This paper presents an alternative adhesive bonding system which is able to join very small parts as well as relatively large parts with high accuracy requirements. The main advantages are the possibility to apply small volumes, to preapply the adhesive with a temporarily delayed joining procedure and extremely short set cycles. The center of micro joining develops suitable joining techniques on the basis of non-viscous adhesive systems (hot melts). The process
development focuses on the suitability for automation, process times and the applicability of batch processes. The article
discusses certain hot melt application techniques that are suitable for batch production e. g. the laser-sintering of hot melt
powder, presents an adapted assembly system and shows an example of an automated assembly process for hot melt
coated micro components. Therefore, using hot melts can be a technologically and economically interesting alternative
for the assembly and packaging of MEMS.
In electrical connections with enameled copper wires, isolation material residue can be found in the solder area when the
coating is not stripped. This residue can lead to mechanical and electrical problems. In electronic devices and MEMS,
quality requirements increase with rising thermal requirements for electrical contacts made from enameled copper wire.
Examples for this exist in the area of automotive electronics, consumer electronics and in the field of machine design.
Typical products with electrical connecting which use enameled wires include: micro-phones and speakers (especially
for mobile phones), coil forms, small transformers, relays, clock coils, and so on. Due to increasing thermal and
electrical requirements, the manufacturer of enameled wires continuously develops new isolating materials for the
improvement of isolation classes, thermal resistance, etc. When using current bonding and solder processes, there exist
problems for contacting enameled copper wire with these insulation layers. Therefore the Institute of Joining and
Welding, Department Micro Joining developed a laser based solder process with which enamels copper wires can enable
high quality electrical connections without a preceding stripping process.
Due to the growing demand of bandwidth in optical communication systems, the step towards 40 Gbit/s is inevitable. This step is limited mainly by the polarization mode dispersion of the fiber infrastructure. To extend the usability of the infrastructure it is necessary to employ PMD-compensation. The On/Off-keying modulation format in conjunction with direct detection is state of the art in high bitrate optical communication systems. But as a drawback, direct detection only provides an output signal which is proportional to the square of the absolute value of the electrical field and therefore transforms linear effects such as PMD into the nonlinear domain, which makes linear compensation schemes less effective. Coherent detection on the other hand delivers amplitude, phase and polarization information of the field and thus enables advanced PMD-compensation in the electrical domain. In our work, we employ optical coherent detection to receive two orthogonal components of the complex valued electrical field of an On/Off-keying modulated optical carrier. This single input multiple output system delivers us up to four output signals, i.e. real and imaginary part of the two detected polarization planes, which can be fed to feed forward equalizers or other electronic processing methods for an effective compensation of signal distortions caused by PMD. The required feed forward equalizer settings and their performance are presented.
The most common model used for PMD simulations visualizes the fiber as a concatenation of a large number of birefringent elements. This system's DGD has the same Maxwellian PDF for each frequency. By measurement of certain links it is shown that the PDF of the DGD is not equal for all of the frequency bands. This behavior could be traced back to the fact that fiber links consist of a certain number of stable buried sections, with nearly no PMD changes over weeks and months. These sections are connected by sections exposed to strong temperature variations, acting as polarization rotators. This new model of a fiber link is known as the hinge model. To characterize these hinges, the temperature dependent behavior of several DCM and patch cords commonly used in WDM systems have been investigated. Measurements showed that DCM are the most active hinges. They produce approximately a full rotation in Stokes space when heated 1°C. This rotation is both reproducible and reversible. An novel model of the analyzed DCM has been developed in Matlab, which is able to reproduce the described measured behavior in simulations. The frequency dependency of the DGD's PDF leads from overall systems outage probability to frequency selective outage probability. That means instead of having a system outage at a certain outage probability, outage probabilities are connected to a number of outage channels.
Polarization mode dispersion (PMD) is one of the major limitations for optical transmission systems at 10 Gb/s and beyond. While first- or second-order PMD compensators (PMDC) can be driven with a feedback signal, more complex broadband PMDCs have to be set feed forward. An exact knowledge of the fiber's PMD characteristics - e.g. the PMD vector - is needed for the feed forward setting. Since PMD changes with time, real-time PMD measurement without data traffic interruption is necessary. Some recently published frequency- and time-domain methods meet these conditions. In this publication we are going to examine and compare different on-line measurement methods. Using numerical simulations, the performance of the measurement methods is assessed in terms of the accuracy of the PMD vector measurement and the qualification as feed forward control signal for setting a PMDC. The measurements exhibit an inherent inaccuracy if the signal is launched close to one of the principal states of polarization (PSP). Although these combinations of PSP and signal polarization result in inaccurate PMD vector measurements, the transmitted signal is not degraded by first order PMD. Consequently, the accuracy of the PMD vector measurement is a bad figure of merit for the performance of a system including a feed-forward set PMDC. Furthermore, due to the averaging over the signal bandwidth, the measured PMD vector is a better control variable for a PMDC than the analytically calculated PMD vector if second order PMD is considered.
This paper presents a new concept for bonding micro-parts with dimensions in the range of 50 μm to 300 μm. Two different kinds of adhesives - polyurethane adhesive foil and hot melt glue - were applied to a basic substrate by different techniques. The focused and concentrated hot gas stream softened glue which had been applied in a solid state. Micro-parts were then embossed in the softened glue, or covered and shielded by it. In this way, a rigid and compact bond was obtained after cooling. For the positioning of micro-parts (optical fibers), it has been necessary to manufacture adequate V-grooves. Finite element analyses using the ANSYSTM program package were performed in order to evaluate parameters which govern the heat transfer to the adhesive and substrate respectively. Experimental results are in good agreement with results obtained by the numerical simulations. The advantages of this new approach are small system size, low capital costs, simple usage, applicability to many material combinations, easy integration into existing production lines, etc.
This paper presents different approaches to enable high-speed
transmission of 10 Gbit/s and beyond on polarization mode
dispersion (PMD) limited fibers. An introduction to the phenomenon
of PMD and its impact on system performance is presented. An
overview of common optical PMD mitigation methods and their basic
concept is given, including the problem of multi-channel PMD
compensation schemes for WDM systems. Furthermore alternative
methods like polarization scrambling, forward error correction and
electrical mitigation are considered. Bit error rate (BER)
determined by error counting is used as quantification for PMD
induced outages and a comparison to eye opening penalty (EOP)
based performance evaluation is given. The performance of basic
PMD mitigation schemes is compared by using the EOP and the BER
based outage criterion.
Chromatic dispersion and polarization mode dispersion (PMD) are the most relevant disturbances in optical high speed transmission systems. The influence of chromatic dispersion can be overcome by different methods such as dispersion compensating fibers or fiber gratings. Because of its stochastic behavior the struggle against
PMD is much more troublesome and essential for bit rates above 10 Gbit/s. The paper describes the influence of polarization mode dispersion derived from basic principles of transmission. It gives some physical understanding and simple derivation of the characteristic equations of PMD. One distinguishes between first and second order PMD. An optical fiber link showing first order PMD only can be modelled by a waveguide with time varying birefringence. If the birefringence additionally is frequency dependent the fiber will show higher order polarization mode dispersion. PMD compensators can be divided in a similar manner: compensators considering first order PMD only and compensators including PMD of higher order. Compensators operating in the optical domain or in the electrical
domain have been proposed.
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