Optimised design of fibre-based pulse compressor for gain-switched DFB laser pulses at 1.5 µm

An optical-fibre based pulse compressor for gain-switched DFB laser pulses has been optimised using a systematic procedure based on the initial complete characterisation of the laser pulses, followed by numerical simulations of the pulse propagation in different types of fibre to determine the required lengths for optimum compression. Using both linear and nonlinear compression techniques, an optimum compression factor of 12 is achieved

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems

Ultra-sensitive all-optical sampling at 1.5 μm using waveguide two-photon absorption

We demonstrate a simple and ultra-sensitive all-optical sampling system suitable for the characterization of high capacity (> 100 Gbit/s) single channel systems operating around 1.5 µm. The system is based on the nonlinear effect of two-photon-absorption in a commercial 1.3 µm semiconductor laser and, using only direct detection of the unamplified two photon absorption photocurrent, we have achieved a temporal resolution of around 2 ps, and a sensitivity of less than 2 mW²

Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source

An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10 GHz in detuning and 5 dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10 ps and pedestal suppression higher than 35 dB. These pulse features are associated with a side mode suppression ratio of about 30 dB and a timing jitter of less than 1 ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems

Pleistocene, Holocene and Recent Bird Gastroliths from Interior Alaska

Describes and discusses the origin of polished and rounded grains of quartz, secondary quartz, and chert from (probably) Holocene loess of Easter Egg Hill near Livengood townsite, peat on the Nenana Road, and redeposited Wisconsin loess from the Eva Creek Mine and Ready Bullion Creek Mine at 64 51 N, 148 02 W. The association of these grains with dull, angular grains of the same materials rules out soil or solifluction abrasion in place. Gizzard-bearing birds such as ptarmigan and grouse in Alaska produce glossy polish on their gizzard stones (gastroliths) comparable to that of the Pleistocene and Holocene gastroliths; the polish and roundness of the stones in living birds are more pronounced in late winter. Because the modal size classes of ancient and Recent polished gastroliths do not coincide, some of the ancient gastroliths are believed to have been produced by birds not now living in interior Alaska.Gastrolithes d'oiseaux pléistocènes, holocènes et récents de l'Alaska intérieur. On trouve dans le loess et la tourbe de l'Alaska intérieur des grains polis et arrondis de quartz, de quartz secondaire et de chert. Le diamètre intermédiaire de ces grains se situe entre 35 et 0.07 mm, les plus abondants mesurant 0.07 mm, de 2 à 4 mm et peut-être, de 10 à 20 mm. Le poli de ces grains est le produit de l'abrasion dans des gésiers d'oiseaux. Les oiseaux à gésier qui vivent aujourd'hui dans l'Alaska intérieur produisent sur leurs gastrolithes un fini poli comparable à celui des gastrolithes des dépôts holocènes et pléistocènes. Sur les gastrolithes d'oiseaux récents, le poli et l'arrondi varient directement, atteignant un maximum pour les oiseaux vivants à la fin de l'hiver. On peut croire que certaines gastrolithes polies de l'Holocène et du Pléistocène ont été produites par des oiseaux qui ne vivent plus aujourd'hui dans l'Alaska intérieur, car les classes dimensionnelles de ces gastrolithes anciennes ne coïncident plus avec celles des gastrolithes des oiseaux d'aujourd'hui

Simulation of a high-speed demultiplexer based on two-photon absorption in semiconductor devices

In this paper, we present a theoretical model of an all-optical demultiplexer based on two-photon absorption in a specially designed semiconductor micro-cavity for use in an optical time division multiplexed system. We show that it is possible to achieve error-free demultiplexing of a 250 Gbit/s OTDM signal (25 × 10 Gbit/s channels) using a control-to-signal peak pulse power ratios of around 30:1 with a device bandwidth of approximately 30 GHz

Grid approximation of a singularly perturbed boundary value problem modelling heat transfer in the case of flow over a flat plate with suction of the boundary layer

AbstractIn the present paper we consider a boundary value problem on the semiaxis (0,∞) for a singularly perturbed parabolic equation with the two perturbation parameters ε1 and ε2 multiplying, respectively, the second and first derivatives with respect to the space variable. Depending on the relation between the parameters, the differential equation can be either of reaction–diffusion type or of convection–diffusion type. Correspondingly, the boundary layer can be either parabolic or regular. For this problem we consider the case when the boundary layer can be controlled by continuous suction of the fluid out of the boundary layer (model problems of this type appear in the mathematical modelling of heat transfer processes for flow past a flat plate). Errors in the approximations generated by standard numerical methods can be unsatisfactorily large for small values of the parameter ε1. We construct a monotone finite difference scheme on piecewise uniform meshes which generates numerical solutions converging ε-uniformly with order O(N−1lnN+N0−1), where N0 is the number of nodes in the time mesh and N is the number of meshpoints on a unit interval of the semiaxis in x. Although the solution of problem has a singularity only for ε1→0, the character of the boundary layer depends essentially on the vector-valued parameter ε=(ε1,ε2). This prevents us from constructing an ε-uniformly convergent scheme having a transition parameter which is independent of the parameter ε2

Overcoming laser diode nonlinearity issues in multi-channel radio-over-fiber systems

The authors demonstrate how external light injection into a directly modulated laser diode may be used to enhance the performance of a multi-channel radio-over-fiber system operating at a frequency of 6 GHz. Performance improvements of up to 2 dB were achieved by linearisation of the lasers-modulation response. To verify the experimental work a simulation of the complete system was carried out using Matlab. Good correlation was observed between experimental and simulated results

100 Gbit/s real-time all-analogue filter bank OFDM based on a gain-switched optical comb

A real-time 5×21.6 Gbit/s WDM electro-optical transceiver is presented. Optical carriers were spaced by 20 GHz and each one transmitted four orthogonally overlapping broadband subcarriers. Only analogue electronics were employed, achieving an unprecedented spectral efficiency in DSP-less SCM links