Markus Wissmann

Hot Embossing of Microoptical Components Prototyped by Deep Proton Writing

In this letter, we present the replication of out-of-plane coupling microcomponents using hot embossing, through the fabrication of a metal mould by electroforming a polymer template patterned by means of deep proton writing (DPW). We compare the surface roughness and the optical performance of the hot embossed replicas with the DPW prototypes and can conclude that the replicated components exhibit only a small increase in surface roughness and a very small decrease in coupling performance. This paves the way towards low-cost mass replication of DPW-fabricated prototypes in a variety of high-tech plastics.

Tailored Surface-Enhanced Raman Nanopillar Arrays Fabricated by Laser-Assisted Replication for Biomolecular Detection Using Organic Semiconductor Lasers

Organic semiconductor distributed feedback (DFB) lasers are of interest as external or chip-integrated excitation sources in the visible spectral range for miniaturized Raman-on-chip biomolecular detection systems. However, the inherently limited excitation power of such lasers as well as oftentimes low analyte concentrations requires efficient Raman detection schemes. We present an approach using surface-enhanced Raman scattering (SERS) substrates, which has the potential to significantly improve the sensitivity of on-chip Raman detection systems. Instead of lithographically fabricated Au/Ag-coated periodic nanostructures on Si/SiO2 wafers, which can provide large SERS enhancements but are expensive and time-consuming to fabricate, we use low-cost and large-area SERS substrates made via laser-assisted nanoreplication. These substrates comprise gold-coated cyclic olefin copolymer (COC) nanopillar arrays, which show an estimated SERS enhancement factor of up to ∼ 10(7). The effect of the nanopillar diameter (60-260 nm) and interpillar spacing (10-190 nm) on the local electromagnetic field enhancement is studied by finite-difference-time-domain (FDTD) modeling. The favorable SERS detection capability of this setup is verified by using rhodamine 6G and adenosine as analytes and an organic semiconductor DFB laser with an emission wavelength of 631.4 nm as the external fiber-coupled excitation source.

Replication of micro-optical components and nano-structures for mass production

Microstructured metallic moulding tools or mould inserts are needed for mass production of micro-optical components. These tools are used for hot embossing or injection moulding of micro components in plastic. Because of the extremely tight specifications like small sidewall roughness and high aspect ratios these tools are usually fabricated by lithographic procedures followed by electroforming. In this case the structural geometry is limited to Manhattan-like structures and only a limited number of technologies can be used to fabricate the master structures. Applicable techniques are e.g. X-ray lithography (LIGA technology) or Deep Proton Writing (DPW). However these processes are not suitable for low-cost mass production. They are limited by the exposure area and the design of the microstructures. To overcome these limitations a new process has been developed which allows the transfer of micro-optical structures fabricated by other technologies as well as assembled structures or structures with varying geometries into a moulding tool. The master structures, either plastic, glass, metal or a combination of these materials, serve as sacrificial parts. With electroforming technology, a negative copy of the microstructured master is built up in the metal subsequently used as a moulding tool. Low-cost mass production is possible with these moulding tools. We present the process chain in this paper and demonstrate its feasibility by producing reliable moulding tools from three challenging and different components. The possibility of mass fabrication of the components by replication was demonstrated.

Replication of deep micro-optical components prototyped by Deep Proton Writing

Using our rapid prototyping technology called Deep Proton Writing (DPW), we have in recent years made a wide range of micro-optical components with a large depth (500-μm) for a variety of applications. One of these components is a pluggable out-of-plane coupler for printed circuit board-level optical interconnections. Whereas DPW is capable of rapidly fabricating high-quality master components, the technology is not suitable for low-cost mass fabrication. Therefore, we investigate the replication of out-of-plane coupling components using hot embossing, through the fabrication of a metal mould of the DPW master by applying electroplating. We compare these hot embossed replicas with components replicated using the elastomeric mould vacuum casting technology.

Mould insert fabrication of a single- mode fibre connector alignment structure optimized by justified partial metallization

For mass production of multiscale-optical components, microstructured moulding tools are needed. Metal tools are used for hot embossing or injection moulding of microcomponents made of a thermoplastic polymer. Microstructures with extremely tight specifications, e.g. low side wall roughness and high aspect ratios are generally made by lithographic procedures such as x-ray lithography or deep proton writing. However, these processes are unsuitable for low-cost mass production. An alternative manufacturing method of moulding tools has been developed at the Karlsruhe Institute of Technology (KIT). This article describes a mould insert fabrication and a new replication process for self-centring fibre alignment structures for low loss field installable single-mode fibre connectors, developed and fabricated by the Vrije Universiteit Brussel (VUB) in collaboration with TE Connectivity. These components are to be used in fibre-to-the-home networks and support the deployment and maintenance of fibre optic links. The special feature of this particular fibre connector is a self-centring fibre alignment, achieved by means of a through hole with deflectable cantilevers acting as micro-springs. The particular challenge is the electroforming of through holes with a centre hole diameter smaller than 125 µm. The fibre connector structure is prototyped by deep proton writing in polymethylmethacrylate and used as a sacrificial part. Using joining, physical vapour deposition and electroforming technology, a negative copy of the prototyped connector is transferred into nickel to be used as a moulding tool. The benefits of this replication technique are a rapid and economical fabrication of moulding tools with high-precision microstructures and a long tool life. With these moulding tools low-cost mass production is possible. We present the manufacturing chain we have established. Each individual manufacturing step of the mould insert fabrication will be shown in this report. The process reliability and suitability for mass production was tested by hot embossing.

Alternative technology for fabrication of nano- or microstructured mould inserts used for optical components

For mass production of multiscale-optical components, micro- and nanostructured moulding tools are needed. Metal tools are used for hot embossing or injection moulding of microcomponents in plastics. Tools are typically produced by classical forming processes such as mechanical manufacturing e.g. turning or milling, laser manufacturing or electrical discharge machining (EDM). Microstructures with extremely tight specifications, e.g. low side wall roughness and high aspect ratios are generally made by lithographic procedures such as LIGA or DPW technology. However, these processes are unsuitable for low-cost mass production. They are limited by the exposure area and structure design. In cooperation with international partners alternative manufacturing methods of moulding tools have been developed at the Institute of Microstructure Technology (IMT). In a new replication procedure, mould inserts are fabricated using micro- and nanoscale optics. The multiscale structured prototypes, either in plastics, glass, metal or material combinations are used as sacrificial parts. Using joining technology, electroforming and EDM technology, a negative copy of a prototype is transferred into metal to be used as a moulding tool. The benefits of this replication technique are rapid and economical production of moulding tools with extremely precise micro- and nanostructures, large structured area and long tool life. Low-cost mass replication is possible with these moulding tools. In this paper, an established manufacturing chain will be presented. Multiscale and multimaterial optical prototypes e.g. out-of-plane coupler or microinterferometer were made by DPW or laser technology. The mould insert fabrication of each individual manufacturing step will be shown. The process reliability and suitability for mass production was tested by hot embossing.

Hot-embossing replication of self-centering optical fiber alignment structures prototyped by deep proton writing

Abstract. This paper presents the hot-embossing replication of self-centering fiber alignment structures for high-precision, single-mode optical fiber connectors. To this end, a metal mold insert was fabricated by electroforming a polymer prototype patterned by means of deep proton writing (DPW). To achieve through-hole structures, we developed a postembossing process step to remove the residual layer inherently present in hot-embossed structures. The geometrical characteristics of the hot-embossed replicas are compared, before and after removal of the residual layer, with the DPW prototypes. Initial measurements on the optical performance of the replicas are performed. The successful replication of these components paves the way toward low-cost mass replication of DPW-fabricated prototypes in a variety of high-tech plastics.

Integrated microinterferometric sensor for in-plane displacement measurement

We present an integrated sensor based on a grating interferometer (GI) for in-plane displacement measurement in microregions of large engineering structures. The system concept and design, based on a monolithic version of Czarneks GI, is discussed in detail. The technology chain of the GI measurement head (MH), including the master fabrication and further replication by means of hot embossing, is described. The numerical analyses of the MH by means of geometric ray tracing and scalar wave propagation are provided. They allow us to determine geometrical tolerance values as well as refractive index homogeneity and nonflatness of MH working surfaces, which provide proper beam guiding. Finally the demonstrative measurement performed with a model of the sensor is presented.

Characterization of the optical parameters of high aspect ratio polymer micro-optical components

Over the last decades the significant grow of interest of photonics devices is observed in various fields of applications. Due to the market demands, the current research studies are focused on the technologies providing miniaturized, reliable low-cost micro-optical systems, particularly the ones featuring the fabrication of high aspect ratio structures. A high potential of these technologies comes from the fact that fabrication process is not limited to single optical components, but entire systems integrating sets of elements could be fabricated. This could in turn result in a significant saving on the assembly and packaging costs. We present a brief overview of the most common high aspect ratio fabrication technologies for micro-optical components followed by some characterization studies of these techniques. The sidewall quality and internal homogeneity will be considered as the most crucial parameters, having an impact on the wavefront propagation in the fabricated components. We show the characterization procedure and measurement results for components prototyped with Deep Proton Writing and glass micromachining technology replicated with Hot Embossing and Elastomeric Mould Vacuum Casting technology. We discuss the pros and cons for using these technologies for the production of miniaturized interferometers blocks. In this paper we present the status of our research on the new technology chain and we show the concept of microinterferometers to be fabricated within presented technology chain.