We propose a six-fold photonic quasi-crystal fibre with a trapezoidal analyte channel based on surface plasmon resonance for the detection of high refractive index liquid analytes and numerically analyse its sensing performance for different liquid analyte refractive indices and heights using the finite element method. In contrast to the common D-shaped structure photonic crystal fibre, we design a trapezoidal analyte channel to investigate the role of the sample liquid height within the channel and discussed the feasibility of the fabrication process. We find that with various liquid analyte heights ratio of 20%, 25%, 30% and 50% of the maximum channel height, the proposed biosensor exhibits linear sensing performance with a maximum refractive index (RI) sensitivity of 4400 nm/RIU, 6100 nm/RIU, 8000 nm/RIU and 17000 nm/RIU respectively, for analytes RI range of 1.44 to 1.57, 1.41 to 1.51, 1.40 to 1.49 and 1.40 to 1.44. This sensor is suitable to detect various high RI chemicals, biochemicals and organic chemical samples. Owing to its simple structure of the proposed biosensor with promising linear sensing performance, we envisage that this biosensor could turn out to be a versatile and competitive instrument for the detection of high refractive index liquid analytes.

In this paper, for sensing and monitoring the biochemical analyte dissolved in liquid, antigen-antibody interaction or protein-DNA/RNA binding process, we design a surface plasmon resonance refractive index based biosensor by using a dual core D-shaped six-fold photonic crystal fibre which is embedded with silver nanowires for multi-detection. We numerically analyze both the dispersion relations and the loss spectra for various analytes by finite element method. This optical fibre bio-sensor monitors the changes of the refractive index for different analytes by measuring the spectral shifts of the fibre loss peaks at their resonance wavelengths. With the wavelength interrogation method, we find that the proposed biosensor with two sensing channels exhibits a maximum refractive index sensitivity of 3400 nm/RIU and a resolution of 2.94 × 10 −5 RIU for a large sensing range from 1.35 to 1.50, which covers most known analytes of proteins, viruses or DNA/RNA. By utilizing 200 nm silver nanowires in the sensing channels, the sensitivity can be enhanced up to 4000 nm/RIU. Due to its special twochannel design for multi-sensing, it is possible to distinguish/study the binding possibility/capability of unknown analyte with two different target proteins simultaneously. Further, by introducing another critical channel, the confinement loss for either channel I or channel II can be greatly enhanced for high accurate result and more reliable sensing. Moreover, we numerically prove that the diameter of nano silver wires has great influences on the sensing peaks and sensitivity of the proposed biosensor.

In this paper, we design a 6-fold D-shaped photonic crystal fibre sensor based on the surface plasmon resonance (SPR). The coupling between fundamental core mode and three surface plasmonic modes which have different electric filed distributions for analytes of various refractive indices. We observe two different types of SPRs, namely, 'dielectric like' resonance with low-loss peak and 'plasmon like' resonance with high-loss peak, by analyzing the electric field distribution of the fibre modes. Further, we discuss the influence of the secondary SPR over the main SPR which is directly related to the detection performance of the proposed sensor. In order to mitigate the adverse effect of the sub-peak of the secondary SPR on the sensor's dynamic sensing range (DSR), we reduce the thickness of analyte's binding layer from 1500 nm to 500 nm. Thus, DSR can be extended to 44.4% from 1.33-1.41 to 1.33-1.45 at the cost of a reduced maximum sensitivity from 7900 nm/RIU to 5300 nm/RIU. Owning to the simple structure design of the proposed sensor, we envisage that this highly sensitive D-shaped PCF-SPR sensor could be developed as a versatile and competitive instrument with a large and flexible refractive index detection range.

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By means of the variational formalism for the nonlinear Schrödinger equation, we find an explicit relation for the power of a pulse in terms of its duration, chirp and fiber parameters (group-velocity dispersion and self-phase modulation parameters). Then, using that relation, we derive the explicit analytical expressions for the variational equations corresponding to the amplitude, width, and chirp of the pulse. The derivation of the analytical expressions for the variational equations is possible for the condition when the Hamiltonian of the system is zero. Finally, for Gaussian and hyperbolic secant ansatz, we show good agreement between the results obtained from the analytical expressions and the direct numerical simulation of the nonlinear Schrödinger equation.