Hi ranjeet…
Well i think i can’t explain all the things you asked,but i will try to give idea of some terms you asked.
An optical circulator is a special fiber-optic component that can be used to separate optical signals that travel in opposite directions in an optical fiber, analogous to the operation of an electronic circulator. So circulators can be used to achieve bi-directional transmission over a single fiber.
For your reference i am attaching few links which might be helpful to you.
1.https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwi_9Oy9z7PLAhWP1I4KHQZRDvkQFggbMAA&url=http%3A%2F%2Foptiwave.com%2Fforums%2Ftopic%2Fcirculator%2F&usg=AFQjCNFi4JYI3b_o_KcaUjQ3-YIeiPwsUg&sig2=22_D_2-7YKL7Kw8MubQABg
2.https://optiwave.com/forums/topic/practical-noise-in-lasers/