Jens Hossfeld

Polarizing computer-generated holograms

Polarizing computer-generated holograms (PCGH) may be useful combining different optical functions such as polarizing, imaging, beam shaping, and beamsplitting in one element. We propose the fabrication of PCGHs based on microstructuring of polarizing or birefringent materials. A simple and useful method of production of binary and grayscale-amplitude PCGHs by laser beam bleaching of polarization foil is shown. Experimental results are presented.

Micro-optical components for parallel optical networks

Key components for parallel optical links are fabricated cost-effectively using LIGA technology. Multifiber ferrules and mechanical splices, 1/spl times/2 and 4/spl times/4 single-mode matrix switches and micro lens arrays with passive alignment structures are presented.

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.

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.

Micro-Optical Components for Information Technology Fabricated Via Liga Technique

We present the design and technical realization of exemplary micro-optical structures and devices for optical communication technology: A precision ferrule with (0.35 ± 0.2) dB coupling loss for 12-fold fibre ribbons, a 4 x 4 fibre-optical cross connect with non-moving mirrors, and a 4 x 4 multimode integrated-optical star coupler with less than 2dB uniformity have been fabricated by combination of the LIGA technique with precision engineering methods, e. g. electro discharge machining or diamond fly-cut milling. Further, “contactless embossing” for the in-place production of microlenses is introduced and discussed. The structures and devices presented are characterized by high precision, high performance, ease of assembly, and mass production capability via standard replication methods. All the main components have been made from thermoplastic materials via precision injection or compression moulding.

Manufacturing microcomponents for optical information technology using the LIGA technique

Recently, splices and connectors for fibers ribbons, optical cross connects and especially planar waveguide devices have been fabricated via LIGA in combination with precision engineering techniques. LIGA combines high precision and mass production capability, necessary for products designed for applications in the telecom and datacom market. In this presentation the fabrication of three-level molding and embossing tools is presented, which have been used for the manufacturing of waveguide prestructures consisting of waveguide channels and bier-to-waveguide coupling grooves. The precision of the tools is better than 1 micrometers in all directions, which allows for simple passive pigtailing. A first product, a precision of the tool is better than 1 micrometers in all directions, which allows for simple passive pigtailing. A first product, sixfold array of 4 X 4 multimode star couplers has been realized. The molding behavior of PMMA and COC material has been tested and compared. Production and assembly was tested by fabricating a series of 300 star couplers. The average insertion los has been found better than 9dB, the uniformity better than 3dB, both measured at 830nm. THe device is designed for application in optical backplanes for high-speed computers.

Rectangular focus spots with uniform intensity profile formed by computer-generated holograms

An optical beam shaping system based on a single Computer Generated Hologram has been realized. It focuses a laser beam with Gaussian profile to a square area with uniform intensity. In order to achieve a rectangular focal spot which is as close as possible to the size of the diffraction spot, we investigated two different hologram calculation methods. The first is based on a ray tracing approach, while the second one uses an iterative Fourier transform algorithm. Computer simulations and experimental results are shown.

Polarization multiplexer/demultiplexer based on polarizing computer-generated holograms

A new type of optical element--the polarizing computer-generated hologram (PCGH)--may integrate different optical functions like polarizing beam splitting, beam shaping, imaging, polarization forming or conversion, and more in one single element. We have produced a polarization multiplexer/demultiplexer for optical telecommunication using a phase PCGH.