New chip-sized, energy-efficient optical amplifier can intensify light 100 times

(Press-News.org) Light does a lot of work in the modern world, enabling all types of information technology from TVs to satellites to fiber-optic cables that carry the internet across oceans. Stanford physicists recently found a way to make that light work even harder with an optical amplifier that requires low amounts of energy without any loss of bandwidth, all on a device the size of a fingertip.

Similar to sound amplifiers, optical amplifiers take a light signal and intensify it. Current small-sized optical amplifiers need a lot of power to function. The new optical amplifier, detailed in the journal Nature, solves this problem by using a method that essentially recycles the energy used to power it.

“We’ve demonstrated, for the first time, a truly versatile, low-power optical amplifier, one that can operate across the optical spectrum and is efficient enough that it can be integrated on a chip,” said Amir Safavi-Naeini, the study’s senior author and associate professor of physics in Stanford’s School of Humanities and Sciences. “That means we can now build much more complex optical systems than were possible before.”

The Stanford-developed device achieves about 100 times amplification, or increase the intensity of a light signal, while only using a couple hundred milliwatts of power – a fraction of what is typically required for existing optical amplifiers of similar size. That efficiency coupled with its small size mean the amplifier could be powered by a battery and used in laptops and smartphones.

Less power and less noise
Just like sound amplifiers, optical amplifiers tend to add unwanted noise when they boost a signal. The researchers demonstrated that this amplifier adds as little noise as possible. It also has a broader bandwidth than current amplifiers, meaning it supports a greater optical spectrum. Together, this indicates it has greater data-carrying capacity with less interference.

This kind of optical amplifier is powered by the energy stored in a light beam acting as a type of “pump,” and its performance depends on the intensity of that light beam.

“By recycling the energy of the pump that powers this amplifier, we made it more efficient, and this doesn't come at a cost to its other properties,” said Devin Dean, co-first author on the study and a doctoral student in Safavi-Naeini’s lab.

The team accomplished this by using a resonant design, which is already used by lasers as an “energy recycling trick,” according to Dean. This involves doubling light back on itself, which increases its intensity, as happens when light gets caught between two mirrors.

In this particular amplifier, the pump light is generated inside a resonator – it travels in a circular loop like a racetrack and builds to higher intensities and therefore can better boost the desired beam. The design provides more intensity for less input power, making it more efficient.

Because of its small size and lower energy requirements, the optical amplifier could be powered by a battery – and be something used in a device as small as a smartphone. 

“When you can do that, then the possibilities are really quite broad because they are so small that you can mass produce them and power them with batteries,” Dean said. “They could be used potentially for data communications, biosensing, making new light sources, or a host of different things.”
 

Additional Stanford co-authors include co-first author Taewon Park, a doctoral student in Safavi-Naeini’s lab; Professor of Applied Physics Martin Fejer; postdoctoral fellow Hubert Stokowski; and doctoral students Sam Robison, Alexander Hwang, Luke Qi, and Jason Herrmann. 

Dean, Park, Safavi-Naeini, and Stokowski are inventors on a patent application that covers methods for achieving quantum advantage in power-constrained photonic sensors.

This work was supported in part by the Defense Advanced Research Projects Agency, NTT Research, and the National Science Foundation.

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