When light signals are put inside an optical fiber,
they move forward by repeatedly
being reflected on the inside of the fiber.
Optical fiber is made of two glass layers
with different refractive indexes.

The outer layer is called the cladding, while the central part is called the core. As the core has a higher refractive index than the cladding, light moving inside the core is reflected at the border of the cladding, which has a lower refractive index. This keeps the light from escaping to the outside.

Professor Nishizawa plainly explains how optical fiber works and the three elements of light.

Professor Jun-Ichi Nishizawa Born in Sendai, Miyagi prefecture in 1926. Graduated from Tohoku University. He previously served as president of Tohoku University, where he is now a professor emeritus. He is also a member of the Japan Academy, and head of the Semiconductor Research Institute at the Semiconductor Research Foundation. Professor Nishizawa has received many awards for research and development work in the fields of semiconductor devices and optical communications, including Japan's Order of Cultural Merit (1989) and a Jack A. Morton Award (1973).

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