject shape classificationand scene shape representation for three-dimensional laserscanned outdoor datardquo Optical Engineering vol 52 p 243012013

[17] M Sieler S Fischer P Schreiber P Dannberg and A BrauerldquoMicrooptical array projectors for free-form screen applica-tionsrdquo Optics Express vol 21 no 23 pp 28702ndash28709 2013

[18] Q-L Zhao Z-Q Wang Q Sun Z-W Lu and B O ChenldquoSimple 40deg head-mounted displayrdquo Optik vol 114 no 4pp 181ndash183 2003

[19] 2012 CES httpswwwcaranddrivercomnewsa187316572012-ces-audis-super-head-up-display

[20] N Kanamori and Y Hatanaka ldquoHead-up display apparatusrdquoPatent US7508356 2009


information e latter merely requires an optical lens tocontrol the imaging distance of a virtual image without areflector on the windshield that the system cost could bereduced [7] As shown in Figure 1(b) the lens imagingprinciple is used for controlling the imaging position behindthe windshield and combining with the street scene beyond3m In this case eye-accommodation is not necessary forhuman eyes that the road safety could be largely enhancede construction of this system is huge among the currentliterature and patents that it is not easily equipped in a vehicleBesides the horizontal angle of view of the eyebox is the anglebetween an image width and human eyes under the premiseof not affecting the image quality that a narrow angle couldeasily result in inconvenient viewing for a driver Accordingto some previous studies [8 9] the HUD systems based on theprinciples of total internal reflections and holographicwaveguides have some advantages such as decreasing the totalvolume and increasing the eyebox However there are someproblems or limitations from the holographic waveguideHUD systems by using many HOEs First the dispersioncould be caused when the light passing through the HOEen the aberration could be also caused by the flatness of theholographic materials ird both the wavelength and theangle of the incident light need to satisfy with the require-ments of HOE and the total internal reflection condition ofthe waveguide In addition the volume of the optic systemwith many HOEs can be decreased but the structure of theHOE system is too difficult to be built for mass productiondue to the very low tolerance of the HOE system Besides it ishard to correct the image after the system completed

By combining an image-dividing element and the virtualimage projection system a wide-view laser-based head-updisplay is produced in this study e high illumination andhigh power of the laser beam source are used for replacingthe LCD image module and eyebox for automobile head-updisplays is designed and expanded e eyebox of a generalvirtual image HUD is not wide enough because of the limitedimage projection size and lens imaging size and the

projected image information is also crowded resulting inviewing difficulty for drivers Two 90-degree prisms and aholographic optical element are therefore combined todivide images with the characteristics of laser wavelengthselectivity and diffraction of the holographic optical elementNot only this system could divide the image projected by thelaser-based pico projector into three horizontal images butalso a virtual image projection lens is designed to projectsuch three images to 160 cm behind the windshield which isused as a combiner e volume of this system is not hugeForevermore this system can be installed and adjusted fordifferent types of cars easily It could prevent a driver fromlooking away from the street and expand the angle of view ofthe eyebox for a driver

2 Materials and Methods

A laser-based pico projector (PicoPreg display) is used for anautomobile head-up display outputting the traffic infor-mation [10] Nevertheless both the vertical and horizontalprojection angles of the laser projector are narrow that theimage can hardly be enlarged in the limited space through aprojection lens For this reason an image dividing element isdesigned to clip and project an original image so as toexpand the eyebox of the head-up display allowing thedriver to view more traffic information

e laser-based pico projector used in this study showsthe resolution 848times 480 and the focus range 200mmndash2500mm In this study the designed original images are threepieces of vertical traffic information side by side includingspeed direction indication and warning light and the in-termediate image reveals the size 1 cmtimes 1 cmWhen an imagegoes through the image dividing element designed in thisstudy the upper middle and lower parts of the original imagewould be divided into three horizontal images side by sideSuch an image dividing element could increase the horizontalfield of view and provide more comfortable and secureviewing images for the driver

Driver eyes

Displaymodule

Windshield

Real image

120kmh

(a)

Driver eyes

Displaymodule

Windshield

Lens

Virtual image

120kmh

(b)

Figure 1 (a) Direct projection HUD (b) virtual image HUD






n2 minus sin2 φi

1113969


(1)








linewidth(mm) 25mm



3 Simulation



160cm

Virtualimage

Windshieldscreen



Original image

Prism 2

Prism 1HOE

HOE



Diffuser

Laserprojector

Prism 2 Prism 1

30kmh

(a)

Diffuser

Laserprojector

HOE

Prism 2 Prism 1

30kmh

(b)







7mm

5mm



θ1

θ2

Oslash2Oslash1

α

Laserprojector

Diffuser


10mm

55deg

7mm

5mm


sd

h

θ

β

Laserprojector

Image 1

Image 2

Image 3

120kmh





10

0

ndash10

3020100X (mm)

Y (m

m)


(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)


100deg

x

z




T S














5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)
















n2 minus sin2 φi

1113969


(1)








linewidth(mm) 25mm



3 Simulation



160cm

Virtualimage

Windshieldscreen



Original image

Prism 2

Prism 1HOE

HOE



Diffuser

Laserprojector

Prism 2 Prism 1

30kmh

(a)

Diffuser

Laserprojector

HOE

Prism 2 Prism 1

30kmh

(b)







7mm

5mm



θ1

θ2

Oslash2Oslash1

α

Laserprojector

Diffuser


10mm

55deg

7mm

5mm


sd

h

θ

β

Laserprojector

Image 1

Image 2

Image 3

120kmh





10

0

ndash10

3020100X (mm)

Y (m

m)


(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)


100deg

x

z




T S














5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)














linewidth(mm) 25mm



3 Simulation



160cm

Virtualimage

Windshieldscreen



Original image

Prism 2

Prism 1HOE

HOE



Diffuser

Laserprojector

Prism 2 Prism 1

30kmh

(a)

Diffuser

Laserprojector

HOE

Prism 2 Prism 1

30kmh

(b)







7mm

5mm



θ1

θ2

Oslash2Oslash1

α

Laserprojector

Diffuser


10mm

55deg

7mm

5mm


sd

h

θ

β

Laserprojector

Image 1

Image 2

Image 3

120kmh





10

0

ndash10

3020100X (mm)

Y (m

m)


(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)


100deg

x

z




T S














5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)
















7mm

5mm



θ1

θ2

Oslash2Oslash1

α

Laserprojector

Diffuser


10mm

55deg

7mm

5mm


sd

h

θ

β

Laserprojector

Image 1

Image 2

Image 3

120kmh





10

0

ndash10

3020100X (mm)

Y (m

m)


(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)


100deg

x

z




T S














5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)














10

0

ndash10

3020100X (mm)

Y (m

m)


(a)

10

0

ndash10

Y (m

m)

3020100X (mm)


(b)


100deg

x

z




T S














5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)























5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)













5 Conclusions


Data Availability




Acknowledgments


References













100mm

(a)

100mm

(b)





















Documents

AnAugmentedRealityHead-UpDisplaySystemwitha Wide-ViewEyeboxdownloads.hindawi.com/journals/ijo/2020/4719268.pdf · ResearchArticle AnAugmentedRealityHead-UpDisplaySystemwitha Wide-ViewEyebox