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