A multinational team of researchers led by Skolkovo Institute of Science and Technology (Skoltech), a private institute in Moscow, Russia, and International Business Machines Corporation (IBM), a leading American computer manufacturer with a sizable market share both internationally and domestically produced a highly energy-efficient optical switch that might substitute electrical transistors for a new generation of photons and not electron computers.
The switch needs no cooling and is really fast. It is between 100 and 1,000 times faster than today’s leading industrial transistors, with 1 trillion operations per second. According to Dr. Anton Zasedatelev, the new technology is extremely energy-efficient because it only requires a few photons to switch. Switching was possible with just one photon at ambient temperature in our Skoltech laboratory.
In addition, Professor Pavlos Lagoudakis, who heads the Skoltech Hybrid Photonics Labs explained that there is a long way to go before such proof-of-principle demonstration is used in an all-optical co-processor. There isn’t much opportunity for development in terms of power consumption because a photon is the tiniest particle of light that appears in nature. The majority of modern electrical transistors require more energy to flip, and it was far slower for those that utilize single electrons to reach related performance.
Aside from performance difficulties, competing power-saving electronic transistors sometimes necessitate large cooling systems, which consume electricity and add to running expenses. All of these issues are avoided by the new switch, which operates at ambient temperature.
Concept of Performance
The switch should act as a device that connects devices by sending data in the form of optical signals, comparable to its basic transistor-like function. It can also function as an amplifier, increasing the strength of an incoming new laser beam by up to 23,000 times.
Two lasers are used to change the device’s state to “zero” or “one” and to switch between them. A completely vulnerable control laser beam is being used to turn on or off any other, brighter laser beam. The device’s remarkable performance is due to the fact that it just takes a few photons in the control beam. Inorganic structures that are extremely reflective are wedged between them.
The switching takes place within a microcavity, which is made up of a 35-nanometer-thick organic semiconducting polymer wedged between highly reflective inorganic layers. Incoming light is trapped inside the microcavity for as long as possible to encourage interaction with the cavity’s substance.
The new technology is built on top of this light-matter interaction. Quasiparticles at the core of the switch’s action such as Exciton-polaritons form when photons actively interact with excitons in the cavity’s material.
When the brighter of the two lasers, which is the pump laser shines on the switch, it sets up millions of similar quasiparticles in the same spot, generating a Bose-Einstein condensate that encodes the device’s “0” and “1” logic states.
The scientists employed a control laser pulse to seed the condensate shortly before the arrival of the pump laser pulse to transition between the two levels of the device. This increased the number of quasiparticles at the condensate by facilitating energy conversion from the pump laser. The high number of particles in there refers to the device’s “1” state.
To achieve minimal power consumption, the scientists made the following changes:
- The vibrations of the semiconducting polymer’s molecules first facilitated effective switching. The difficulty was to correlate the energy difference between the pumped and condensate states to the energy of a single molecular vibration in the polymer.
- Second, the researchers discovered the best wavelength for tuning their laser to and developed a fresh measurement technique that enabled single-shot condensate detection.
- Third, the seeding laser and detection technique for the condensate were linked in such a way that noise from the device’s “background” emission was minimized.
These measures maximized the signal-to-noise level of the device and prevented an excess of energy from being absorbed by the microcavity, which would only serve to heat it through molecular vibrations.
“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. A route toward that goal could be perovskite super crystal materials like those we’re exploring with collaborators. They have proven excellent candidates given their strong light-matter coupling which in turn leads to a powerful collective quantum response in the form of superfluorescence,” the team comments.
More broadly, scientists view their new switch as just one of the evolving optic component tools they have accumulated over the past few years. It includes, among other things, a low-loss silicon waveguide for switching optical signals between transistors. The improvement of these elements brings the researchers even closer to optical computers that will alter photons rather than electrons, resulting in much higher efficiency and lower energy consumption.
Research paper: Single-photon nonlinearity at room temperature, Nature (2021). DOI: 10.1038/s41586-021-03866-9 , www.nature.com/articles/s41586-021-03866-9