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