Wide Y-junctions with low losses in three-dimensional dielectric optical waveguides

This paper proposes a simple structure (antenna coupled
Y
- junction) which reduces radiation losses of
Y
-junctions in 3-D optical waveguides by decreasing refractive indexes near the branching regions. A principle to reduce radiation losses and a design theory are presented for the new
Y
-junction by using geometrical optics. It is theoretically shown that losses of the properly designed 3-D
Y
-junctions can be reduced by around an order of magnitude compared to those of conventional ones when the branching angles are large.