The coupled-mode equations for fiber Bragg grating （FBG） and long period fiber grating （LPFG） undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.
We report an organic/inorganic hybridized nanocomposite consisting of a bi-functional poly（N-vinyl）-3-[p-nitrophenylazo]carbazolyl serves as a polymeric charge-transporting and second-order nonliner optical matrix, and CdS nanoparticles as photosensitizers to manifest photorefractive （PR） effect. The unpoled PVNPAK film exhibits a second harmonic generation （SHG） coefficient of 4.7 pm/V due to the possibility of self-alignment of the azo chromophore. Significant enhancement of photoconductivity is noticed with the increase of CdS nanoparticles concentration. The photorefractive property of the polymer nanocomposites were determined by two-beam coupling （TBC） experiment. The TBC gain and diffraction efficiency of 11.89 cm-1 and 3.2% were obtained for PVNPAK/CdS at zero electrical field.
Based on thinned fiber Bragg grating and polymer material, we propose a novel high-sensitivity pressure sensor and obtained a new contribution to the pressure sensitivity, which is dependent on the derivative of the effective refractive index （RI） of core mode with respect to the surrounding medium RI, as well as on the relationship between the polymer RI and the pressure; moreover, it is inversely proportional to Young＇s modulus of the polymer material. For the polymer with Young＇s modulus of 1.0 MPa, the total pressure sensitivity 1.54×10-2 MPa-1 can be obtained.
