Search

This contribution shows the interrogation of 4000 serial fiber-Bragg gratings (FBGs) by means of a hybrid code-division multiplex (CDM) - wavelength-division multiplex (WDM) scheme. A strain measurement shows no influence of a strained WDM-section to another non-strained WDM-section. Polarization effects are diminished by the implementation of a semi-conductor optical amplifier.

Massive optical sensor networks gained a lot of attention in recent years. They offer new advances in the fields of smart structures and health monitoring. All serial optical sensor networks rely on multiplexing techniques that provide huge amounts of sensors in a single optical fiber. Wavelength-division Multiplex (WDM) which has been established in many applications, is restricted to the spectral width of the used light source that needs to be shared by several non-overlapping Fiber-Bragg-Grating (FBG) spectra. Time-division Multiplex (TDM) uses short impulses and a different optical path length between all optical sensors, to distinguish each single FBG. Short impulses lead to a low Signal-to-Noise Ratio (SNR). Optical Frequency Domain Reflectometry (OFDR) offers a high spatial resolution of FBGs within a short fiber length. This contribution deals with a Code-division Multiplex (CDM) interrogation technique that provides numerous sensors in a single optical fiber, a better SNR, and a long range of distributed sensing points. It requires codes with good autocorrelation behavior which is characterized by certain criteria. The detectable criteria are limited which narrows significantly a search for best possible codes for the interrogation system.

The profound understanding of time-variance in an intensity modulation and direct detection system is required for the transmitter and receiver design. In this contribution, two methods for analyzing this time-variance are studied when transmitting through an multi-mode fiber (MMF) channel in conjunction with mode-selective launching. The first method involves the camera-based measurement of the near field intensity profile at the MMF end-face. Secondly, a repeated measurement of the channel’s impulse response is performed using a least squares channel estimation. By introducing a vibration to the MMF it is shown that both methods are able to detect these frequencies and their occurring harmonics when calculating the Doppler spectrum. However, compared to the DC component the vibration frequency amplitudes are negligibly small. Therefore, the channel can be assumed as time-invariant in the measured span of a few seconds, benefiting decision-aided adaptive signal processing.

Massive optical sensor networks applied in smart structures or for health monitoring have attracted a lot of attention within recent years. Different multiplexing techniques for interrogation have been investigated in order to increase the number of sensors within a network. Whereas optical frequency-domain reflectometry (OFDR) offers a high resolution at short distances, time-division multiplex (TDM) provides long distance sensing at the cost of lower resolution. In this contribution, a code-division multiplex (CDM) interrogation scheme is analysed which overcomes these restrictions. A massive enlargement of fiber-Bragg-grating (FBG) sensors in an optical fiber is obtained allowing spectral overlapping. While TDM makes use of extreme short impulses, CDM profits from several light pulses that form a code. This leads to an improved signal-to-noise ration (SNR) of the measurement. Optical CDM, applied in this work, is realized with the aid of a transmitter and a receiver modulator. Those provide the required optical correlation. In this paper the non-ideal optical correlation is studied when imperfect modulators are utilized. Despite of non-ideal components our theoretical approach, computer simulations and measurements outline that CDM interrogation of spectrally overlapping FBGs is robust and applicable. Scaling effects based on the extinction of both modulators and an error introduced particularly by an offset of the transmitter modulator are pointed out.

The multiple-input multiple-output (MIMO) technology has attracted a lot of interest in the optical fiber community: MIMO allows higher data rates with no loss regarding bandwidth and transmit power. The inherent interferences within a MIMO system call for appropriate signal processing strategies. Polynomial schemes such as polynomial matrix singular value decomposition (PMSVD) have attracted the research interest since they do not require any block transmission compared with schemes such as spatio-temporal vector coding (STVC). In comparison to SVD-based STVC schemes, where the whole MIMO system is transferred into a number frequency non- selective non-interfering single-input single-output (SISO) systems, PMSVD transfers the MIMO system into independent SISO layers exhibiting a frequency-selective characteristic. In this work optimal power allocation solutions in PMSVD-assisted optical MIMO systems with layer-based zero-forcing equalization are investigated. As shown by our computer simulations and testbed measurements, optimal power allocation (PA) leads to the best BERs at the cost of a high complexity compared to suboptimal PA solutions. However, as highlighted by our simulation results, suboptimal PA schemes seem to be a good alternative for achieving nearly optimum bit-error rate (BER) at a significantly lower complexity.

The multiple-input multiple-output (MIMO) concept is of high interest in fiber-optic communication since it is able to overcome the capacity limits of current transmission systems. In this work different receiver-side interference compensation techniques are studied in a spatially multiplexed fiber-optic transmission through 0.5 km multi-mode fiber with a gross bit-rate of 5 Gbps using intensity modulation and direct detection. Broadband successive interference cancellation (SIC) and broadband zero forcing (ZF) equalization are compared as electronic interference compensation methods in a (2×2) MIMO transmission. The results show that ordered SIC can significantly improve the transmission quality compared to the ZF equalization approach in the studied testbed configuration. Also, spatial filtering as an interference reduction technique is studied with respect to its effect on the bit-error rate (BER) performance, showing that in the analyzed channel scenario the use of such a filter is beneficial. Using a spatial filter improves the mode group separation at the receiver and hence reduces the MIMO signal processing complexity.

Interference in frequency-selective multiple-input multiple-output (MIMO) systems can be removed by applying a block-transmission description based on spatio-temporal vector coding and using singular value decomposition (SVD). In this contribution a newly developed SVD algorithm for polynomial matrices (PMSVD) is analyzed and compared to the commonly used SVD-based MIMO equalization. Since the PMSVD processing results in independent single-input single-output layers exhibiting a frequency-selective characteristic, a simple zero forcing equalizer or an optimal Viterbi detector is applied in this work so as to remove the occurring inter-symbol interferences. The PMSVD orthogonalization is compared with the conventional SVD in terms of the achievable spectral efficiencies, showing that there is no loss applying PMSVD over SVD processing. In addition, the bit-error rate performances in different channel scenarios are evaluated and optimized by applying combined bit and power allocation schemes. One scenario involves the measured specific impulse responses of a (2×2) optical MIMO channel, consisting of a 1.4 km multi-mode fiber, optical fusion couplers for mode multiplexing and demultiplexing when operating at a wavelength of 1576 nm. The computer simulation results show that the PMSVD could be an alternative signal processing method compared to conventional SVD-based approaches in frequency-selective MIMO channels.

Within the last years the multiple-input multiple-output (MIMO) technology has revolutionized the optical fiber community. Theoretically, the concept of MIMO is well understood and shows some similarities to wireless MIMO systems. Interference in frequency-selective MIMO systems, also known as broadband MIMO systems, can be removed by applying a spatio-temporal vector coding (STVC) channel description and using singular value decomposition (SVD) in combination with signal pre- and post-processing. In this contribution a newly developed SVD algorithm for polynomial matrices (PMSVD) is analyzed and compared to the commonly used SVD-based STVC. The PMSVD is implemented by an iterative polynomial matrix eigenvalue decomposition (PEVD) algorithm, namely the second order sequential best rotation algorithm (SBR2). The bit-error rate (BER) performance is evaluated and optimized by applying bit and power allocation schemes. For our simulations, the specific impulse responses of the (2×2) MIMO channel, including a 1.4 km multi-mode fiber and optical couplers at both ends, are measured for the operating wavelength of 1576 nm. The computer simulation results show that the PMSVD could be an alternative signal processing approach compared to conventional SVD-based MIMO approaches in frequency-selective MIMO channels.

Optical multiple-input multiple-output (OMIMO) system has attracted a deep research interest during the past decade. This contribution presents a linear simulation model for OMIMO. The model sequentially propagates the transmitted signal through the components of an optical link and considers chromatic and modal dispersion as well as modal cross-coupling in a serial manner. The OMIMO system is partitioned into a certain number of segments from transmitter to receiver. Within each segment chromatic and modal modal dispersion is considered whereas modal crosstalk appears at the crossover between two segments. The calculation model resolves all linearly polarized (LP) modes of the used fiber, which is shown by comparing impulse responses between testbed measurements and its simulation.

Singular-value decomposition (SVD) is well-established in multiple-input multiple-output (MIMO) signal processing where a broadband MIMO channel is transformed into a number of weighted single-input single-output (SISO) channels. However, applying SVD to frequency-selective MIMO channels results in unequally weighted SISO channels requiring complex resource allocation techniques for optimizing the channel performance. Therefore, a different approach utilizing polynomial matrix singular-value decomposition (PMSVD) for removing the MIMO interference is studied, outperforming conventional SVD-based MIMO systems in the analyzed channel scenarios. As shown by the bit-error rate (BER) simulation results as well as the obtained spectral efficiencies, the proposed PMSVD-based solution seems to be a good alternative to conventional SVD-based MIMO systems.

Quality requirements are an often neglected part of requirements engineering. If specified at all, they tend to be either too abstract or very technical and without a rationale. In this paper, we evaluate a quality requirements approach, which makes use of activity-based quality models. To this end, we conduct a comparative case study at Siemens in which we compare the requirements resulting from applying our quality model with the requirements previously used in the same environment. The results indicate an improvement of the requirements regarding, e.g., structured ness and trace ability, but also that the productivity perceived by the industry participants could not be increased. The study thus gives first insights into strengths and limitations of using a quality model in an industrial requirements engineering process.

GaAs-based edge-emitting diode lasers designed for the near-infrared spectral region usually contain waveguide and cladding layers consisting of Al x Ga 1−x As. Al x Ga 1−x As-on-GaAs is known to be almost perfectly lattice matched. We have grown Al x Ga 1−x As y P 1−y /Al x Ga 1−x As test samples targeting a partial compensation of the room temperature wafer bow by incorporating up to 4% phosphorus in Al 0.85 GaAs. The proposed strain compensation scheme has been applied in complete laser devices by partially replacing Al 0.85 Ga 0.15 As with Al 0.85 Ga 0.15 As y P 1−y . The results will be discussed.

Published software quality models either provide abstract quality attributes or concrete quality assessments. There are no models that seamlessly integrate both aspects. In the project Quamoco, we built a comprehensive approach with the aim to close this gap. For this, we developed in several iterations a meta quality model specifying general concepts, a quality base model covering the most important quality factors and a quality assessment approach. The meta model introduces the new concept of a product factor, which bridges the gap between concrete measurements and abstract quality aspects. Product factors have measures and instruments to operationalise quality by measurements from manual inspection and tool analysis. The base model uses the ISO 25010 quality attributes, which we refine by 200 factors and 600 measures for Java and C# systems. We found in several empirical validations that the assessment results fit to the expectations of experts for the corresponding systems. The empirical analyses also showed that several of the correlations are statistically significant and that the maintainability part of the base model has the highest correlation, which fits to the fact that this part is the most comprehensive. Although we still see room for extending and improving the base model, it shows a high correspondence with expert opinions and hence is able to form the basis for repeatable and understandable quality assessments in practice., Comment: 10 pages, 2 figures, Proc. 34th International Conference on Software Engineering (ICSE'12). IEEE, 2012

In this contribution a coherent (2×2) (multiple input multiple output) MIMO transmission with iterative detection over a measured multimode fiber channel is studied. Extrinsic information transfer (EXIT) charts are used for analyzing and optimizing the convergence behaviour of the iterative demapping and decoding. The results show BER and energy-per-bit improvements when using optimized MIMO transmission as compared to conventional (single input single output) SISO transmission techniques.

In vivo determination of tissue optical properties (OP) is still a challenging aspect in the field of optical diagnostics. This paper describes the calibration of an optical fiber sensor that uses laser diodes (LD) of different wavelengths for spatially resolved reflectance measurements.

In this paper the low pressure response and resolution of a temperature compensated miniature all-glass Fibre Optic Pressure Sensor (FOPS) is evaluated. The active temperature compensation of a diaphragm based all-silica Extrinsic Fabry Perot Interferometric (EFPI) FOPS is established by encapsulating a Fibre Bragg Grating (FBG) within the EFPI cavity. The evaluation is performed by using an extended White Light Interrogation (WLI) system. Due to its several advantages the reported FOPS has already been successfully applied in measuring pressure in an exhaust system of a vehicle as well as in a simulated geothermal well.

Self-organized quantum dots (QDs) demonstrated recently their excellent capability for compact electrically driven single and entangled photon sources [1]. Electrical pumping of single QDs embedded in pin-diode structures poses two main challenges: The first is the control of the current path in a way that only one QD is pumped, and the second is to assure that the QD is equally filled by electrons and holes to achieve emission from uncharged excitons. Thus the uncharged biexciton-exciton decay cascade can be used for the creation of entangled photon pairs (provided the fine-structure splitting (FSS) is small enough) or single polarized photons (for large FSS), prerequisite for the BB84 protocol. The second key specification of single photon sources for the realization of a quantum cryptography system is a high repetition rate and a low fraction of empty pulses. The repetition rate in QD based single photon sources is limited by the exciton life time and the parasitic electrical bandwidth of the device, whereas the number of empty pulses is mainly controlled by the out-coupling efficiency.

A fibre-cavity design based on highly reflective gold coatings, vapor-deposited to the two end faces of a large core multimode waveguide, is presented. In contrast to common fibre-cavity approaches, the laser pulses are not coupled through the reflective coatings into the cavity but through a micro hole in one of the fibre end faces, which reduces the commonly very high coupling loss to less than 1%. Accordingly, lower demands on the source power and the sensitivity of the receiver circuit result in lower costs of ring-down sensor approaches. An estimate of the ringdown time constant of the fibre-cavity is given and the influence of the micro-hole on the reflection loss is discussed.

This paper presents the findings of a survey on quality models in practice conducted among four software companies in Germany. In the first phase of the study, 25 quality managers and users of software quality models were interviewed regarding the use of quality models, quality assurance techniques, and problems arising from the current situation in their companies. We present qualitative and quantitative findings as well as our plans for the second study phase including an international online questionnaire.

There is a great number of platforms and security protocols which can be used for wireless sensor networks (WSN). All these platforms and protocols have different properties with certain advantages and disadvantages. For a good choice of platform and an associated protocol, these advantages and disadvantages should be compared and the best for the appropriate WSN chosen. To select a Security protocol and a wireless platform suitable for a specific application a software tool will be developed. That tool will enable wireless network deployment engineers to easily select a suitable wireless platform for their application based on their network needs and application security requirements.

In this poster, we present our outdoor AR game MoleARlert. The idea behind this research prototype was to exploit the enormous potential of AR in combination with classical game play based on the well-known game Lemmings by Psygnosis [2]. Real players interact with virtual moles on a real playing field. The moles are guided through the harzardous environment to their final goal. The multiplayer game is observered through a stationary video see-through monitor. The team leader directs the real players around the field in order for them to steer the game with special markers and human gestures. Thus, the game requires a lot of action from players and is very entertaining.

A novel fibre-cavity design based on highly reflective gold coatings, vapor-deposited to the two end faces of a 400um multimode waveguide, is presented. In contrast to common passive fibre-cavity approaches, the laser pulses are not coupled through the reflective coatings into the cavity but through a micro hole in one of the fibre end faces, which reduces the coupling losses from generally almost 100% to less than 1%. An OTDR-graph is presented as proof of principle and the influence of the cross section ratio of the remaining reflective area after milling and the overall fibre core cross section is theoretically evaluated.

A fibre-optic fluid concentration sensor based on refractive index measurements is reported. Its working principle is validated for some simple aqueous primary alcohol mixtures, such as Acetone, Ethanol, Methanol, 1-Propanol, and 2-Pro-panol, covering a concentration range from 0%vol to 10%vol. With a simple and low cost LED based measurement setup a resolution of about 0.00005 refractive index units was achie-ved, which approximately corresponds to 0.2% methanol, 0.75% ethanol and acetone, and 0.05% 1-propanol and 2-propanol. Moreover, described sensing method is applicable for all fluids that show different refractive indices at different concentrations, which by far is the case for almost all fluids, since the refractive index of a mixture is related to its density.

A micro diaphragm-based Extrinsic Fabry-Perot Interferometric (EFPI) pressure sensor with high temperature immunity is described. The EFPI pressure sensor consists of a single mode silica glass optical fiber, a glass capillary and a glass diaphragm, which are fused together using a conventional fusion splicer. This eliminates the need for the use of other joining materials, e.g. epoxy, allows any thermal mismatch between different materials to be almost completely eliminated and hence the sensor is capable of high temperature operation. In addition, the EFPI pressure sensor is cheap and relatively easy to produce as only splicing, polishing and wet etching are necessary. Moreover, due to its small size, a frequency response of several MHz can be achieved

Advances in wireless sensor networks (WSN) have opened up new opportunities and many applications. To achieve security in these kinds of networks, it is important to encrypt messages. This requires the use of key distribution protocols. Due to resource constraints, achieving such key distribution in WSN's is not trivial. We evaluate deterministic, probabilistic and hybrid key distribution algorithms for distributing pairwise, group wise and network wise keys.