p.s.
One interesting thing to note in the diagram is the faraday isolator... That's the rolls royce of making beams go one way! With two units, you can even send unpolarized light go one way (using two PBS cubes and 2 faraday isolators)... The way those work is so neat, it's almost a violation of the laws of physics! Luckily for the well heeled, it's not.