Michal Lucki

Software design of segment optical transmitter for indoor free-space optical networks

During recent years, there has been rapid development in optical networks. This includes not only fiber optical networks but also free space optical networks. The free space optical networks can be divided into indoor and outdoor ones. The indoor free space optical networks have been experiencing dramatic progress in the last years, allowed by the newest IEEE norm 802.15.7, which enabled development of different types of transmitter receivers, modulation formats, etc. The team of authors is dealing with software design of segment optical transmitters for an indoor free space optical network based on the multi-mode optical 50/125 or 62.5/125 μm fiber. Simulated data are then evaluated from the point of view of optical intensity uniform distribution and space spot light size radiating from segment optical transmitter.

Nearly zero dispersion-flattened photonic crystal fiber with fluorine-doped three-fold symmetry core

Abstract. A novel design of a photonic crystal fiber is presented. A nearly zero dispersion regime of operation has been achieved by using a three-fold symmetry core, which is improved by the avoidance of high-index doping in a central region. The core consists of pure silica surrounded by three fluorine-doped regions and three airholes. It can be confirmed by the numerical simulations using the finite difference frequency domain method that flattened dispersion characteristics upon wavelength over the range of 1250 to 1700 nm can be achieved in an optical fiber. Further, the potential fiber geometry imperfections caused some concern. Finally, the presented fiber design is compared to selected fiber designs with a dispersion close to zero.

Optimization of microstructured fiber for dispersion compensation purposes

A new dispersion compensating microstructured optical fiber is presented. The dispersion slope of the designed fiber is opposite to the dispersion of standard PCF for potential broadband dispersion compensation. Since chromatic dispersion is optimized for wide bandwidth, the considered structure is suitable for repeaters in transmission systems with wavelength division multiplex. Another contribution of this work is a new flat-dispersion PCF operating at telecom wavelengths. Required dispersion, achieved by balancing material and waveguide dispersion are done for wide spectrum of wavelengths. For example, dispersion of −0.025 ps/nm/km from a wavelength of 1200 nm to 1700 nm is achieved using a highly nonlinear photonic crystal fiber. The results are obtained by using the full-vectorial finite difference frequency domain method.

Flexible control of dispersion in index guiding photonic crystal fibers governed by geometrical parameters

This letter deals with the possibilities of flexible control of dispersion governed by geometrical parameters such as cores size and normalized hole diameter d/Λ. Curves of total dispersion in function of wavelength, normalized hole diameter and cores size are presented. Limitations of possible run of total Group Velocity Dispersion like possibility of high order mode zero-dispersion wavelengths appearance is presented as well as possibility of deterioration of further important transmission parameters such as loss or modal regime is discussed. The set of structural set of the fiber is described.

Broadband submicron flattened dispersion compensating fiber with asymmetrical fluoride doped core

The goal of this paper is to investigate selected fluoride optical materials and to present a photonic crystal fiber designed for specific applications in dispersion compensation by using those materials. The idea how to restrict chromatic dispersion is to increase the index contrast by using calcium fluoride or barium fluoride in the first ring of holes, which lower the effective index. In general, fluoride materials compared to standard silica glass in many aspects offer better mechanical and optical properties. The use of fluorides allows achieving broadband dispersion suppression impossible to achieve in standard fibers with similar geometry. The presented result comprises a numerical model of a photonic crystal fiber in a submicron lattice, specific for its negative dispersion coefficient achieved for broad spectrum of telecommunication wavelengths, i.e. 1300 – 1700 nm. The core consists of pure silica surrounded by three doped regions and three air-holes. Holes doped with fluoride materials enhance negative dispersion coefficient to -438 ps.nm-1.km-1. The diameter of doped regions is about 1 micrometer. Simulations were done by using the full-vector FDFD method. The wavelength evolution of refractive index of materials was introduced by using the Sellmeier approximation. The major advantage of the designed fibers is their material composition, low attenuation and broadband utilization.

Broadband dispersion decreasing photonic crystal fiber for compression of optical pulses

A novel photonic crystal fiber for compression of optical pulses is designed and studied in this paper. The fiber comprises a silica core surrounded by nine rings of air-holes, where air-hole diameter of the innermost ring is gradually reduced along the entire fiber length. In order to obtain the required wavelength dependence of the effective refractive index, finite difference frequency domain method is employed. The calculated chromatic dispersion is flat from 1250 to 1700 nm at the fiber output, and therefore the photonic crystal fiber can be used at a desired wavelength in this range. On the contrary to other studies, chromatic dispersion in this paper is decreasing along the fiber length with the effective mode area. Therefore, during the propagation of solitary waves, the fiber nonlinear parameter increases and consequently the compression ratio is increased. Compression of solitary waves is investigated at the wavelengths of 1250, 1310, 1400, 1550, and 1700 nm. The compression ratio up to 30 for the first-order solitary wave with the length of 1550 nm can be achieved primarily by dispersion varied from 137 to 6 ps·nm-1·km-1 during the wave propagation.

Modeling of the multi-carrier modulation benefits for data transmission

More efficient data transmission is an important element for increasing an overall transmission performance in broadband access networks. Advanced access network infrastructure can have a dual nature. First, it may entirely consist of optical elements, which mean that the network has a nature of a passive optical access network. In addition, in a network topology there can be found elements that work with signals in an electrical form. Then, the network has a character of a hybrid access network. Modulation principles for user signals transmission in the second part of the hybrid access network belong to the group called multi-carrier modulation. This paper is focused on finding a more suitable simulation principles used when calculating the benefits of multi-carrier modulation used for user data transmission. Consecutive chapters describe a simplified method of modeling the user data transmission performance with regard to the real parameters of the transmission environment. Concrete results for typical situations are calculated and discussed.

System improvements in dense wavelength division multiplexing networks by using advanced optical modulation formats

In this paper we focus on modulation formats for optical transmission networks. The most widely used intensity formats such as Non Return to Zero, Return to Zero, Carrier-Suppressed Return to Zero and duobinary are investigated in terms of bit error rate, Q-factor, optical reach and dense wavelength division multiplexing grid, in order to find out their physical limitations and system performance in a transmission system with given parameters. However, phase-based modulation formats like Differential Phase-Shift Keying and Differential Quadrature Phase-Shift Keying can perform better at the cost of increased transceivers complexity. Some formats can benefit from polarization division multiplexing to enable higher spectral efficiency, optical reaches, optical to signal noise ratio and chromatic dispersion tolerances. Simulations are performed in OptSim software environment based on the Time Domain Split Step method which uses full band simulation and offers aliasing errors immunity, accurate differential group delays, parallel computing, etc.

An improved non-linear nearly-zero dispersion flattened photonic crystal fiber with the threefold symmetry core

A new type of dispersion flattened photonic fiber is presented. The fiber has an improved threefold symmetry core that consists of a silica core surrounded by three low-index regions and three air-holes. It can be observed from numerical simulation employing the full-vectorial finite difference frequency domain method that nearly-zero ultra-flattened dispersion can be obtained over the wavelength range of 1250-1700 nm. All fibers parameters are found to be non-immune to imperfections of geometry. An attention should though be paid to the potential fabrication process. The chromatic dispersion behavior with fabrication tolerances of 1 % and 2 % has been numerically demonstrated. Finally, fiber designs with five different hole-to-hole spacing (pitch) have been proposed. Each of the proposed fibers exhibits remarkable chromatic dispersion properties, such as nearly-zero ultra-flattened dispersion over wide wavelength range or zero dispersion at the wavelength of 1550 nm.

Broadband dispersion compensating photonic crystal fiber

Presented work is a study of dispersion properties of photonic crystal fibers. The main objective is to design photonic crystal fibers suitable for potential compensation of group velocity dispersion of optical signals. New fiber structures are proposed, for example, a flattened-dispersion compensating photonic crystal fiber for broadband utilization in high-speed transmission systems is presented. The structure shows flattened negative value of dispersion over the O, C, and L bands. The fiber can eventually get applied in broadband optical signal recovery in systems with wavelength division multiplexing. Last but not least, a dual-core compensating microstructured fiber is optimized in order to achieve low dispersion and low loss at the C-band. Results presented in this work are obtained by using the FDFD method.