An integrated photonic chip developed at the University of Rochester could significantly increase the sensitivity of optical interferometers. Researchers packaged an experimental method for the amplification of interferometric signals — without a corresponding increase in noise — on a 1-mm2 integrated photonic chip. The work is based on a theory of weak value amplification with waveguides developed by Andrew Jordan, a professor of physics at Rochester.

The team applied mode analysis in a novel way on a free space interferometer with weak value amplification, bridging the gap between free space and waveguide weak value amplification.

In doing so, it was able to prove the theoretical feasibility of integrating weak value amplification on a photonic chip.


A 1-mm2 integrated photonic chip developed by Jaime Cardenas, assistant professor of optics, and Ph.D. student Meiting Song (lead author) will make interferometers — and therefore precision optics — even more powerful. Potential applications include more sensitive devices for measuring tiny flaws on mirrors, or dispersion of pollutants in the atmosphere, as well as quantum applications. Courtesy of J. Adam Fenster, University of Rochester.


 

“Basically you can think of the weak value amplification technique as giving you amplification for free. It’s not exactly free since you sacrifice power, but it’s almost for free, because you can amplify the signal without adding noise — which is a very big deal,” professor Jaime Cardenas said.

Weak value amplification is based on the quantum mechanics of light; essentially, only certain photons, those containing the necessary information, are directed to the detector. Teams have demonstrated the concept before. “But it’s always with a large setup in a lab with a table, a bunch of mirrors and laser systems, all very painstakingly and carefully aligned,” Cardenas said.

The small size of the interferometer chip enables it to have a multitude of potential applications, Cardenas noted. “You can put it on a rocket, or a helicopter, in your phone — wherever you want — and it will never be misaligned.”

Jaime Cardenas (left) and Meiting Song in the Cardenas Lab at Rochester’s Institute of Optics. Courtesy of J. Adam Fenster, University of Rochester.


Jaime Cardenas (left) and Meiting Song in the Cardenas Lab at Rochester’s Institute of Optics. Courtesy of J. Adam Fenster, University of Rochester.


 

The device, developed by Ph.D. student and first author Meiting Song, doesn’t look like a traditional interferometer. Rather than using a set of tilted mirrors to bend light and create an interference pattern, Song’s device includes a waveguide engineered to propagate the wavefront of an optical field through the chip.

In traditional interferometers, the signal-to-noise ratio can be increased, resulting in more meaningful input, simply by increasing the laser power. There is, however, a limitation, as traditional detectors used with interferometers can handle only so much laser power before they become saturated, at which point the signal-to-noise ratio can’t be increased, Cardenas said.

The new device overcomes that limitation by reaching the same interferometer signal with less light at the detectors. This leaves room to increase the signal-to-noise ratio by continuing to add laser power.

“If the same amount of power reaches the detector in Meiting’s weak value device as in a traditional interferometer, Meiting’s device will always have a better signal-to-noise ratio,” Cardenas said. “This work is really cool, really subtle, with a lot of very nice physics and engineering going on in the background.”

The researchers plan to adapt the device for coherent communications and quantum applications using squeezed or entangled photons to enable devices such as quantum gyroscopes.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-021-26522-2).



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