If we credit the integrated circuit with one thing, it should be the taming of the electromagnetic spectrum. If you want to create or capture visible photons, there are plenty of compact devices to choose from, incorporating everything from miniature photodiodes and lasers to LEDs and slim charge-coupled devices. And if you want to pick up or send a radio signal, there are a staggering number of receivers, transmitters, and antennas to suit your needs.
But the IC hasn't conquered every bit of the spectrum, and one region stands out: the terahertz frontier, a range that extends from the highest frequency radio waves to the lowest frequency infrared light. Over the decades, engineers have made many attempts to create compact, solid-state devices that can harness it, but terahertz radiation has proven particularly tricky to use.
Why does it matter? For one thing, terahertz radiation has a lot of promise for noninvasive imaging in industry, medicine, and security. Unlike X-rays, terahertz waves are too low in energy to knock electrons off atoms, which could damage living tissue. And because of their shorter wavelength, they can produce pictures that are far sharper than those made with microwaves, the current safe imaging alternative.
Terahertz waves also occupy a unique window of the electromagnetic spectrum where a large number of molecules emit and absorb radiation. The signals produced when a molecule jumps among rotational modes form a unique and highly distinctive chemical fingerprint. If we can devise compact, easy-to-manufacture terahertz spectrometers that can detect these fingerprints, we could, for example, use them to identify the constituents in a patient's breath or flag a potentially dangerous substance.
For a long time, these sorts of applications were out of reach. Until recently the only sources capable of creating significant power in the terahertz range have been custom-built, temperamental affairs that take up entire optical tables, are difficult to transport and calibrate, and can cost hundreds of thousands of dollars.
But recent research has shown that miniature sources can be just as powerful. And we've used these sources to make the first integrated devices that can simultaneously emit and detect terahertz radiation. These devices are proof that terahertz signals can be handled in a small, portable, mass-producible package. For the first time, we can begin to imagine a bright future for terahertz technology, one full of innovation.