Shape sensing of reflecting free form surfaces is achieved by deflection of an array of light pencils. The pencils showing very high depth of focus are produced by means of micro-optical components. Each pencil that interacts with the surface under test is redirected by reflection. Imaging intensity measurements, e.g. by a CCD-camera, at several propagation distances allow for determination of the propagation angle of each reflected pencil. By using the vector law of reflection the local slope of the surface at the location of reflection can be determined. Height data is obtained by depth from gradient methods known, e.g., from Hartman-Shack sensors. Both simulations and experimental results show a typical resolution of a view μm or 0.1 mrad for height or angle measurements, respectively.
The mask structured ion exchange in glass (MSI) is a powerful tool for realizing general planar phase distributions and in particular custom designed planar GRIN micro lenses with diffraction limited performance and high fill factor. For lens characterization the numerical aperture is a key parameter. However the classical geometrical definition of the N.A. disregards aberrations. Here we suggest an addition to this classical definition, which is based on diffraction limited performance. For a testing of micro lens arrays, global process parameters are assessed by interferometric measurements of a subset of the lenses. Local process variations typically result in small non-symmetric aberrations. These aberrations mainly lead to a lateral shift of the focus. Thus, for rapid quality control of micro lens arrays we analyze all focal positions in parallel. From the lateral deviations of the focal positions a quality criterion for each individual micro lens can be derived.
A novel technique for the realization of guiding structures for passive / automatic alignment is proposed. The technique is based on a recently available special photoresist. This photoresist can be processed by standard lithographic processes and shows a mechanical stability close to glass. Guiding structures may thus be realized in the same process as the functional structures on a substrate. We discuss the material behavior in terms of processing, change of shape due to shrinking or swelling and shear stability. First results of accuracy experiments are shown. As an example we demonstrate fiber ferrules for horizontal and for vertical mounting. We also show alignment structures for fiber/fiber coupling.
Angle Division Multiplexing (ADM) has recently been proposed for fibre-based parallel short distance interconnects. Here, practical issues are discussed such as robustness against environmental stress, alignment requirements for micro-integration and the interconnection of 8 workstations as a demonstration.
Angle division multiplexing (ADM) is a multiplexing scheme which is applicable to optical signal transmission through multimode step-index fibers. ADM allows for parallel and high-bandwidth transmission by using passive components, i.e. no external control is necessary. The fiber quality limits the simultaneous optimization of transmission distance, number of channels and cross-talk. This paper reports on first experiments with an ADM based data link over 10 m between workstations with 8 Gigabit-Ethernet channels at a cross-talk of better than -10 dB. For a micro-optical integration of the ADM system design rules and tolerance considerations are discussed.
The propagation angle 9 between the symmetry axis of a fiber and the principle propagation direction of a beam is conserved over short distances within a step-index multimode fiber. This conservation behavior can be used for multiplexed transmission by assigning different channels to different propagation angles. Furthermore, due to the reduction of the angular spread in the fiber, the temporal bandwidth is increased compared to multi-mode transmission. To realize this angular coding, suitable optical setups for multiplexing and demultiplexing operations were designed. The experimental results on the transmission capabilities of an angular multiplexed multimode fiber are presented.
The propagation angle of a beam is conserved when traveling through a multi-mode step-index fiber over short distances. We show that this feature can be used for multiplexed signal transmission thus providing a high bandwidth single-fiber interconnection between chips, boards or racks. With respect to this application the transmission properties of a fiber are analyzed. Concepts for optical multiplexing and de- multiplexing set-ups are outlined. A fiber transmission line consisting of a fiber and an optical de-multiplexing unit is characterized to obtain experimental results on the transmission capabilities in terms of efficiency, channel separation, number of multiplexed channels and cross-talk.
Optical signal transmission benefits, among other features, from its huge potential of multiplexing. Besides WDM or time multiplexing a new kind ofmultiplexing is possible: directional multiplexing. Measurements are presented showing that in short fiber transmission lines the angle 9 between the symmetry axis of a fiber and the principle propagation direction of a beam is conserved over distances in the order of 1 meter. So, provided a beam is coupled into a fiber under a certain off-axis angle 3 it will couple out of the fiber with the same off-axis angle. This conservation behavior can be used for coding different channels for multiplexed transmission and can provide a high bandwidth interconnection between chips or boards, i.e. within computers in a single fiber. Based on the experimental set-up used in this work an estimation on the degree ofmultiplexing will be given. Additionally, suitable components for multiplexing and de-multiplexing have to be designed. That is, on the one hand different signal channels have to be coded into different angles before being coupled into the fiber. On the other hand the directional spectrum of the outcoming beams has to mapped to different positions on a detector plane. Particular attention is paid to the de-multiplexing component: A specially designed diffractive optical element (DOE) serves as a mapping device between directional spectrum and spatial positions on the detector plane.
Optical board-to-board interconnects for 1 - 100 cm distances are presented. A thick light- guiding plate (typically 5 - 10 mm) is used for confinement and transport of the optical signals with low loss (-0.1 dB/cm), highly efficient holographic optical elements in dichromated gelatin are used for coupling (-0.5 dB) and binary phase gratings for broadcasting of signals. Several experiments were performed: (1) point-to-point interconnects operating at a data rate of 650 Mbit/s per channel, (2) a parallel interconnect with high packing density up to 1000 channels/cm2, (3) an optical permutation stage for data permutation networks, and (4) an optical star coupler for signal broadcasting within light- guiding plates. Holographic optical elements in dichromated gelatin have shown excellent diffraction efficiency and low level of straylight at wavelengths ranging from 488 nm to 1.5 micrometers .
A new pattern generator, initially designed for ASIC fabrication, is employed for writing synthetic holograms and other micro-optical components. The specifications and limits of this machine are investigated. Test structures and synthetic holograms are shown. Arbitrary patterns with micrometer resolution, submicrometer positioning accuracy, large area patterns (up to 150 x 150 mm2 possible), and good quality microprofiles are demonstrated.
A new pattern generator, initially designed for ASIC fabrication, is employed for writing synthetic holograms and other micro-optical components. The specifications and some limits of this machine have been investigated. Test structures and synthetic holograms are shown. Arbitrary patterns with micron resolution, submicron positioning accuracy, large area (up to 150 X 150 mm2 possible), and good quality of the microprofile were demonstrated.
Computer generated holograms (CGH) consist of patterns which have been calculated numerically starting from the desired function of the optical component and the known physical laws of diffraction. The real fabrication of such holograms poses two different tasks. First the computed pattern has to be converted into one mask or a set of masks. Thereby submicron resolution is required for CGHs that are to be used for visible light. This means that one has to use microlithographic techniques such as electron-beam or laser lithography. The second task is to achieve the necessary groove depth and profile. Wet etching techniques have been quite common for this purpose but they have two disadvantages: it is difficult to obtain a precise etch stop particularly with very fine structures due to capillary effects and mostly one is constrained to certain crystallographic orientations. This makes it hardly possible to achieve directional anisotropic etching in glass. Dry etching techniques overcome both of these problems. The foundry for micro-optical elements in Erlangen makes use of laser lithography and reactive-ion etching. Both technologies are discussed in some detail. The scope of computer generated holograms ranges from the well known Dammann-gratings, gratings which produce arrays of light spots of equal intensity, to very complex two- dimensional structures for example for the correction of aberrations or for three-dimensional displays. In his paper we also describe some results with the production of microlenses that can be realized using our technologies.