How do I strip the outer jacket without damaging the glass fiber core?
In the fields of optical communications and fiber sensing (such as Fiber Bragg Grating inscription), stripping the fiber coating (typically the acrylate coating) without damaging the underlying high-purity silica cladding and core is a critical process for ensuring the fiber’s mechanical strength and transmission performance.
To achieve “stripping the coating without damaging the glass core” primarily relies on precise control of the physical structure and operating angle of the stripping tool. Here are the general engineering principles and methods to achieve this process:
1. Typical Physical Dimensions of Optical Fiber
Taking a standard single-mode fiber (e.g., OFSCN® G.652D Optical Fiber) as an example, its internal spatial structure and material hierarchy are as follows:
- Core: Approximately 9\ \mu\text{m} in diameter
- Cladding: 125\ \mu\text{m} in diameter (silica glass material)
- Coating: 255\ \mu\text{m} in outer diameter (typically acrylate material)
The goal of fiber stripping is to completely remove the 255\ \mu\text{m} diameter acrylate coating without touching or scratching the 125\ \mu\text{m} diameter glass cladding. This is because the surface of silica glass is extremely sensitive; any minuscule mechanical scratch (micro-crack) can rapidly propagate into macroscopic fracture under tensile stress.
2. Three Main Methods for Damage-Free Stripping
Method 1: High-Precision Mechanical Stripping (Using Fiber Strippers / Miller Tools)
This is the most common method for on-site operations.
- Physical Principle:
Professional fiber strippers (such as three-hole or two-hole Miller tools) are designed with highly precise semi-circular notches and V-grooves at their jaws. For 125\ \mu\text{m} cladding fiber, the closed diameter of the stripper jaw is typically precisely controlled between 130\ \mu\text{m} and 140\ \mu\text{m}.
When the jaws are fully closed, the blades just cut into the coating (255\ \mu\text{m}), while maintaining a physical gap of several micrometers between the blade and the inner glass cladding (125\ \mu\text{m}). - Operating Essentials:
- Cleanliness: Before stripping, the jaws must be cleaned with anhydrous ethanol to prevent residual coating fragments from elevating the blade, leading to uneven force application.
- Angle: The grip angle of the stripper should be approximately 30^\circ to 45^\circ relative to the fiber axis.
- Force and Speed: Pull the stripper smoothly and quickly along the fiber axis in a single motion. Avoid reciprocating pulling or rotating the fiber, as this can cause the side of the blade to scrape the glass surface.
Method 2: Thermal Stripping
Often used for stripping harder, thicker coatings, or multi-core fibers, and in industrial scenarios requiring extremely high mechanical strength (such as pre-processing for Fiber Bragg Grating inscription).
- Physical Principle:
Thermal stripping equipment heats a section of the fiber using built-in heating elements. Acrylate and other coating materials rapidly soften at high temperatures (typically around 100^\circ\text{C} to 150^\circ\text{C}), drastically reducing their adhesion to the silica glass surface. - Advantages:
As the material is softened, the shear force required for stripping is greatly reduced. The mechanical blade needs minimal radial pressure to slide off the coating completely, thereby minimizing the probability of micro-scratches on the glass surface.
Method 3: Chemical Stripping
This is the method with the least physical damage and is the most thorough, typically used in high-precision laboratories or for specialty fiber fabrication.
- Physical Principle:
Chemical solvents (such as concentrated sulfuric acid H_2\text{SO}_4, acetone, etc.) are used to immerse the coating. The solvent breaks down the polymer’s cross-linked structure, causing it to swell, dissolve, and detach from the glass. - Advantages:
The entire process involves no mechanical contact, ensuring 100% retention of the silica glass cladding’s original tensile strength as delivered from the factory.
3. Special Notes and Industry Applications
It should be clarified that common “fiber strippers” (Miller tools), thermal strippers, or fusion splicing accessory tools are standard industry tools for basic installation and construction and are not part of Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®)'s core product line.
Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) focuses on providing high-quality specialty fibers, passive optical components, and fiber sensing systems. For instance, during the preparation of OFSCN® Polyacrylate Fiber Bragg Gratings / FBG Strings (Bare) (single-mode Fiber Bragg Gratings), before UV light exposure for inscription via a photomask, R&D personnel precisely etch the gratings after rigorous hydrogen loading and the aforementioned precision coating stripping process without damaging the silica glass. After inscription, high-precision recoating protection is applied to ensure its mechanical tensile lifespan.
In practical engineering operations, to verify if the glass core has been damaged after stripping, the bare fiber is typically wiped with anhydrous ethanol after stripping and inspected under a high-power microscope for longitudinal scratches. Alternatively, simple bending and tensile tests (Proof Test) can be performed to verify whether the mechanical strength has been compromised.