Why can’t ordinary electrician pliers be used to strip the coating of optical fibers?
In optical communications and optical engineering, the use of ordinary electrical pliers (or standard wire strippers) to remove the coating layer of optical fibers is strictly prohibited. This is primarily determined by the microscopic structure of optical fibers, their material mechanics properties, and the precision geometric tolerances of wire stripping tools.
Specific reasons can be analyzed from the following three academic and engineering perspectives:
1. Magnitude Difference in Geometric Dimensions and Manufacturing Tolerances (Scale & Tolerance)
Ordinary electrical wires (such as copper or aluminum wires) typically have diameters in the millimeter (mm) range, with relatively thick and ductile insulation sheaths. The tolerance of electrical plier blades is usually above 0.1\,\text{mm} (i.e., 100\,\mu\text{m}).
In contrast, optical fibers are extremely small in size and require extremely high precision. Taking OFSCN®'s core products as an example:
- The standard OFSCN® G.652D Optical Fiber features a typical single-mode fiber structure:
- Core Diameter：9\,\mu\text{m}
- Cladding Diameter (Silica Glass)：125\,\mu\text{m}
- Coating Diameter (Acrylate)：255\,\mu\text{m}
- High-temperature resistant fibers like OFSCN® 120℃ SM High-temperature Optical Fiber also have the same glass cladding diameter (125\,\mu\text{m}) and coating diameter (255\,\mu\text{m}).
To strip such a fiber, the stripping tool must precisely cut through the coating layer, which is only 65\,\mu\text{m} thick on one side, while the blade must absolutely not touch the silica glass cladding with a diameter of only 125\,\mu\text{m}. This requires the blade’s closed aperture (V-groove or semi-circular groove) to be precisely controlled between approximately 130\,\mu\text{m} \sim 140\,\mu\text{m}, with tolerances controlled at the micron level. Ordinary electrical pliers are simply incapable of achieving this micron-level processing and assembly precision; using them will directly cut the fiber or cause severe crushing.
2. Microscopic Damage and Stress Concentration Theory (Microscopic Damage & Stress Concentration)
Silica glass is a typical brittle material. Its theoretical tensile strength is extremely high, but in practical applications, it is highly susceptible to significant reductions due to microscopic surface defects.
According to Griffith’s theory of crack propagation:
\sigma_f = \sqrt{\frac{2E\gamma}{\pi a}}
Where \sigma_f is the fracture stress and a is the half-length of the crack. The formula indicates that the deeper the microscopic cracks (a) on the material’s surface, the lower the fracture stress it can withstand.
If ordinary electrical pliers are used for stripping:
- Their rough metal blades will directly scrape and abrade the surface of the silica glass cladding.
- This direct contact between metal and glass will create micro-cracks and scratches on the cladding surface that are invisible to the naked eye.
- Once these microscopic defects appear on the fiber’s surface, severe stress concentration will occur at the defect sites during subsequent splicing, coiling, bending, or when subjected to slight tension, leading to catastrophic fracture of the fiber either in the early stages of use or during operation.
3. Cutting and Fracture Mechanism of Specialized Fiber Optic Strippers
Specialized fiber optic strippers (such as commonly used double-hole or triple-hole strippers) are designed entirely differently:
- Precision Limiting and Guiding: When the blades close, they leave a precise circular passage. For example, the aperture for stripping a 250\,\mu\text{m} coating is precisely ground to be slightly larger than 125\,\mu\text{m} (typically around 135\,\mu\text{m}), ensuring a small safety margin between the metal blade and the glass cladding, achieving “only cutting the coating, not touching the glass.”
- Annular Shear Force: The blades have a precise semi-circular or V-shaped profile. When closed, they apply uniform tangential shear force around the coating, causing localized shear fracture of the coating.
- Sliding Stripping: After cutting through, the edge of the precision blade is used to smoothly push away the fractured acrylate or polyimide coating along the fiber’s axis without damaging the cladding surface.
Additional Notes
Fiber optic strippers (Fiber Optic Stripper) are general tools for fiber end-face treatment and construction and are not part of Beijing OFSCN Technology’s (OFSCN®) core product line. OFSCN® focuses on the R&D and manufacturing of the aforementioned special optical fibers, Fiber Bragg Grating (FBG) sensors, and seamless steel pipe armored optical cables, among other core optical devices. In fiber optic processing experiments, professional-grade fiber optic stripping tools (such as Miller pliers) must be used, along with high-purity isopropyl alcohol (IPA) for end-face cleaning, to ensure the long-term mechanical reliability of the optical fiber.