Metasurface Polarimeter Meets Telecom, Nanotechnology Demands

A novel architecture for in-line polarimeters enables monolithic, on-chip integration of polarization sensors for applications as varied as drug design and telecommunications, as well as for emerging nanotechnologies.

A research team led by professor Federico Capasso of Harvard University sought to address the slow, bulky and expensive nature of existing polarimeters, which are the ubiquitous technology for measuring the polarization of light.

The team reduced the complexity and size of standard polarimeters by building a 2D metasurface covered with a thin array of metallic antennas, smaller than a wavelength of light, embedded in a polymer film.

Light from an optical fiber illuminates the metasurface and is scattered in four directions. The intensities are measured by four detectors, and from this measurement, the state of polarization of light is detected. Courtesy of the Capasso Lab/Harvard SEAS.

As light propagates down an optical fiber and illuminates the array, a small amount scatters in four directions. Four detectors measure the intensity of the scattered light and combine the data to give the state of polarization in real time.

"One advantage of this technique is that the polarization measurement leaves the signal mostly intact," said graduate student J.P. Balthasar Mueller. "This is crucial for many uses of polarimeters, especially in optical telecommunications, where measurements must be made without disturbing the data stream."

In telecommunications, optical signals propagating through fibers will change their polarization in random ways. New integrated photonic chips in fiber optic cables are extremely sensitive to polarization, and if light reaches a chip with the wrong polarization, it can cause a loss of signal.

The researchers said their method provided polarization state measurements matching those of a state-of-the-art commercial polarimeter. Chip-based polarimeters could provide comprehensive and real-time polarization monitoring to boost network performance and security, and help providers keep up with the increasing demand for bandwidth.

Researchers led by Kristjan Leosson at Innovation Center Iceland are now working on incorporating the metasurface component into a prototype polarimeter system.

"This device performs as well as any state-of-the-art polarimeter on the market but is considerably smaller," said Capasso. "A portable, compact polarimeter could become an important tool for not only the telecommunications industry but also in drug manufacturing, medical imaging, chemistry, astronomy, you name it. The applications are endless."

The research was published in Optica (doi: 10.1364/optica.3.000042 [open access]).