1,721,020 research outputs found
Narrow linewidth, Q-switched erbium doped fibre laser
No full textWe report a narrow linewidth, diode pumped, high power Q-switched Erbium doped fibre laser for the application of Landau-Placzek temperature sensing. An output coupler consisting of an in-fibre Bragg grating enables narrow linewidth operation. A linewidth of 1.3 GHz is reported with a peak power of 100 Watts and a pulse width of 20 ns at a repetition rate of 200 Hz
Moving fibre/phase mask-scanning beam technique for enhanced flexibility in producing fibre gratings with a uniform phase mask
No full textWe demonstrate a new and flexible technique for producing photorefractive fibre gratings with a uniform phase mask. By slowly moving the fibre relative to the mask as the writing beam is scanned, wavelength shifts, pure apodisation and phase-shifted gratings can be achieved
Advanced fibre Bragg grating structures for WDM networks
No full textFibre Bragg gratings are the most important new fibre component since the Erbium doped fibre amplifier (EDFA); this because they give a large potential for the design of new all fibre devices. These include narrow-band filters, sensors and chirped gratings for dispersion compensation. Through a modulation of the refractive index profile in fibre gratings a series of exciting grating structures can be obtained. Among the are multi-channel dispersion compensators, devices that represents an interesting approach to the WDM solution. The advantages of multi-channel gratings are that they exhibit characteristics similar to those of several single channel gratings but are written within a single length of fibre hence offering higher stability when packaged and potentially lower cost. We will discuss recent advances in the area of more complex structured fibre Bragg gratings, e.g long continuously chirped fibre gratings for combined compensation of linear and 3rd order dispersion to allow for exact compensation of the actual dispersion different wavelength channels experience. Furthermore square filter fibre gratings for dense WDM systems and the recently developed sinc-sampled fibre Bragg grating with identical characteristic wavelength-channels for WDM-systems will be discussed
Compensation of imperfect phase mask with the moving fibre-scanning beam technique for production of fibre gratings
No full textWe experimentally demonstrate that the moving fibre-scanning beam technique is able to compensate for imperfections in a phase mask and thus improve the quality of the resulting fibre gratings. A 10 cm long 'uniform' phase mask which normally produces gratings with a 0.23 nm uncontrolled chirp has been corrected with our new writing technique to produce narrow band gratings with 0.10 nm bandwidth
Low coherence technique to characterise reflectivity and time delay as a function of wavelength within a long fibre grating
No full textA new technique for obtaining both time delay and reflectivity as a function of wavelength within a long fibre Bragg grating is presented. A narrowband wavelength-tunable reflector with 0.18nm bandwidth is used to select the interrogation wavelength, while optical coherence-domain reflectometry is used to obtain the time delay with better than 2ps accuracy
Sinc-sampled fibre Bragg grating for identical multiwavelength operation
No full textThrough a periodic sinc modulation of the refractive index-profile in a 10 cm fibre Bragg grating we demonstrate 4, 8, and 16 equally spaced wavelength channel filters with identical 100 GHz passbands
Comparison of DSF and SOA based phase conjugators employing noise-suppressing fibre grating
No full textWe compare the performance of dispersion-shifted-fibre (DSF) and semiconductor-optical-amplifier (SOA) based phase conjugators in a 10 Gb/s non-return-to-zero transmission system with respect to conversion efficiency, noise figure and distortion. Fibre gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF based conjugator has the advantage of distortion tolerance at higher input power
Optimised square passband fibre Bragg grating filter with in-band flat group delay response
No full textThrough a controlled apodised sinc-shaped refractive index profile, an optimised square reflection band Bragg grating filter is demonstrated. The filter is 5cm long and has a flat dispersion profile within the photonic bandgap and an edge steepness of 7.9dB/GHz
Optimisation of DSF and SOA based phase conjugators by incorporating noise-suppressing fibre gratings
No full textWe compare the performance of dispersion-shifted-fibre (DSF) and semiconductor-optical-amplifier (SOA) based phase conjugators for a 10 Gb/s non-return-to-zero system with respect to conversion efficiency, noise figure and distortion. Fibre gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF based conjugator has the advantage of distortion tolerance at higher input power. Introduction: Optical phase conjugation has attracted much recent research attention due to its potential application for group-velocity-dispersion and self-phase-modulation compensation in mid-point spectral inversion (MPSI) systems, and also for coherent wavelength conversion in optical switching and routing. The two most promising optical phase conjugation techniques are four-wave mixing (FWM) in either dispersion-shifted fibre (DSF), or semiconductor optical amplifiers (SOA). A DSF based conjugator requires phase matching close to its zero dispersion wavelength for efficient four-wave mixing. This restricts its wavelength flexibility compared to an SOA based conjugator which offers a much wider conversion bandwidth. Furthermore, the low FWM conversion efficiency in passive DSF seems to make the SOA a preferred phase conjugating medium. However, in a practical communication system, conjugation optical signal-to-noise ratio (SNR) is more important than conversion efficiency. The noise at the conjugate wavelength is usually dominated by the amplified spontaneous emission (ASE) noise from the pump and signal. The reduction of this noise has been demonstrated in an SOA based conjugator (i) by bandpass filtering of the pump and/or signal waves before mixing, and (ii) by the insertion of a notch filter at the conjugate wavelength before the conjugator. In this letter, SOA and DSF based conjugators are compared by investigating the conversion efficiency, noise and eye opening in a 10 Gb/s non-return-to-zero (NRZ) externally-modulated system, using an identical filtering network. We report for the first time the use of fibre gratings for efficient ASE noise filtering and conjugate signal extraction. The performance enhancement using these noise-suppressing gratings is also investigated
Recent advances in long dispersion compensating fibre Bragg gratings
No full textA great variety of versatile grating techniques have been developed over the past years, such that grating designs to meet nearly any application now can be manufactured. Long fibre gratings have received increased attention from a dispersion compensation point of view, due to the increased bandwidth over which the chromatic dispersion compensation can be performed. The application of long gratings to dispersion compensation is a schizophrenic one though, as on one hand, the linearity of the dispersion is highly improved when longer gratings are employed. The dispersive response of the gratings can also easily be tailored to meet specific applications, whilst the sensitivity to imperfections such as phase-errors caused by the fabrication process and even effects from the fibre imperfections will play a greater role. We will in this paper discuss some of the recent advances in the area of long fibre gratings and discuss theoretical designs to increase the useful bandwidth of gratings designed to compensate both linear and combined linear and higher order dispersion. Furthermore design rules to reduce the effects of environmental caused imperfections from the fibre will be given. Techniques to increase the dispersion bandwidth product, D•Δλ, will also be shown through the use of sampled gratings. All designs will be supported be experimental verifications and the application of some of the grating designs to transmission system experiments
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