1,720,991 research outputs found
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
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
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
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
Polarisation effects in nonlinear microcoils
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
Improved design of a DFB Raman fibre laser
Get PDFA Raman fibre laser based on phase shifted DFB structures is modelled for the first time. Using parameters of realistic devices, the model predicts low-threshold and highly-efficient laser output. The change of position and width of the phase shift were found to have a substantial impact on laser performanc
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