Influence Of Linear Birefringence Research Articles

Reflective Detection Method of Partial Discharge Using Optical Fiber Sensor

AbstractAiming at the characteristic of small amplitude of partial discharge current signal, all-optical fiber current sensing system is designed. Two kinds of optical fiber current sensor structures are proposed, which are linear and reflective. The optical path systems of two kinds of fiber optical current sensor are modeled based on Jones matrix. In addition, the output sensitivities of two structures are compared. The results indicate that the sensitivity of the two current sensor structures can be improved, and the output sensitivity of the reflective fiber optical current sensor is twice as high as that of the linear sensor. At the same time, the complete optical path model of optical fiber sensing system is established under the influence of fiber birefringence errors. Finally, the birefringence errors of sensing fiber are simulated. It is concluded that the reflective fiber optical current sensor can suppress the influence of linear birefringence on the accuracy of the sensing system by introducing a large amount of circular birefringence in the sensing fiber.

Influence of linear birefringence on Faraday effect measurement for optical fibers

The influence of the linear birefringence on magneto-optical property measurement for optical fibers is investigated theoretically and experimentally. The evolution of polarization in fibers is simulated by the Jones matrix. To verify this theoretical model, a magneto-optical system is built to measure the input azimuth, output azimuth and ellipticity. The Faraday rotation of spun fibers with different pitches is measured. The Verdet constant increases, while the linear birefringence decreases as the pitch becomes smaller. For spun fibers with 1 mm pitch, the Verdet constant can be enhanced by about 20.7% at 660 nm, compared with that of the unspun fiber. The results indicate that smaller linear birefringence can provide more accurate Faraday rotation measurement.

Influence of cubic nonlinearity on accuracy of polarization transformation by means of a quarter-wave plate

We consider the propagation of powerful laser radiation in an anisotropic medium with natural birefringence and cubic nonlinearity. By the example of a quarter-wave plate, we show theoretically and experimentally that, under the simultaneous influence of linear birefringence and nonlinearity, the accuracy of polarization transformation decreases in proportion to squared В-integral.

Influence of linear birefringence in the computation of scattering phase functions

Birefringent media, like biological tissues, are usually assumed to be uniaxial. For biological tissues, the influence of linear birefringence on the scattering phase function is assumed to be neglectable. In order to examine this, a numerical study of the influence of linear birefringence on the scattering phase function and the resulting backscattering Mueller matrices was performed. It is assumed that the media consist of spherical scattering particles embedded in a nonabsorbing medium, which allows us to employ the Lorenz-Mie theory. In the Monte Carlo framework, the influence of linear birefringence on the components of the electric field vector is captured through the Jones N-matrix formalism. The Lorenz-Mie theory indicates that a given linear birefringence value Δn has a bigger impact on the scattering phase function for large particles. This conclusion is further supported by Monte Carlo simulations, where the phase function was calculated based on the refractive index once in the ordinary direction and once in the extraordinary one. For large particles, comparisons of the resulting backscattering Mueller matrices show significant differences even for small Δn values.

Linearization of fiber-optic polarimetric current sensors

A linearization technique for a fiber-optic current sensor based on the magneto-optical effect is described. The linearization is achieved by an optimized polarizer orientation. Particular attention is payed to the use of several kinds of optical fibers. The influence of linear birefringence on the output signal is discussed. Experimental investigations confirm the applicability of the linearization technique in fiber-optic current sensors.

Magneto-optic waveguide hysteresis loops of ‘‘planar’’ magnetic garnet films

Epitaxial films of modified yttrium iron garnet which are used as optical waveguides for magneto-optic devices have nominally planar anisotropy so that their magnetization can be aligned by small in-plane fields. Films grown on (111) substrates usually have some residual cubic anisotropy that is difficult to measure in the active layer of the double- or triple-layer films used in single-mode waveguides. A new method to determine the magnetic properties of the optically active layer itself has been developed. It is based on magneto-optical hysteresis loops in which the Faraday rotation of the waveguided light is plotted against one component of a rotating in-plane magnetic field. Steps in these hysteresis loops are directly related to the sixfold symmetry of the magnetocrystalline anisotropy of these films. The influence of linear birefringence on the measured Faraday rotation, the magnetostrictive effects associated with the pressure of the prism used for optical coupling into the waveguide, and the advantages of end-fire coupling are discussed. These hysteresis loops are being used in the design of materials for magneto-optic isolators and other waveguide devices.