Browsing by Subject "Optical communication"

Now showing 1 - 20 of 23

Open Access
45 GHz bandwidth-efficiency resonant cavity enhanced ITO-Schottky photodiodes
(OSA, 2001) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Özbay, Ekmel; Gökkavas, M.; Ünlü, M. S.
We demonstrated high-performance resonant cavity enhanced ITO-Schottky photodiodes. We achieved a peak efficiency of 75% around 820 nm with a 3-dB bandwidth of 60 GHz resulting in a bandwidth-efficiency product of 45 GHz.
Open Access
Adaptive and efficient nonlinear channel equalization for underwater acoustic communication
(Elsevier B.V., 2017) Kari, D.; Vanli, N. D.; Kozat, S. S.
We investigate underwater acoustic (UWA) channel equalization and introduce hierarchical and adaptive nonlinear (piecewise linear) channel equalization algorithms that are highly efficient and provide significantly improved bit error rate (BER) performance. Due to the high complexity of conventional nonlinear equalizers and poor performance of linear ones, to equalize highly difficult underwater acoustic channels, we employ piecewise linear equalizers. However, in order to achieve the performance of the best piecewise linear model, we use a tree structure to hierarchically partition the space of the received signal. Furthermore, the equalization algorithm should be completely adaptive, since due to the highly non-stationary nature of the underwater medium, the optimal mean squared error (MSE) equalizer as well as the best piecewise linear equalizer changes in time. To this end, we introduce an adaptive piecewise linear equalization algorithm that not only adapts the linear equalizer at each region but also learns the complete hierarchical structure with a computational complexity only polynomial in the number of nodes of the tree. Furthermore, our algorithm is constructed to directly minimize the final squared error without introducing any ad-hoc parameters. We demonstrate the performance of our algorithms through highly realistic experiments performed on practical field data as well as accurately simulated underwater acoustic channels. © 2017 Elsevier B.V.
Open Access
Comparison of local and global computation and its implications for the role of optical interconnections in future nanoelectronic systems
(Elsevier, 1993) Özaktaş, Haldun M.; Goodman J. W.
Various methods of simulating diffusion phenomena with parallel hardware are discussed. In particular methods are compared requiring local and global communication among the processors in terms of total computation time. Systolic convolution on a locally connected array is seen to exhibit an asymptotic advantage over Fourier methods on a globally connected array. Whereas this may translate into a numerical advantage for extremely large numbers of ultrafast devices for two-dimensional systems, this is unlikely for three-dimensional systems. Thus global Fourier methods will be advantageous for three-dimensional systems for foreseeable device speeds and system sizes. The fact that optical interconnections are potentially advantageous for implementing the longer connections of such globally connected systems suggests that they can be beneficially employed in future nanoelectronic computers. Heat removal considerations play an important role in our conclusions.
Open Access
Complex signal recovery from two fractional Fourier transform intensities: order and noise dependence
(Elsevier, 2005-01) Ertosun, M. G.; Atlı, H.; Özaktaş, Haldun M.; Barshan, B.
The problem of recovering a complex signal from the magnitudes of two of its fractional Fourier transforms is addressed. This corresponds to phase retrieval from the transverse intensity profiles of an optical field at two arbitrary locations along the optical axis. The convergence of the iterative algorithm, the effects of noise or measurement errors, and their dependence on the fractional transform order are investigated. It is observed that in general, better results are obtained when the fractional transform order is close to unity and poorer results are obtained when the order is close to zero. It follows that to the extent that conditions allow, the fractional order between the two measurement planes should be chosen as close to unity (or other odd integer) as possible for best results.
Open Access
Design of translucent optical networks: Partitioning and restoration
(Kluwer, 2004) Karasan, E.; Arisoylu, M.
We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We develop an integer linear programming (ILP) formulation for partitioning an optical network topology into subnetworks, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations, and it is two-connected. A greedy heuristic partitioning algorithm is proposed for planar network topologies. We use section restoration for translucent networks where failed connections are rerouted within the subnetwork which contains the failed link. The network design problem of determining working and restoration capacities with section restoration is formulated as an ILP problem. Numerical results show that fiber costs with section restoration are close to those with path restoration for mesh topologies used in this study. It is also shown that the number of transponders with the translucent network architecture is substantially reduced compared to opaque networks.
Open Access
Differentiated ABR: a new architecture for flow control and service differentiation in optical burst switched networks
(IEEE, 2005) Akar, Nail; Boyraz, Hakan
In this paper, we study a new control plane protocol, called Differentiated ABR (D-ABR), for flow control and service differentiation in optical burst switched networks. Using D-ABR, we show using simulations that the optical network can be designed to work at any desired burst blocking probability by the flow control service of the proposed architecture. This architecture requires certain modifications to the existing control plane mechanisms as well as incorporation of certain scheduling mechanisms at the ingress nodes; however we do not make any specific assumptions on the data plane for the optical core nodes. Moreover, with this protocol, it is possible to almost perfectly isolate high priority and low priority traffic throughout the optical network as in the strict priority-based service differentiation in electronically switched networks.
Open Access
Dual-frequency division de-multiplexer based on cascaded photonic crystal waveguides
(Elsevier, 2012-02-28) Akosman, Ahmet E.; Mutlu, Mehmet; Kurt, H.; Özbay, Ekmel
A dual-frequency division de-multiplexing mechanism is demonstrated using cascaded photonic crystal waveguides with unequal waveguide widths. The de-multiplexing mechanism is based on the frequency shift of the waveguide bands for the unequal widths of the photonic crystal waveguides. The modulation in the waveguide bands is used for providing frequency selectivity to the system. The slow light regime of the waveguide bands is utilized for extracting the desired frequency bands from a wider photonic crystal waveguide that has a relatively larger group velocity than the main waveguide for the de-multiplexed frequencies. In other words, the wider spatial distribution of the electric fields in the transverse direction of the waveguide for slow light modes is utilized in order to achieve the dropping of the modes to the output channels. The spectral and spatial de-multiplexing features are numerically verified. It can be stated that the presented mechanism can be used to de-multiplex more than two frequency intervals by cascading new photonic crystal waveguides with properly selected widths.
Open Access
High-performance 1.55 μm resonant cavity enhanced photodetector
(IEEE, 2002) Kimukin, İbrahim; Bıyıklı, Necmi; Özbay, Ekmel
A high speed and high efficiency resonant cavity enhanced InGaAs based photodetector was demonstrated. A peak quantum efficiency of 66% was measured along with 31 GHz bandwidth with the device. The photoresponse was found to be linear upto 6 mW optical power, where the device 5 mA photocurrent.
Open Access
High-speed 1.3 μm GaAs internal photoemission resonant cavity enhanced photodetector
(IEEE, 2000) Kimukin, İbrahim; Özbay, Ekmel; Bıyıklı, Necmi; Kartaloğlu, Tolga; Aytür, Orhan; Tuttle, G.
Resonant cavity enhanced (RCE) photodetectors offer the possibility of overcoming the low quantum efficiency limitation of conventional photodetectors. The RCE detectors are based on the enhancement of the optical field within a Fabry-Perot resonator. The increased field allows the use of a thin absorbing layer, which minimizes the transit time of the photogenerated carriers without hampering the quantum efficiency. Recently, we fabricated high-speed RCE p-i-n and Schottky photodetectors, where a 90% quantum efficiency along with a 3-dB bandwidth of 50 GHz has been reported. We used the transfer matrix method to design the epilayer structure and to simulate the optical properties of the photodiode. The samples were fabricated by a microwave-compatible process and high-speed measurements were made with an optical parametric oscillator.
Open Access
High-speed resonant-cavity-enhanced Schottky photodiodes
(IEEE, 1998) Ata, Erhan P.; Bıyıklı, Necmi; Demirel, Ekrem; Özbay, Ekmel; Gökkavas, M.; Onat, B.; Ünlü, M. S.; Tuttle, G.
The top-illuminated Schottky photodiodes were fabricated by a microwave-compatible monolithic microfabrication process. Fabrication started with formation of ohmic contacts to n+ layers. Mesa isolation was followed by a Ti-Au interconnect metallization. Following this, a semitransparent Au Schottky metal and a silicon nitride layer was deposited. Finally, a thick Ti-Au layer was deposited to form an air bridge connection between the interconnect and the Schottky metal. The optical properties of the photodiodes were simulated using a transfer matrix method.
Open Access
Homodyne detection of multimode optical signals
(1991) Haq, Mujtaba Fidaul
The feasibility of coherent hoinodyne detection for multimode optical sources is experimentally investigated. By employing the self-homodyne detection, it is observed that a considerable amount of mixing can take place between the signal and local oscillator fields despite the relatively small coherence length of multimode lasers. The experiment was carried out using an a.ll-a.tmosplieric set-up, uecessitating a thorough calculation of power losses due to beam misahgnment. Power losses in the interference term for radial and angular misalignments were calculated for first order Gaussian beams. It is seen that radial misalignment is intolerable lor beam radii ratios smaller than 0.35 whereas angular misalignment becomes intolerable for angular deviations greater than a few tens of milli degrees.
Open Access
Maximum likelihood estimation of Gaussian mixture models using particle swarm optimization
(IEEE, 2010-08) Arı, Çağlar; Aksoy, Selim
We present solutions to two problems that prevent the effective use of population-based algorithms in clustering problems. The first solution presents a new representation for arbitrary covariance matrices that allows independent updating of individual parameters while retaining the validity of the matrix. The second solution involves an optimization formulation for finding correspondences between different parameter orderings of candidate solutions. The effectiveness of the proposed solutions are demonstrated on a novel clustering algorithm based on particle swarm optimization for the estimation of Gaussian mixture models. © 2010 IEEE.
Open Access
Optical restoration at the wavelength-multiplex-section level in WDM mesh networks
(Institute of Electrical and Electronics Engineers, 1998-09) Karasan, E.; Goldstein, E.
In the presence of rapidly growing demand, long-haul multiwavelength lightwave networks face the increasingly critical task of not only transporting large traffic volumes, but also of restoring them in the event of failures. This may be naturally done in two distinct ways: by rerouting individual wavelengths (wavelength-paths), or by rerouting full bundles of multiplexed wavelengths (wavelength-multiplex sections). We here evaluate the prospects for restoration at the wavelength-multiplex-scction level in national-scale long-haul wavelength-division-multiplexed mesh networks. The approach is found to offer the potential of substantial economic benefits, given current transponder costs. These benefits will largely vanish, however, if transponder costs decline by an order of magnitude.
Open Access
The optimal electromagnetic carrier frequency balancing structural and metrical information densities with respect to heat removal requirements
(1992) Özaktaş, Haldun M.; Goodman J.W.
The use of higher electromagnetic carrier frequencies for communication in a computing results in both increased spatial information density and larger available modulation bandwidth. However, assuming that the communication energies are dissipated, the heat that must be removed from unit volume per unit time increases quickly with higher frequencies, resulting in a maximum useful frequency based on our limited ability to remove heat. We show that this frequency is relatively insensitive to system specific parameters and estimate its order of magnitude to lie near the infrared and visible bands of the spectrum. © 1992.
Open Access
Performance of WDM transport networks
(Institute of Electrical and Electronics Engineers, 1998-08) Karasan, E.; Ayanoglu, E.
Wavelength division multiplexed point-to-point transport is becoming commonplace in wide area networks. With the expectation that the next step is end-to-end networking of wavelengths (in the optical domain without conversion to electronics), there is a need for new design techniques, a new understanding of the performance issues, and a new performance evaluation methodology in such networks. This paper describes approaches to that end, summarizes research results, and points to open problems.
Open Access
Regenerator location problem and survivable extensions: a hub covering location perspective
(Elsevier, 2015) Yıldız, B.; Karaşan, O. E.
In a telecommunications network the reach of an optical signal is the maximum distance it can traverse before its quality degrades. Regenerators are devices to extend the optical reach. The regenerator placement problem seeks to place the minimum number of regenerators in an optical network so as to facilitate the communication of a signal between any node pair. In this study, the Regenerator Location Problem is revisited from the hub location perspective directing our focus to applications arising in transportation settings. Two new dimensions involving the challenges of survivability are introduced to the problem. Under partial survivability, our designs hedge against failures in the regeneration equipment only, whereas under full survivability failures on any of the network nodes are accounted for by the utilization of extra regeneration equipment. All three variations of the problem are studied in a unifying framework involving the introduction of individual flow-based compact formulations as well as cut formulations and the implementation of branch and cut algorithms based on the cut formulations. Extensive computational experiments are conducted in order to evaluate the performance of the proposed solution methodologies and to gain insights from realistic instances.
Open Access
Research on optical core networks in the e-Photon/ONe network of excellence
(IEEE, 2006) Callegati, F.; Aracil, J.; Wosinska, L.; Andriolli, N.; Careglio, D.; Giorgetti, A.; Fdez-Palacios, J.; Gauger, C.; Klinkowski, M.; Gonzáles De Dios, O.; Hu, G.; Karasan, Ezhan; Matera, F.; Overby, H.; Raffaelli, C.; Rea, L.; Şengezer, Namık; Tornatore, M.; Vlachos, K.
This papers reports the advances in Optical Core networks research coordinated in the framework of the e-Photon/ONe and e-Photon/ONe+ networks of excellence.
Open Access
Space-bandwidth product of conventional Fourier transforming systems
(Elsevier, 1993-12-15) Özaktaş, Haldun M.; Urey, H.
It is shown that the space-bandwidth product of conventional "2f" Fourier transforming configurations can be increased without bound by increasing the diameter D and focal length fof the lens simultaneously to Docf 3/4. This results in spacebandwidth product growth ocf ~/2 and accompanying system linear extent growth ocf ~/4. These are derived by considering the validity of the Fresnel approximation, the thin lens approximation, and the effects of aberrations.
Open Access
Subnetwork partitioning and section restoration in translucent optical networks
(SPIE, 2003) Karasan, Ezhan; Arısoylu, M.
We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We formulate the problem of designing restorable subnetworks in translucent networks as an Integer Linear Programming (ILP) problem, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations and it is 2-connected. A greedy heuristic algorithm for the same problem is also proposed for planar network topologies. We propose section restoration for translucent networks where failed connections are rerouted inside the subnetwork which contains the failed link. The network design problem of determining working and restoration capacities with section restoration is formulated as an ILP problem. Numerical results show that section restoration generates fiber costs which are close to those with the path restoration technique for the mesh topologies used in this study. It is also shown that the number of transponders with the translucent optical network is substantially reduced compared to opaque networks.
Open Access
A survey on scheduling in IEEE 802.16 mesh mode
(Institute of Electrical and Electronics Engineers, 2010) Kas, M.; Yargicoglu, B.; Korpeoglu, I.; Karasan, E.
IEEE 802.16 standard (also known as WiMAX) defines the wireless broadband network technology which aims to solve the so called last mile problem via providing high bandwidth Internet even to the rural areas for which the cable deployment is very costly. The standard mainly focuses on the MAC and PHY layer issues, supporting two transmission modes: PMP (Point-to-Multipoint) and mesh modes. Mesh mode is an optional mode developed as an extension to PMP mode and it has the advantage of having an improving performance as more subscribers are added to the system using multi-hop routes. In 802.16 MAC protocol, mesh mode slot allocation and reservation mechanisms are left open which makes this topic a hot research area. Hence, the focus of this survey will mostly be on the mesh mode, and the proposed scheduling algorithms and performance evaluation methods. © 2010 IEEE.