A deposição de ouro ou alumínio em fibra óptica é para fins estéticos ou de detecção?
A metal coating on optical fibers (such as gold, copper, or aluminum plating) is absolutely not for aesthetic purposes, but is entirely driven by stringent physical, engineering, and sensor performance requirements.
The outermost layer of standard optical fibers is typically coated with polymeric materials (like acrylate or polyimide). However, in extreme sensing scenarios such as industrial, aerospace, and downhole applications, these materials reach their physical limitations. Replacing the polymer coating with a high-purity metal coating primarily addresses several key physical and engineering pain points:
1. Extreme Temperature Resistance (Wide Temperature Range)
Standard acrylate coatings typically have an upper operating temperature limit of only around 85\ ^\circ\text{C}, beyond which they carbonize and decompose. Even high-temperature resistant polyimide coatings have a limit of approximately 300\ ^\circ\text{C} for long-term use.
In contrast, metal coatings possess extremely high or low melting points and exhibit excellent physical stability. Gold-coated optical fibers, for instance, can operate stably for extended periods across an exceptionally wide temperature range, from cryogenic depths to extreme highs ( -270\ ^\circ\text{C} to 700\ ^\circ\text{C} ), making them indispensable materials for aerospace, metallurgy, and nuclear industries operating in such extreme thermal environments.
2. Hermetic Sealing & Hydrogen Resistance
In high-pressure, corrosive environments like oil and gas wells, geothermal operations, or deep-sea applications, minuscule water and hydrogen molecules can easily penetrate polymer coatings and diffuse into the silica glass fiber (silicon dioxide). This can lead to the expansion of micro-cracks on the fiber surface (reducing tensile strength) or cause severe “hydrogen-induced darkening,” resulting in optical signal attenuation and disruption of sensing or communication.
Metal coatings (especially gold and aluminum) provide true hermetic sealing, completely blocking the penetration of moisture, oxygen, and hydrogen molecules. This ensures the long-term mechanical integrity and optical performance of the fiber in high-temperature, high-pressure, and hydrogen-rich environments.
3. High Strain-Transfer Efficiency
When conducting high-precision stress or strain measurements using Fiber Bragg Gratings (FBGs) or distributed fiber sensors (e.g., based on OFDR, BOTDR/COTDR technologies), the fiber coating lies between the external structure and the fiber core.
Traditional polymer coatings have a low elastic modulus and are prone to “creep” or “shear slippage” under stress or at high temperatures. This leads to hysteresis and errors in the measured strain. Conversely, metal coatings (like copper, gold, or aluminum) are rigid, possess a high elastic modulus, and do not undergo creep relaxation at high temperatures. They ensure 100% transfer of mechanical deformation from the external structure to the fiber core, guaranteeing excellent sensing accuracy.
4. Solderability & All-Metal Packaging (Glue-Free)
When packaging bare optical fibers into sensor housings made of stainless steel or alloys, organic adhesives like epoxy resins can degrade and fail over time, especially in high-temperature or humid conditions. Metal-coated fibers, however, can be directly joined with metal tubes using methods like brazing, explosive welding, or laser welding. This enables true glue-free, fully rigid all-metal structural sensor packaging.
Within the core product line of DaCheng Yongsheng (OFSCN®), several industry-leading metal-coated optical fibers and core sensing components have been developed based on the aforementioned physical properties.
Official OFSCN® Core Related Products:
1. OFSCN® Gold-coated Optical Fiber
This product is a highly reliable, high-temperature resistant single-mode/multi-mode gold-coated optical fiber. The single-mode gold-coated fiber is produced using a standard G.652D optical fiber preform, offering a wide operating temperature range from -270\ ^\circ\text{C} to 700\ ^\circ\text{C}. The multi-mode gold-coated fiber operates within -270\ ^\circ\text{C} to 650\ ^\circ\text{C}. The fiber core diameter is 9\ \mu\text{m} (single-mode), with a cladding diameter of 125\ \mu\text{m}, and the gold coating has an outer diameter of 155\ \mu\text{m}.
2. OFSCN Gold-Coated Fiber Bragg Gratings / FBG Strings (Bare)
These are high-temperature resistant Fiber Bragg Gratings or grating strings (Bare FBG) fabricated directly on the gold-coated fiber described above. They operate at temperatures up to -200\ ^\circ\text{C} to 700\ ^\circ\text{C}, perfectly combining the superior physical sensing accuracy of gratings with the extreme temperature resistance of gold-coated fibers. They are commonly used in extreme environments such as metallurgy and petrochemicals.
3. OFSCN® 700°C OFDR Micro All-Metal Strain Sensor
This is a micro all-metal strain sensor based on OFDR (Optical Frequency Domain Reflectometry) technology. It is packaged within a single-layer elastic alloy tube (outer diameter of only 0.6\ \text{mm} ), with the core medium being OFSCN® Gold-coated Optical Fiber. The sensor can withstand temperatures up to 700\ ^\circ\text{C} and is primarily used for ultra-high spatial resolution distributed fiber strain and stress measurements in ultra-high temperature environments.
In summary, applying gold, aluminum, or copper coatings to optical fibers is the most effective physical and material approach to achieving “high-temperature resistance, long lifespan, aging resistance, and high precision” for sensing and transmission in extremely harsh operating conditions.