Enhanced Small Diameter Optical Fiber with Integrated Gratings
This invention is a small diameter single-mode optical fiber that has optical gratings formed directly within its core through an intact, protective coating. This novel method eliminates the time-consuming and fiber-damaging process of removing and reapplying the coating, significantly improving the efficiency and reliability of forming Bragg gratings in optical fibers.
Description
The core innovation is a method for forming optical gratings within a single-mode optical fiber without stripping its protective polymer coating. The optical fiber has a core and cladding with a small combined outer diameter of 100 μm to 125 μm and a thin coating with a thickness of less than or equal to 20 μm. This coating is a single high-modulus layer (Young's modulus ≥0.5 GPa) or a two-layer structure composed of a low-modulus layer (Young's modulus ≤5 MPa) surrounded by a high-modulus layer (Young's modulus ≥0.5 GPa). To form the grating, the optical fiber is exposed to a pattern of ultraviolet (UV) radiation directly through the coating and into the core. The thin, specialized coating and small diameter allow the UV light to pass through and create a change in the refractive index (an optical grating) within the fiber's core. This process can be performed continuously while the fiber is transferred from one reel to another, providing a method to manufacture optical fibers with integrated gratings over long lengths, which is a significant improvement over existing techniques that are limited by fiber vibration during the draw process or coating removal after the draw.Applications
- Distributed Optical Fiber Sensors (DOFS): For detecting changes in temperature, strain, pressure, and chemical concentration.- Pipeline Monitoring: Used for security and leak monitoring on oil and gas pipelines.
- Intrusion Detection Systems: Can be used in perimeter and area security for detecting unwanted entry.
- Down-Hole Sensing: Applicable in oil and gas wells for monitoring conditions deep underground.
- Compact Medical Devices: The small diameter makes them suitable for use in minimally invasive medical sensing applications.
Advantages
- Improved Fiber Reliability: The protective polymer coating remains intact during grating formation, preventing surface defects on the glass that can cause reliability issues.- Reduced Manufacturing Complexity and Cost: The costly and time-consuming steps of coating removal and re-application are eliminated.
- Enhanced Grating Uniformity: Gratings can be fabricated on long fiber lengths at high speed without issues caused by fiber draw vibration, leading to more uniform grating properties.
- Increased Sensing Sensitivity: The fiber structure, which may include a Titania-doped layer in the cladding, increases the Rayleigh scattering backscattered power, improving the resolution and sensitivity of fiber sensors.
- Small Diameter Profile: The fiber and its coating maintain a compact size (coated diameter ≤145 μm), enabling easier packaging and deployment, especially in small spaces.