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Resistance thermometry, a time-tested method for taking temperature measurement, relies on taking accurate temperature-dependent resistance measurement of a strain-free metal wire or thin film. Platinum resistance thermometers (PRTs), for example, rely on electrical resistance measurement of a loose, suspended bundle of Platinum wires that is sensitive to humidity and mechanical shock induced strain. In a manufacturing setting, PRTs require frequent time-consuming and expensive recalibrations to ensure peak performance. In the Thermodynamic Metrology group, we have launched a comprehensive research program to replace voltage-based thermometry with photonic thermometry.
Close-ups of two "packaged" photonic thermometers, each with its ponytail of optical fibers. A droplet of hardened, transparent epoxy (center) connects a fiber optic array (top) to a photonic chip containing two temperature-sensing devices (bottom). The thermometer package depicted on the right is having its epoxy cured with ultraviolet light. The chips' surfaces are each about 9 mm x 7 mm.
Why Photonic Thermometry:
The principle advantage of photonic sensor technology is that it is a low cost, lightweight, portable, and electromagnetic interference-resistant solution that can be deployed in a wide variety of settings ranging from controlled laboratory conditions to a noisy factory floor to the variable environment of a residential setting.
Realization of photonic temperature sensors will move us 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-diagnosing and self-calibration capabilities. Such sensor networks will impact a broad swath of industries including aerospace; green chemistry; fossil fuel energy production; environmental monitoring in office, laboratory, and manufacturing settings; and biomedical devices for bio-telemetry applications.
We are focusing on photonic devices that exploit the thermo-optic effect to translate thermal changes into frequency shifts. The principle focus of our efforts is silicon photonics, where we are developing a range of devices including optical whispering gallery mode resonators (ring resonators), Bragg waveguides, photonic cavities, and photonic crystal structures.
Our preliminary results indicate that silicon photonic devices provide measurement capabilities that are at the minimum competitive with current state-of-the-art devices in photonic and resistance thermometry. In addition to developing novel silicon photonic temperature sensors, we are exploring the use of fiber Bragg gratings in embedded sensor applications.
Our goal is to utilize our know-how of silicon photonic devices to develop cavity opto-mechanical devices that serve as deployable self-calibrating sensors.
For manufacturing application 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 resonant frequency shows a temperature-dependent shift due to changes in the material properties, namely thermal expansion and the thermo-optic effect.
If you are interested in joining our team as a post-doc, guest researcher, collaborator, or student volunteer, or if you would like to visit the lab and see the latest developments in thermodynamic metrology, send us an email.
|An experimental setup, with optical fibers mounted on cantilever arms above the microchip. Close-up photo of a chip and fibers appears above.|
Pub No. US 2014/0321502 A1