14.4 / E. Buckley


14.4: Novel Human-Machine Interface (HMI) Design Enabled by Holographic
                           Las...
14.4 / E. Buckley

                                                                                         Uniquely, the ...
14.4 / E. Buckley

Long depth of field - The combination of the diffractive nature of         resultant aberration in soft...
14.4 / E. Buckley

important since, not only do users find the artefact very                 Robustness and fault toleranc...
14.4 / E. Buckley

                                        Screen                          time by the driver. The new ins...
14.4 / E. Buckley




Figure 9 – A photograph of the Mini Globe display concept in operation, showing images produced by L...
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Novel Human Machine Interface (Hmi) Design Enabled By Holographic Laser Projection

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Despite the current proliferation of in-car flat panel displays, designers continue to investigate alternatives to flat and rectangular thin-film transistor (TFT) panels - principally to obtain differentiation by freedom of design using, for example, free-form shapes, round displays, flexible displays or mechanical 3D solutions. A perfect demonstration was provided at the 2008 Paris Motor Show by the BMW Mini Center Globe, a novel instrument cluster design which combines lighting, a circular flat panel and a holographic laser projector provided by Light Blue Optics (LBO) to redefine the state of the art in human-machine interface (HMI).
In this paper, the authors will show how the incorporation of LBO’s holographic laser projection technology can allow the construction of a unique display technology like the Mini Center Globe, and how such a combination of technologies represents a significant advance in the current state of the art in automotive displays. From UK based. from light blue optics (LBS)

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Novel Human Machine Interface (Hmi) Design Enabled By Holographic Laser Projection

  1. 1. 14.4 / E. Buckley 14.4: Novel Human-Machine Interface (HMI) Design Enabled by Holographic Laser Projection Edward Buckley Light Blue Optics Inc., 4775 Centennial Blvd., Colorado Springs, CO 80919, USA Dominik Stindt Light Blue Optics Ltd., Platinum Building, Cowley Road, Cambridge CB4 0WS, UK Robert Isele BMW AG, Knorrstrasse 147, 80788 Muenchen, Germany Abstract of display makers, lighting companies and laser projector Despite the current proliferation of in-car flat panel displays, manufacturers, has been employed in realising an automotive designers continue to investigate alternatives to flat and display. rectangular thin-film transistor (TFT) panels - principally to obtain differentiation by freedom of design using, for example, free-form shapes, round displays, flexible displays or mechanical 3D solutions. A perfect demonstration was provided at the 2008 Paris Motor Show by the BMW Mini Center Globe, a novel instrument cluster design which combines lighting, a circular flat panel and a holographic laser projector provided by Light Blue Optics (LBO) to redefine the state of the art in human-machine interface (HMI). In this paper, the authors will show how the incorporation of LBO’s holographic laser projection technology can allow the construction of a unique display technology like the Mini Center Globe, and how such a combination of technologies represents a significant advance in the current state of the art in automotive displays. Figure 1 - Artist’s rendition of the BMW Mini Center Globe instrument cluster, incorporating circular TFT, laser 1. Introduction projection and lighting technologies. In the last decade, thin-film transistor (TFT) panels have reigned supreme in automotive applications and a continued increase in In this paper, the authors will show how the incorporation of volume sales of automotive TFT panels is expected in the next Light Blue Optics’ holographic laser projection technology few years. The proliferation of such displays is driven both by the provides unique features which can revolutionise the HMI, increased desire for more communication and entertainment creating a new class of automotive display technologies and functions and by the steep, and continued, price erosion in flat- further increasing the in-car display density. panel display technologies. Indeed, the extent to which these twin market forces have influenced the human-machine interface 2. Holographic Laser Projection (HMI) is aptly demonstrated by the availability of automotive- Technology qualified TFT displays with diagonals in excess of 40” [1]. LBO’s technology represents a revolutionary approach to the projection and display of information. Unlike other commercially- Despite the popularity of flat panel displays they are available projection technologies, LBO’s projection engine fundamentally limited as a design element since, by definition, exploits the physical process of two-dimensional diffraction to they are flat, regular and opaque. This conflicts with the desire of form video images. the automotive industry for HMI differentiation by freedom of design using, for example, free-form shapes, round displays, A typical imaging projection system works by displaying the flexible displays or mechanical 3D solutions. For this reason, an desired image Fxy on a microdisplay, which is usually sequentially increasing number of car manufacturers are discussing and illuminated by red, green and blue light to form colour. In this exploring free-programmable cluster concepts [2] employing case, the microdisplay simply acts to selectively block (or large displays and hybrid solutions. amplitude modulate) the incident light; after passing through some magnification optics, the projected image Fxy appears. A perfect example of such a hybrid solution was provided by the Conversely, holographic laser projection forms the image Fxy by BMW Mini Crossover concept car demonstrated at the 2008 Paris illuminating a diffraction (or hologram) pattern huv by laser light Motor Show. The instrument cluster design, termed the Mini of wavelength λ. If the hologram pattern is represented by a Center Globe and shown in Figure 1, presented a completely display element with pixel size ∆ then the image Fxy formed in the revolutionary approach to transforming displays to real 3D components by combining TFT, laser projection and lighting focal plane of the lens is related to the pixellated hologram pattern technologies into a complete solution. It is the first time that a huv by the discrete Fourier transform F [·], and is written as multi-disciplinary approach, combining the common development
  2. 2. 14.4 / E. Buckley Uniquely, the key to holographic laser projection technology lies Fxy = F [huv ] (1) not in the optical design but in the algorithms used to calculate the as shown in Figure 2 below. hologram patterns huv from the desired image Fxy. LBO has developed and patented proprietary algorithms for the purposes of calculating sets of N holograms both efficiently and in real time, as first demonstrated in 2004 [4]. Crucially, such algorithms can be efficiently implemented in a custom silicon chip. A practical realisation is rather simple and is shown in the schematic of Figure 4. A desired image is converted into sets of holograms by LBO’s proprietary algorithms and displayed on a phase-modulating microdisplay which is time-sequentially illuminated by red, green and blue laser light respectively. The subsequent diffraction pattern passes through a demagnification lens pair L1 and L2, which can be chosen to provide ultra-wide projection angles in excess of 100°. Due to the nature of Fraunhofer diffraction, the image remains in focus at all distances from the lens L2. Figure 2 – The relationship between hologram huv and image Fxy present at the back focal plane of a lens of focal length f, when illuminated by coherent monochromatic light of L2 wavelength λ. L1 The crucial efficiency advantage of LBO’s system occurs because the hologram huv is quantised to a set of phase only values ϕuv, where huv = exp jϕuv, so that the incident light is steered into the Microdisplay desired image pixels – without blocking – by the process of coherent interference, and the resultant instantaneous projected image appears as a direct consequence of Fourier optics. To achieve video-rate holographic display, a dynamically- addressable display element is required to display the hologram patterns; LBO’s system uses a custom-manufactured ferroelectric liquid crystal on silicon (LCOS) microdisplay manufactured by Displaytech, Inc. Lasers To achieve high image quality, a fast microdisplay is used to display N holograms per video frame within the 40ms temporal bandwidth of the eye, each of which produces an image Fxy Figure 4 - A schematic diagram of LBO’s holographic laser exhibiting quantisation noise [3]. If the intensity of the ith projection technology illustrating lasers, phase- 2 displayed image is I xy = Fxy ) (i then the time-averaged percept modulating microdisplay and demagnification lens pair L1, L2. over N subframes is 3. Advantages of Holographic Laser 1 N 2 V xy = N ∑ i =1 Fxyi ) ( (2) Projection Technology There are several exacting requirements imposed upon the light which is noise-free, as illustrated in Figure 3. engine by automotive applications. In addition to the high brightness and contrast ratios required to display cluster imagery [5], the entire projection subsystem must be robust, fault-tolerant and optically efficient whilst maintaining wide operating and storage temperature ranges. Finally, the projection subsystem must be small and exhibit a wide throw angle to enable integration into space-limited dashboards. To the authors’ knowledge, only LBO’s system is able to achieve these requirements whilst simultaneously providing efficient Hologram Video Subframe Video Frame display of bright symbology and cluster imagery, with low 1 N speckle contrast. A number of these important advantages are (i ) 2 huv = exp jϕuv I xy = F (i ) 2 xy Vxy = N ∑F i =1 xy described in more detail below. Figure 3 - The relationship between hologram huv, subframe Fxy and frame Vxy in LBO’s holographic projection technology.
  3. 3. 14.4 / E. Buckley Long depth of field - The combination of the diffractive nature of resultant aberration in software; in the same way, the optical LBO’s technology and the use of laser light sources ensures that subsystem can be designed with a far wider range of tolerances the projected image is always in focus, regardless of projection than would ordinarily be possible. Not only does this allow cost distance or projection surface geometry. This property, coupled effective assembly, but it provides a degree of insensitivity to with the ability to correct for distortion in the projected image [6], process tolerances which is crucially important when integrating allows the projection of images of arbitrary non-plane geometries optical subsystems into, for example, automotive instrument - thereby allowing the realisation of curved displays which cannot clusters. A demonstration of this powerful capability is provided be achieved with current flat panel display technologies. in Figure 5 below. The laser spot shape of Figure 5(a), after Aberration correction - Due to the diffractive nature of LBO’s propagation through the projector optics, demonstrates that technology, which by definition exerts accurate control over the significant aberration is present. As a result, the quality of the optical wavefront, it is possible to correct for aberrations caused projected images (b) and (c) is severely impacted. Appropriate by the projector optics by appropriate modification of the correction for the optical aberrations, however, results in a laser hologram patterns. It is therefore possible to construct a projector spot that is almost diffraction limited (d), leading to recovery of using simple, cost effective optical elements and correct for any the image fidelity in (e) and (f). (a) Laser spot shape after (b) Aberrated projected image (c) Close-up of projected propagation through image projector optics (d) Laser spot shape after (e) Resultant projected image after aberration (f) Close-up of projected aberration correction correction image Figure 5 - Aberrations caused by the optical system result in imperfect projected image (c). Correction is performed by appropriate modification of the hologram patterns leading to near diffraction-limited spot (d) and projected image (f). Wide throw angle - The small field sizes incident upon the The wide-throw capability of LBO’s projector allows the demagnification output optic of LBO’s diffractive projection construction of a very thin rear-projection display, which is system allows for the realisation of ultra-wide throw angles (>100 particularly important for instrument cluster applications. The degrees). It is simply not possible to achieve such projection ability to provide a throw angle in excess of 100 degrees, coupled angles with scanned-beam or imaging systems. Imaging systems with the small opto-mechanical assembly size of ~25cc, allows encounter both distortion and aberration due to challenging LBO’s technology to overcome the fundamentally incompatible optical requirements at large field angles whilst in the case of requirements of projecting a large image from a projector mounted scanned-beam systems, unacceptable pincushion distortion would in a shallow console. result due to the fundamental MEMS action. This typically limits Low speckle contrast - One of the advantages of LBO’s imaging and scanned-beam systems to projection angles of technology is the ability to substantially reduce laser speckle, a approximately 45º though, even then, some scanned-beam phenomenon which makes the image ‘sparkle’ due to scattering of systems exhibit residual distortion. coherent light from an optically rough projection and subsequent interference at the retina. The ability to reduce speckle is
  4. 4. 14.4 / E. Buckley important since, not only do users find the artefact very Robustness and fault tolerance - Due to the diffractive nature of unpleasant, it also severely impacts the perceived image quality the technology, LBO’s system does not exhibit a one-to-one and effective resolution. Furthermore, the distracting nature of correspondence between microdisplay pixels and projected image laser speckle is unacceptable in safety-critical applications such as pixels, as imaging systems do. In fact, each pixel on the automotive. microdisplay contributes to every pixel in the image, so that faulty It is, however, possible to substantially reduce the speckle contrast display element pixels do not correspond to ‘dead’ image pixels. by employing a combination of methods within the optical This allows the realisation of a truly fault-tolerant display with subsystem of a holographic laser projector [3]. This represents a built-in redundancy, since multiple microdisplay pixel failures can significant advantage over laser-based scanned-beam systems, be tolerated without compromising the integrity of the displayed which exhibit unacceptably high speckle contrast ratios [7, 8, 9] data. that can only be reduced by the use of expensive custom projection screens [10]. 4. Novel projection geometries enabled by High brightness, wide colour gamut and high efficiency - It has holographic laser projection previously been shown [11] that, due to the phase-modulating approach to image formation, a holographic projector can display One of the advantages of the LBO technology is the ability to significantly brighter sparse images - with far greater dynamic realise novel projection geometries which, as previously range - than imaging and scanned-beam systems. This is a huge discussed, is one of the key requirements for next-generation advantage when displaying symbology and video, which have automotive instrument clusters. By combining the wide depth of average pixel intensities of approximately 10% and 25% field, wide throw angle, distortion correction and aberration respectively. This allows brightness targets to be met using just correction capabilities of the projector it is possible to realise three small laser sources. In addition, laser sources can provide some truly unique projection geometries. Due to the images with extremely wide colour gamuts, due to their narrow phase-modulating nature of the light engine, the luminous flux of spectral bandwidth. The Helmoltz-Kohlrausch [12] effect can the projector remains unchanged despite the geometry correction. further increase perceived brightness due to the psychophysical This is contrast to conventional imaging systems which will effects of highly saturated primaries. always block light due to the unused (cropped) pixels. The use of laser sources and a phase-modulating hologram Figure 6 gives a succinct demonstration of these capabilities. In provides a highly power-efficient method of projection since, (a), LBO’s projection technology is demonstrated in wide-angle unlike imaging displays, no light is blocked in the system. In (90°), front-projection mode; the image diagonal is 13.5” and the addition, the phase-modulating nature of the projector means that horizontal distance from the projector aperture to the screen is it is not necessary to continuously illuminate the microdisplay; the approximately 6”. Using the same projector optics, however, it is lasers are modulated in accordance with the frame brightness, possible to project in a table-down mode; by appropriate pre- thereby only utilising the power required to illuminate “on” distortion, shown in (b), the table down operation of (c) is pixels. The correspondingly low laser modulation frequency also obtained. The image has a diagonal of 9” and the vertical distance allows efficient digital modulation schemes to be used for each of the projector from the surface is approximately 3.5”. colour, in contrast to the high frequency, low efficiency, approach employed by scanned-beam systems. (a) Standard wide-angle, front- (b) Pre-distorted image to allow for (c) Table-down projection geometry projection geometry table-down projection Figure 6 - The LBO projection technology can demonstrate truly novel projection geometries. Both front (a) and table-down projection geometries (c) can be achieved using the same projection optics. The ability of LBO’s projection technology to form images with geometry (b) can be achieved and, regardless of the arbitrary geometry was also used in the BMW Mini Center configuration of the projection surface, the focus is maintained Globe. As shown in Figure 7, virtually any non-plane projection at all points of the output image as shown in (c).
  5. 5. 14.4 / E. Buckley Screen time by the driver. The new instrument adds a further, three- Projector dimensional element with displays stratified on various levels and highlighted to a greater or lesser degree, depending on the driver’s and front passenger’s requirements. 5. Conclusion The authors have demonstrated that current HMI limitations imposed by flat panel displays can be overcome by combining several novel display technologies. In particular, the advantages provided by LBO’s holographic laser projector allow the construction and integration of a curved instrument cluster display. By transforming displays to real 3D components, the BMW Mini Center Globe has redefined the state of the art in human-machine interaction and created a new class of automotive display. 6. References (a) Input image (b) Projection (c) Projector output [1] CONRAC GmbH. (2008) CONRAC 6040 AD 40 geometry LCD/TFT automotive display. Weikersheim, Germany. [Online]. Available: www.conrac.us/6040ad.pdf Figure 7 - Projection onto arbitrary non-plane surfaces using [2] M. Heimrath, “Keynote address: Modern display LBO’s projection technology. Images (a) are integration,” in Proc. SID Conference 15th Annual Symposium appropriately processed to account for the projection on Vehicle Displays, Dearborn MI, 2008. geometry (b); the captured images at the output of the projector (c) demonstrate that, in all cases, the images [3] E. Buckley, “Holographic laser projection are in focus. technology,” in Proc. SID Symposium 2008, no. 70.2, 2008, pp. 1074–1078. The construction of the BMW Mini Center Globe is shown in Figure 8 below; the LBO projector is configured to project on [4] A. J. Cable, E. Buckley, P. Mash, N. A. Lawrence, the outside and inside of the spherical surface, above the round T. D. Wilkinson, and W. A. Crossland, “Real-time binary TFT display. The horizontally rotating hemisphere is therefore hologram generation for high-quality video projection effectively used as a projection screen to enable the use of the applications,” in Proc. SID Symposium, vol. 35, no. 53.1, 2004, third dimension. The image size can be varied by changing the pp. 1431–1433. distance between the projector and the spherical projection [5] E. Buckley, “PVPro projection technology for screen, without the need to refocus, allowing a greater degree of automotive applications,” in Proc. SID Conference 14th Annual freedom to present driver and front-passenger oriented Symposium on Vehicle Displays, Dearborn MI, 2007, pp. 93–98. information simultaneously. Using this arrangement, for [6] E. Buckley and D. Stindt, “Full-colour holographic example, the passenger can watch a movie or use web services laser projector HUD (invited address),” in Proc. SID Conference whilst the driver receives all necessary navigation and other 15th Annual Symposium on Vehicle Displays, Dearborn MI, driving-related information from the same HMI display. 2008, pp. 131–135. Although dual-view TFT displays [13] have addressed similar use cases, they have the previously stated disadvantage of being [7] M. Schmitt and U. Steegmuller, “Green laser meets limited to flat, rectangular form-factors. mobile projection requirements,” Optics and Laser Europe, pp. 17–19, May 2008. [8] M. Handschy, “Moves toward mobile projectors raise issue of panel choice,” Display Devices, pp. 6–8, Fall 2007. [9] Insight Media LLC, “Large display report,” pp. 71–72, June 2008. [10] J. W. Goodman, Speckle Phenomena in Optics - Theory and Applications, Englewood CO, 2008, p. 223. [11] E. Buckley, A. Corbett, P. Surman, and I. Sexton, “Multi- viewer autostereoscopic display with dynamically- (a) Side view (b) Plan view addressable holographic backlight,” in Proc. SID Symposium, Figure 8 – Construction of the Mini Center Globe, showing the no. 25.1, 2008, pp. 340–344. circular TFT display and LBO’s holographic laser [12] Spectral luminous efficiency functions based upon projector. brightness matching for monochromatic point sources, 2° and This innovative three-dimensional concept allows even more 10° Fields, CIE Central Bureau Std. 75, 1988. consistent integration of functions and the appropriate [13] Robert Bosch GmbH. (2008, February) Press release: presentation of entertainment and information options; safety “Dual view from Bosch”. Germany. [Online]. critical information can be displayed very bright and in highly Available: http://www.blaupunkt.com/press/blob_pdf.asp?id=2 saturated colours to allow quick perception and a fast response 197
  6. 6. 14.4 / E. Buckley Figure 9 – A photograph of the Mini Globe display concept in operation, showing images produced by LBO’s laser projector.

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