(Nanowerk Spotlight) Every time you send a text message or browse the internet, your device processes information using tiny electronic switches that flip on and off millions of times per second. But as our data needs grow exponentially, these electronic switches are reaching their physical limits. Current computer chips operate at gigahertz speeds – billions of cycles per second. To achieve the next great leap in computing speed and communication capacity, scientists are turning to terahertz waves, which oscillate trillions of times per second.
Terahertz waves occupy the electromagnetic spectrum between microwaves and infrared light. Their high frequency makes them ideal for ultra-fast computing and communication – a single terahertz channel could transmit thousands of 4K video streams simultaneously. However, harnessing these waves has proven exceptionally difficult.
Current methods require complex combinations of electrical, thermal, and optical controls, making devices bulky and slow to respond. Most existing systems take microseconds to switch states – far too slow to realize the potential of terahertz technology.
Researchers from China and Singapore have now developed a device that controls terahertz waves using only light pulses, achieving unprecedented switching capabilities. The device can switch between three different states in as little as 1.25 picoseconds (trillionths of a second) when oriented in one direction, and between two states in 2.25 picoseconds when oriented perpendicularly, with additional states possible at 4.75 picoseconds. To put this speed in perspective: if a microsecond were stretched to the length of a day, these picosecond switches would occur in mere fractions of a second.
The researchers built their device by precisely combining two materials – silicon and germanium – on a sapphire base. When struck by laser pulses, these materials temporarily become electrically conductive, similar to how a solar panel converts light into electricity. Each material responds differently: silicon activates quickly with weak light pulses but takes longer to reset, while germanium requires stronger light to activate but resets faster. By arranging these materials in a precise pattern, the researchers created what they call a metasurface – essentially a microscopic maze for light waves that can control their behavior.
The schematic diagram of ultrafast programming of THz logic devices. a) Controlled by the THz polarization, optical pumping power, and ultrafast time scale, the independently excited pixelated region can show switchable functions such as time-frequency selectable logic gates including NOR, XNOR, and OR with multiple degrees of freedom. (The details of logic operations are mapped in the Bloch sphere, where the red and black spheres represent 1 and 0). The switchable excited states of the meta-atom are shown in the enlarged bubble diagram, in which the Si, Ge, Gold, and sapphire aremarked in brown, black, yellow, and blue, respectively. b) The optical microscope diagram of the fabricated sample and detailed structure of unit cells with details as: Px = 120 μm, Py = 70 μm, L = 90 μm, g1 = 5 μm, g2 = 5 μm, and L1 = L2 = 35 μm. c) The simulated results of transmission in various states with polarization anisotropy, could be manipulated in spatial and temporal domains. (Reprinted with permission from Wiley-VCH Verlag) (click on image to enlarge)
The device’s unique architecture allows for independent control of how it responds to light waves oriented in different directions, a property known as polarization. This polarization-decoupled operation, combined with multiple temporal states, creates a programmable system that can be precisely tuned for different applications. Think of it as having several independent traffic systems that can be coordinated for maximum efficiency, each operating at different speeds and responding to different signals.
This combination of ultra-fast switching and directional sensitivity allows the device to perform multiple types of basic computing operations – specifically XNOR, NOR, and OR logic gates. These fundamental building blocks of computer processing can be programmed and switched at different times and frequencies, providing flexible computational capabilities that weren’t previously possible at these speeds. For instance, the same device can function as different types of logic gates depending on how the light pulses are timed and oriented.
The implications extend far beyond faster computing. In telecommunications, this technology could form the backbone of future 6G networks, enabling wireless speeds hundreds of times faster than current 5G systems. The researchers demonstrated this versatility by creating a prototype security system where information can only be decoded using specific combinations of timing, direction, and power levels of light pulses.
The system requires a precise sequence of light pulses at different power levels, oriented in specific directions, and timed at particular intervals – creating a complex optical combination lock that’s extremely difficult to crack without knowing the exact parameters.
The device’s simple control mechanism – requiring only light pulses rather than complex combinations of electrical and thermal controls – makes it particularly promising for practical applications. Previous attempts at controlling terahertz waves needed elaborate setups with multiple types of controls, making them impractical for real-world use. The new approach’s simplicity, combined with its multi-state switching capability, could accelerate the development of practical terahertz devices.
This achievement represents a crucial step toward practical terahertz technology. By demonstrating precise control over terahertz waves with multiple switching states and programmable operations, these researchers have opened new possibilities for next-generation computing and communication systems. As we continue to demand faster and more secure data processing and transmission, this technology offers a promising path forward, bringing us closer to an era where light-based computing could make today’s fastest computers look like calculating machines from the last century.
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