A high-temperature fiber sensor based on two paralleled fiber-optic Fabry–Perot interferometers (FPIs) with ultrahigh sensitivity is proposed and experimentally demonstrated. Unlike the structures of the traditional Vernier effect composed of the cascaded components, the proposed fiber sensor is made up of two paralleled FPIs for high-temperature sensing with advantages of simple fabrication, high sensitivity, and low noise. One FPI for sensing is obtained by fusing a short section of polarization-maintaining photonic crystal fiber into the lead-in single-mode fiber (SMF). The other for reference is obtained by fusing a short section of hollow core silica tube between two SMFs. The two FPIs have similar free spectral range, with the spectral envelope of the paralleled sensor shifting much more than the single-sensing FPI. Experimental results indicate that the proposed sensor possesses considerable temperature sensitivities of −45 and −92  pm  /    °  C, respectively, in the measurements of 100°C to 300°C and 300°C to 800°C.

We use the iterative split-step Fourier method to simulate the eight quadrature amplitude modulation all-optical orthogonal frequency division multiplexing (OFDM) system employing different constellation design schemes. It is found that properly narrowing down the modulus difference between constellation points has an impact on the whole system’s ability to resist nonlinear effects. The results show that by means of changing the modulus values of the constellation points, the system bit error rate will be significantly reduced when the optical signal-to-noise ratio is high. Furthermore, by comparing four different constellation diagrams, we propose an alternative solution to reduce the distortion brought by the nonlinear effects on all-optical OFDM systems, that is, the constellation points can be appropriately redesigned to improve the performance of high nonlinear effect systems.