Low-loss coherent-coupling Y branches

We propose the design of low-loss waveguide Y branches with coherently coupled bends. According to results of beam-propagation simulations, the excess loss of a complete Ti:LiNbO(3) Y branch with a nominal half-branching angle of 1 degree can be as low as -0.18 dB. Similar to the case of other cascaded Y branches, when two coherently coupled Y branches are cascaded, the power distribution at the output varies with the length of the straight connecting waveguide. Details of the Y-branch design that gives low loss and equal power splitting are presented.