A standard shortcut, used since the 1970s, hides a magneto-optic effect in ordinary glass fiber

For more than 50 years, engineers have described light in optical fiber using a convenient shortcut, one that works so well it is rarely questioned. Engineers at the University of the Witwatersrand (Wits University) in Johannesburg, South Africa, have now shown that this shortcut hides a small but real effect. A magnet placed beside a multimode fiber, rather than along it, can change the light traveling inside.