MEMS Spatial Light Modulator Demonstrator at LASER 2007 show

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.