A four-order asymmetric Y-junctions mode (de)multiplexer ((de)MUX) was theoretically proposed for highly integrated on-chip mode-division systems. The high-order mode in the stem waveguide of asymmetric Y-junctions is designed to be separated from the lower-order mode and evolve into the fundamental mode in the narrow arm. Through the widths optimization of branch arms by effective index matching and beam propagation method, the footprint of four-order mode (de)MUX was controlled to be 140×7.1μm<sup>2</sup>. The calculated excess loss and crosstalk were less than 0.3 dB and -18 dB within the operation wavelength range from 1460 to 1660 nm, respectively. This scheme may be expanded to higherorder modes (de)MUX design.
Dynamic optical power distribution has great importance to network optimization. A three-dimensional (3-D) polymer thermo-optic switch is designed and fabricated to work at 650 nm. Two rectangular poly(methyl-methacrylate-glycidly-methacrylate) waveguides in neighboring and parallel layers couple with each other in a vertical direction. The lightwave is routed in two layers through a metal heater control. Waveguide configuration and relative position are optimized theoretically through beam propagation method calculations. The fabricated switch demonstrates an extinction ratio of 27.5 dB at a driving power of 57.7 mW. Measured rise time and fall time are 639.8 and 758.2 μs, respectively. Reliability characterizations within 125 days prove good operation stability at different extinction ratios. This work has potential in 3-D optical connections and visible light communication.