Scientists Fabricate a Multiplexer/Demultiplexer Module Based on Untapped Property of Light

Researchers at Tokyo Institute of Technology have developed a multiplexer/demultiplexer module on the basis of a light property that was not being utilized in communications systems: the optical vortex.

The multiplexing/demultiplexing module fabricated (a, d) employs a property of light called the “optical vortex” to transmit/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). (Image credit: The optical networking and communication conference and exhibition 2019)

Such devices will be vital for advancing optical networks, which are the strength of the present Internet so that they can fulfill the traffic requirements of the future.

In this communication-centered age, Internet traffic has been rising quickly. The huge amounts of data that travel via the Internet are powered by vast backbone networks, generally involving millions of connections organized using optical communication technology. Scientists around the world predict that this increase in data flow will not stop in the near future, and hence they are looking for ways to further develop and enhance optical communications.

One omnipresent method in modern electronic communications is multiplexing, which involves increasing the use of the available bandwidth. Multiplexing is performed by packing multiple signals into a single signal that can be transmitted through a shared medium, for example, an optical fiber. The obtained complex signal is subsequently demultiplexed at the receiver and each simple signal is directed to its planned destination. Currently, several multiplexing methods are being used to realize speeds of more than 100 gbits/second via optical networks.

However, it is necessary to find a new approach to pack more data into optical signals with minimum energy and at a low cost, which means that new multiplexing technologies are indispensable. In recent promising techniques, the properties of light that are not used before for communication are exploited to encode independent signals. For instance, the polarization of light has already been used and practical applications have been presented.

Conversely, there is another property of light, known as the “optical vortex,” that can be taken advantage of. A study conducted at Tokyo Institute of Technology, led by Assistant Professor Tomohiro Amemiya, focused on this property.

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.

Tomohiro Amemiya, Assistant Professor, Tokyo Institute of Technology

The use of the optical vortex for signal multiplexing is an unexploited territory with great promise.

Obviously, it is first essential to design and execute the required circuitry for both the multiplexing and demultiplexing operations to even consider encoding signals into light waves with different optical vortexes and send them. Hence, the team of researchers designed and developed an orbital angular momentum multiplexing/demultiplexing module.

Their device was developed such that it takes five independent signals as input. With a combination of two tiny circuit structures, known as a star coupler and an optical-vortex generator, each of the five signals is “encoded” with a distinctive optical angular momentum. The output signal includes a combination of the five signals, and the receiver circuit only has to perform the multiplexing operation in reverse, or demultiplexing, to end up again with the five independent signals.

The figure above illustrates the fabricated module. The curved tips of the waveguides of the optical-vortex generator were composed of silicon and measured a few microns. The optical-vortex generator fabrication process had been explained in the prior research, and the current research carried out by the scientists represents a solid application of this technology.

Devices and multiplexing methods such as those represented by the team will be important in the very near future. “It is certain that the demand for high capacity systems with low cost and less energy losses will further increase in the future,” states Amemiya. Luckily, more methods to enhance present communications systems by taking advantage of the unexploited properties of light will certainly become available to help move forward in this age of communication.

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