{HEAD ~ This feedback signal} is for changing the optical path length of {TAIL ~ at least one waveguide arm} of the optical switch, the change for maintaining a particular switch state 
{ HEAD ~ This feedback signal } is for changing the optical path length of { TAIL ~ at least one waveguide arm } of the optical switch , the change for maintaining a particular switch state
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH