1,720,977 research outputs found
Effects of random phase and amplitude errors in optical fiber Bragg gratings
Full text linkThis paper studies the influence of random phase and amplitude fabrication errors on the performance of optical filters based on fiber Bragg gratings (FBGs). In particular, we analyze two effects of particular importance for optical communications: the excess crosstalk induced in apodized gratings commonly used in wavelength-division-multiplexing (WDM) systems, and the time-delay fluctuations that appear in chirped gratings employed to compensate the fiber dispersion. A statistical model is presented to explain these effects in terms of the coherence length of the grating fabrication procedure
Synthesis of fiber gratings
No full textThe main design methods, developed so far for the synthesis of fiber Bragg gratings, are reviewed. We particularly focus on a very efficient method based on a differential layer-peeling algorithm and apply it to design high performance gratings
Broadband fibre Bragg gratings for pure third-order dispersion compensation
No full textSingle fibre Bragg gratings designed to compensate pure 3rd-order dispersion are demonstrated for the first time. The shown devices exhibits dispersion-profiles of ~20ps/nm2, ~40ps/nm2 and ~225ps/nm2 over bandwidths of 4.5nm, 6nm and 3nm respectively, they have peak reflectivities of ~75% and are only 8mm, 23mm and 40mm long. IntroductionAdvances in internet traffic and a steadily increasing demand for bandwidth and better bandwidth utilisation have started to pull systems providers towards higher bit-rate systems to achieve reduced channel and component count. Increasing the channel bit-rate can impose penalties to the dispersion performance of the system though and therefore close attention has to be paid to the dispersion slope generated in this. A number of approaches have been proposed previously to accommodate this. These include the use of dispersion-slope compensating fibres [1], long chirped Bragg gratings for combined linear and third-order dispersion [2], combinations of two non-linearly chirped Bragg gratings [3] and thin-film filters [4]. With the recent advances in grating design and manufacturing techniques it is now believed that a level has been reached where almost any filter response can be generated. For example we have recently demonstrated filters for add-drop applications with linear-phase performance for dispersion-free filtering up to 40Gbit/s [5], filters for rectangular pulse generation [6] and other pulse manipulating applications [7]. In this paper we demonstrate examples of even more complex profiled Bragg gratings through the design and, for the first time, experimental realisation of single gratings with broad spectral bandwidth profile and pure dispersion-slope compensation abilities. The demonstrated gratings require very high maximum index modulations together with full control of both phase and amplitude profiles. Examples of short Bragg gratings with dispersion-slopes of -20ps/nm2, -40ps/nm2 and -225ps/nm2 over a 1dB reflection bandwidth of 3nm, 5nm and 2nm respectively with reflectivities of ~75% are shown.<br/
An efficient inverse scattering algorithm for the design of nonuniform fiber Bragg gratings
No full textThis paper presents an efficient method for the design of complex fiber Bragg gratings. The method relies on the synthesis of the impulse response of the grating by means of a differential layer-peeling algorithm. The algorithm developed takes into account all the multiple reflections inside the grating, giving an exact solution to the inverse scattering problem. Its low algorithmic complexity enables the synthesis of long fiber gratings. The method is illustrated by designing several filters with interest for optical fiber communication systems: dispersionless bandpass filters and second- and third-order dispersion compensators
Grating add-drop multiplexer based on a compact non-uniform fused fiber coupler
No full textAdd-drop multiplexers are key components for enabling wavelength division multiplexing (WDM) optical transmissions. Different solutions using both planar and fiber geometries have been proposed in the literature. The traditional configuration using a fiber Bragg grating between two optical circulators is an efficient but costly device and introduces undesirable insertion losses
Dynamic acousto-optic filters for gain flattening of optical amplifiers
No full textAcousto-optic all-fibre filters are a promising technology for dynamic gain equalisation of optical fibre amplifiers. In this paper, we show that a controlled tapering of optical fibres can be regarded as a new degree of freedom for the design of acousto-optic filters. In particular, we investigate the coupling between the fundamental and several cladding modes, studying the evolution of the resonance conditions as the fibres are progressively tapered. Theoretical predictions are in agreement with experimental results for several tapered fibres. The application of this acousto-optic filter for gain equalisation of optical fibre amplifiers is demonstrated. The design consists of two cascaded tapered fibre lengths driven by only one acoustic frequency. The spectral characteristics are determined by the taper profile. The amplified spontaneous emission of an erbium doped fibre amplifier is flattened to within 1dB over a spectral range of 30nm for different saturation levels of the amplifier. This method results in a simplified implementation of the acousto-optic filter in contrast to other multi-frequency design approaches. Optimum filter designs can be achieved by the combination of both degrees of freedom: taper control and multi-frequency tuning
40Gbit/s high performance filtering for DWDM networks employing dispersion-free fibre Bragg gratings
No full textNear penalty-free filtering with high bandwidth utilisation at 40Gbit/s is demonstrated for the first time using fibre Bragg gratings. When tested in a typical add-drop configuration a 100GHz dispersion-free Bragg grating show Q-penalty variations of less than 1.0dBQ over most of the 1dB reflection-bandwidth confirming its superior performance
Dispersion-free fibre Bragg gratings
No full textFibre Bragg gratings with reduced/eliminated in-band dispersion are presented. When tested in add-drop configurations at 10Gbit/s both 25GHz and 50GHz bandwidth gratings are shown to exhibit superior performance with no dispersion-induced penalties in the stopband. Furthermore, the demonstrated linear-phase Bragg gratings have >70% channel filling factor values and reflectivities in excess of 99.9%
Acousto-optic attenuation filters based on tapered optical fibres
No full textThis paper studies the acousto-optic interaction induced by an acoustic flexural wave among the optical propagation modes supported by tapered optical fibres. We have investigated the evolution of the acousto-optic resonance condition as the fibre is progressively tapered, showing that the taper radius can be regarded as a new degree of freedom in the design of acousto-optic filters. Finally, we demonstrate a novel acousto-optic filter based on nonuniform tapers for dynamic gain flattening of optical fibre amplifiers
Nondestructive characterization of fiber couplers by a local perturbation method
Full text linkA technique for the nondestructive characterization of fiber couplers is demonstrated. A CO2 laser beam is scanned along the coupler length inducing a local perturbation to the coupler eigenmodes. Information about the power evolution and the coupling-constant variation along the coupler length can be obtained by applying an asymmetric and symmetric perturbation, respectively. Experimental results of the characterization of a half- and a full-cycle fiber coupler using this technique are presented
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