Magnetooptic sensor based on electrogyration compensation is proposed and experimentally demonstrated by using single quartz crystal. The sensing unit is composed of single quartz crystal and two polarizers. Quartz crystal exhibits magneto-optic, electro-optic and electrogyration effects, thus magneto-optic Faraday rotation angle can be compensated by the electrogyration angle induced by the compensating voltage applied to the crystal. The compensating voltage is sensitive to both the deviation angle between light beam and principal crystalline axis, and the azimuth angle of polarizer. The 50Hz ac magnetic flux density within 267Gs has been measured, the compensating voltage is 0.72V/Gs for a single quartz crystal with a length of 23mm. The proposed sensor has potential application to closed-loop measurement of magnetic field.
Sensing principles and main problems to be solved for optical voltage sensors are briefly reviewed. Optical effects used for voltage sensing usually include electro-optic Pockels and Kerr effects, electro-gyration effect, elasto-optical effect, and electroluminescent effects, etc. In principle, typical optical voltage sensor is based on electro-optic Pockels crystals and closed-loop signal detection scheme. Main problems to be solved for optical voltage sensors include: how to remove influence of unwanted multiple optical effects on voltage sensing performance; how to select or develop a proper voltage sensing material and element; how to keep optical phase bias to be stable under temperature fluctuation and vibration; how to achieve dc voltage sensing, etc. In order to suppress the influence of unwanted optical effects and light beam coupling-related loss on voltage sensing signals, we may pay more attention to all-fiber and waveguide voltage sensors. Voltage sensors based on electroluminescent effects are also promising in some application fields due to their compact configuration, low cost and potential long-term reliability.
Two novel magnetooptic sensors are proposed which are based on mutual compensation of external field-induced linear or circular birefringence. One is based on mutual compensation of the external field-induced linear birefringence produced by both magnetooptic Cotton-Mouton effect and electrooptic Kerr effect. The other one is based on mutual compensation of the external field-induced circular birefringence in crystals exhibiting both Faraday magnetooptic effect and electrogyration effect, such as lead molybdate (PbMoO4) crystal. The 50Hz ac magnetic field in the range of 167Gs was measured by means of electrogyration compensation. Compensating voltage was about 16.5V/Gs for single lead molybdate crystal with a length of 5mm along its principal optical axis. The two proposed magnetooptic sensors can be used in the closed-loop measurement of magnetic field.
Verdet constants of beta-barium borate (BBO) and lead molybdate (PMO) crystals are measured experimentally by the
method of comparison with a block of terbium-doped glass with a known Verdet constant. Experimental setups mainly
include two prism polarizers, a solenoid and ac current supply, and signal processing circuits. The influences of light
intensity fluctuation, applied magnetic field and signal processing circuits on measurement result of Verdet constant can
be removed by using the method of comparison. For light wavelength of 635nm, the measured Verdet constants
respectively are 5.80±0.06 rad/(T.m) for the BBO crystal and 54.6±1.1 rad/(T.m) for the PMO crystal. A novel optical current sensor based on electrooptic compensation is designed in principle using the BBO crystal.
A novel optical voltage sensor is proposed and experimentally demonstrated by use of single Fresnel rhomb bismuth germanate crystal. Different from previous polarimetric voltage sensors, the proposed voltage sensor can provide the π/2 optical bias by two times of total internal reflection of light wave in the crystal, thus any additional quarter wave plate is not necessary. In principle, the influences of measurand voltage and temperature on the π/2 optical bias are neglectable. The 50Hz ac voltage in the range of 2~2000V is measured with good linearity.
A novel optical electric-field sensor is proposed and experimentally investigated by using single beta barium borate (β-
BaB2O4, BBO) crystal. The optical sensing unit is only composed of single BBO crystal and two polarizers, the π/2
optical bias is provided by natural birefringence of the BBO crystal itself. Advantages of the BBO crystal over previous
lithium niobate crystal used as electric-field sensor mainly include larger measurement sensitivity and no ferroelectric
ringing effect. The 50Hz ac and lighting impulse electric fields in the range of (10~400)kV/m have been measured in
experiment with good linearity and fast response.
An optical current sensor with adjustable sensitivity is proposed and investigated in experiment. A single bismuth
germanate crystal is used as both current-sensing element and electro-optic modulator. When a rectangular pulse
modulating voltage is applied to the crystal, the current-sensing signal can be obtained from the peak-to-peak intensity of
output light. Both the measurement sensitivity and its temperature stability of the proposed sensor can be controlled by
the modulating voltage, additionally its linear and monotone varying measurement range is larger than that of
conventional optical current sensor. Direct current of ±(0.1~10)A was measured with electro-optically adjustable
sensitivity, and maximum measurement uncertainty was less than 1.2%.
Based on mutual compensation characteristic of the photoelastic and electrooptic birefringence or phase retardation in
crystal or glass, an optical stress sensor is designed in principle by use of single bulk crystal or glass. Particularly, the
crystal is used as both stress sensing element and electrooptic phase modulator. The configuration of conventional
optical stress sensor is simplified, and closed-loop stress measurement is also possible.
Based on the logarithmic relationship between photovoltaic voltage and incident light intensity of a photo-detector, a
simple and low-cost method is proposed to linearize the measurement of nonlinear variables related to light intensity.
Theoretical analysis shows that this linear measurement method is feasible in a large measurement range if we choose a
proper load resistance for the photodiode. Based on the Lambert-Beer law and the photovoltaic voltage-based
measurement method, the linear measurements of liquid level and liquor concentration have been achieved
experimentally by directly detecting the output voltage of a solar cell, and their nonlinearities are both less than 2.0%.
The Jones vector and matrix with step function are introduced to simplify the analysis and design of optical polarization multiplexing system. By use of step functions, one Jones vector can express the alternately polarized light with multiple polarization states, and one Jones matrix can describe multiple polarization conversions. Some optical design examples demonstrate the effectiveness of the Jones vector and matrix with step functions, and they are suitable for the analysis and design of the optical polarization multiplexing system.
A novel photoelastic stress multiplier is proposed for the first time, which can perform the multiplication operation of two external stresses or forces. The basic structure of this stress multiplier mainly includes two polarizers and two cascaded photoelastic modulators, and theoretical analysis has demonstrated its feasibility. This novel photoelastic stress multiplier will have potential applications in many interdisciplinary fields.
Optical fiber sensors for the measurement of electric power are reviewed. We focus on the direct measurement approach, which allows electric-power-sensing signal to be directly obtained from light wave canier. Based on Pockels and Faraday effects, three kinds of optical electric-power sensors have been developed, including the combination of a Faraday medium with a Pockels medium in cascade; utilization of the single crystal exhibiting both Faraday effect and Pockels effect; and application of the electro-optic crystal multiplier. Potential applications of optical electric-power sensors lie in electric power industry and the field of electromagnetic compatibility. Measurement of active power, uncertainty and effects of temperature variations and vibration are key problems to be solved for optical electric-power sensor. Some corresponding solutions are proposed.
An optical electric-power sensor is proposed and experimentally carried out. Only one block of bismuth germanate crystal is utilized as the sensing element, which exhibits both the Faraday effect and the Pockels effect. The polarized light passing through the crystal can be modulated by the product signal of applied electric and magnetic fields, therefore, instantaneous electric power signal can be obtained when load current and load voltage are simultaneously applied to the sensing crystal by use of an air-cored coil and two plane electrodes. The active power and apparent power within 2000W(or VA) have been measured simultaneously under different power factors. The maximum relative errors are 2.7% for active power measurement and 1 .9% for apparent power measurement. The sensitivity and uncertainty ofthe sensing system are also discussed.
A new multi-function optical fiber sensing system is presented to measure voltage and current simultaneously. This sensing system includes Faraday cell and Pockels cell, Faraday effect is used for current sensing and Pockels effect is used for voltage sensing. To detect sensing light signal, we developed a pulse-controlled polarization converter based on Pockels effect in LiNbO3 crystal. Four polarization components of polarized light can be obtained through one optical channel by the polarization converter. Some sensing experiments are carried on, and the result of experiments are given.
A novel method of measuring the two-dimensional electrostatic field is presented. Based on the dual transverse Pockels effect in some crystals, the electro- optic phase retardation and the azimuth angle of the principal axis in this type of crystal are separately controlled by the applied electric field magnitude and its direction. Therefore, the magnitude and direction of the unknown electric field can be determined by measuring the phase retardation and the azimuth angle. Within the range of 50 kV/m, the experiment on measuring the two-dimensional electrostatic field by using a z-propagating LiNbO3 crystal shows that the nonlinearity errors are less than 4.5% for the field magnitude measurement, and less than 2.3% for its direction. This method will probably be applied to the spot measurement on the two-dimensional electrostatic field.