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 reduce part from the Michel-Levy chart (x-axis) marks the orders of retardation in multiples of somewhere around 550 nanometers. The area amongst zero and 550 nanometers is known as the initial get of polarization colors, as well as the magenta coloration that happens inside the 550 nanometer location is commonly termed very first-order red.
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。
Birefringence is formally defined as the double refraction of light inside a clear, molecularly requested material, which happens to be manifested with the existence of orientation-dependent variations in refractive index. Quite a few transparent solids are optically isotropic, meaning which the index of refraction is equal in all Instructions throughout the crystalline lattice.
Birefringence would be the assets of some transparent optical elements which the refractive index depends on the polarization route - which is described as the way of the electric field.
In laser technology and nonlinear optics, the phenomenon of birefringence takes place mostly while in the context of non-isotropic crystals:
Figure 7 illustrates a birefringent (anisotropic) crystal placed between two polarizers whose vibration Instructions are oriented perpendicular to each other (and lying in directions indicated by the arrows next to the polarizer and analyzer labels).
In other situations, birefringence is often induced in originally isotropic optical components (e.g. crystals with cubic framework, glasses or polymers) could become anisotropic because of the applying of some external impact which breaks the symmetry:
That is the commonest method of period matching for various different types of nonlinear frequency conversion for example frequency doubling and optical parametric oscillation.
In some instances, mechanical worry has that effect. That can easily be noticed using a bit of acrylic involving two crossed polarizers: when stress is applied to the acrylic, a person observes colored patterns ensuing from your wavelength-dependent outcome of tension-induced birefringence.
Depending on the situation, the beams could be subject to polarization-dependent refraction angles. You then have two different output beams, Though click here their variance in propagation path could possibly be inside their beam divergence, so that they're strongly overlapping and are tough to different based on spatial qualities. If they may be thought of just one beam, that beam is needless to say not polarized.
These phenomena are illustrated in Figures two by way of four. The calcite crystal offered in Figure 3(b) is positioned over the cash letter A on a white sheet of paper demonstrating a double image observed through the crystal. If the crystal had been to become gradually rotated across the letter, certainly one of the images of your letter will keep on being stationary, though the opposite precesses within a 360-degree round orbit throughout the very first. The orientation of the electric vector vibration planes for the two the normal (O) and remarkable (E) rays are indicated by lines with doubled arrows in Determine 3(b).
Anisotropic crystals, which include quartz, calcite, and tourmaline, have crystallographically distinct axes and interact with mild by a mechanism that's dependent upon the orientation from the crystalline lattice with respect for the incident mild angle. When gentle enters the optical axis of anisotropic crystals, it behaves in the way just like the interaction with isotropic crystals, and passes by at only one velocity.
In Determine three, the incident light-weight rays giving rise towards the regular and remarkable rays enter the crystal in the course that is oblique with respect on the optical axis, and they are chargeable for the observed birefringent character. The actions of an anisotropic crystal differs, nonetheless, In case the incident mild enters the crystal within a direction that's either parallel or perpendicular towards the optical axis, as presented in Determine 4. When an incident ray enters the crystal perpendicular into the optical axis, it is divided into everyday and incredible rays, as explained earlier mentioned, but in lieu of getting diverse pathways, the trajectories of those rays are coincident.
Returning for the calcite crystal offered in Determine two, the crystal is illustrated getting the optical axis positioned at the highest remaining-hand corner. On coming into the crystal, the standard light-weight wave is refracted devoid of deviation from the normal incidence angle as though it have been touring through an isotropic medium.