Researchers develop tiny sensor for measuring subtle pressure changes inside the body

Researchers have developed an extremely sensitive miniaturized optical fiber sensor that could one day be used to measure small pressure changes in the body.

The researchers describe their new optical fiber sensor in The Optical Society (OSA) journal Optics Letters. The sensor, which is based on a fiber Bragg grating (FBG) inscribed into a fiber made from a new polymer called Zeonex, was able to detect pressure changes of just 2 kilopascals.

Many fiber optic sensors are based on FBGs, tiny periodic microstructures that can be inscribed onto a fiber. When pressure rises the fiber stretches slightly, increasing the grating period in a way that changes its refractive index and shifts the light output toward the red end of the spectrum. Similarly, a decrease in pressure produces a blue shift.

Making an FBG sensor from a traditional silica optical fiber is not ideal for medical applications, especially those involving long-term use in the body, because these fibers exhibit a relatively high stiffness and can be brittle. FBGs embedded in silica fibers also have limited sensitivity to small pressure changes because the material does not stretch and contract very easily. Although polymer optical fibers have been developed, they tend to absorb water -- which can affect measurements -- and are not very easy to inscribe with an FBG.

To overcome these hurdles, the researchers turned to the advanced polymer Zeonex. This new material is not only chemically inert and works well in the aqueous environments like those found in the body, but also exhibits a higher light shift in response to a pressure change compared to silica fibers. Although substances called dopants are often used to make materials with different refractive indexes for the inner core and outside cladding of fibers, the researchers simplified the fabrication process by using different grades of Zeonex to make a single-material fiber.