Wolfgang Gramann

Microsystems and wafer processes for volume-production of highly reliable fiber optic components for telecom- and datacom-application

In development and fabrication of highly reliable active fiber optic components, first the application of great fields of microsystem techniques enabled the breakthrough in volume-production. Micro-mechanical methods allowed the big scale fabrication of microoptical silicon lenses with methods, machines and materials of the semiconductor technology on wafer. With the simultaneous application of micro-mechanical methods, such as anodic bonding processes of optical components and semiconductor-laser heated solder bonding techniques, it was possible to realize also hybrid integrated fiberoptic subcomponents on silicon wafer with the neccessary dimensions, tolerances and mechanical stability in the submicrometer region. We have realized a technology with micro-systems that enables on an (about 1 mm sq.) chip in a silicon wafer compound the hybrid integration of complete active fiberoptic modules with their different active semiconductor chips and the micro-optics for direct coupling in and out of the SM- and MM-fibers for different applications. With this technology of a compact design of the neccessary materials and components we could assemble components as laser- and detector-modules with the highest standard of microoptical stability and reliability. With this technique we can use the already in microelectronics well-established low cost production methods on wafer scale also for active fiber optic components. This means the complete fabrication, burn-in and testing procedures are practicable for example on a 5 inch silicon-wafer. So the main module-functions are separated from the cost intensive packaging efforts. It is rather possible to provide with a standard-submount base-component a fiber optic product family for different applications with adapted packages. This means that on the base of these module-subcomponents the volume production as well of low cost as also of high end components for fiber optics are possible. As all the essential opto-electrical and mechanical functions are combined in the highly stable subcomponent chip with well adapted materials, in minimal dimensions and symmetrical design, all the derived fiber optic components can provide the imperative reliability for these products. In some examples we show proposed exploitations of these technique for highly expedient realization of fiber optic transmission systems. One very important field for application of low cost components is the access network. Fiber to the home needs medium datarates (up to 155 Mbit/s) and medium length (up to 10 km). The techniques described here allows to find the optimum between performance and cost for these applications. Using the bi-directional transmission the effort for the bit transport can be reduced near to the level of copper lines. Therefore the German Telekom has installed a lot of subscriber lines using modules for bi-directional optical transmission.

Binary and multilevel diffractive lenses with submicrometer feature sizes

Binary and multilevel diffractive lenses with submicrometer feature sizes are realized on silicon and galliumphosphide wafers using CAD methods, direct write e-beam lithography, reactive ion etching, antireflection coating, and wafer dicing. Measurements prove aberration-free imaging and maximum diftraction efficiencies of 70% for lenses with high numerical aperture (NA) of 0.5. Comparisons to other miniature and micro-optical elements are carried out with respect to laser-to-single-mode-fiber coupling and show the competitive performance of the diffractive lenses. Arrays for 18-channel parallel receiver modules are fabricated in on-axis and off-axis versions. Optical crosstalk is estimated.