Microwave signal with high frequency and low phase noise is generated based on a parity-time (PT) symmetric optoelectronic oscillator (OEO). The PT-symmetric OEO based on normal and reversed traveling-wave modulation is formed by normal and reversed modulation in a travelling-wave intensity modulator (IM) using the radio-fiber (RF) input and termination ports. Gain and loss balance can be realized to achieve PT symmetry thanks to the different modulation efficiencies for microwave signals applied via different RF ports. The operation of the proposed OEO has been experimentally verified. A microwave signal is generated at 10 GHz with a phase noise of -110.7 dBc/Hz at an offset frequency of 10 kHz and a sideband suppression ratio of 46.46 dB. The approach has potential applications in high-quality microwave signal generation and simplify the structure of PT-symmetric OEO system.
A demodulation based on the principle of fiber Bragg grating edge filter method is used to measure impact energy of acrylic plate (PMMA) and aluminum plate in this paper. A new demodulation method based on damping attenuation principle is proposed. Fiber Bragg grating sensing system is built in the experiment. The complex vibration wave generated by impact energy is processed by using the envelope of peak value in MATLAB. The experimental results show that using the time length corresponding to the peak attenuation of 10% as the demodulation basis has a higher Goodness of fit. The linear fitness of PMMA plate and aluminium plate is 0.94 and 0.89, respectively. At the same time, it is concluded that this method can be used to preliminarily determine whether the plate is viscoelastic or not. This is a new potential demodulation method for practical impact energy detection based on fiber Bragg grating.
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