A multiplexer/demultiplexer module based on an optical vortex, built by scientists at Tokyo Institute of Technology, could be used to strengthen optical networks so they can meet increasingly heavy traffic demands. The multiplexing/demultiplexing module fabricated (a,d) employs a property of light called the optical vortex to transmit and receive multiple signals simultaneously through a shared optical medium. The required light waves with different optical vortexes are generated using a combination of a star coupler (b) and an optical-vortex generator (c). Courtesy of the Optical Networking and Communication Conference & Exhibition 2019. The Tokyo Tech team developed an optical-vortex multiplexer/demultiplexer using vertically curved silicon waveguides. Multiplexing/demultiplexing with the lowest crosstalk of 23 decibels was demonstrated for five multiple optical vortexes. To encode signals into light waves with different optical vortexes and then transmit them, the researchers first required circuitry for both the multiplexing and demultiplexing operations. They designed and fabricated an orbital angular momentum (OAM) multiplexing/demultiplexing module that was able to take five independent signals as input. Using a combination of two tiny circuit structures called a star coupler and an optical-vortex generator, the researchers gave each of the five signals a unique OAM. The five signals were packed into a single output signal and a receiver circuit was used to execute the multiplexing operation in reverse (demultiplexing), resulting in output of five independent signals. The application of the optical vortex for signal multiplexing shows potential, according to the team. “The optical vortex carries the orbital angular momentum of light and can be used to multiplex signals by assigning each signal to a light wave of different momentum,” said professor Tomohiro Amemiya. The research was presented at the Optical Fiber Communication Conference, March 3-7, 2019, in San Diego, Calif. (https://doi.org/10.1364/OFC.2019.M1C.7).