Showing papers presented at "International Conference on Transparent Optical Networks in 2002"

Influence of temperature on birefringence and polarization mode dispersion in photonic crystal holey fibers

Abstract: Summary form only given. Applying a fully vectorial method, we calculated the dependence of modal birefringence and polarization mode dispersion upon wavelength in photonic crystal holey fibers of different structure. We also determined the sensitivities of these two parameters to temperature. Our results show that in the analyzed spectral range modal birefringence increases while polarization mode dispersion decreases with wavelength in both structures. The sensitivity of modal birefringence to temperature is positive and increases with wavelength while the sensitivity of polarization mode dispersion is negative and decreases with wavelength. The spectral behavior of both sensitivities is opposite to that observed in classical elliptical-core fibers.

An optical packet switch design with shared electronic buffering and low bit rate add/drop inputs

Abstract: An optical packet switch design using optical switching and shared electronic buffering is described and analyzed. The electronic buffering and add/drop unit allows random memory access, variable packet length, and aggregation/segregation of low bit rate streams. The design is scalable to a large number of wavelengths, and employs contention resolution by using the wavelength dimension combined with electronic buffering. The number of buffer inputs, i.e. the number of optoelectronic conversions, is minimized. The packet loss and delay performance when using fixed packet length and electronic buffering are investigated by simulation. If the link utilization is moderate, the buffering requirements becomes minimal. If number of wavelengths in the link is increased, the number of buffer inputs can be reduced. With a sufficiently high number of wavelengths, the buffer requirements is minimal, even when the link utilization is high.

A comparison of different radio over fibre system concepts with regard to applications in mobile Internet and multimedia

Abstract: The paper presents a comparison of different radio over fibre system concepts with regard to applications in broadband services transmission. Several concepts of radio over fibre systems have been studied around the world, and each of them seems to be very attractive because of low loss and extremely wide bandwidth necessary for mobile broadband services. Commercial deployment of the millimeter-wave optical links for future mobile broadband services depends on the expected full costs of the systems. The paper discusses an impact of development of new technologies on possibility of commercial deployment of the systems.

Fabrication of photonic crystal slabs and defects using laser interference lithography and focused ion beam-assisted deposition

Abstract: A method is described for fabricating photonic crystal slabs, using a combination of laser interference lithography for generating a regular periodic structure (the crystal lattice), and focused ion beam-assisted deposition for defining defects in this lattice, which may act as waveguides or resonators. As an example, results will be shown of a photonic crystal slab with a line defect in silicon nitride.

Method of single expression-advanced powerful tool for computer modelling of wavelength scale nonuniform frequency-selective 1D photonic structures

Abstract: Main principles of the method of single expression (MSE) for boundary problems solution in classical electrodynamics are presented. In the MSE the solution of the Helmholtz's equation is presented in the special form of a single expression. As a consequence, attained liberty from the obligation of the superposition principle permits to solve both linear and nonlinear problems with the same ease. In the MSE the Helmholtz's equation is reformulated to the set of first order differential equations and the boundary problem is solved numerically. Using the MSE steady-state boundary problems are investigated for wavelength scale multilayer and modulated 1D photonic structures including loss, amplification and nonuniformity evoked by intense electromagnetic field.

Dimensioning of a transport network being robust to changes of the traffic pattern

Abstract: The planning and dimensioning of circuit-switched networks is investigated where the expected traffic pattern is uncertain. To model the vagueness, the static traffic matrix is replaced by a matrix with random variables for the predicted traffic. With the choice of the distribution for these variables, a scenario of different realizations may be characterized. A measure for the accuracy of the prediction is introduced. An algorithm for the dimensioning of the necessary network resources for realizations of this random process is presented and discussed. A case study for a pan-European network is performed.

RINGO: demonstration of a WDM packet network architecture for metro applications

Abstract: This paper presents the work carried out by the Optical Communications Group at Politecnico di Torino in the framework of the RINGO project. The RINGO network is based on a WDM optical ring, with an input queuing access protocol and multicast capabilities. We start by presenting the RINGO architecture, protocol, and the experimental demonstration. Then, we compare our solution with both the "traditional" solutions (i.e. SONET/SDH rings) and with today's complex "truly all-optical" packet switched proposals.

Dispersion compensating fibers

Abstract: In this paper we briefly review the work on dispersion compensating fibers (DCFs) in the last few years. Starting with the basic principle behind DCF, its need for upgrading the 1310 nm optical fiber links is discussed. The experimental and theoretical results of some researchers have been cited. The latest trend in optical communication has been to use dense wavelength division multiplexed (DWDM) systems in the gain window of an optical fiber amplifier. However, nonlinear effects like four wave mixing (FWM) impose serious limitations. To overcome this difficulty use of fibers with non-zero dispersion has been suggested. For long distance repeater less transmission this dispersion will go on accumulating and will limit the number of bits one can send at each wavelength. Properly designed dispersion compensating fibers can overcome this difficulty. Already there has been some work in this direction by various researchers.

Dispersion and polarization properties in photonic crystal fibers

Abstract: Systematic knowledge of the particular guiding properties of photonic crystal fibers (PCF's) permits the achievement of structures with flattened, or even ultraflattened, positive, negative, or nearly-zero group velocity dispersion for different wavelength ranges. On the other hand, we have identify a PCF, called super-square PCF, in which the introduction of an off-lattice hole generates a highly anisotropic intraband guidance, and then the structure operates as a polarization maintaining fiber. Moreover, the combination of this anisotropy and intraband guidance gives rise to a radically new mechanism of polarization discrimination, which leads to a new class of single-polarization single-mode fibers. In both cases the goal is to control the dispersion and polarization properties in PCFs by modifying solely the geometrical parameters of these fibers. Keywords: fiber design, flattened dispersion.

Nonlinear refractive index and chromatic dispersion simultaneous measurement in non zero dispersion shift optical fibres

Abstract: This paper reports the simultaneous measurement of the nonlinear refractive index and chromatic dispersion in dispersion shifted fibers, based on the power measurement of the mixing products generated by four pump waves. This method is also appropriated to be used with other low dispersion chromatic dispersion fibers as the non-zero dispersion shifted fibers.

Assessment of packet loss for an optical feedback buffer node using slotted variable-length packets and heavy-tailed traffic

Abstract: The new telecommunication networks scenario is characterised by a very rapid increase of the volume of traffic, and also very variable and unpredictable traffic demands. In this context, all-optical packet switching is emerging as the most promising technology for covering such new requirements. In this paper, we deal with the performance analysis of an optical packet switch with a feedback delay line buffer configuration. The network mode operation is slotted and the case of a realistic traffic model (i.e., variable-length packets modelled by self-similar traffic) fitted into trains of fixed-size slots is considered. Results from contention resolution performed by using both the time and the wavelength domains show that they must be exploited as combined tools in order to obtain good node performance.

Asynchronous optical performance monitor techniques for DWDM optical networks

Abstract: The current techniques of optical system performance monitoring are described and characterized. From the available techniques, we focus our attention on the asynchronous Q method, and it is described and evaluated for several working conditions. This technique allows optical performance monitoring without synchronization, thus allowing the performance monitor to work at a much lower ratio and without performing clock recovery/synchronization, which is quite a hard and expensive task to perform, especially if considering different bit rates and pulse formats. The results of this technique are discussed, taking into account linear and nonlinear effects. Its resilience to the pulse format is also observed by considering a square pulse, where the "on" time is much more evident than the transition time, and a raised cosine pulse where the conditions are reversed. Some experimental results are shown and validated with the synchronous BER testing standard technique.

Fiber nonlinear coefficient measurement scheme based on four-wave mixing method with externally modulated laser source

Abstract: In this paper, we present measurement scheme for determining the optical fiber non-linear coefficient /spl gamma/, using externally modulated continuous wave laser source. The measurement technique is based on four-wave mixing. The measurement source which uses one laser and one optical erbium-doped fiber amplifier only is described precisely. The proposed simple measurement scheme is polarization independent, enables high sensitivity and accuracy, and is applicable to all currently available types of fiber.

Review of so far proposed fiber n/sub 2/ measurement schemes

Abstract: Accurate determination of fiber nonlinearities is important issue in the design of all-optical transport networks. In this paper, the second-order refractive index (n/sub 2/) has been discussed and its measurement techniques overviewed. The brief description of each measured method is given. This paper focuses on the comparison of different interferometric and non-interferometric measurement schemes in terms of their simplicity and versatility of testing various types of fibers.

Photonic crystal fibres- novel fibres, new applications

Abstract: Photonic crystal fibres with an air-silica micro-structured cross-section, offer novel fibre designs and new fibre characteristics, compared to standard silica fibres, such as new guiding mechanisms, different group velocity dispersion characteristics and new possibilities when designed as non-linear fibres.

Rectification of near-field images

Abstract: Significant enhancement of resolution in the scanning near-field optical microscopy (SNOM) and in microwave subsurface imaging is achieved by deconvolution of measured 2-D distributions using Tikhonov's method. This method makes it possible to obtain much better sharpness of images.

Modeling of 2D photonic crystals by using the method of lines

Abstract: In our work we examined 2-dimensional photonic crystals. For modeling we used the method of lines (MoL). We analyzed waveguides, filters and concatenation of two bends. Results are in good agreement with results presented in the literature.

A thermal model for silicon-on-insulator-based waveguide modulators

Abstract: In the proposed thermo optic modulator a metal heater, deposited on the top of a SOI rib, generates thermal energy. It is assumed that the waveguide structure is infinite in extent in the direction of the propagating wave (into the page). Consequently longitudinal heat flow can be neglected and only the cross-sectional temperature distribution is studied. Heat transfer from the heater to the air cladding is also neglected. By controlling the electrical power applied to the heater the temperature profile inside the structure, and hence the associated change in refractive index, can be calculated. The present paper focuses on the thermal design.

Performance of wavelength convertible multi-hop optical network under deflection routing with a delay-line optical buffer

Abstract: We proposed a hybrid solution to solve the packet contention problems by combining a delay-line optical buffer in a wavelength convertible multi-hop optical network. The computed result shows that the deflection probability is much reduced. Furthermore, the required number of wavelength converters becomes smaller at full load compared to wavelength convertible multi-hop optical network under hot-potato routing scheme.

Application of the Monte-Carlo method for account of losses in integrated-optical devices

Abstract: Using of Monte Carlo method for definition of losses level in integrated-optical devices is offered in this work. The example of calculation of losses of the optical waveguide curve is given. Limits of applicability of the method are pointed.

10 Gb/s chirped duobinary transmission (CDBT) over 277 km of uncompensated standard single mode fibre

Abstract: We have performed the first experimental demonstration of chirped duobinary transmission (CDBT). The enlarged transmission distance of this modulation format compared to conventional chirp-free duobinary transmission has only been shown by simulation previously. Thus we enlarge the maximum transmission distance of chirp-free duobinary transmission up to the new record distance of 277 km of standard single mode fibre without dispersion compensation.

Modified Airy function solutions to optical waveguide problems

Abstract: Modified Airy function (MAF) method gives an approximate solution of the wave equation for planar waveguides with an arbitrary refractive index distribution. Unlike WKB method, the MAF solution does not diverge at the turning points and there is no need of connection formulae. Comparison with exact results for practical wave guides show that the errors in MAF solutions are small. Use of a first order perturbation theory together with the MAF solution reduces very much the error in the eigenvalues. It has been shown that an improvement of the method gives almost exact eigenvalues and the eigenfunctions. Though the method will be illustrated with examples of optical wave-guides, it is equally applicable to problems in quantum mechanics and other areas of physics and engineering.

Fast power transients in Raman fibre amplifiers

Abstract: We have investigated, both experimentally and theoretically, the effect of channel removal/addition on surviving channel power transients in distributed Raman fibre amplifier (RFA). Signals from two laser diodes were transmitted through counter-directionally pumped RFA consisting of 15.6 km of dispersion compensating fibre (DCF). Light of on of the laser diodes was square wave modulated at 500 Hz to simulate channel addition/removal. At the output of the RFA, the modulated channel was eliminated with an optical band-pass filter and power fluctuations of the c.w. channel were recorded with a high speed digital oscilloscope. Output power transients in RFA were studied theoretically using a large-signal numerical model that includes time variation effects and takes into account pump-to-pump and signal-to-signal interactions and generation of amplified spontaneous emission.

All-optical routing - progress and challenges

Abstract: There is a recognized trend to extend the functionality of the optical plane beyond mere point-to point transmission of data. Enabling devices for optical networking are beginning to appear on the market. All-optical routing is the one technology that has to be developed and deployed to fully fulfil the promises of optical networking. The objective of this article is to set up the scene for a fruitful discussion on the subject of all-optical routing.

Optical switching technologies for fast optical packet switching

Abstract: A survey of optical switching technologies being candidates for an optical packet switched (OPS) network is presented. Switching time range for optical switching fabrics is found through analysis. In light of this, and based on reported switch devices, switching technologies are identified as candidates for OPS. Their suitability from a network perspective is then discussed.

Modeling of uniaxial anisotropic fibers with noncircular cross-section by the method of lines

Abstract: Summary form only given. Only in ideal case optical fibers are of circular cross section. Furthermore, sometimes noncircular cross sections are of great interest. Especially elliptical cross sections and cross sections of star form should be mentioned. Therefore, a new algorithm for the analysis of fibers with nearly arbitrarily cross sections will be presented in this contribution. This algorithm is based on the method of lines with discretization lines of various length. Impedance/admittance transformation formulas between the interfaces of the layers are developed. The materials are assumed to be uniaxial anisotropic. The algorithm can also be used for planar optical waveguides with layers of non-constant thicknesses. The proposed algorithm is verified by numerical results.

Modeling and process design for laser interference lithography used in fabricating two-dimensional periodic structures

Abstract: Laser interference lithography (LIL) is a technique that can be successfully used for realization of 2D periodic structures, with excellent uniformity over large areas. However, detailed modeling is needed in order to extract the optimum design parameters. In this paper, we refer to a design procedure for LIL applied to fabricating photoresist templates for photonic crystal semiconductor slabs with periodic lattices of holes.

Nonlinear coefficient measurement in non zero dispersion shifted fibre based on FWM method

Abstract: In this paper measuring technique for determining fiber nonlinear coefficient /spl gamma/, using four wave mixing, are presented. The proposed measurement scheme is simply, taking into account polarization states and allow, after some modifications to simultaneously measure fiber dispersion.

Two-photon absorption induced applications in the visible range: optical limiting and polymerization

Abstract: Two-photon absorption (TPA) induced applications in the visible spectral range (optical limiting and 3D microfabrication by photopolymerization) are reported. A work of molecular engineering was performed for each application to design organic systems exhibiting efficient effects. In the case of optical limiting, the new "oligomer" strategy based on exciton coupling between monomers leads to a large enhancement of TPA properties with the length of the system and to promising optical limiting properties. Microfabrication of 3D structures, using low-cost microlasers, is described from optimized organic photoinitiators, whereas commercial UV resins require intense pulses; different objects are shown.

An approach to an IP over WDM transmission network modelling

Abstract: The paper describes an approach to the optical transmission network modeling. The modeling process is based on two main assumptions -transmission network carries IP datagrams using the layer 2 protocol as a framing technique and wavelength division multiplexing (WDM) is used as a transmission technique on the physical layer. Protection and restoration mechanisms have been implemented on the photonic layer and QoS is supported by the Internet protocol. An IP over WDM network structure has been presented, along with the description of the optical component modeling process.