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In this paper, the spectral response of uniform and apodized (Gaussian, hyperbolic tangent, apod1, sine, and raised sine) FBGs is analyzed for sensing applications. The reflectivity at Bragg wavelength as well as for sidelobes was assessed as a function of grating length and apodization profiles. The FBG strain and temperature sensors were simulated and a linear response between applied strain or temperature and the wavelength shift is observed. The results indicate that the sensitivity of the sensor is found to be affected both by the grating length and apodization type. The typical strain and thermal sensitivity values are 1.223 pm/$\mu 𝜀$ and 13.60 pm/${}^{\circ }$C, respectively. The results suggest that Gaussian, sine, and raised sine profiles have lower sidelobe strength and reliable sensitivities. The key finding from this study specifies that the ideal grating length must be preferably between 5 and 10 mm for a good sensing behavior.

The defect layer is introduced to the insulator-metal-insulator (IMI) Bragg waveguide structure. The micro-cavity structure of long-range surface plasma is proposed based on the defect mode. The liquid crystal is the defect layer in the structure of Bragg. The energy band characteristics of the long-range surface plasmon Bragg micro-cavity structure are analyzed by using the finite difference time domain method. The influence of the period number and the length of the micro-cavity on the quality factor Q and the volume V of the Bragg grating are discussed. The results show that the photonic energy can be confined very well in the micro-cavity by the structure of the micro-cavity. By controlling the birefringence of liquid crystal, the resonance wavelength of the micro-cavity appears with redshift phenomenon. The tuning range is 42 nm. The tuning of the working window of the long-range surface plasmon filter is realized. The photonic energy is the strongest in the insulating layer and the metal interface. The increase of cycles number has certain limitation on the improvement of the quality factor Q of the cavity. The influence of the defect-cavity length on the resonant wavelength, the quality factor Q and the mode volume V is obvious. The performance of the micro-cavity can be improved by adjusting the number of the micro-cavity and the length of the defect-cavity, and the ratio of Q/V can reach 43,750 in the communication band. The nano micro-cavity provides a new design idea and basis for the fabrication of tunable long-range surface plasmon wave filter in this paper.

A study of nonlinear Bragg grating has been carried out using a modified scheme of approximation originally proposed by Iizuka and de Sterke. A complete classification of the solitonic solutions in the system was given. We further demonstrated in this work the existence of in-gap dark and antidark soliton, in addition to the out-gap solutions reported previously. We also found at the boundaries in the bifurcation diagram, the large-amplitude out-gap antidark soliton and broad in-gap dark soliton.

A numerical study on the hysteretic responses of deep nonlinear Bragg grating systems with symmetric three-layer unit cells has been carried out on the basis of a generalized coupled mode theory modified to accommodate deeper nonlinear refractive index modulation. The results show that the in-gap bistability offers the most favorable features in terms of switching width and threshold for optical switching application. Calculated variations of these operational features with respect to the layer thickness, operating wavelength and nonlinear index contrast provide useful guidance for the design of grating systems intended for specific optical switching applications.

We have demonstrated by Hirota's bilinear method the existence of a new class of bright spatial soliton solutions from the same model of nonlinear optical Bragg grating considered previously by another group of researchers. The explicit expressions obtained from these soliton profiles are distinctly different from the previous results and offer a much more flexible choice of physical parameters for device design. It was further shown that the present formulation provides a classification scheme incorporating previous results as special cases of different parameter sets. Finally, due to the diffraction effect, these solitons were shown to exhibit a certain degree of instability in their perturbed profiles as they propagate along the grating.

Nowadays tools based on Scanning Probe Methods (SPM) have become indispensable in a wide range of applications such as cell imaging and spectroscopy, profilometry, or surface patterning on a nanometric scale. Common to all SPM techniques is a typically slow working speed which is one of their main drawbacks. The SPM speed barrier can be improved by operating a number of probes in parallel mode. A key element when developing probe array devices is a convenient read-out system for measurements of the probe deflection. Such a read-out should be sufficiently sensitive, resistant to the working environment, and compatible with the operation of large number of probes working in parallel. In terms of fabrication, the geometrical uniformity i.e. the realisation of large numbers of identical probes, is a major concern but also the material choice compatible with high sensitivity, the detection scheme and the working environment is a challenging issue. Examples of promising applications using parallel SPM are dip-pen-nanolithography, data storage, and parallel imaging.