New Tool to Measure Polarization of Light

View of the semitransparent polarization detector. The square area is one of the gold electrodes, underneath which is the organic photovoltaic material which converts polarized light into an electrical signal (Source: NCSU)

View of the semitransparent polarization detector. The square area is one of the gold electrodes, underneath which is the organic photovoltaic material which converts polarized light into an electrical signal (Source: NCSU)

Researchers from North Carolina State University have developed a new tool for detecting and measuring the polarization of light based on a single spatial sampling of the light, rather than the multiple samples required by previous techno­logies. The new device makes use of the unique properties of organic polymers, rather than tradi­tional silicon, for polari­zation detection and mea­surement.

Light consists of an electric field. That electric field oscil­lates, and the direction in which that field oscillates is the light’s polarization. If the field oscillates randomly, it’s referred to as unpolarized light. The polari­zation of light can be affected in predictable ways when light bounces off, or is scattered by, physical objects. “We want to detect and measure polari­zation, because it can be used for a wide variety of applications,” says Michael Kudenov, an assistant professor of electrical and computer engineering at NC State and lead inves­tigator on this research. “For example, polari­zation detectors can be used to pick out man-made materials against natural surfaces, which has defense and security appli­cations. They could also be used for atmo­spheric monitoring, measuring polarization to track the size and distri­bution of particles in the atmosphere, which is useful for both air quality and atmo­spheric research appli­cations.”

The new device incor­porates three polari­zation detectors made of organic polymer conductors. Each of the detectors is sensitive to a specific orien­tation of the polari­zation. As light enters the device, the first detector measures one orien­tation of the polari­zation, and the remainder of the light passes through. This is repeated with the subsequent detectors, effectively allowing each detector to take a partial polari­zation measurement of the same beam of light. The measure­ments from all three detectors are fed into a model that calculates the overall polari­zation of the light.

“Most types of polarized light, parti­cularly in natural environments, have a large linear polari­zation signature,” Kudenov says. “And three measurements are sufficient for us to calculate the state of linear polari­zation in a light sample.” Previous techno­logies rely on multiple light samples, either taken at different times or at the same time but from different points in space, which can influence the accuracy of results.

The researchers have tested the new device using a laser to provide initial proof-of-concept data. Early tests show that the device can achieve measurement error as low as 1.2 percent. “It’s a good starting point, though not as good as the best polari­zation detectors currently on the market,” Kudenov says. “However, we’re opti­mistic that we’ll be able to reduce the measure­ment error signi­ficantly as we improve the device’s design. We’re really just getting started.” (Source: NCSU)

Reference: S. G. Roy et al.: Intrinsic coincident linear polarimetry using stacked organic photovoltaics, Opt. Exp. 24, 14737 (2016); DOI: 10.1364/OE.24.014737

Link: Dept. of Electrical and Computer Engineering, North Carolina State University, Raleigh, USA

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