At the first splitting/coupling point, {HEAD ~ a tangential line} of {TAIL ~ 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 
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At the first splitting / coupling point , { HEAD ~ a tangential line } of { TAIL ~ 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
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL 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 OTH