A novel fiber-optic acoustic sensor using an erbium-doped fiber amplifier (EDFA)-based fiber ring laser and a balanced Sagnac interferometer for acoustic sensing of the partial discharge (PD) in power transformers is proposed and demonstrated. As a technical background, an experimental investigation on how the variations of the fiber birefringence affect the sensor performances was carried out, and the results are discussed. The operation principles are described, and the relevant formulas are derived. The analytical results show that an EDFA-based fiber ring laser operating in chaotic mode can provide a degree of polarization (DOP) tunable light beam for effectively suppressing polarization fading noises. The balanced Sagnac interferometer can eliminate command intensity noises and enhance the signal-to-noise ratio (SNR). Furthermore, it inherently operates at the quadrature point of the response curve without any active stabilizations. Several experiments are conducted for evaluating the performances of the sensor system, as well as for investigating the ability of the detection of high-frequency acoustic emission signals. The experimental results demonstrate that the DOP of the laser beam can be continuously tuned from 0.2% to 100%, and the power fluctuation in the whole DOP tuning range is less than 0.05 dBm. A high-frequency response up to 300 kHz is reached, and the high sensing sensitivity for detections of weak corona discharges, as well as partial discharges also is verified.

A novel fiber optic in-line distributed sensor system for location of an intrusion is proposed. A 3 dB coupler and a Faraday rotation mirror (FRM) are employed to form an interferometer. There are two light paths that have the same optical length but travel different sequence paths in the interferometer. These two paths pass through the intrusion point at different time, so the phase difference is existent. After interference, a fast Fourier transform (FFT) is applied on the output signal to obtain the phase angle in the double intrusion frequency. And then the position of the intrusion point can be determined. Simulation results show that this fiber optic in-line distributed sensor system can locate the intrusion point at a distance of 40 km, with the deviation no more than 130 m, and the relative error is 0.32%.

A novel method is proposed to determine the minimum embedding dimension on the basis of the false nearest nodes (FNN) and the averaged false neighbors (AFN). We take all the false nearest nodes into account and develop two parameters G₁ and G₂ instead of E₁ and E₂ defined by AFN method for analyzing time series. Several short chaotic time series were tested. The proposed method shows more precise than AFN method and requires less subjective parameters than FNN method. The method is effective even if a time series suffers the corruption with a white Gaussian noise of 20%. It can deal with the experimental chaotic signals from the fiber ring laser based on a semiconductor optical amplifier (SOA), while AFN method fails.

A new scheme of variable optical buffer for IP packets is reported. It may be used in access control of HORNET (Hybrid Optoelectronic Ring NETwork), to avoid collision of added packet and the packet already on the ring and improve the loss ratio of the packets. In this scheme, a new multi-wavelength fiber loop memory technique is employed. This architecture uses the wavelength converter (WC) to specify the packets delay and wavelength conversion is accomplished by the technique of four-wave-mixing (FWM) with a semiconductor optical amplifier (SOA). The range of delay is 10 to 9990 bytes periods. First, architecture, operation principle, characteristics and applications of this scheme of variable optical buffer are introduced. Next, a new unslotted CSMA/CA MAC scheme based on the variable optical buffer is briefly introduced too. Finally, the simulation results are presented.