Silicon-tipped optical fiber makes microscopic heater/thermometer

Researchers at the University of Nebraska-Lincoln (Lincoln, NB) and the Naval Research Laboratory (Stennis Space Center, MI) have created a laser-heated, silicon-tipped fiber-optic device that can exceed 1000°C, going from room temperature to 150°C in fractions of a second.¹ The tip of the device is only 100 µm in diameter and, depending on the version, 10 or 200 µm long.

The device's heating capability could find use in contexts that range from monitoring greenhouse gases to prepping specimens for biological research to producing microbubbles for medical or industrial applications.

It also acts as a thermometer whose performance at extreme heat would allow it to monitor temperature in the demanding environments of engines and power plants, according to Ming Han, a University of Nebraska researcher.

The design evolved from Han's prior work on a fiber-optic temperature sensor suitable for oceanography. Like the new design, that sensor featured a microscopic silicon pillar attached to the end of an optical fiber. But the glue that bonded the silicon and fiber-optics would soften at roughly 90°C, restricting its use at higher temperatures.

"Then we had a breakthrough," Han says. After again bonding the fiber-optic and silicon pillar with glue, the team used an extremely hot electric arc to fuse another fiber-optic strand with the opposite side of the pillar. The process simultaneously softened the glue on the other side and detached the original fiber-optic strand, leaving just the newly fused device.

Heater and thermometer in one device
Two wavelengths of light are fed through the fiber-optic -- one 80-nm laser light that gets absorbed by the silicon to heat it, and the other broadband light centered at 1550 nm that passes through it.

Because the absorbed laser produces heat, its remote-controlled power dictates the temperature of the device. Meanwhile, the broadband light that enter the silicon gets partially reflected by the two ends of the pillar, which thus serves as an interferometer that allows temperature measurement.

Han and co-designer Guigen Liu say the device's ability to generate a broad swath of wavelengths in the near- to far-infrared range could prove especially useful in detecting gases based on how they interact with those waves. And the ability to gauge and adjust its temperature, Han says, lends the device a functional versatility unmatched by existing microheaters.

Source: http://news.unl.edu/newsrooms/today/article/husker-engineers-craft-microscopic-heater-thermometer/

REFERENCE:

1. Guigen Liu et al., Optics Letters (2017); https://doi.org/10.1364/OL.42.001412