At {TAIL ~ the first splitting/coupling point}, {HEAD ~ a tangential line} of the first circular arc optical waveguide portion and a tangential line of the third circular arc optical waveguide portion are parallel to and spaced from each other 
At { TAIL ~ the first splitting / coupling point } , { HEAD ~ a tangential line } of the first circular arc optical waveguide portion and a tangential line of the third circular arc optical waveguide portion are parallel to and spaced from each other
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH