Birefringence - Examples of Uniaxial Birefringent Materials

Examples of Uniaxial Birefringent Materials

The best-studied uniaxial birefringent materials are crystalline, the refractive indices of several of which tabulated to the right (at wavelength ~ 590 nm). Silicon carbide, also known as Moissanite, is strongly birefringent.

Many plastics are birefringent, because their molecules are 'frozen' in a stretched conformation when the plastic is molded or extruded. For example, cellophane is a cheap birefringent material, and polarizer sheets are commonly used to examine for orientation in birefringent plastics like polystyrene and polycarbonate. Birefringent materials are used in many devices that manipulate the polarization of light, such as wave plates, polarizing prisms, and Lyot filters.

As stated above, birefringence can also arise in magnetic materials, but substantial variations in magnetic permeability of materials are rare at optical frequencies.

Birefringence can be observed in amyloid plaques such as are found in the brains of Alzheimer's patients when stained with a dye such as Congo Red. Modified proteins such as immunoglobulin light chains abnormally accumulate between cells, forming fibrils. Multiple folds of these fibers line up and take on a beta-pleated sheet conformation. Congo red dye intercalates between the folds and, when observed under polarized light, causes birefringence.

Cotton (gossypium hirsutum) fiber is birefringent because of high levels of cellulosic material in the fiber's secondary cell wall.

Slight imperfections in optical fiber can cause birefringence, which can cause distortion in fiber-optic communication; see polarization mode dispersion. The imperfections can be geometrically based, or a result of photoelastic effects from loading on the optical fiber.