Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a prototype device capable of absolute measurements of optical power delivered through an optical fiber.
The device is the world's first fiber-coupled cryogenic radiometer that links optical fiber power measurements directly to fundamental electrical units and national standards. It uses a microscopic forest of carbon nanotubes—the world's darkest material—to measure values that are about one-thousandth of the levels typically attained with a cryogenic radiometer lacking direct fiber input capability.* With improvements in temperature control and speed, the device could meet the needs for ultraprecise calibrations at ultralow power in telecommunications, medical devices and other industries.
Optical power and energy are traceable to fundamental electrical units. Radiometers absorb optical energy and convert it to heat. Then the electrical power needed to induce the same temperature increase is measured. Because optical and electrical heating are not exactly equivalent, measurement uncertainties can be relatively large from a metrology point of view.
The demonstration is also a step toward converting radiometry from a classical practice based on electrical units to a quantum practice based on single particles of light (photons).
"We have many customers who request optical power measurements in fiber, mainly for optical communications," project leader John Lehman says. "Also, our single-photon measurements are done in fiber."
NIST aims to develop an absolute quantum standard for optical power and energy based on single photons. The effort includes development of sources and detectors spanning a wide range of optical power measurements, from single photon counts to trillions of photons. Single photons are already used in quantum communications systems, which offer novel capabilities such as detecting extremely weak optical signals and providing quantum guarantees on security.
* D. Livigni, N. Tomlin, C.L. Cromer and J.H. Lehman. Fiber-coupled cryogenic radiometer with carbon nanotube absorber. Paper presented at 11th International Conference on New Show allDevelopments and Applications in Optical Radiometry (NEWRAD 2011), Maui, Hawaii, Sept. 19-23, 2011.
D.J. Livigni, N.A. Tomlin, C.L. Cromer and J.H. Lehman. Optical fiber-coupled cryogenic radiometer with carbon nanotube absorber. Metrologia. Forthcoming.
** See the 2010 NIST Tech Beat article, "Extreme Darkness: Carbon Nanotube Forest Covers NIST's Ultra-dark Detector" at www.nist.gov/pml/div686/dark_081710.
Contact: Laura Ost firstname.lastname@example.org 303-497-4880 National Institute of Standards and Technology (NIST)