Functionalization of surfaces equips products and components with new features like hydrophilic behavior, adjustable gloss level, light management properties, etc. Small feature sizes demand diffraction-limited spots and adapted fluence for different materials. Through the availability of high power fast repeating ultrashort pulsed lasers and efficient optical processing heads delivering diffraction-limited small spot size of around 10μm it is feasible to achieve fluences higher than an adequate patterning requires. Hence, parallel processing is becoming of interest to increase the throughput and allow mass production of micro machined surfaces.
The first step on the roadmap of parallel processing for cylinder embossing dies was realized with an eight- spot processing head based on ns-fiber laser with passive optical beam splitting, individual spot switching by acousto optical modulation and an advanced imaging. Patterning of cylindrical embossing dies shows a high efficiency of nearby 80%, diffraction-limited and equally spaced spots with pitches down to 25μm achieved by a compression using cascaded prism arrays. Due to the nanoseconds laser pulses the ablation shows the typical surrounding material deposition of a hot process.
In the next step the processing head was adapted to a picosecond-laser source and the 500W fiber laser was replaced by an ultrashort pulsed laser with 300W, 12ps and a repetition frequency of up to 6MHz. This paper presents details about the processing head design and the analysis of ablation rates and patterns on steel, copper and brass dies. Furthermore, it gives an outlook on scaling the parallel processing head from eight to 16 individually switched beamlets to increase processing throughput and optimized utilization of the available ultrashort pulsed laser energy.
In the last decade much improvement has been achieved for ultra-short pulse lasers with high repetition rates. This laser technology has vastly matured so that it entered a manifold of industrial applications recently compared to mainly scientific use in the past. Compared to ns-pulse ablation ultra-short pulses in the ps- or even fs regime lead to still colder ablation and further reduced heat-affected zones. This is crucial for micro patterning when structure sizes are getting smaller and requirements are getting stronger at the same time. An additional advantage of ultra-fast processing is its applicability to a large variety of materials, e.g. metals and several high bandgap materials like glass and ceramics.
One challenge for ultra-fast micro machining is throughput. The operational capacity of these processes can be maximized by increasing the scan rate or the number of beams – parallel processing. This contribution focuses on process parallelism of ultra-short pulsed lasers with high repetition rate and individually addressable acousto-optical beam modulation. The core of the multi-beam generation is a smooth diffractive beam splitter component with high uniform spots and negligible loss, and a prismatic array compressor to match beam size and pitch. The optical design and the practical realization of an 8 beam processing head in combination with a high average power single mode ultra-short pulsed laser source are presented as well as the currently on-going and promising laboratory research and micro machining results. Finally, an outlook of scaling the processing head to several tens of beams is given.
Highly efficient beam splitters are important for a variety of high power laser applications. We prove different approaches like aperture and amplitude splitting for practicability for single- and multimode laser sources. Combining of micro- and macro-optical fabrication technologies allows novel monolithic free form splitting components with implemented segmented or stepless diffractive optical surfaces. The monolithic components are robust, compact and low weight and easy in handling. Here, we present two monolithic components: a segmented free form 1-to-17 beam splitter for fibre coupled lasers and a diffractive 1-to-11 beam splitter for single mode lasers with peak-to-peak pitch of 1.25mm and 0.8mm, respectively. The optical designs, the manufacturing of the prototypes as well as surface and performance measurements are reported. The prototypes from Fused Silica and Calcium Fluoride are designed for 532nm and 1064nm wavelength. Simulations show efficiencies larger than 98% and peak-to-peak non-uniformity below±3.2%. First laboratory results confirm efficiencies of < 95% and peak-to-peak non-uniformity of less than ±5%.
Semiconductor lasers play an important role in many applications. Depending on the wavelength of the emitted laser
light in the blue (e.g. 405-445 nm), red (~ 650 nm), near infrared (780 - 1070 nm) and e.g. the eye-safe wavelength
region around 1500 nm a manifold of applications exist. Due to their increasing power and brightness single emitter
devices are becoming increasingly widely used for the assembly and packaging of high power diode lasers. In the near
infrared typical emitter widths are 50, 90 (100) and 200 μm with power levels available > 15 W. Also larger stripes are
available - up to 1000 μm - with power levels > 25W. For highest power laser devices not only the power of the emitter
is important - but of equal importance is the subsequent optics to collect all the emitted power while maintaining the
brightness of the source. High NA acylindrical micro-lenses very well account for the strong asymmetric emitter
characteristics of the fast and slow axis and thus, result in best collimation and coupling efficiencies in contrast to
spherical lenses. LIMO's cost-effective micro-optics wafer technology is most suited for such acylindrical optics. It
allows the manufacture of different materials to cover wavelengths ranges from the UV to the NIR, e.g. 380 - 2000 nm.
Since both sides of a wafer can be structured with crossed cylindrical lenses one single monolithic optical element
simultaneously shapes the fast and slow axis of the emitted light. Additionally, mechanical reference planes can be
integrated in such monolithic optics for precise and simple integration. Application examples for collimation and fiber
coupling optics in the near infrared as well as focussing/pump optics in the blue wavelength range are shown.
High power laser sources are used in various production tools for microelectronic products and solar cells, including the
applications annealing, lithography, edge isolation as well as dicing and patterning. Besides the right choice of the laser
source suitable high performance optics for generating the appropriate beam profile and intensity distribution are of high
importance for the right processing speed, quality and yield.
For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction
behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as
lead times for prototyping and introduction into series production. LIMO has developed its own software founded on the
Maxwell equations taking into account all important physical aspects of the laser based process: the light source, the
beam shaping optical system and the light-matter interaction.
Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics
beam shaping designs a number of novel solar cell production tool sub-systems have been built. The basic
functionalities, design principles and performance results are presented with a special emphasis on resilience, cost
reduction and process reliability.
Direct laser patterning of various materials is industrially implemented into several micro-system production lines such
as inkjet printing, solar cell technology, flat-panel display production and medical engineering.
In contrast to applications of single-mode sources, multi-mode lasers can provide very high power. This allows multi
channel material processing and thus high operation speed if uniform light fields can be provided.
Here within an illumination system is presented based on a high power multi-mode laser source that generates several
uniform spots simultaneously without high stability requirements for the incoming laser source. These spots can be
generated in various sizes and at various distances and can be located periodically and non-periodically.
The concept consists of two beam processing steps: First the beam is homogenized by use of cylindrical micro-optic lens
arrays. Secondly anamorphotic telecentric microoptic objectives split the beam into several uniform segments and image
the spots onto the working plane. Because of LIMO's unique production technology the lens arrays can be optimized
freely. It results in accurate dimensions and uniform intensity distributions for every single illuminated area. Field dimensions
are only restricted by the diffraction limit.
Applications could be direct material processing as well as mask illumination approaches.
The use of the third spatial dimension in optical systems is of interest for many applications such as sensing and data
communications. Furthermore, the need for small size and low cost requires suitable concepts for integration and
packaging. Here, free-space optical integration based on a planarized configuration is described. Recent advances are
shown in the fabrication of the elements using grey-scale lithography and micromachining. Systems demonstrations will
be presented for the field of optical interconnection.
The advantages of optical interconnections, like low latency and large bandwidth, are currently becoming more important for on-board or multi-board systems. Clock distribution and data transfer with high channel density and high frequency over areas in order of several centimeters up to a few meters are of interest, e.g., in multi-processor systems. As an approach to solve the challenges of interconnections and fanning we investigate planar integrated free-space optical systems (PIFSO). In the "High-speed Opto-eLectronic Memory System" project (short: HOLMS), supported by the European Commission, a multi-processor system with optical processor memory interconnection is being demonstrated. The system combines different optics technologies. The PIFSO technology is used as the interface between opto-electronic components and optical fibers and/or PCB-embedded waveguides. The tasks of this interface are to realize the pitch transfer, e.g. from the waveguide array to the opto-electronic device array, fan-in and fan-out. To realize the different aspects of these tasks, suitable micro-optical imaging techniques and fan-out approaches are considered. To handle the large numerical aperture of the optical multimode field emerging from the VCSEL-diodes and the waveguides (up to around 0.2), the concept of pupil division is being investigated for the fan-out operation. Practical aspects such as footprint and tolerances are also considered. The feasibility of implementation of the PIFSO interconnect will be shown by means of simulations and experimental demonstration.
In computer architecture bandwidth and memory latency represent a major bottleneck. One possibility for solving these problems is the use of optical interconnections with their inherent capability for large fanin and fanout, low skew, etc. Today the possibilities to produce integrated chips with optical and electronic connections are advanced and the barrier for their adoption in computer systems gets smaller. The European Union project 'High-Speed Opto-Electronic
Memory Systems' (HOLMS) aims at demonstrating the feasibility of an optical bus system for CPU memory access. The bus system is based on planar integrated free-space optics (PIFSO) in combination with fibre and PCB integrated waveguide optics. The goal is to demonstrate a novel architecture of low latency memory access. Here, we will discuss the task of the free-space optics. The assignment of the PIFSO is to perform all fanin and fanout operations for the interconnection between CPU and memory. Longer distances like connections between CPU and memory will be broadcasted by waveguides in the PCB; and fibres are used to combine two PCBs to a multiprocessor system. The first task consists of the design and the realization of the interface between the PIFSO and the PCB integrated
waveguides. Besides the optical coupling, it is the main aspect to find an optical solution that allows large mechanical tolerances in the packaging of the different parts of the system. The large number of optical lines and their fanout and fanin are a challenge for design and construction, too. Design issues will be discussed and first experimental results will be presented.
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