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