各向异性透明晶体如方解石、石英等的折射率，是其固有的特性，称为永久双折射。

The polarization dependence on the refractive index might have several different effects, a few of that happen to be very crucial in nonlinear optics and laser engineering:

直光纤只有很小的随机双折射，即使这样其中的光传输一段距离后偏振状态也会发生变化。存在保偏光纤，是利用了很强的双折射来抑制这些效应。 

In other situations, birefringence is usually induced in at first isotropic optical elements (e.g. crystals with cubic composition, Eyeglasses or polymers) may become anisotropic on account of the appliance of some external influence which breaks the symmetry:

Because 1 wave is retarded with respect to the opposite, interference (either constructive or damaging) takes place concerning the waves since they go through the analyzer. The online result is that some birefringent samples purchase a spectrum of shade when noticed in white gentle as a result of crossed polarizers.

弯曲光纤中也存在类似的效应，由于激光器晶体中的热效应，会产生去极化损耗。 

For an arbitrary angle among propagation route and optical axis, one particular can discover two linear polarization directions exhibiting distinct refractive indices. The very first a single is perpendicular for the vector as well as the optical axis; right here, we have the ordinary index , and such a wave known as a standard wave.

The time period birefringence is typically also used like a quantity (see down below), ordinarily described as the distinction between amazing and standard refractive index at a particular optical wavelength.

By far the most delicate area in the chart is initially-get red (550 nanometers), due to the fact even a slight improve in retardation leads to the color to shift substantially possibly up in wavelength to cyan or all read more the way down to yellow.

双折射现象的明显例子是方解石。透过方解石的菱面体就可以看到明显重影。

The birefringence of nonlinear crystal products permits birefringent period matching of nonlinear interactions. In essence, Which means birefringence compensates the wavelength dependence in the refractive index.

当线偏振激光光束在双折射晶体中传输时，如果偏振方向与双折射轴不重合，这时会包含两个方向具有不同波数的偏振部分。因此，在传输过程中，由于两偏振分量之间存在相对相位变化，于是偏振状态发生变化。

As a way to study a lot more intently how birefringent, anisotropic crystals communicate with polarized light within an optical microscope, the Qualities of someone crystal is going to be considered. The specimen substance is really a hypothetical tetragonal, birefringent crystal acquiring an optical axis oriented inside a course that's parallel to your lengthy axis with the crystal. Light getting into the crystal within the polarizer will likely be touring perpendicular to the optical (extended) axis with the crystal. The illustrations in Determine 8 existing the crystal as it will eventually seem while in the eyepieces of the microscope under crossed-polarized illumination as it really is rotated round the microscope optical axis.

In other scenarios, application of a robust electric subject has equivalent effects, e.g. in Eyeglasses. The non permanent application of such a industry can even bring about a frozen-in polarization, meaning the induced birefringence continues to be even soon after getting rid of the exterior discipline.

Whenever a beam is refracted in the surface of the birefringent crystal, the refraction angle will depend on the polarization route. An unpolarized mild beam can then be break up into two linearly polarized beams when hitting surfaces of the fabric with non-typical incidence (