The birefringence is the difference between the refractive index of a fiber in a direction at parallel to the fiber axis and in a direction at right angles. It is caused by asymmetric core shape for the two axes, and majorly one of the manufacturing imperfections. It helps in controlling polarization property inside the fiber.
Inevitable manufacturing imperfections in optical fiber leads to birefringence, which is one cause of pulse broadening in fiber-optic communications. Such imperfections can be geometrical (lack of circular symmetry), due to stress applied to the optical fiber and/or due to bending of the fiber.
Quaternary structure of proteins is composed of two or more polypeptide chains. Insulin has two; one alpha and one beta chain. The two chains are joined together by disulfide bonds at two points (at cysteines). Other examples of quaternary proteins structures are DNA polymerase and hemoglobin.
