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)

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. 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. 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. 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. 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. 14.4 / E. Buckley
Figure 9 – A photograph of the Mini Globe display concept in operation, showing images produced by LBO’s laser projector.