hi ranjeet,
i am am attaching few links, hope they may help
http://www.fiber-optic-equipment.com/the-working-principle-of-the-optical-circulator.html
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwizq4jU7LPLAhUNCo4KHWRrCo0QFggiMAE&url=http%3A%2F%2Fwww.fiber-optic-tutorial.com%2Fpassive-optical-components-optical-circulator.html&usg=AFQjCNFER7VUWJt4uwMoSpN3x5vLn388Ag&sig2=OwOSGMmj0RNoqx6fcn-RwQ&bvm=bv.116573086,d.c2E
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwizq4jU7LPLAhUNCo4KHWRrCo0QFggbMAA&url=http%3A%2F%2Fwww.fs.com%2Foptical-circulator-tutorial-aid-455.html&usg=AFQjCNFenMrBP6L8lKPKFN1jJ6reqoXy7w&sig2=aCl8yqZey2fl94jobYiq1w&bvm=bv.116573086,d.c2E
with regards