A New Optical Switch Proves 1,000 Times Faster Than Traditional Transistors

October 07, 2021 by Adrian Gibbons

Optical computers have long been on the horizon. Now, IBM and Skoltech are teaming up to bring optical circuits into the mainstream.

Last week Skoltech, the Russian Institute of Science and Technology, in collaboration with IBM, announced an optical switch transistor that operates between 100 to 1,000 times faster than traditional transistors. Their research into single-photon nonlinearity at room temperature is published in Nature


Hybrid Photonics Lab

From the Hybrid Photonics Lab. Image used courtesy of Skoltech


In addition to the switching speed, the optical switch is said to have several other key advantages. The switch can be used as a component for the movement of optical data or can act as an amplifier with a gain factor of up to 23,000. Most importantly, it requires no bulky cooling elements, and it has extremely low energy requirements. 

“What makes the new device so energy-efficient is that it only takes a few photons to switch,” the first author of the study, Dr. Anton Zasedatelev commented. “In fact, in our Skoltech labs we achieved switching with just one photon at room temperature.”


How It Works: Skoltech’s Optical Switching 

Fundamentally, the new optical system is still boolean; that is, it produces a zero or one state based on finite switching. The device operates using two lasers: one control beam and one state-defining beam. 

The switching state is held inside a microcavity. The microcavity used in this experiment is a 35-nanometer thin organic semiconducting polymer placed between reflective inorganic surfaces. 

The switching is achieved through "quasiparticles" within the cavity by using the pump (the state-changing beam) laser. These quasiparticles are said to be the result of photons bonding with electron-hole pairs, giving rise to exciton-polaritons


IBM's research team in Zurich

Two years ago, IBM's research team in Zurich conducted similar research, creating the world's first all-optical room temperature transistor. Image used courtesy of IBM 

To switch the device state to a logical one, the control beam first seeds the bose-einstein condensate inside the cavity, prior to the application of the pump laser. 

The team focused on lowering the power consumption through three "tweaks":

  • Efficient switching, aided by vibrations in the microcavity molecules
  • A highly tuned wavelength and a new measurement technique for condensate detection
  • Minimized system noise through their control laser seeding scheme

These tweaks reduce the energy being absorbed by the microcavity, thereby reducing heating and maximizing the signal-to-noise ratio.


General Principles of Optical Computing

Optical computing has several advantages over electron-based computing, as well as several disadvantages. Moving from a single storage bit (in the form of a transistor state) to a logic gate increases the complexity of the circuit, involving multiple beams. 

Optical logic gates can be built using semiconductor optical amplifiers (SOA) or can be built using alternative configurations


Second stage of an all-optical conical control logic unit with SOA

Second stage of an all-optical conical control logic unit with SOA. Image used courtesy of Singh et al.


A key advantage of optical computing is the inherent multiplexing capability of light wavelengths. Photons of different wavelengths do not interact, so information can be encoded on several “channels” of light and transmitted along with the same medium. 

There are two main types of optical computers. An electro-optical computer shuttles data optically between processors but is computed electronically.

Alternatively, a pure optical computer can be much faster with higher bandwidth, using multiple frequencies and completing all processing with light. Optical computers allow for all-optical switching states using constructive and destructive interference.


Will Optical Switches Spearhead the Future of Computing?

With shrinking node sizes approaching the viability limit for electron mobility, it appears that the writing is on the wall regarding the future of silicon-based semiconductors and electron-based computing technology in general.

Optical computers are one potential technology that may overcome these limitations. IBM could offer research institutions like Skoltech a long-term advantage in commercializing viable optical computing technology.  

Optical computers offer increased speeds, lower heating, and lower power consumption. This last feature, lower power consumption, is a major criterion in the competitiveness of all electronic designs. The research team at Skoltech notes, “There’s still some work ahead of us to lower the overall power consumption of our device, which is currently dominated by the pump laser that keeps the switch on.”

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