Optical circulator

An optical circulator is a special kind of optical device with three or four ports, or openings, for light to pass through. It works in a unique way: when light enters one port, it comes out of the next port in line. For example, if light goes into port 1, it leaves from port 2. But if some of that light bounces back toward the device, it won’t exit from the same port it came from—instead, it leaves from the next port after that, like port 3. This helps control the direction of light in ways that are useful for communication and sensing.

Optical circulators are very important in fiber-optic technology. They help separate light signals that are traveling in opposite directions along a single optical fiber. This allows two-way communication to happen on one strand of fiber, which saves space and materials. Because they do this very well, with strong isolation between the incoming and reflected light and very little insertion loss, they are used in many advanced fiber-optic communications and fiber-optic sensor systems.

These devices are also special because they are non-reciprocal. This means that when light passes through them one way, certain changes to the light don’t reverse when the light goes the opposite way. This unusual behavior can only happen when something, like an external magnetic field, breaks the normal symmetry of the system. Another device that works this way is a Faraday rotator, and some optical circulators are built using this principle.

History

In 1965, someone named Ribbens created an early version of an optical circulator using special tools called a Nicol prism and a Faraday rotator. Later, as new technologies like fiber and guided-wave optics were developed, better optical circulators were made that could work with any light direction. In 2016, scientists showed a new type of circulator that uses a single atom to control how light moves.

In 2013, two researchers suggested a tiny device made with special materials that could also guide light in one direction.