Optical technologies for automobiles

Micro-optics for automotive headlamps: Square polymer lenses enable more precise light modeling.

Optical Automotive Technologies at Fraunhofer IOF

Miniaturized Sensors for Autonomous Driving

Miniaturized array camera, that is as big as a fingernail, is shown between the fingers of a scientist.
© Fraunhofer IOF
Miniaturized array camera.
Samples of the ultra-flat array camera.
© Fraunhofer IOF
Samples of the ultra-flat array camera.
Tile images of a toy figure for the calculation of 3D-information.
© Fraunhofer IOF
Tile images for the calculation of 3D-information.

The ongoing development of driver assistance systems towards autonomous driving cars is a current trend in automotive industry. This changes the driver’s task from active driving to passive monitoring of the system, and as a result, many new scientific questions arise in the field of human-machine interaction. For example, it has to be guaranteed that the style of the autonomous driving is comfortable for the driver and for all the passengers. Therefore, the interior of the car needs to be captured in all three dimensions with high resolution.

Conventional sensor systems are generally only able to fulfill this task to a limited extent. Consequently, the scope of the work within the joint project COMFYDrive is the development and investigation of a new 3D multi sensor system for monitoring the interior of an autonomous driving car. The system will combine for the first time three principles that are capable of the generation of three-dimensional information – namely the principles of the array camera, stereoscopy, and active pattern projection techniques.

The system is based on two miniaturized array cameras with a field of view of 70° (diagonal) and a f-number smaller than 3. Natural compound eyes of insects have been the archetype for the design of the array camera. The micro objective itself consists of two freeform micro lens arrays that are molded on a lithographically structured glass substrate.

In order to prevent optical cross talk of neighboring imaging channels, a three-dimensional aperture array is placed above a commercial CMOS imaging sensor. The manufacturing of the freeform micro lens arrays is carried out by the combination of an ultra-precision micro machining process and a step&repeat micro replication technique. This approach allows the cost-effective realization of a huge quantity of elements on a wafer level scale.

The imaging optics possesses a height of less than 2 mm and is therefore well suited for integration in the interior of a car. The single camera module generates 15 x 9 partial images that are subsequently transformed via image processing into a reconstructed image of the full scenery or into corrected tile images. Based on image data, three-dimensional point clouds can be generated in high resolution. First, this data should be used in order to collect information on the condi-tion of the passengers with regard to the current driving situation. In the future, feedback on the driving style of the autonomous car will also be an option.

 

Authors: Jens Dunkel, Alexander Oberdörster, Christin Gassner, Andreas Reimann, Andreas Brückner

Micro-optics for Automotive Headlamps

Fig. 1: Segmented automotive LED high-beam unit realized as a microoptical, irregular fly’s eye condenser.
© Fraunhofer IOF
Fig. 1: Segmented automotive LED high-beam unit realized as a microoptical, irregular fly’s eye condenser.
Fig. 2: The deactivated segment prevents glare from blinding oncoming traffic.
© Fraunhofer IOF
Fig. 2: The deactivated segment prevents glare from blinding oncoming traffic.
Fig. 3: Microlens arrays for the dipped beam (left) and for a glare-free main beam (right).
© Fraunhofer IOF
Fig. 3: Microlens arrays for the dipped beam (left) and for a glare-free main beam (right).
 

Well-established optical technologies for automotive headlamps like freeform mirrors, aspheres, and lightguides are reaching their limits in terms of miniaturization, flexible contouring, and modularization. The Fraunhofer internally funded project “SSL-StructuredSpotLight” investigates the use of tandem microlens arrays as beam-shaping tertiary optics for automotive LED lightsources, which enable multi-channel optics architectures with minimal system length and area.

Tandem lens arrays as micro-optical fly’s eye condenser enable efficient, etendue-conserving homogeneous illumination of rectangular or hexagonal areas. The micro-optical multi-channel slide projector with additional buried apertures offers continuous light intensity distributions at the expense of lowered system transmission /2 /. We developed a new optics design combining advantages of both approaches: Irregular fly’s eye condensers /3 / form automotive high and low beam intensity distributions. Switchable segmentation for glare-free driving beam uses controlled array channel cross-talk. The chips of a linear LED array address either regular operation of the fly ́s eye condenser or channel-crosstalk of different order (Fig. 3).

Grayscale lithography is employed for the mastering of the fly ́s eye condensers. Irregular lens arrays (Fig. 2) with sag height of more than 50 μm and diffraction limited profile quality were generated /4 /. Subsequent replication by UV-molding realizes double sided, aligned polymer-on-glass elements. The driving beam demonstrator (Fig. 1) consists of two identical modules, each incorporating LED array, collimation optics (field lens and collimation asphere) and tandem array in a metal housing. Tilted assembly of the two modules enables switching of horizontal segmentation with 1.5° width and a ECE conform luminous intensity of > 50 kcd. A total of about 800,000 micro-optics are installed, which optimally bundle the light in the direction of travel and ensure good visibility even at night and bad weather.

 

Authors: Peter Schreiber, Christoph Wächter, Stephanie Fischer, Chen Li, Dirk Michaelis, Robert Leitel, Ralf Rosenberger, Marko Stumpf, Felix Kraze

Arrayed Projector for Displaying Graphics on the Street

Micro lens array developed by Fraunhofer IOF.
© Fraunhofer IOF
Micro lens array developed by Fraunhofer IOF.

Increasing integration of automated functionalities and driver assistance systems in future cars requires continuous improvement of status indicators and user guidance. For in-car applications, consoles with displays are available but communication with persons outside the car remains a problem. A current popular approach is projection of symbols on the street in the vicinity of the car.

Static array projector projecting two switchable icons.
© Fraunhofer IOF
Static array projector projecting two switchable icons.

Using modern monochrome high power LEDs, improved collimators and advanced microlens arrays e.g. with high refractive index polymer lenslets, illuminance of 3000 lux at a distance of 45 cm from the car was achieved enabling operation in daylight conditions. A further improvement is projection of animated graphics by arranging arrayed projectors onto the same substrate in front of a multitude of individually switchable collimated LED light sources.

Optics scheme for projection of switchable image content.
© Fraunhofer IOF
Optics scheme for projection of switchable image content.

This requires hi-flux, efficient, miniaturized, and cost-saving projectors displaying a limited number of different images. Use of common LED-illuminated pico projectors with DLP microimagers fails because the projected flux is too small, the size too large, and because of the cost. Fraunhofer IOF's arrayed projector technology, which was commercially applied for the first time in the BMW 7 in 2015, enables the realization of strongly miniaturized luminaires for structured illumination near the car entrance area at night.

Array projection next to the vehicle.
© Fraunhofer IOF
Array projection next to the vehicle.

In a project with the company Brose Fahrzeugteile GmbH und Co. KG, such projectors were developed for automatically opening cars, as a welcome light for the driver, and a warning signal for cyclists. The assembled projector’s position in the car chassis ensures projection independent of the opening angle of the door. A second projector application guides the user for trunk opening by foot kick with a three channel projected graphics running light and a two channel animated graphic.

 

Authors: Peter Schreiber, Christoph Wächter, Stephanie Fischer, Chen Li, Ralf Rosenberger