Three-dimensional waveguide structure forming mode manipulating devices

Mode multiplexing technology is a promising technology to increase the optical communication capacity, where a 3D waveguide structure is a neat solution for manipulating the modes with their symmetry in horizontal and vertical direction or their combination. Three-dimensional photonic-integrated vertical directional couplers are applied to form the mode multiplexer, where the mode (de)multiplexer serves for spatial (de)multiplexing the spatial guide modes in a few-mode waveguide. These guide modes are the waveguide modes such as the E11, E21, and E12 modes. In addition, the directional couplers (either the horizontal directional couplers or the vertical directional couplers) can be formed by using adiabatic tapered waveguides. The usage of the tapered waveguide can be functioned as a wavelength expander. In addition, the fabrication of the 3D waveguide structure can be utilized by using the multi-step photolithography processing methodology. For example, we have demonstrated the fabrication of a hybrid-core planar waveguide forming mode multiplexer by using multi-step photolithography processing for the realization of a high-order-mode band-passed function. Also, the passive device can be further developed to be an active device for dynamically manipulating the guided modes. In conclusion, the 3D waveguide structure forming mode manipulating devices are powerful in a mode division multiplexing system for the optical communication.