Fiber optic sensor counts photons to determine temperature

Edinburgh, Scotland--A fiber optic temperature sensor offering a unique combination of high spatial resolution, accurate temperature determination, and fast readout has been demonstrated by researchers at Heriot-Watt University and the National Institute of Standards and Technology (NIST; Boulder, CO). A pulse of infrared light is launched into a test fiber and the faint return signal produced by Raman scattering is sampled at the single-photon level using high performance superconducting nanowire detectors.

By comparing the weak Raman scattering signals at frequencies above and below the launch frequency, the temperature can be extracted. The temperature profile along the fiber can be determined via a time of flight method exploiting the high timing precision of the superconducting detectors.

This measurement technique holds promise for practical temperature monitoring, says Mike Tanner at Heriot-Watt University: "The temperature along the fiber can be determined with centimeter precision and a temperature uncertainty less than 3 K in readout intervals under 1 minute. This technique is potentially useful for monitoring temperatures in large structures such as buildings and pipelines, or in mechanical objects with moving parts."

Furthermore, this technique is an advance in absolute temperature metrology. Shellee Dyer at NIST adds, "If the properties of the detectors, filters, and optical fiber are known, this system could potentially be used as a primary reference standard, providing accurate measurements without any external temperature calibration."

This work is reported in Applied Physics Letters 99, 201110 (2011), High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors.

SOURCE: Heriot-Watt University