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.
With the demand for broadband connectivity on the rise due to various services like video-on-demand and cloud computing becoming more popular, the need for better connectivity infrastructure is high. The only future- proof option to supply this infrastructure is to deploy "fiber to the home" (FTTH) networks. One of the main difficulties with the deployment of FTTH is the vast amount of single-mode fiber (SMF) connections that need to be made. Hence there is a strong need for components which enable high performance, robust and easy-to- use SMF connectors. Since large-scale deployment is the goal, these components should be mass-producible at low cost. We discuss a rapid prototyping process on the basis of hot embossing replication of a self-centering alignment system (SCAS) based on three micro-springs, which can position a SMF independently of its diameter. This is beneficial since there is a fabrication tolerance of up to ±1 μm on a standard G.652 SMF's diameter that can lead to losses if the outer diameter is used as a reference for alignment. The SCAS is first prototyped with deep proton writing (DPW) in polymethylmethacrylate (PMMA) after which it is glued to a copper substrate with an adhesive. Using an electroforming process, a nickel block is grown over the PMMA prototype followed by mechanical finishing to fabricate a structured nickel mould insert. Even though the mould insert shows non- ideal and rounded features it is used to create PMMA replicas of the SCAS by means of hot embossing. The SCAS possesses a central opening in which a bare SMF can be clamped, which is designed with a diameter of 121 μm. PMMA replicas are dimensionally characterized using a multisensor coordinate measurement machine and show a central opening diameter of 128.3 ± 2.8 μm. This should be compared to the central opening diameter of the DPW prototype used for mould formation which was measured to be 120.5 μm. This shows that the electroforming and subsequent replication process is possible for complex micro-scale components and could be accurate after optimisation. We characterized the sidewall roughness of PMMA replicas using a non- contact optical profiler, resulting in a root-mean-square roughness of 48 nm over an area of 63.7 μm×47.8 μm. This low sidewall roughness is especially important in the replication of high aspect ratio structures to facilitate demoulding since the sidewalls cause the most friction with the mould insert.
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
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
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.
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.