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Photonic Thermometry

Close-up of probes over chip.

Ring-resonator photonic thermometer configurations -- each about 10 micrometers in diameter -- are fabricated on the surface of a microchip.  On either side is a single optical fiber used to measure each device's output.

For nearly a century, accurate temperature measurements in the manufacturing and bio-medically relevant range of –189.3442 ˚C to 961.78 ˚C have been made using electrical measurements. The standard bearer for temperature measurements in this range, a Standard Platinum Resistance Thermometer (SPRT), relies on electrical resistance measurement of a loose, suspended bundle of platinum wires. SPRTs are difficult to fabricate, expensive to calibrate, and require careful handling. In a manufacturing setting, the SPRT requires frequent, time-consuming and expensive re-calibrations to ensure peak performance. In the Thermodynamic Metrology Group, we have launched a comprehensive research program to replace voltage-based thermometry with photonic thermometry.

For manufacturing applications requiring 10 mK accuracy, we are developing a ring resonator-based photonic thermometer. Ring resonators are known to exhibit a periodic notch filter-like response where the resonant frequency shows a temperature-dependent shift due to changes in the material properties, namely thermal expansion and the thermo-optic effect.

The ring resonator design provides high temperature sensitivity and is easy to manufacture using standard CMOS compatible technologies. For low-cost applications with less stringent accuracy requirements, we are pursuing Fiber Bragg Grating (FBG) for temperature and pressure sensing applications. FBGs, a standard component in fiber optics-based telecommunication systems, are inexpensive to fabricate and easy to deploy.

The principal advantages of photonic sensor technology are low cost, light weight, portability, and resistance to electromagnetic interference. Such devices can be deployed in a wide variety of settings, from controlled laboratory conditions to a noisy factory floor to the variable environment of a residential setting.

Realization of photonic temperature sensors will enable a transition away from electrical measurements- along with their attendant limitations- and into frequency measurement, opening up an entirely new landscape of possibilities where photonic temperature sensors can be built with self-diagnostic and self-calibration capabilities. Such sensor networks may impact a broad swath of industries including aerospace, green chemistry, fossil fuel energy production, environmental monitoring in office, laboratory and manufacturing setting, and biomedical devices for small animal telemetry.

This line of inquiry seeks to develop mass-producible, low-cost, field-deployable, rugged photonic sensor with self-calibrating capabilities that could be utilized in a broad range of applications, from advanced manufacturing to citizen-scientist initiatives. This is a multi-disciplinary project involving various scientists from different groups at NIST.

Setup2_1_500
The experimental setup, with optical fibers mounted on cantilever arms above the microchip containing the ring-resonator devices. Close-up photo of chip and fibers appears above.