from June 18 to June 21, 2007 in Munich/Germany

Joint Booth of the Fraunhofer Gesellschaft
Hall B2 Stand 261

The Fraunhofer IPMS carries out customer specific developments in fields of microelectronic and micro systems technology in Dresden, serving as a business partner that supports the transition of innovative ideas into new products. The Fraunhofer IPMS develops and fabricates modern CMOS technology products in its own clean room facilities, up to small pilot series production. With modern equipment and about 200 scientists, the range of projects and expertise covers sensor and actuator systems, microscanner, spatial light modulators, lifetronics and organic materials and systems.

At the LASER 2007 in Munich the Fraunhofer IPMS presents:

1. MEMS Adaptive Optic Demonstrator for optical wavefront control and imaging enhancement

Adaptive Optics (AO) is mainly used for the compensation of spatially and timely varying wavefront disturbances within an optical system for an enhancement in optical imaging through inhomogeneous or turbulent media. Originally evolved from astronomy to compensate for atmospheric turbulences, AO techniques also can be used for aberration correction of the human eye in ophthalmology, for imaging through biological tissue in optical microscopy or for any kind of object recognition in machine vision. Furthermore, there are applications in laser beam shaping as well as in ultra-fast laser pulse modulation. The key component is formed by the actual wavefront controlling device. For that purpose MEMS (Micro-Electro-Mechanical-System) micro mirror arrays possess several attractive features. Due to their integrated fabrication capability they can support large pixel numbers providing an exceptional high spatial resolution for an improved reproduction especially of higher order phase aberrations. They also benefit from a step function display capability, fast mechanical response times, low power consumption, broad spectral bandwidth from IR down to DUV and polarization insensitivity. Compared to previous macroscale systems micro mirrors also offer the potential of a substantial cost decrease as well as a significant device miniaturization just facilitating completely new opportunities for a broader commercial exploitation. The Fraunhofer IPMS therefore has developed a complete MEMS Phase Former Kit. The key component is a high-resolution MEMS micro mirror array of 240 x 200 piston-type mirror elements with 40 µm pixel size providing 400 nm stroke at 8 bit resolution suitable for a 2π phase modulation in the visible. Full user programmability and control is established by a comfortable driver software for Windows XP® PCs supporting both a Graphical User Interface as well as an open ActiveX® programming interface for open-loop and closed-loop operation. High-speed data communication is accomplished by an IEEE1394a FireWire interface together with an electronic driving board allowing for maximum frame rates of up to 500 Hz. In order to visualize the potential for optical imaging enhancement a complete AO demonstrator system has been implemented. It basically comprises a projection system, where objects of different complexity are imaged through adaptive optics onto a CCD camera. Phase errors of different severness are introduced by rotating phase plates. Using a Shack-Hartmann sensor and the Fraunhofer IPMS MEMS micro mirror for wavefront sensing and correction respectively, the obtainable imaging improvement can be assessed by means of the recorded CCD picture, which is also projected onto a large screen. For a more quantitative anlaysis also some wavefront data without and with correction are made available.

Addressed business fields are optical system developer and manufacturer in the following areas:

• Machine Vision (in-situ process control through turbulent media)
• Optical Microscopy
• Ophthalmology
• Astronomy
• Laser Pulse Shaping
• Laser Beam Shaping
• Diffractive Optics (especially optical tweezers)

2. RGB-Laser projector

Fraunhofer IPMS shows a full color laser projection system based on its own two dimensional micro scanning mirror. The system contains an ultra compact projection head and a separate laser and signal processing unit. It allows the projection of arbitrary images and video sequences with a geometrical resolution of 640 x 480 pixels, 256 brightness levels per pixel and elementary color, and 50 hertz frame rate. The projection modules developed by Fraunhofer IPMS and Fraunhofer IOF overcome limitations of conventional projection systems – like rather large components for light deflection and high power light sources that consume lots of electrical power and radiate most of it thermally – by deploying the micro scanning mirror as key element for image generation and lasers as light sources. The patented micro scanning mirror of Fraunhofer IPMS is an ideal base for the development of compact projection heads. It distinguishes itself by high mechanical robustness and ease of both electrical control and optical coupling of the laser beam. Besides the expertise of Fraunhofer IPMS in design and manufacturing of this mirror, the competence of the institute for development of all necessary hardware and software for the projection system was used to build the overall projection system. The projection system addresses markets like Infotainment in mobile devices (PDA, Laptop, …), Automotive industry (driver assistance, Head-Up Display, Infotainment), Medicine electronics (acquisition of biometrical data, positioning aid for X-Ray diagnosis and treatment), Production technology (projection of reference points for drilling etc., pattern generator for tailoring of steel plates), and Metrology (structured lighting).

3. MEMS Spatial Light Modulator Demonstrator

MEMS Spatial Light Modulators (SLMs) are used to arbitrarily modulate the entire cross section of an incident beam of light simultaneously. We use MEMS thin film technology to fabricate an array of micromirrors on top of a CMOS backplane. Each mirror can be addressed and moved individually to control either intensity or phase of one pixel. SLMs are used in a range of applications from projectors (Texas Instruments' DLP) to Adaptive Optics (astronomy, ophthalmology) and mask writers in the semiconductor industry. Contrary to the digitally addressed SLMs in the projectors that use time multiplexing to generate grey levels, the SLMs developed by Fraunhofer IPMS are addressed with analogue voltages that enable the chip to directly generate analogue intensities. Micronic Laser Systems' mask writers exploit this feature to shift the generated patterns with an accuracy far smaller than the system's pixel resolution. The mirrors of the Fraunhofer IPMS device are specified for monochromatic light between 248 nm and 520 nm, enabling not only the use of the DUV excimer wavelengths, but also the less aggressive (and less costly) near UV and visible light sources. One example where the mirrors could be used is pattern generation for High Definition Interconnect (HDI) for Laser Direct Imaging (LDI) of printed circuit boards, but also other areas that require a combination of both highest resolution and throughput. The SLM is capable of patterning 1 million pixels at a frequency of 2 kHz (that is 2 Gpixel/s). The demonstator setup visualizes the function of the SLMs. A green LED generates a pulsed beam; lenses and mirrors collect the light and send it to the SLM, where it is modulated. The modulation generates higher orders in the fourier plane, which are filtered out by an aperture. The remaining zeroth order contains the pattern information and is projected onto a camera. The captured image is displayed on the screen.