Efficient light management is one of the key issues in modern energy conversion systems, might it be to collect optical
power or to redistribute light generated by high power light emitting diodes. One problem remains: How can one realize
small size elements with high quality of light management. We propose a novel scheme by using miniaturized angle
transformers or concentrators that have size of several millimeters. none In this size range diffraction effects play rarely a
role and the design can be based on classical ray tracing. Dimensions are chosen to allow effective solution for high
power light emitting diodes as well as solar cells. In most solar cell designs, the photocurrent is extracted through a
conducting window layer in combination with a silver grid at the front of the device. The trade-off between series
resistance and shadowing requires either buried contacts or screen printing of narrow lines with high aspect ratio. We
propose an alternate approach where an array of parabolic concentrators directs the incoming light into the cell. The front
metallization can thus be extended over the area between the paraboloids without shadowing loss. High power light
emitting diodes are source with certain far field distribution and composed often out of several chips. Applying the
concentrator array technology not on the whole source but locally on each chip promises small and effective solutions.
We demonstrate realization of linear and hexagonal arrays of micro-concentration systems, discuss details of application
and results of simulation of their optical properties in applications.
We show a laser beam shaping device made of a deformable continuous reflective membrane fabricated over a scanning
stage. The combination of two actuator schemes enables shaping and smoothing of a laser beam with a unique compact
device. It is designed to shape an input laser beam into a flat top or Gaussian intensity profile, to support high optical load
and to potentially reduce speckle contrast. One single electrode is needed to deform the whole membrane into multiple
sub-reflecting concave elements. The scanning stage is used simultaneously to smooth out the remaining interference
patterns. The fabrication process is based on SOI wafer and parylene refilling to enable the fabrication of a 100 % fill
factor 5 by 5 mm2 deformable membrane. Applications for such device are laser machining and laser display.
Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital
micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and
widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based
tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse
shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for
shaping light in the space and time domain.
We present a dynamic laser beam shaper based on MEMS technology. We show a prototype of a dynamic diffuser made
of single crystal silicon. A linearly deformable silicon micromembrane is used to diffuse a laser beam in one dimension.
Resonance frequencies of the membrane can range from 1 kHz to 20 kHz. Mode shapes of the deformable mirror are
excited using magnetic actuation. Diffusing angle can be tuned by adjusting the driving current in the membrane. We
measured a diffusing angle of 1° for an applied current of 40 mA. The aluminum coated mirror can handle 140 W/cm2 of
visible to infrared optical power. Application to smooth out interference pattern generated by a static diffuser is shown.
Laser manufacturing of microstructures using a single focus is a well known technology. Multi-spot optics are applied
for process parallelizing if the demand on throughput in mass production rises or large areas of material have to be
processed. Diffractive optical elements (DOEs) are used for parallel laser processing of a repetitive structure. These
elements split the beam into a periodic spot pattern, where each spot shows the same shape and energy. This allows
simultaneous manufacturing of several equal shaped structures at the same time. For patterning a surface this is state of
the art and the appropriate technique to reduce processing time while maintaining a high lateral resolution as well as a
good relative positioning of the structure due to the DOE.
We investigate the usage of microlens arrays as multifunctional elements for forming an arbitrary shaped laser beam into
a spot-, a ring-spot- or a line-array pattern. It can be shown that the intensity distribution of each spot is equal to the
intensity distribution of all other spots in the whole pattern. The shape of the spots is defined by the angular distribution
of the incident beam. We demonstrate that besides other optical properties the output beam profile strongly depends on
the Fresnel-Number and is influenced by diffraction and interference effects. We present important design rules which
consider geometrical and physical optics. The properties of the spot arrays, like spot diameter, Rayleigh length and beam
divergence in dependency of beam and system properties are investigated. Finally we will show some laser micro
structuring and micro drilling results in different materials.
Certain high power laser applications require thin homogeneous laser lines. A possible concept to generate
the necessary flat-top profile uses multi-aperture elements followed by a lens to recombine separated beamlets.
Advantages of this concept are the independence from entrance intensity profile and achromaticity. However, the
periodic structure and the overlapping of beamlets produce interference effects especially when highly coherent
light is used. Random optical elements that diffuse only in one direction can reduce the contrast of the interference
pattern. Losses due to undesired diffusion in large angles have to be minimized to maintain a good quality and
high efficiency of beam shaping. We have fabricated diffusers made of fused silica for a wide range of wavelengths
that diffuse only in one direction. Structures are based on an array of concave cylindrical microlenses with locally
varying size and position following a well defined statistical distribution. The scattering angle can be influenced
by process parameters and is typically between 1° and 60°. To predict the influence of process parameters on
the optical properties, a simplified model for the fabrication process and geometrical optics have been used.
Characterization of the fabricated devices was done by stylus measurements for the surface shapes, microinterferometry
to measure phase profiles and high resolution goniometry to obtain far field distribution of light. The simulated data compare very well to measured optical properties. Based on our simulation tool we discuss limits of our fabrication method and optimal fabrication parameters.
A wide range of lasers from the UV to the IR are selected based on their optical power and spectral characteristics to
match the particular absorption behavior for the material to be processed. Periodic microlens arrays are often used as
multi-aperture integrators to transform the Gaussian or non-uniform beam profile into a homogenized intensity profile
either in 1-D or 2-D distribution. Each microlens element samples the input inhomogeneous beam and spreads it over a
given angular distribution. Incoherent beams that are either temporally or spatially incoherent can produce very uniform
intensity profiles. However, coherent beams will experience interference effects in the recombination of the beams
generated by each individual microlens element. For many applications, for example pulsed laser sources, it is not
possible to use a rotating or moving element, such as a rotating diffuser, to circumvent the interferences resulting from
the beam coherence. Micro-optical elements comprised of a randomly varying component can be used to help smooth
out the interference effects within the far-field intensity profile.
Refractive, diffractive and reflective micro-optical elements for laser beam shaping and homogenizing have been manufactured and tested. The presented multifunctional optical elements are used for shaping arbitrary laser beam profiles into a variety of geometries like, a homogeneous spot array or line pattern, a laser light sheet or flat-top intensity profiles. The resulting profiles are strongly influenced by the beam properties of the laser and by diffraction and interference effects at the micro-optical elements. We present general design rules for beam shaping and homogenizing. We demonstrate the application of such multifunctional micro-optical elements for a variety of applications from micro-laser machining to laser diagnostic systems.