Kewei fiber's Three-port Optical Circulator allows light to travel in only one direction. A signal entering to Port 1 will exit Port 2 with minimal loss, while a signal entering Port 2 will exit Port 3 with minimal loss. Light entering port 2 experiences a large amount of loss at port 1, and light entering port 3 experiences a large amount of loss at ports 2 and 1. Optical circulators are non-reciprocal devices. This means that any changes in the properties of the light caused by passing through the device are not reversed by traveling in the opposite direction.