First, in order to get the low-loss and small-size 2-arc S-shaped bend, the lateral offset between waveguides with different curvature was optimized to reduce the mode mismatch. To get the smoother S-shaped bend, which also has the overall bending loss as small as possible, another S-shaped bend based on functional approximation theory of B-spline was put forward. By this means, the transition loss at the junctions can be completely eliminated and also make the pure bending loss as small as possible. A comparison among sine-generated, cosine-generated, 2-arc and numerical calculated S-shaped bends was also been conducted. Using Beam Propagation Method (BPM) and analytical method, the result was verified and good agreement was got.
Y-branch is an important optical passive component. It can be used as power splitter and mode conversion. In this paper, a variable optical attenuator was designed using an asymmetric Y-branch. The device was simulated by FDBPM (Finite Difference Beam Propagation Method). It has the characteristics of compact size, large scale dynamic attenuation and low power consumption.