1,721,056 research outputs found
Viewpoint: optical rogue waves on demand
No full textResearchers achieve generation of stable and coherent optical rogue waves. A Viewpoint on: Seeded Supercontinuum Generation with Optical Parametric Down-Conversion D.R.Solli, B.Jalali and C.Ropers Phys. Rev. Lett. 105(23), 233902 (2010) – Published November 29, 2010 Among the myriad of nonlinear optical effects, supercontinuum generation is perhaps the most visually stunning and useful in applications ranging from tomography to frequency metrology. When a high-intensity optical pulse propagates through a nonlinear dielectric medium, its spectrum broadens, with the degree of broadening depending on the strength of the interaction. If the interaction is strong enough (i.e., the interaction length is long or the intensity is high enough), then this spectral broadening can be dramatic, resulting in a supercontinuum (SC) whose width can include the entire visible spectrum. While SC can be produced in many different ways, the most common way today is to use a photonic crystal fiber, which has a small core to confine the light, resulting in a high intensity and low loss, allowing for long interaction lengths [1]. Despite the ease of generating SC, the dynamics behind it are extremely complicated, involving a cascade of different nonlinear effects. In a paper appearing in Physical Review Letters [2], Daniel Solli and Bahram Jalali from the University of California, Los Angeles, with Claus Ropers from the University of Göttingen in Germany have gone a long way towards clarifying the role that various nonlinear effects play. More importantly, they have shown that it is possible to control the relative importance of different nonlinear interactions, giving researchers control over the bandwidth and coherence properties of the supercontinuum, effectively allowing it to be used in ever more sophisticated ways. &more..
Taper designs for semiconductor filled fibres
No full textRecently there has been much interest in designing optical tapers for nonlinear pulse manipulation in both standard[1] and semiconductor filled fibres[2]. Such tapers can be used to overcome the large linear losses in semiconductor filled fibres while allowing parabolic pulse generation or soliton propagation for example. However once the taper profile has been chosen to overcome the linear loss problem in semiconductor filled fibres the problem of two photon absorption (TPA) and associated free carrier effects remain. In this work we show that it is possible to use a genetic algorithm to design tapers that alleviate both linear and nonlinear losses and hence should allow high quality pulse propagation over several centimetres of semiconductor filled fibres
Improved flatness of a supercontinuum at 1.55 microns in tapered microstructured optical fibres
No full textSupercontinuum (SC) generation occurs when high-power ultrashort optical pulses propagate through a nonlinear optical medium and it has been investigated since 1970s. Microstructured optical fibres (MOFs) have enabled major advances in obtaining SC spectral broadening over the past decade, leading to the development of new inexpensive and efficient sources. Low cost SC will find new applications in diverse areas such as telecommunications, optical frequency metrology, spectroscopy etc
Design of λ/4 phase shifted DFB fibre Raman laser
No full textThe feasibility of building a distributed feedback fibre Raman laser based on a long uniform fibre Bragg grating was suggested by Perlin et al. [1]. However, such a laser requires good grating uniformity along a very long length, e.g. 1m, and has not been investigated experimentally. In this study, we demonstrated an improved design of a DFB fibre Raman laser with an optimised λ/4 phase-shifted grating structure, which enables highly efficient laser operation at low threshold with a relatively short cavity length
Parabolic pulse generation using tapered microstructured optical fibres
Get PDFIn this paper we present simulations of pulse shaping in a microstructured optical fibre (MOF) taper. The MOF has been modelled in the normal dispersion regime and taper parameters proposed. We show results of parabolic pulse generation in the linearly tapered optical fibre, for Gaussian input pulses of different widths and powers
Theoretical study of noise reduction of NRZ signals using nonlinear broken micro-coil resonators
No full textNonlinear microcoil resonators are extremely attractive devices for nonlinear optics; however, due to their high-Q values, their use at high speeds is limited. In this letter, we analyze a simple way of increasing their bandwidth, namely breaking the fiber in several places, and show that the resulting device is suitable for noise reduction in realistic systems. Simulations show that an in-line broken resonator can significantly reduce the impact of amplitude noise on the bit-error rate of nonreturn-to-zero signals
Approximate method for gap soliton propagation in nonuniform Bragg gratings
No full textAn effective particle picture developed earlier for gap soliton propagation in piecewise uniform gratings is extended to treat gratings that vary gradually. In particular, we consider gratings in which the strength or the Bragg frequency varies linearly with position. We use this to analyze propagation in more complicated structures corresponding to localized grating defects, and gradual interfaces between two different gratings
Nonlinear polarisation effects in optical microcoil resonators with fibre twist and birefringence
No full textWe study the nonlinear response of optical microcoil resonators (OMRs) based on twisted birefringent microfibres by incorporating Kerr nonlinearity into the underlying coupled mode equations. The resulting hysteresis characteristics were found to be highly polarisation dependent, with both the switching powers and contrast levels strongly influenced by the twist-induced cross-polarisation coupling. In addition, the existence of multiple bistability in OMRs is explored when the two orthogonal polarisations' resonances are spectrally close enough to influence the propagation of a monochromatic pump. Both the bistability and nonlinear switching may potentially be utilised for implementing polarisation-sensitive devices, especially for signal processing purposes, and benefit from the low threshold powers needed to observe nonlinear effects in OMRs
Resonantly enhanced third harmonic generation in microfiber loop resonators
No full textWe theoretically study third harmonic generation in silica microfiber loop resonators wherein the large resonant field strength is exploited to increase the efficiency and reduce the required pump power, with a focus on the influence of loop parameters such as loss and coupling. For a 3 mm length loop, the conversion can reach several percent, that is, 640 times greater than an equivalent straight microfiber, for input powers as low as 100 W. The harmonic signal can be toggled between a high- and low-output state due to hysteresis at higher powers, and the efficiency can be further enhanced if the harmonic light is recirculated and coresonant with the pump
Polarisation effects in optical microcoil resonators
No full textOptical microcoil resonators (OMRs) fabricated by wrapping a microfibre around a rod to allow evanescent coupling between adjacent turns as in Fig 1. (a) have recently attracted much interest due to their high Q-factor and large extinction ratios resonances, low input and output coupling losses, large evanescent field and compactness [1,2], with applications such as sensing [3] and signal processing [4]. However, theoretical models published so far have neglected polarisation effects, and hence in order to develop a more detailed understanding we have modelled the OMR with polarisation-dependent coupled mode equations in the linear [5] and nonlinear regimes
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