A performance study of a nonlinear all Fibre Michelson interferometer,add-drop multiplexer,based in Fibre Bragg grating mirrors

In this paper we report a numerical investigation of an all-fibre narrowband transmission filter in the arrangement of two identical photo-imprinted Bragg gratings symmetrically located in each arm of a Michelson Interferometer, simulating, thus, an add-drop filter. The transmission characteristics and in addition the crosstalk level and extinction ratio, were studied. The coupled mode theory and the fourth-order Runge-Kutta method were applied, respectively, to solve the coupled differential equations. This is the first study, as far as we now, of the performance of this device considering the nonlinearity of the fibre coupler and linearity of the fibre Bragg gratings. The device is presenting a highly nonlinear behavior dependence in dephasing and pump power.     

Super-FM and analogue-to-digital-conversion technologies for next-generation wireless access in optical fibres

Fibre-in-the-loop (FITL) or hybrid fibre coaxial (HFC) networks are the ideal transmission infrastructure for next-generation wireless communication networks, such as digital microcells, personal communication networks (PCNs) and wireless local area networks (LANs). In this paper, the feasibility of two cost-effective optical fibre transmission technologies, super-frequency-modulation (FM) and analogue-to-digital conversion, for wireless access in broadband optical fibres are experimentally demonstrated. Associated circuit and system implementation issues are investigated. Furthermore, by using a statistical model of multiple access in different microcellular environments, we find that both transmission technologies can meet the dynamic range requirements with a significant safe margin.     

Berry phase in a generalized nonlinear two-level system

In this paper, we investigate the behaviour of the geometric phase of a more generalized nonlinear system composed of an effective two-level system interacting with a single-mode quantized cavity field. Both the field nonlinearity and the atom-field coupling nonlinearity are considered. We find that the geometric phase depends on whether the index k is an odd number or an even number in the resonant case. In addition, we also find that the geometric phase may be easily observed when the field nonlinearity is not considered. The fractional statistical phenomenon appears in this system if the strong nonlinear atom-field coupling is considered. We have also investigated the geometric phase of an effective two-level system interacting with a two-mode quantized cavity field.     

Berry phase in a generalized nonlinear two-level system

In this paper, we investigate the behaviour of the geometric phase of a more generalized nonlinear system composed of an effective two-level system interacting with a single-mode quantized cavity field. Both the field nonlinearity and the atom--field coupling nonlinearity are considered. We find that the geometric phase depends on whether the index $k$ is an odd number or an even number in the resonant case. In addition, we also find that the geometric phase may be easily observed when the field nonlinearity is not considered. The fractional statistical phenomenon appears in this system if the strong nonlinear atom--field coupling is considered. We have also investigated the geometric phase of an effective two-level system interacting with a two-mode quantized cavity field.     

Four-wave mixing crosstalk in optical fibre parametric amplifiers with orthogonal pumps

We experimentally investigated the generation of new unwanted frequencies generated by four-wave-mixing in fibre optical parametric amplifiers with two orthogonally polarised pumps and 17 dB of small signal gain. At these gain levels, we simultaneously observe two distinct types of mixing interactions and demonstrate that they vary with changing output power and gain at different rates. We also demonstrate that a combination of high pump power and low nonlinearity fibre results in less power in the unwanted peaks than a combination of low pump power and highly nonlinear fibre. Because these new unwanted four-wave mixing peaks result in crosstalk between wavelength division multiplexed channels, building parametric amplifiers with a combination of high pump power and fibre of low nonlinearity is desirable.     

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk-off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high-dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20×80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold (for Q > 10 dB) about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/(nm·km) dispersion coefficients.     

Performance comparison of pre-, post- and symmetrical-dispersion compensation techniques using DCF on 40 Gbps OTDM system for different fibre standards

Various factors like polarization mode dispersion, non-linear effects, Kerr effect, second and third order dispersion impose limit on the performance (transmission distance, pulse broadening) of Optical Time Division Multiplexed (OTDM) transmission system. In this paper, the performance comparison of 40 Gbps OTDM transmission system with pre-, post-, and symmetrical-dispersion compensation techniques for different fibre standards has been carried out. It has been observed that for pre compensation, ITU 655 [D = 3.78 ps/nm/km] came to be best suitable fibre with the dispersion compensating fibre length of 2.36 km for maximum reach of 3000 km. For post- and symmetrical-compensation, the behaviour of alcatel [D = 8 ps/nm/km] is almost similar with maximum transmission distance of 3200 and 3050 km respectively.     

Highly nonlinear chalcogenide fibres for all-optical signal processing

Chalcogenide glasses offer many attractive properties for all-optical signal processing including large Kerr nonlinearity (up to 500 × silica glass), an intrinsic ultrafast response time and low to moderate two-photon absorption (TPA). These properties together with the convenience of a fibre format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this paper, several nonlinear processing functions will be demonstrated including: femto-second pedestal free, pulse compression; all-optic wavelength conversion; and all-optical regenerator. In addition, we show enhanced nonlinearity for more efficient signal processing by tapering the As₂Se₃ fibre. These applications show chalcogenide glass fibres are very promising candidate materials for nonlinear all-optic signal processing.     

Generalized Gaussian analysis of fibres with non-Kerr-law nonlinearities

We provide analytic results for fibres with non-Kerr-law nonlinearities and saturation, using an accurate and versatile approach — the generalized Gaussian analysis. These results can be useful in analysis and design of nonlinear devices using fibres with non-Kerr-law or saturable nonlinearity. In the case of nonlinear fibre tapers, for example, we show how optimum design parameters can be found for various forms of nonlinearity.     

Nonlinear acoustic approach to material characterisation of polymers and composites in tensile tests

The paper reports on experimental study of elastic nonlinearity of polymers and glass fibre-reinforced (GFR-) composites in a wide range of tensile stress applied (up to a fracture limit). Focused slanted transmission mode (FSTM) of air-coupled ultrasound is adapted for remote generation and detection of flexural waves in the samples of plastics. Local noncontact measurements of flexural wave velocity as a function of static strain are used to calculate the second-order nonlinearity parameters beta2 and study their behaviour through a loading cycle. Molecular untangling and crazing phenomena are identified, respectively, with maxima of positive and negative beta2 in thermoplastics. In composites, mechanics of fibre-matrix interaction is considered for brittle and plastic fractures. Hysteresis in velocity variation during loading-unloading cycle is used as an indicator of residual defect accumulation.     

Determination of the optimum electrical bandwidth for spectral slicing

The implementation of wavelength division multiplexing (WDM) in communication access networks is dependent upon the availability of low cost optical sources. One possible alternative to lasers is to employ slices of a broadband optical source obtained via optical filters, which may be tuneable. This paper considers the behaviour of such a spectrally sliced optical transmission system as a function of the bandwidth of a realistic receiver electrical filter for the first time. The treatment includes distortion from optical fibre dispersion over several kilometres of fibre. The optimum ratio between the electrical bandwidth and the optical bit rate is found to be ~0.6 for a fifth-order Bessel filter     

Perturbation of Transmission Matrices in Nonlinear Random Media

Random media with tailored optical properties are attracting burgeoning interest for applications in imaging, biophysics, energy, nanomedicine, spectroscopy, cryptography, and telecommunications. A key paradigm for devices based on this class of materials is the transmission matrix, the tensorial link between the input and the output signals, that describes in full their optical behavior. The transmission matrix has specific statistical properties, such as the existence of lossless channels, that can be used to transmit information, and are determined by the disorder distribution. In nonlinear materials, these channels may be modulated and the transmission matrix tuned accordingly. Here, the direct measurement of the nonlinear transmission matrix of complex materials is reported, exploiting the strong optothermal nonlinearity of scattering silica aerogel (SA). It is shown that the dephasing effects due to nonlinearity are both controllable and reversible, opening the road to applications based on the nonlinear response of random media.     

Experimental study of stability properties of injection-locked InGaAsP/InP laser diodes

Single-mode operation of the laser is a basic condition in an optical wide-band transmission link. Lasers stabilized by injection locking showed excellent side-mode suppression. Slight detunings within the locking range between the master laser and slave laser caused by modulation, bias current variations or optical feedback led to unstable behaviour and disturbed the BER of a 1.12 Gbits^–1 transmission experiment via a 21-km single-mode fibre.     

Equilateral pentagon polarization maintaining photonic crystal fibre with low nonlinearity

A new pentagon polarization maintaining photonic crystal fibre with low nonlinearity is introduced. The full vector finite element method was used to investigate the distribution and the effective area of modal field, the nonlinear properties, the effective indices of two orthogonal polarization modes and the birefringence of the new PM-PCF effectively. It is found that the birefringence of the new polarization maintaining photonic crystal fibre can easily achieve the order of 10^-4, and it can obtain higher birefringence, larger effectively mode-field area and lower nonlinearity than traditional hexagonal polarization maintaining photonic crystal fibre with the same hole pitch, same hole diameter, and same ring number. It is important for sensing and communication applications, especially has potential application for fibre optical gyroscope.     

Theoretical modelling of the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers

By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.     

Theoretical modelling of the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers

By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.     

Fractional-calculus analysis of human immunodeficiency virus and CD4+ T-cells with control interventions

It is undeniable that HIV infection has been a censorious public health concern over the past four decades. It is reported that HIV is the main reason for AIDs which has decimated the global population of humans and imposed a significant economic burden on affected areas. Hence, it is significant to study the transmission of HIV viruses in the body of a human host. In this study, we use a fractional framework to organise the intricate interactions of CD4⁺ T-cells and HIV viruses in order to investigate HIV infection with control interventions. We apply the operators of Caputo and Atangana–Baleanu to interrogate the transmission phenomena of HIV viruses. For the analysis of our system, we present the basic concepts of the fractional operators. Numerical schemes are provided to show the solution pathways of the system with the variation of input parameters. Furthermore, the findings emphasise the chaotic and dynamical behaviour of HIV. We run several simulations to visualise the influence of input factors and quantitatively illustrated the dynamics of HIV. Chaos and oscillatory behaviour are intimately linked, and this is owing to the system's nonlinearity. Furthermore, our findings indicate the most important factors for infection control and prevention.     

Highly nonlinear optical fibre loop mirror for reshaping femtosecond pulses from a soliton-compressed electro-absorption modulator source over a wide repetition rate and wavelength range

Highly nonlinear fibre (HNF) applied to a nonlinear optical fibre-loop mirror (NOLM) proves very effective for high quality femtosecond pulses shaping. The HNF exhibiting about four times larger nonlinearity than either dispersion flattened fibre or dispersion-shifted fibre excites higher-order soliton propagation enabling significant pulse compression, while shortening the loop length required for efficient switching, which advantageously reduces both the detrimental higher-order chromatic dispersion effects and sensitivity to environmental perturbations. A short NOLM consisting of a 60 m HNF demonstrates effective reshaping and compression of 254–394 fs pulses from a fibre-soliton compressed electro-absorption modulator source to produce pedestal-free and transform-limited 186–243 fs pulses over a wide wavelength (1550–1570 nm) and repetition-rate (6.8–18 GHz) range.     

Influence of Non-uniform Temperature Field on Spectra of Fibre Bragg Grating

We simulate the spectrum characteristics of fibre Bragg grating （FBG） with non-uniform temperature using the transmission matrix method, and the results are analysed. It is found that firstly the modulated coefficient of average refractive index is a very important parameter that influences the spectrum characteristic of the fibre Bragg grating, and secondly the spectrum curves are different in different temperature fields at the same parameter. Hence, we can determine the metrical temperature by analysing the spectrum of fibre Bragg grating.