Showing papers presented at "International Conference on Transparent Optical Networks in 1999"

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Novel algorithms for the analysis of optical fiber structures with anisotropic materials

Abstract: Fibers are today not only important as waveguides for long distance transmission of optical signals, but also in circuits as special phase filters or reflectors. Therefore, in this paper the analysis of a general class of fiber structures will be described. The material may show anisotropic behavior. The formulation in this paper is given in such a way that generalized transmission line equations are obtained in cylindrical coordinates. The analytical solution should be obtained in the propagation direction of the wave. General impedance/admittance and field transformation formulas will be derived which allow an accurate analysis of the devices. Furthermore, based on the generalized transmission line equations a novel BPM algorithm in cylindrical coordinate system will be proposed.

A decision feedback equalizer for dispersion compensation in high speed optical transmission systems

Abstract: We investigate a class of decision feedback equalizers, which are suitable for the equalization of dispersion effects in optical fiber channels. Since the widely used standard single mode fiber can be described by a simple linear transfer function for the optical signal, the overall system, including electrical/optical conversion and vice versa is nonlinear. We derive equalizer structures that account approximately for the nonlinear nature. These structures are investigated by simulation. An improvement of approx. 10 dB in the BER is achieved with a simple 1/sup st/ order equalizer that may be implemented at high speed systems at 10 Gb/s and beyond.

System impact of ripples in grating group delay

Abstract: We present simple analytical expressions which relate fiber grating group-delay ripples to system performance and allow the estimation of expected penalties. Experiments show excellent agreement with our theory. A WDM transmission experiment shows that the system performance can be drastically improved if the channels are slightly detuned in wavelength.

Modeling of oxide-confined vertical cavity surface emitting lasers

Abstract: The given work is devoted to a problem of numerical simulation and analysis of the vertical cavity laser's parameters with the purpose of improving numerical simulation methods. The analysis of the VCSEL with the help of the mathematical model based on thermal conduction and carrier diffusion equations are presented.

Optical duobinary modulation schemes using a Mach-Zehnder transmitter for lightwave systems

Abstract: We compare the different modulation schemes of generating an AM-PSK duobinary signal by a MZ modulator. We have simulated both schemes of duobinary transmitters to consider their influence to dispersion sensitivity. We have especially considered the difference between the two possible modulation schemes of the asymmetrically driven MZ modulator.

Some aspects of photonics and electronics in communications and interconnects

Abstract: The rapid development of fiber optics and photonics in general has led to research regarding a wider role for photonics such as the transparent or all optical network in telecommunications, and optical interconnects at different levels. The talk will try to critically assess some of these applications, taking the development in electronics into account.

Transparency of optical networks: how to manage it?

Abstract: The concept of optical transparency in fibre networks and its positive and also negative impact on data transmission is reviewed and discussed. ITU-T Study Group 15 standardisation effort on optical transparency is reported.

A simple method for analysis of VHF and optical filters using dielectric waveguide ring resonators

Abstract: The development of millimeter-wave integrated circuits continues to stimulate research on dielectric resonators in the millimeter wave frequency band. At millimeter wavelength devices the cylindrical dielectric resonators used on their conventional TE,TM, or hybrid modes are practically small. When used in their whispering gallery modes (WGM's) these cylindrical ring DR's have dimensions larger than normal for millimeter wavelength. One of the most important advantages of the WGM of DR's is its analogy with a traveling wave ring resonator. In this paper we define both amplitude-frequency and phase-frequency characteristics of band pass ring resonator filter.

Design and characteristics of widely tunable quantum-well heterostructure lasers in the Littman and Metcalf cavity configuration

Abstract: Analysis of light-current and tuning characteristics of a quantum-well laser in an external cavity is performed. The band diagram of the proposed tunable asymmetric multiple quantum-well heterostructure laser source under the forward bias is shown. The heterostructure consists of the GaAs-AlGaAs system.

Analysis of very long distance analog CATV link with distortions self-compensation due to fibre dispersion and nonlinearity

Abstract: The effectivity of the presented simulation model of an analog CATV link taking into account nonlinear effects present in an optical fibre has been confirmed through comparison with the results of the theoretical analysis. The model can be used to investigate the method of compensation utilizing prechirping in the transmitter, as well as other parasitic phenomena, as for example phase shift between modulating signals or non-flat EDFA spectral characteristic. The possibility of nonlinear compensation of a fibre working with large powers of order tens of mW, and distance exceeding 100 km was presented.

Bistable laser diodes and their applications for optical networks

Abstract: Recent progresses in research on bistable laser diodes and their applications in optical communication and photonic switching are reviewed. Bistability in two-mode lasers via gain saturation has recently attracted attention, because of its ultra high-speed.

Advances in the spectral index method for optoelectronic design

Abstract: The spectral index (SI) approach can be applied for 3D problems. The SI approximation that the small field penetration into the air regions can be modelled by using a slightly larger rib geometry can be carried over to the 3D case. Obviously, this presupposes that any discontinuities primarily scatter into the substrate and not the air regions. A 2D variational boundary condition applied in the plane of the base of the rib when used in conjunction with a suitable decomposition of the field amplitudes on this plane, can be used to solve fully 3D rib circuit problems. The principal advantage of this approach is that it ultimately only requires solution of a small set of linear equations to completely determine the fields in the full structure. The SI method is a valuable analysis tool for the optoelectronics designer.

Numerical analysis of total field propagation in linear and nonlinear single-mode tapered fibers

Abstract: Total field propagation in linear and nonlinear step-index infinite-cladding tapers is investigated by use of a grid method. Spot-size and transmittance variation of the field along the taper axis is calculated for different taper angles. Interaction of the the fundamental mode with radiation field leads to spot size oscillations about the adiabatic curves, the character of the oscillations depending on the taper angle.

Polarization properties of optical fibers

Abstract: Summary form only given. The paper discusses particular polarization properties of optical fibers and presents the general approaches of their polarization phenomena description. The first one treats an optical fiber as an optical waveguide in which light can be guided in the form of waveguide modes. This approach identifies basic polarization eigenmodes of a fiber and relates them to the polarization state of the guided light. Changes in output polarization are described in terms of polarization-mode coupling due to birefringence changes acting as perturbations along the fiber. The polarization coupling is described by the coupled mode theory. Another approach treats an optical fiber like any other optical device which transmits light and the fiber can be divided into separated sections behaving like polarization state shifters. The paper describes three general formalisms of polarization evolution in a fiber: the Jones method, the Stokes Mueller formalism, and the Poincare's sphere representation.

Propagation of chirped ultra-short optical pulses

Abstract: Ultra-short optical pulses having initial linear chirp in nonlinear guides are discussed. The nonlinear Schrodinger equation for complex initial conditions is solved numerically by split-step Fourier method and beam propagation method. Some selected results for solitons are presented. The computations confirm physical expectations of an influence of the chirp magnitude on pulse propagation in nonlinear guide.

Analysis of blocking probability in WDM all-optical networks with non-Poisson traffic statistics

Abstract: We study blocking probability in wavelength division multiplexing (WDM) optical networks. We consider two type of networks: with and without wavelength conversion, and two types of wavelength assignment policies: random wavelength assignment and first fit. We have shown that difference between values of blocking probability is significant for the cases when input flow characteristics are distributed according to memoryless and general distribution. We have found that values of blocking probability for models with general distribution are upperbounded by the values of memoryless distribution case. We have also considered a model with non-uniformly distributed destination node for an incoming connection request.

Multimode laser diodes for WDM transmission

Abstract: Our recent investigations of erbium doped fibre amplifiers with chosen cheap laser diodes at a wavelength of 1534 nm which behaved, depending on supply conditions, as either a quasi-single-mode, multi-mode, or luminescent diode shows that the idea of multichannel transmission can be realised by specially designing the multimode signal diode laser.

Analysis of optical waveguides using the two-dimensional integral equations

Abstract: Integral equations (IE) for optical waveguides (OW) with arbitrary anisotropic inhomogeneous media may be formulated using the principle of secondary fields and two-dimensional Green's functions. The losses presented are in a good agreement with those obtained using the mode matching. The method is easy modified for discontinuities in OW, for bianisotropic medium, and applied for arbitrary shaped structures. To reduce the number of finite elements and the order of determinant the two-dimensional cubic polynomials approximations may be used.

Optical wavelength path and optical virtual wavelength path comparison

Abstract: All-optical network technologies employing wavelength division multiplexing (WDM) will play the major role in constructing large bandwidth networks. Since such networks require not only transmission line capability enhancement, WDM should be utilised in combination with wavelength routing. The function of routing must be implemented for reaching high connectivity and flexibility of optical network. This paper presents a proposal for a WDM optical networks suitable for high capacity traffic. Two different approaches supporting optical paths will be described: wavelength path (WP) and virtual wavelength path (VWP). The paper focuses on the comparison of WP and VWP in terms of non-hierarchical transport system with blocking and non-hierarchical transport system with waiting queue.

Analysis of random signals in optoelectronic systems

Abstract: We study the substantiation of applying of linear random functions (processes, vectorial processes, fields) both for the description of random signals and for the analysis of their conversions at optoelectronic system (OES) links.

Optical light controlled band edge switch

Abstract: We study a mechanism of the light-by-light control, based on changing the refractive index of the narrow-band layers in a semiconductor photonic band gap structures (PBGS). This changing is caused by the contribution of the non-equilibrium charge carriers generated by the controlling radiation. We show that this mechanism can be efficient if an optimal controlling light wavelength is taken near the proper absorption edge of the narrow-band semiconductor layers, since the little changes of the layers refractive indexes at the band gap edge of PBGS cause essential change of the transmission characteristics. The modulation depth of the controlled light of more than 90% is achieved for the PBGS based on GaAs at the wavelength 1.5 /spl mu/m under the controlling light power equal to 5.9 kW/cm/sup 2/. The inertia of the mechanism considered is determined by the lifetime of the non-equilibrium charge carriers in semiconductor layers and is equal to 10/sup -7/ s in our case.

Nonlinear optical properties of monocrystal ZnSe

Abstract: From nonlinear transmittance at 532 nm, we have evaluated two photon absorption coefficient and calculated the imaginary part of the third order nonlinear optical susceptibility. The real part describe the nonlinear refractive index change and from degenerate four wave mixing (DFWM) measurements, we obtain the absolute value of the third order nonlinear susceptibility for the investigated ZnSe. Combined with independent measurement of TPA coefficients in this material, this indicates that the measured susceptibility in ZnSe at 532 nm is dominated by nonlinear refraction changes.

First ion-exchanged dual thermo-optic variable optical attenuator

Abstract: The first dual ion-exchanged integrated variable attenuator with tap-couplers was fabricated. The thermal cross-talk was found to be about 2.1 dB and the simple S-bend tap-coupler exhibit high voltage dependency, due to re-coupling of radiation modes.

Efficient 3D-BPM method for semiconductor integrated optics

Abstract: A novel implementation of the Finite Difference Beam Propagation Method for optical rib waveguide structures with air cladding is presented. Typical calculations for practically useful rib waveguide tapers confirm that the new approach is faster, requires less memory and maintains accuracy when compared with previously used techniques.

Reflection from layered dielectric structures with combined regular and random inhomogeneities

Abstract: Optical wave reflection from a layered half-space with regular and random inhomogeneities where the regular perturbations correspond to a linear waveguide near the half-space boundary. Random inhomogeneities are simulated in the frame of the white noise model. The problem is solved analytically in a framework of the embedding method which reduces a boundary problem to the problem with initial values considering the field as a function of the half-space boundary coordinate and obtaining then its solution as a steady-state probability density of the reflection coefficient phase. Numerical calculations revealed some features of the field behavior under the combined influence of regular and random inhomogeneities such as the reflection coefficient phase increasing inhomogeneity from uniform distribution for small regular inhomogeneities toward a strong peak at the phase equal to /spl pi//2 for increasing ones, and some fine effects which are still greater than the calculation accuracy.

Analysis and design of optical waveguide components with metallization

Abstract: Planar optical waveguide components with metallization are analyzed with a mode-matching method that takes into account surface plasmons on the metallization, the plasmon character of TM-modes as well as to any significant extend also radiating modes. A waveguide modulator and a triple waveguide polarization splitter serve as examples also for the optimum design of such waveguide components.

Light propagation in optical anti-guiding structures with Kerr-like nonlinearity

Abstract: Propagation of light beams along graded-index and step-index anti-guiding structures is studied in comparison with the propagation along the conventional fibers and free space propagation. Kerr-like nonlinearity is taken into consideration. Self-focusing of the light beams is shown to depend on the matching conditions of the structures. Nonlinear narrowing of the beams occurs to be more effective in the anti-guiding structures.

Strategies for extending the existing standard fibre network to transmission rates of 40 Gbit/s and beyond

Abstract: Summary form only given. The majority of the existing optical fiber network consists of standard single mode fibers with their large chromatic dispersion at 1.55 /spl mu/m. If no dispersion compensation is introduced, the chromatic dispersion yields a limit in the transmission distance of 60 km (4 km) for a TDM 10 Gbit/s (40 Gbit/s) link. In order to overcome these limits, several methods are discussed: NRZ transmission with soliton support; dispersion supported transmission; mid-span spectral inversion; and dispersion compensation with dispersion compensating fibers. With respect to the last point several compensation schemes are considered such as pre- or post-compensation or symmetrical compensation schemes.

Submillimeter wave surface-emitting difference frequency generation in periodically poled lithium niobate waveguide

Abstract: The submillimeter wave difference frequency generation (DFG) in periodically poled lithium niobate (LiNbO/sub 3/) (PPLN) waveguide structure is considered theoretically. It is shown that the PPLN waveguide is capable of emitting difference frequency radiation in direction normal to the surface of a waveguide if the poling period is equal to L=/spl lambda//n/sub g/ (/spl lambda/ is a wavelength of submillimeter radiation and n/sub g/ is a mean refractive index of the optical group velocity). In contrast to the optical waves, the PPLN waveguide with such period can be easily fabricated for the submillimeter wave DFG.