Reconfigurable Three-Mode Converter Based On Cascaded Electro-Optic Long-Period Gratings

We propose an optical waveguide switch to realize complete reconfigurable mode conversion for three spatial modes. This device consists of three cascaded long-period grating mode converters of different types integrated along a three-mode lithium-niobate (LiNbO3) waveguide, where the gratings can be electro-optically controlled to activate mode conversion independently. We fabricate the device with z-cut LiNbO3, which employs graphene electrodes to drive the gratings and an electrode heater to achieve wavelength matching for the three gratings. The half-pi voltages of the three gratings in a typical fabricated device, which is 26 mm long and operates at 1545 nm, are 48, 37, and 43 V, respectively. The proposed mode switch could find applications in reconfigurable mode-division-multiplexing communication systems based on few-mode fibers and other areas where programmable mode conversion is required.