Chiral Photonics recently introduced the newest addition to its Helica products - a robust fiber optic temperature sensor designed for the most demanding industrial and R&D applications that require stability to 1000°C. Helica™ fiber optic temperature sensors, fabricated from chiral long period gratings, can be used to optically sense environmental factors, such as chemical composition, temperature, and pressure. They can be used to probe harsh environments with high levels of radiation, high temperature, or corrosive chemicals such as might exist in nuclear power plants or in bore holes in oil fields and in deep mines. Customers have been enthusiastic about this monolithic glass solution which does not rely on photoinduced gratings or coatings or moving parts, thereby offering the reliability inherent to glass.

The Helica fiber optic temperature sensor is based on Chiral Photonics’ patented chiral grating, which is fabricated by twisting, or microforming, the fiber as it is passed through a miniature heat zone to produce a distinct dip in the transmission spectrum. The spectral position of the dip in this chiral fiber changes with temperature allowing it to be used as a temperature sensor. Chiral gratings are structurally formed into fiber. As such, Helica™ Sensors do not require the use of photosensitive fibers or rely on applying or relieving stress in the fiber. As a result, they are highly stable at high temperature and in other environmental conditions that can cause conventional long period gratings to degrade.

The fiber optic temperature sensor was designed for applications ranging from weld monitoring and control to turbine engine service and design. The sensing element is a monolithic glass fiber and is as stable as the silica glass. It is not reliant on any moving parts or coatings and the sensor packaging can be tailored to suit the application needs. Helica™ Sensors come in two varieties: single helix or double helix, as shown below. In both, the optical fiber’s refractive index is modulated by twisting a fiber with noncircular or nonconcentric cross section as it is passed through a miniature oven to produce the highly stable grating. A concentric core is used to produce a double helix structure and a non-concentric core is used to produce a single helix structure.

Specifications:

• Temperature Range: Up to 1000°C
• Accuracy: 1%
• Sensitivity : 0.01 nm/°C (nominal)
• Sensor Placement: 25 mm from probe tip - Other configurations available upon request
• Probe (metal sheathing) Length: 300 mm standard - Other lengths available upon request
• Sensor/Grating Length: 15 mm - Other lengths available upon request
• Connector Type: FC/APC - Other connectors available upon request

Product features:

• Flexible, continuous manufacturing process
• Second polarization may be used for normalization or second channel
• UV irradiation of photosensitive glass not required
• Suitable for harsh environments
• Narrow dip enables high sensitivity

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