Hans-Dieter Bauer

ArF-excimer laser ablation experiments on Cycloolefin Copolymer (COC)

To determine the capability of Cycloolefin Copolymer (COC) for excimer laser microstructuring, ablation experiments have been performed at 193 nm using an ArF excimer laser workstation. A matrix of square holes was structured in COC, the ablated structures were examined qualitatively and quantitatively by optical methods and scanning electron microscopy. It turned out that COC can be structured with high accuracy and is therefore suited for laser rapid prototyping of micro optical and microfluidic devices. The maximum ablation depth of COC (0.17 μm/pulse) is smaller than of PMMA (0.58 μm/pulse), but is sufficient for prototyping and allows fine depth tuning. Flat structures less than 200-μm deep nearly show no amount of redeposited material and yield smooth surfaces.

Injection-moulded fibre ribbon connectors for parallel optical links fabricated by the LIGA technique

Using the LIGA technique prototypes of twelve-fibre-wide ribbon connector ferrules have been developed that provide low-loss physical-contact multimode connections for parallel interfaces. The ferrules are injection moulded and the modular mould insert has been fabricated by means of microtechnology (LIGA) and electro-discharge machining. After assembling, mated couples of these ferrules show average insertion loss values of 0.35 dB and have been used to successfully transmit data with a transfer rate of 250 Mbit per fibre over a 100 m distance.

Polymer waveguides for telecom, datacom, and sensor applications

LIGA, the process sequence of deep lithography, electroforming and molding has been used for the fabrication of polymer waveguide components with passive fiber-to-chip coupling. The variety of 3D structures that can be realized, the high precision that can be achieved and especially the possibility of cost-effective mass production make these components most relevant for telecom, datacom and sensor applications. A novel waveguide design for a singlemode Y- splitter acting as telecommunication wavelengths was developed and realized together with the coupling scheme described above. It shows superior performance to conventional layouts and is ideally adapted to a fabrication using LIGA. Combining LIGA with high precision diamond machining multi-level tools with the complementary waveguide and fiber alignment structures were fabricated. For the first time a very high precision of better than 1 micrometers was achieved for heights and widths of all critical structures. A large number of molded parts was fabricated by hot embossing in PMMA. Detailed investigations proved that a reproducibility of better than 0.5 micrometers for the replicated structures is possible. By filling in a suitable core material into the waveguide prestructures and fixing fibers in the fiber grooves, fully pigtailed Y-splitters have been fabricated. This is an easy passive fiber-to-waveguide alignment with a significant reduction of manufacturing costs. First optical measurements on the samples showed an excess loss of 3.5 dB. Uniformity values were less than 0.6 dB and already meet Bellcore specifications. As another application of this fiber-to-waveguide coupling scheme a novel 4 X 4 star coupler for use in multimode optical bus systems is presented. First samples show an insertion loss of less than 9 dB and a uniformity better than 2 dB.

Application of micro- and nanotechnologies for the fabrication of optical devices

The development of micro-opto-electro-mechanical systems (MOEMS) and devices no longer focuses on feasibility studies and expensive demonstrators. On the contrary, fabrication of micro-optical components is already feeding dynamic markets with a large variety of products that are more or less on the verge of inexpensive mass production. A major application area for MOEMS is, without any doubt, tele- and datacommunications, while miniature optical sensors (e.g. spectrometers and interferometers) have a growing part in many kinds of biotechnological, chemical and pharmaceutical applications. In this presentation numerous examples for optical microstructures are given that range from the field of low cost fiberoptic components to polymer waveguide elements, from fiber switches to mass-producible microlenses made of thermoplastics or glass, and from microstructured photonic bandgap materials to optical sensor tips for investigating nanostructures. It is emphasized that for realizing MOEMS very different materials have to be processed while the necessary hybrid integration demands for specific automated assembly methods. In particular, the examples given show now microtechnologies can be adapted and combined with each other to take into account the special requirements of the product.

Combination of guided wave and free-space micro-optics for a new optical backplane concept

High data rates, immunity against electro-magnetical interference and the ability for low-cost mass production are the basic reasons for the replacement of electrical wire networks by their optical equivalents. The highly integrated micro-optical backplane concepts discussed in this paper are based on a combination of guided wave and free space micro- optical elements and are compatible to multi-fiber MT connectors. The required positioning accuracy of the micro- optical elements is guaranteed by the LIGA technique. Monolithic integration in one substrate allows to reduce the degree of freedom for critical alignment.

Polymer microsystems by excimer laser ablation: from rapid prototyping to large-number fabrication

Excimer laser ablation of polymers is demonstrated to be a well suited technology for cost effective fabrication of prototypes of polymer microstructures in relatively short times. Prototyping is realized by ArF excimer laser ablation (193 nm) using mask projection techniques in combination with high precision sample movement as well as mask movement. Different techniques and their restrictions in structural diversity are illustrated by examples from micro-optics, like fiber switches and waveguide couplers. Microparts the functionality of which has been proven by prototypes can be fabricated in large numbers by the Laser-LIGA technique. For the Laser-LIGA process a master structure is generated in PMMA that is coated onto a titanium wafer, using the same CNC data as for rapid prototyping without additional expenditure. From the PMMA master a mould insert of Ni or Cu can be generated by electroforming that allows time and cost effective mass fabrication via hot embossing or injection moulding if the required part numbers are large. Advantages and disadvantages of the laser ablation prototyping technique compared to other rapid prototyping methods are discussed and the Laser-LIGA technique is compared to the standard LIGA process using deep X-ray lithography.

Custom specific fabrication of integrated optical devices by excimer laser ablation of polymers

Excimer laser ablation was used for direct writing of multimode waveguide structures with passive fiber alignment grooves in polymers. First, integrated optical multimode components were simulated by the method of beam propagation to optimize the optical performance of the design. Then the CNC codes for laser machining were created directly from the corresponding CAD data. ArF Excimer laser radiation of wavelength (lambda) equals 193 nm was used for ablation of adjacent grooves with a cross sectional area of 50 X 50 micrometers 2 and lengths in the order of several mm. The laser-written grooves were filled with a liquid pre-polymer which after UV-curing served as the waveguiding structures. The smoothest surfaces during laser ablation were achieved by applying several ablation scans with reduced material removal rates but higher feedrates. Debris formation, also influencing the surface roughness, was suppressed or minimized by making use of capable polymers. With the method of laser ablation linear waveguides of length 1 equals 10 mm with insertion losses Li in the rang of 1.3 to 1.9 dB have been realized for (lambda) equals 1310 nm, depending on the polymer used. By means of 1 X 2-splitters, 4 X 4 as well as 4 X 16 starcouplers it was shown that laser ablation is a well suited tool for rapid prototyping of integrated optical multimode elements.

Design of an opto-electronic VLSI/parallel fibre bus

We present a design for an opto-electronic bus system based on commercial parallel fibre ribbon transmission systems and opto-electronic VLSI smart pixel arrays. We describe the design of the individual components, their integration, the performance limits and potential applications.

Polymeric optical MEMS

As micro-opto-electro-mechanical systems and devices evolve from prototypes to products, the need for cost-effective mass production techniques becomes crucial. This challenging cost goal can be reached using mass replication techniques like injection molding and hot embossing.In order to meet the special demands of miniaturization these replication techniques have been modified incorporating variothermal process control, an evacuation of the mold chamber and a modification of the molding parameters including elevated temperatures. Based on these techniques numerous micro- optical systems have been developed including a twelve fold multi-fiber connectors with an average insertion loss of 0.35 dB, an optical bench using polymeric alignment structures on a silicon substrate, a 4 by 4 star coupler with passive fiber alignment, a 1 by 2 singlemode fiber switch, and a singlemode 4 by 4 optical matrix switch. In these systems geometrical tolerances of one micrometers and below have been obtained allowing passive alignment of multimode and singlemode fibers during the assembly process and high precision positioning of fibers during operation.

Achieving mass fabrication of microoptical systems by combining deep-x-ray lithography, electroforming, micromolding, and embossing

The paper reviews the application of deep X-ray lithography in conjunction with electroforming, plastic molding, and stamping (LIGA) for a mass production of micro- and submicron-structured photonic devices. LIGA technology offers almost total design freedom in lateral structuring and a high aspect ratio of 100. Vertical walls with heights up to 1 mm and optical grade surfaces enable their use as functional optical surfaces. It is possible to process a variety of materials such as metals and different polymers, including those with nonlinear optical properties. Therefore, Y-branches, couplers, and structures for the positioning and fixing of fibers, detectors, and light emitters can be integrated on one chip to build up hybrid optoelectronic devices.