The Need

Optical fibers are lightweight, small in diameter, and immune to electromagnetic interference. Signal attenuation over great distances is minimal and there is a high potential for large bandwidth data transfer. These qualities make optical fiber-based sensors an ideal candidate for measurements where space is limited. Silica fibers are chemically inert and have a high melting point, 1400 C, making these fibers the current gold standard for harsh environment sensing. As engineers take on ever more challenging projects the limits of silica fiber optic sensors will be pushed. Testing of silica optical fiber beyond its limits has already demonstrated problems, during increased temperature exposure the sensing capabilities of silica optical fiber began to fail and the fiber itself began to crystallize. A plethora of markets will be interested in increasing the limits of optical sensing fibers, new materials and manufacturing processes must be developed in order to move past the 1400 C threshold.

The Technology

Researchers at the Ohio State University, led by Dr. Thomas Blue, have developed a method for enhancing the transmission qualities of sapphire optical fibers by adding an internal cladding. A variety of optical and material sciences engineering challenges have prevented sapphire from becoming the dominate optical fiber material. The first challenge to using sapphire fibers in a sensing network was to increase signal transmission efficiency to that of silica fibers. The best way to increase optical signal transmission is to add a cladding to the optical fiber. However under harsh conditions the cladding needs to maintain its integrity through the whole temperature range and remain chemically inert. Dr. Blue’s brilliant solution was to create a cladding layer by irradiating the sapphire fiber this displaces the atoms a few micrometers deep which changes the index of refraction. This modified layer works as a cladding with identical thermal and chemical properties of sapphire. Dr. Blues technology has shown under lab conditions that it can withstand temperatures of up to 1500 C. This breakthrough will allow engineers to monitor temperatures in confined spaces under extremely harsh conditions.

Commercial Applications

This technology can be utilized to develop sensors and smart structures for:

• Aerospace/Defense
• Oil and Gas
• Utilities and Construction
• Nuclear reactor monitoring
• Chemical plant monitoring
• Life Sciences

Benefits/ Advantages

• Can operate at temperatures higher than silica optical fiber, 1500 C.
• Resists degradation by the environment compared to traditional thermocouples, due to sapphire being chemically inert.
• Reduces the amount of light modes in the sapphire optical fiber so that the fiber can be used for distributed temperature measurements.
• Sensing capability of the sapphire optical fiber has been demonstrated and its transmission performance is comparable to a multi-modal silica fiber with an increased thermal operating range.