Chuansheng Li

Design principle for sensing coil of fiber-optic current sensor based on geometric rotation effect

The design principle exploiting the geometric rotation effect for the sensing coil of the fiber-optic current sensor (FOCS) on the basis of the polarization-rotated reflection interferometer is investigated. The sensing coil is formed by winding the low birefringence single-mode optical fiber in a toroidal spiral. The effects of the linear birefringence on the scale factor of the sensor can be suppressed with the reciprocal circular birefringence by appropriately designing the geometric parameters of the sensing coil. When the rated current is 1200 A(rms), the designed sensing coil can ensure the scale factor error of the sensor to satisfy the requirements of the 0.2 S class specified in IEC60044-8 over a temperature range from -40 °C to 60 °C.

Birefringence elimination of bismuth germanate crystal in quasi-reciprocal reflective optical voltage sensor.

Bismuth germanate (Bi(4)Ge(3)O(12), BGO) has been widely utilized for the application of Pockels effect-based voltage and electric field sensors, because it possesses no unwanted effects ideally. However, there are multiple birefringences in BGO crystal induced by natural imperfections, temperature-dependent strain, and external pressure (or stress), which influences the demodulation of the Pockels effect induced by the voltage to be measured. For a Pockels effect-based quasi-reciprocal reflective optical voltage sensor, the influences of the multiple birefringences in BGO crystal are investigated and an elimination scheme is also proposed in this paper. The feasibility of the proposed elimination scheme is simulated and experimentally verified.

Influences of Imperfect Polarization Induced Effects to the Quasi-Reciprocal Reflective Optical Voltage Sensor

The influences of imperfect polarization induced effects are investigated in this paper for a novel optical voltage sensor (OVS), which consists of quasi-reciprocal reflective optical interferometer and digital closed-loop detection scheme. The numerical models are established to describe the relationship between the characteristic parameters of imperfect polarization and the performances of the OVS, which is also simulated to investigate quantitatively. The numerical models and the simulated results are experimentally verified with typical imperfect polarization induced errors. Accordingly, the primary characteristic parameters of imperfect polarization are illuminated. Whats more, the conclusions of this paper can provide useful references for the design and performance improvement of the novel Pockels effect based OVS.

Error analysis and experiment for reflective sagnac interferometer-type fiberoptic current sensor

A reflective Sagnac interferometer-type fiber-optic current sensor (RS-FOCS) is presented with Y-branch integrated-optics phase modulator and polarization beam splitter. The digital closed-loop Fiber gyroscope technology is employed for signal detection and processing. The variation of linear birefringence and Verdet constant of sensing fiber and phase retardation of quarter-wave retarder with temperature is indicated as the primary scale factor error source. The effect of linear birefringence was suppressed by winding the sensing fiber spirally, and the ratio error caused by the temperature dependence of the Verdet constant is reduced by elliptical-core fiber quarter-wave retarder. The performance of RS-FOCS is tested, and the results show that: the error is less 0.1% for high current whereas more than 1% for low current; the maximal variation of scale factor is 0.066% in a month; the scale factor error is less than 0.2% at −40°C∼60°C.

Analysis and elimination of bias error in a fiber-optic current sensor

Bias error, along with scale factor, is a key factor that affects the measurement accuracy of the fiber-optic current sensor. Because of polarization crosstalk, the coherence of parasitic interference signals could be rebuilt and form an output independent of the current to be measured, i.e., the bias error. The bias error is a variable of the birefringence optical path difference. Hence, when the temperature changes, the bias error shows a quasi-periodical tendency whose envelope curve reflects the coherence function of light source. By identifying the key factors of bias error and setting the propagation directions of a super-luminescent diode, polarization-maintaining coupler and polarizer to fast axis, it is possible to eliminate the coherence of parasitic interference signals. Experiments show that the maximum bias error decreases by one order of magnitude at temperatures between -40°C to 60°C.

Influence of polarization-dependent crosstalk on scale factor in the in-line Sagnac interferometer current sensor

Abstract. The scale factor of the in-line Sagnac interferometer current sensor associated with the polarization-dependent crosstalk introduced by optical devices is theoretically investigated. The variations of output pigtail polarization crosstalk of the Ti-indiffused LiNbO3 phase modulator and polarization crosstalk of the polarization-maintaining (PM) delay optical fiber with the temperature can lead to the scale-factor error. The white-light interferometry is utilized to measure the pigtail polarization crosstalk of the phase modulator. The variation of the scale factor with the temperature has been tested over a range from −40°C to 60°C experimentally. The results confirm the influence of output pigtail polarization crosstalk of phase modulator and polarization crosstalk of the PM delay optical fiber on the scale factor. To ensure the scale factor error to be within ±0.2%, the output pigtail polarization crosstalk of phase modulator and polarization crosstalk of the PM delay optical fiber should not exceed −30  dB for the current sensor operating in the outdoor environment.

A novel interferometric fiber-optic magnetometer with double digital closed-loop detection scheme

A novel interferometric fiber-optic magnetometer with double digital closed-loop detection scheme is presented in this paper. The particular design of optical circuit is performed to the conventional Michelson interferometer based fiber-optic magnetometer. The digital correlation detection technique with double closed-loop is applied to demodulate the weak magnetic field. One digital closed-loop with square-wave phase modulation is realized to eliminate the low-frequency environmental phase drift. The other is utilized to suppress the hysteresis effects of the magnetostrictive material and recover the magnetic field to be measured. Simulation results on the digital closed-loop algorithms verify the feasibility of the proposed scheme.