Volker Guyenot

Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation.

We report on the investigation of the thermo-optical behavior of air-clad ytterbium-doped large-mode-area photonic crystal fiber lasers. Analytical and numerical models are applied to calculate the heat distribution and induced stresses in a microstructured fiber. The results are compared to conventional double-clad fiber lasers and design guidelines are provided to ensure maximum heat dissipation and scalability to power levels of several kWs.

Automated assembly of micro-optical components

In the field of microsystem technologies one future trend is recognized. Manufacturing microsystems monolithically is becoming less reasonable and practicable with increasing applications and complexity. Assembly processes will be needed for the majority of microsystems due to difficulties arising in manufacturing complex structure out of one piece, the need for components to be manufactured by different processes, or simply to connect the microsystem with the macroscopic environment. Additionally, high production output at competitive costs is attainable only by replacing manual assembly with new automatic handling, positioning and joining technologies. To assist in development of microassembly processes, techniques from macroassembly technology may be transferred. Especially in microoptics existing know-how from macroscopic lens-assemblies might be transferred. The microsystem presented a microoptical beam forming system consisting of one SELFOC- and two GRIN- microlenses joined by adhesive bonding, fixed in a protection-mount, which serves additionally as a coupling unit of a multimode fiber, and finally adjusted to a laser diode at a defined distance according to an optical design. Besides complications due to the sensitive optical surfaces and the small and varying geometries of the system components, there is the additional requirement of high accuracies, of 0.1 to 2 micrometers and down to 1 arcsec, needed to realize the optical function of the microsystem. The assembly system, based on a six-axis-precision robot accurate to less than 1 micrometers , consists of a modular designed tool changing system, specially-adapted, self- adjusting grippers, several sensors to monitor positioning, dosage devices to dispense measured quantities of adhesive, in the range of nanoliters, and a specially designed assembly platform to clamp microparts of different geometries.

Air-clad large-mode-area photonic crystal fibers: power scaling concepts up to the multi-kW range

Most recently the output power of fiber lasers with diffraction limited beam quality has been significantly increased. Further power scaling is usually limited by damage of the fiber end facets, thermo-optical problems or nonlinear effects. Microstructuring the fiber adds several preferable features to the fiber to overcome these restrictions. We review the advantages of rare-earth-doped photonic crystal fibers for power scaling of fiber lasers to the multi kW range with excellent beam quality.

Centering of optical components by using stick-slip effect

Centering of optical lenses is necessary for obtaining the required resolution of an optical system, especially minimization of distortion. Advantage is the systematic approximation of an minimized centering error of the individual lens in relation to its housing. A method by using stick-slip effect has been developed. The process has an automatic numerical control which operates during rotation of the lines. The adjustment tool is driven by electro-magnetic hammers in a step-by-step mode.

Design of a fast and high-precision polygonal scanner for HDTV

With the continuing development of laser-display-technology, a new possibility for the production high level image projection is forwarded and with it the beginning of a new era in television: TV picture formats previously thought impossible, the sharpness, color intensity and unsurpassed resolution of which make the dream of home cinema a reality. The key to this experience is visible laser light in red, green and blue, projected on a screen with the aid of horizontal and vertical deflection units. In this paper, a primarily horizontal deflection system in the form of a rotating polygonal scanner is described. The design of this scanner assembly combines a double spherical air bearing with an integrated polygonal mirror for deflection and a high torque inside drive for quickly reaching high rotation. The Fraunhofer Institute of Applied Optics and Precision Engineering (IOF Jena) develops, from conception to assembled prototype, new self-acting precision bearing systems. This new scanner solution developed out of IOFs previous developments resulting in the first ever sealed, minimal-maintenance, self- acting bearing.

Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation

We report on the investigation of the thermo-optical behavior of air-clad ytterbium-doped large-mode-area photonic crystal fiber lasers. Analytical and numerical models are applied to calculate the heat distribution and induced stresses in a microstructured fiber. The results are compared to conventional double-clad fiber lasers and design guidelines are provided to ensure maximum heat dissipation and scalability to power levels of several kWs.

Adjustment of multi-CCD-chip-color-camera heads

The principle of beam-splitter-multi-chip cameras consists in splitting an image into differential multiple images of different spectral ranges and in distributing these onto separate black and white CCD-sensors. The resulting electrical signals from the chips are recombined to produce a high quality color picture on the monitor. Because this principle guarantees higher resolution and sensitivity in comparison to conventional single-chip camera heads, the greater effort is acceptable. Furthermore, multi-chip cameras obtain the compete spectral information for each individual object point while single-chip system must rely on interpolation. In a joint project, Fraunhofer IOF and STRACON GmbH and in future COBRA electronic GmbH develop methods for designing the optics and dichroitic mirror system of such prism color beam splitter devices. Additionally, techniques and equipment for the alignment and assembly of color beam splitter-multi-CCD-devices on the basis of gluing with UV-curable adhesives have been developed, too.

Handling and mounting of micro-optical components

The manufacturing of beam shaping optics consisting of two or more microoptical components in a hybrid microsystem places high demands on the assembling process for positioning accuracy making a manual alignment process inadequate. The basis for the micro-assembly forms a robotic system. This robot makes it possible to handle, to grip and to join the components with very small position deviations and to apply very small drops of adhesives. The dispensing of adhesive drops of approximately 1 nl volume is an essential part of the task.

Adjustment robot for fiber optics assemblies

Precise adjustment of the optical components may be achieved by stepped transfer of momentum via special stroke actuators (impulse hammers), which act onto a pre-stressed fiber- optical component. The motion of the component is controlled by a computer and a measurement device. The present paper discusses theory and experiment of this adjustment method, in particular motion behavior of pushed components under the influence of applied momentum, pre-stressing and frictional forces. Additionally it describes generically the wide application range of this adjustment method. In particular the article describes an innovative, automatic adjustment machine (robot) for the alignment of a single- mode fiber assembly, which was developed by the German Fraunhofer-Institute for Applied Optics and Precision Engineering (IOF) in collaboration with Agilent Technologies Inc., a global technology leader in communications, electronics and life sciences. The achieved adjustment accuracy for the fiber optical assembly is in a low micron range for the focusing motion and in a sub-micron for entering of the optics.

Novel micro-optical components made from optical adhesives

Using a drop-on-demand print head allows for PC-controlled production of various types of microlenses as well as lens arrays. The possibility to place microlenses on arbitrarily shaped substrates allows for novel optical elements like beam splitters or non-planar scattering discs. Another interesting possibility opened by pre-shaped substrates is the production of concave lenses, which are key elements for aberration correction in micro-optical systems.