Light plays a central role in modern technology, powering everything from televisions and satellites to the fiber-optic cables that carry Internet data around the world. Now, physicists at Stanford University have developed a way to push light even further. They created a compact optical amplifier, about the size of a fingertip, that can enhance optical signals while maintaining full bandwidth using very little energy.
Optical amplifiers are similar to audio amplifiers, except that they amplify light rather than sound. Traditional compact versions require significant power to operate, which limits their efficiency. The new device, published in the journal Nature, overcomes this challenge by reusing much of the energy needed to operate.
“We have demonstrated for the first time a truly versatile, low-power optical amplifier that can operate across the optical spectrum and is efficient enough to be integrated on a chip,” said Amir Safavi Naini, lead author of the study and associate professor of physics in Stanford University’s School of Humanities and Sciences. “This means we can now build much more complex optical systems than before.”
An amplifier developed at Stanford University can increase the strength of an optical signal by about 100 times while using only a few hundred milliwatts of power. This is much less energy than similar devices typically require. Efficient and small, they run on batteries and can be integrated into devices such as laptops and smartphones.
Reduce noise and increase bandwidth
Like their audio counterparts, optical amplifiers can introduce unwanted noise when boosting the signal. The researchers showed that their design minimized this noise. It also operates over a wider range of wavelengths than existing amplifiers, allowing it to transmit more data with less interference.
This type of amplifier relies on energy stored in a beam of light to act as a “pump.” Its performance is determined by the intensity of the pump light.
“By recycling the energy of the pump that powers this amplifier, we increased the efficiency of the amplifier, without sacrificing the other properties of the amplifier,” said Devin Dean, co-lead author of the study and a doctoral student in Safavi-Naini’s lab.
Recycle light energy for a stronger signal
The research team achieved this efficiency using a resonant design similar to the method already used in lasers. Dean described this as an “energy recycling trick.” Simply put, this system can send light back to itself, increasing its intensity over time, much like light reflecting between two mirrors.
Inside this amplifier, pump light is generated within a resonator and travels in a continuous circular path resembling a racetrack. The light increases in intensity as it loops, allowing it to more effectively amplify the target signal. This approach produces more powerful output while requiring less input energy.
The device is compact and energy efficient, allowing it to operate on battery power and be integrated into small electronic devices.
“If we can do that, the possibilities are huge, because it’s so small that it can be mass-produced and it can be powered by batteries,” Dean said. “They could be used for data communications, biosensing, creating new light sources, or a variety of other things.”
Potential applications and research support
Other Stanford co-authors include co-first author Taewon Park, a doctoral student in Safavi Naini’s lab. Professor of Applied Physics Martin Fejer. Postdoctoral researcher Hubert Stokowski. and doctoral students Sam Robison, Alexander Huang, Luke Chee, and Jason Herman.
Dean, Park, Safavi-Naeini, and Stakowski are inventors on a patent application covering how to achieve quantum benefits in power-constrained photonic sensors.
This research was supported in part by the Defense Advanced Research Projects Agency, NTT Research, and the National Science Foundation.
