By matching the phases, the light from {HEAD ~ the coupler} is input to the fiber traveling in a circular direction, i.e., the path of {TAIL ~ the light} down the fiber forms a corkscrew 
By matching the phases , the light from { HEAD ~ the coupler } is input to the fiber traveling in a circular direction , i.e. , the path of { TAIL ~ the light } down the fiber forms a corkscrew
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH