Institute of Telecommunications

Vienna, Austria

Institute of Telecommunications

Vienna, Austria
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Koliander G.,Institute of Telecommunications | Pichler G.,Institute of Telecommunications | Hlawatsch F.,Institute of Telecommunications
IEEE Transactions on Information Theory | Year: 2016

Entropy and differential entropy are important quantities in information theory. A tractable extension to singular random variables-which are neither discrete nor continuous-has not been available so far. Here, we present such an extension for the practically relevant class of integer-dimensional singular random variables. The proposed entropy definition contains the entropy of discrete random variables and the differential entropy of continuous random variables as special cases. We show that it transforms in a natural manner under Lipschitz functions, and that it is invariant under unitary transformations. We define joint entropy and conditional entropy for integer-dimensional singular random variables, and we show that the proposed entropy conveys useful expressions of the mutual information. As first applications of our entropy definition, we present a result on the minimal expected codeword length of quantized integerdimensional singular sources and a Shannon lower bound for integer-dimensional singular sources. © 2016 IEEE.


Lateral photonic integration of oxide-confined leaky vertical-cavity surface-emitting lasers enables their application in data communications and sensing. Vertical-cavity surface-emitting lasers (VCSELs) that operate at 850nm and are based on oxide-confined apertures are widely used in optical interconnects in data centers, supercomputers, wireless backbone networks, and consumer applications.1 As the processor productivity in these applications increases, it is necessary to continuously improve performance and scale transmission speeds accordingly. In recent years, developers have produced a generation of devices capable of transmitting 40Gb/s at moderate current densities,2, 3 and they have recently demonstrated 54Gb/s non-return-to-zero transmission through 2.2km of multimode fiber.4 Now, 108Gb/s per wavelength transmission can be realized over 100–300m of multimode fiber through the use of advanced modulation formats: discrete multi-tone,5 multiCAP,6 and PAM4.7 All of these achievements are made possible through the use of VCSELs operating in a single transverse and longitudinal mode (SM VCSELs). When manufacturing SM VCSELs, developers typically make the oxide aperture in a VCSEL very small (around 2–3μm in diameter). This approach, however, may result in very low optical power, high resistance, and low manufacturing yield. To extend single-mode behavior toward more conventional aperture sizes (5–7μm), several alternative approaches have been proposed, including surface patterning, etching, overgrowth, and ion implantation in combination with photonic crystals.8, 9 These approaches require additional processing steps that must be precisely aligned (oxide aperture and surface pattern). The resulting complexity can reduce the yield and increase the cost of manufacturing. Our approach uses oxide-confined leaky VCSELs, which—through the application of proper epitaxial design—enable the generation of high optical leakage losses for high-order transverse modes. Using these devices, we extend the single-mode behavior of the laser toward large oxide aperture diameters. With our approach, we aim to create an additional cavity at a wavelength longer than the VCSEL cavity mode. Upon oxidation, the relative intensity distribution of the optical field between the coupled cavities can be strongly affected in the oxidized section. This induces a break in the orthogonality of the VCSEL mode and the second cavity mode (when at a certain tilt angle), which enables in-plane leakage to occur. High-order modes with the field intensity maxima close to the oxide periphery have thus much higher leakage losses.10 We have designed and manufactured oxide-confined leaky VCSELs and observed their leakage process through tilted narrow lobes in the far-field spectrum. The emission comes from the area outside the aperture, and thus does not suffer from diffraction-induced broadening. To model the VCSELs in 3D, we applied finite element analysis based on Maxwell's vector equations in a rotational symmetric system.11 Figure 1 shows a cross section of the simulated electric field of the fundamental and first excited optical modes of an oxide-confined aluminum gallium arsenide-based leaky VCSEL. A simulated far-field profile of the excited mode can be seen in Figure 2. The simulations show that the leakage effect results in a specific tilted emission over the VCSEL surface at ∼35–37°. Most of the intensity of the leaking light is channeled in the direction parallel to the surface. Figure 1. Radial distribution of the simulated electric field of oxide-confined leaky vertical-cavity surface-emitting laser (VCSEL) optical modes. (a) Fundamental optical mode. (b) First excited mode. An active region (magenta line) placed within the cavity is confined by aluminum gallium arsenide distributed Bragg reflectors. The structure contains oxide apertures (white lines). A semiconductor-air interface is shown as a dotted line in the figure. arb. u.: Arbitrary units. Figure 2. Far-field profile simulation of the excited VCSEL mode presented in Figure 1. We manufactured and tested VCSELs according to our design. The far-field measurements of the devices at two current densities can be seen in Figure 3, which shows that at high current densities during multimode operation, narrow lobes arise at ∼35° angles. These lobes are related to the leakage process (see Figure 2). Figure 3. Far-field profiles of a leaky VCSEL operating in fundamental mode (blue, 10kA/cm2) and multi-mode (red, >25kA/cm2). Electroluminescence spectra of the leaky VCSEL at different current densities are shown in Figure 4. We concluded that the VCSEL was predominantly single mode at all the current densities examined, despite the relatively large aperture diameter (5μm). In contrast, the non-leaky VCSEL with thick oxide apertures was heavily multimode, with the excited modes dominant even at small current densities.12 Figure 4. Electroluminescence spectra of an oxide leaky VCSEL with a 5μm aperture. The graph shows dominance of the fundamental mode up to high currents (5.5mA, red). Insert: An optical eye diagram (PRBS7) at 32Gb/s. To summarize, we have shown that it is possible to significantly improve VCSEL spectral quality without involving any additional processing steps. Furthermore, we confirmed the occurrence of in-plane leakage through leakage lobes in the far-field profile of the device. Our findings create opportunities for engineering photonic integrated circuits, for example, by coherent coupling of two or more devices. Therefore, it may be possible to use the technique for beam steering.13 By operating one VCSEL in a couple under reverse bias, it is possible to realize an on-chip integrated monitor photodiode, thus drastically reducing the cost of packaging (since fewer of the elements require alignment and assembly). Our future work will focus on optimization of the leakage effect in order to manufacture high- power and high-speed single-mode VCSELs. This project received funding from the European Union's Horizon 2020 research and innovation program under grant 666866. VI Systems GmbH Nikolay Ledentsov Jr. received his MSc in physics at the Technical University of Berlin while developing indium gallium arsenide-based LEDs. At VI Systems he is responsible for the design and numerical simulation of optoelectronic devices, and operates an automated testbed for spectral and high-speed characterization. Vitaly Shchukin received a diploma in physics and engineering in the field of semiconductor physics from St. Petersburg State Polytechnical University, St. Petersburg, Russia, and a PhD (1987) and doctor of science (1999) in physics and mathematics from the Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg. He is co-author of more than 190 published papers, and holds 22 patents and a monograph. Joerg Kropp holds a doctor of science in the field of atomic physics with optical spectroscopy and laser applications. He has more than 25 years' experience in industry in the field of optical communications through management positions with Siemens and Infineon. Mikel Agustin received a diploma in telecommunications engineering from the Public University of Navarra, Spain, and completed his education at the Institute of Telecommunications, Warsaw University of Technology, Poland. At VI Systems he is responsible for developing energy-efficient ultrafast vertical-cavity surface-emitting lasers and photodetectors. Nikolay N. Ledentsov received a diploma in electrical engineering from the Electrical Engineering Institute in Leningrad (LETI, now Electrotechnical University, St. Petersburg, Russia) in 1982. He obtained his PhD (1987) and doctor of science (1994) in physics and mathematics from the Ioffe Physical-Technical Institute. He has been professor of electrical engineering at LETI since 1994 and professor of physics and mathematics at the Ioffe Physical-Technical Institute since 2005. 1. T. R. Fanning, J. Wang, Z.-W. Feng, M. Keever, C. Chu, A. Sridhara, C. Rigo, et al., 28-Gbps 850-nm oxide VCSEL development and manufacturing progress at Avago, Proc. SPIE 9001, p. 900102, 2014. doi:10.1117/12.2039499 3. S. A. Blokhin, J. A. Lott, A. Mutig, G. Fiol, N. N. Ledentsov, M. V. Maximov, A. M. Nadtochiy, V. A. Shchukin, D. Bimberg, 850nm VCSELs operating at bit rates up to 40Gbit/s, Electron. Lett. 45, p. 501-503, 2009. 4. G. Stepniak, A. Lewandowski, J. R. Kropp, N. N. Ledentsov, V. A. Shchukin, N. Ledentsov, G. Schaefer, M. Agustin, J. P. Turkiewicz, 54 Gbit/s OOK transmission using single-mode VCSEL up to 2.2km MMF, Electron. Lett. 52, p. 633-635, 2016. 5. B. Wu, X. Zhou, Y. Ma, J. Luo, K. Zhong, S. Qiu, Z. Feng, et al., Close to 100 Gbps discrete multitone transmission over 100m of multimode fiber using a single transverse mode 850nm VCSEL, Proc. SPIE 9766, p. 97660K, 2016. doi:10.1117/12.2208901 6. R. Puerta, M. Agustin, L. Chorchos, J. Tonski, J.-R. Kropp, N. Ledentsov, V. A. Shchukin, et al., 107.5Gb/s 850nm multi- and single-mode VCSEL transmission over 10 and 100m of multi-mode fiber, OSA Opt. Fiber Commun. Conf. Th5B, p. Th5B.5, 2016. 7. G. Stepniak, L. Chorchos, M. Agustin, J.-R. Kropp, N. N. Ledentsov, V. A. Shchukin, N. N. Ledentsov, J. P. Turkiewicz, Up to 108Gb/s PAM 850nm multi and single mode VCSEL transmission over 100m of multi mode fiber, 2016. Paper accepted at the 42nd Euro. Conf. Opt. Commun. in Düsseldorf, 18-22 September 2016. 8. E. Haglund, A. Haglund, J. Gustavsson, B. Kögel, P. Westbergh, A. Larsson, Reducing the spectral width of high speed oxide confined VCSELs using an integrated mode filter, Proc. SPIE 8276, p. 82760L, 2012. doi:10.1117/12.908424 10. V. Shchukin, N. N. Ledentsov, J. Kropp, G. Steinle, N. Ledentsov, S. Burger, F. Schmidt, Single-mode vertical cavity surface emitting laser via oxide-aperture-engineering of leakage of high-order transverse modes, IEEE J. Quantum Electron. 50, p. 990-995, 2014. 11. N. Ledentsov, V. A. Shchukin, N. N. Ledentsov, J.-R. Kropp, S. Burger, F. Schmidt, Direct evidence of the leaky emission in oxide-confined vertical cavity lasers, IEEE J. Quantum Electron. 52, p. 1-7, 2016. 12. N. N. Ledentsov, J. Xu, J. A. Lott, Future Trends in Microelectronics: Frontiers and Innovations, ch. Ultrafast nanophotonic devices for optical interconnects, Wiley, 2013. doi:10.1002/9781118678107.ch11


Choras M.,Institute of Telecommunications
Pattern Analysis and Applications | Year: 2010

In many cases human identification biometric systems are motivated by real-life criminal and forensic applications. One of the most interesting emerging method of human identification, which originates from the criminal and forensic practice, is human lips recognition. In this paper we consider lips shape and color features in order to determine human identity. We present standard and original geometrical parameters used in lips biometric system. Moreover Zernike and Hu moments as well as color features have been used. The presented results are yet not as good as these achieved in other known biometric systems. However, we believe that both lips biometrics as well as our approach and results, are worth to be presented to a wide research community. © Springer-Verlag London Limited 2009.


Choras M.,ITTI Ltd. | Choras M.,Institute of Telecommunications | Kozik R.,ITTI Ltd. | Kozik R.,Institute of Telecommunications
Communications in Computer and Information Science | Year: 2011

In this paper we present semantic approach to network event correlation for large-scale federated intrusion detection system. The major contributions of this paper are: network event correlation mechanism and semantic reasoning based on the ontology. Our propositions and deployments are used in Federated Networks Protection System as a part of the Decision Module. © 2011 Springer-Verlag.


Borowik G.,Institute of Telecommunications | Luba T.,Institute of Telecommunications | Tomaszewicz P.,Institute of Telecommunications
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

The paper presents logic synthesis method targeted at FPGA architectures with specialized embedded memory blocks (EMB). Existing tools/compilers treat ROM modules described in HDLs as indivisible entities and in consequence do not ensure effective utilization of the possibilities provided by such modules. In order to address this problem effectively we propose applying functional decomposition. The main contribution is based on the use of r-admissibility measure to guide decomposition structures for ROM-based synthesis. © 2012 Springer-Verlag.


Choras M.,Institute of Telecommunications
Advances in Intelligent Systems and Computing | Year: 2013

In this paper an overview of image processing methods for feature extraction applied to knuckle biometrics also termed as FKP (finger-knuckle-print) is presented. Knuckle is a part of hand, and therefore, is easily accessible, invariant to emotions and other behavioral aspects (e.g. tiredness) and most importantly is rich in texture features which usually are very distinctive. In this paper a short overview of the known recent approaches to human identification on the basis of knuckle images is given. © Springer International Publishing Switzerland 2013.


Dobos J.,Pan European University | Rakus M.,Institute of Telecommunications
Current Issues of Science and Research in the Global World - Proceedings of the International Conference on Current Issues of Science and Research in the Global World | Year: 2015

In digital transmission and storage systems, Error-Control Codes (ECC) provide a security mechanism allowing the detection and correction of a certain amount of errors, which can be caused by the presence of noise in these systems. ECC are denoted as [n, k, dmin], where “n” denotes the codeword length, “k” number of information symbols and “dmin” is the minimum code distance. The minimum code distance determines the error correction/ detection capabilities of a given code. Theoretically computed bounds of minimum code distance for many ECC have been found but to find generator matrices for many codes reaching theoretical bounds still remains a research problem. The presented paper describes an improved version of a proposed algorithm used for searching for the generator matrices of binary ECC. The described algorithm is based on an alteration of generator matrices of already found ECC. The presented algorithm reduces the total amount of tests required by the basic algorithm in order to reduce the execution time of the whole search process. The final part of this paper compares the execution time and memory requirements of the basic and improved version of the search algorithm. © 2015 Taylor & Francis Group, London.


Kozik R.,Institute of Telecommunications
Advances in Intelligent Systems and Computing | Year: 2014

In this article a simplified model of biologically inspired mechanisms for an object recognition is presented. The proposed approach is based on the HMAX hierarchical cortex model that was proposed by Riesenhuber and Poggio [1] and later extended by Serre et al [2]. The work described in this paper is an extension of a previous research [3, 4, 5, 6] focused on a computer vision software (named SMAS - Stereovision Mobility Aid System) dedicated for visually impaired persons. Therefore, the emphasis here is put on a one-class detection problem of dangerous objects with the possibility of a future deployment of the proposed solution on a mobile device. The conducted experiments show that the introduced modifications of the hierarchical HMAX model allows for an efficient feature extraction and a visual information coding without decreasing the effectiveness of an object detection process. © Springer International Publishing Switzerland 2014.


Kozik R.,Institute of Telecommunications | Choras M.,Institute of Telecommunications | Choras M.,ITTI Ltd
Advances in Intelligent Systems and Computing | Year: 2014

The increased usage of cloud services, growing number of users, changes in network infrastructure that connect devices running mobile operating systems, and constantly evolving network technology cause novel challenges for cyber security that have never been foreseen before. As a result, to counter arising threats, network security mechanisms, sensors and protection schemes have also to evolve in order to address the needs and problems of nowadays users. © Springer International Publishing Switzerland 2014.


Choras M.,Institute of Telecommunications | Kozik R.,Institute of Telecommunications
Pattern Analysis and Applications | Year: 2012

In this paper, biometric methods for contactless and unrestricted access control for mobile devices are proposed. The major contribution of this paper are palmprint and knuckles feature extraction methods dedicated for the mobile contactless biometrics. We use texture mask-based features for the palmprint. For the knuckles, we use Probabilistic Hough Transform and Speeded Up Robust Features as well as the 3-step classification methodology. We prove the efficiency of the presented methods by reporting promising results. © 2011 The Author(s).

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