Optical Fiber Stripping
You can get optical fiber stripper from Fiber Optics For Sale Co.
>> Single Fiber Coating Structure
Depending on fiber’s application, different optical fiber coating designs exist. However, 250um UV coating is the most popular among today’s single mode and multimode bare fibers. The following illustration shows this common design.
The polymer coating is a soft, UV cured, urethane acrylate. It has a higher refractive index than the cladding layer, so it can strip out unwanted light. This polymer coating may consist of one or two layers.
If there are two layers, the inner layer is called primary coating and the outer layer is called secondary coating. The primary coating has a diameter of 180um. It is made of very soft acrylate to reduce fiber’s microbend loss. The secondary coating usually has a diameter of 250um and is made of much harder acrylate to provide good abrasion resistance.
>> Ribbon Fiber Coating Structure
The individual strands comprising a ribbon fiber are also usually coated with a dual acrylate layer, and the strands are bonded together by an acrylate polymer matrix. These relatively soft polymer materials facilitate the stripping process.
>> Why Optical Fiber Stripping?
Fiber stripping is the first step in fiber preparation for fusion splicing.
- High temperature in fusion splicing process will damage polymer coatings or even the heated portion of glass contacting the coating.
- Fiber alignment accuracy. Fiber’s glass (core/cladding) part has much higher dimensional tolerance than the polymer coating part. Holding on bare fiber (glass) part when doing fiber alignment in the splicing process is far more accurate.
- The polymer coating tends to curl which makes holding fiber and fiber alignment more difficult.
>> Side Effects
However, there is some drawback on stripped bare fiber.
- The stripping process usually degrades the pristine glass surface which reduces the fiber’s mechanical strength and long term reliability.
- Stripped bare glass fiber (or silica fiber) may incur more surface flaws which further reduces its strength.
- The length of fusion splice protection sleeve. The protection sleeve much be as long as the fused stripped fiber. The length ranges from 5mm to 20mm. This presents some fiber management problems in splice trays and other fiber assembly housings.
- Stripped fiber’s long term mechanical reliability. A fusion splice’s tensile strength is directly determined by the details of the stripping process. The ultimate tensile strength of as-drawn, coated, 125μm diameter fiber is about 57N, which is equivalent to about 5.5GPa or 800 kpsi (kpsi stands for kilopounds force per square inch) of tensile stress. Stripping can reduce this tensile strength by as much as or even more an order of magnitude.
- Any coating residue left on the glass fiber’s surface can interact with the heated fiber during joint formation leading to significantly lower tensile strength and reduced long term reliability.
>> Fiber Coating Stripping Methods
There are mainly four types of fiber stripping on the market today
- Mechanical fiber stripper
- Thermal fiber stripper
- Chemical fiber coating stripping
- Vaporization fiber stripping
Mechanical fiber strippers closely resemble wire stripping tools and they have the same working principle. Mechanical fiber strippers are mostly hand-held tools and they are the most commonly used in field fusion splicing and also plays a big roll in factory fusion splicing.
Mechanical fiber strippers cut into the coating with a precisely laser cut blade, then translate the stripper along the fiber to peel the coating from the fiber and push it off the surface.
The hole on the stripper’s blade usually laser cut in a precise tolerance. The hole diameter is so that it will cut enough into the coating but will not contact the glass surface. This prevents from the stripper from damaging the glass fiber.
Thermal fiber stripper is most commonly used on ribbon fiber stripping. Even ribbons containing 12 or 24 fibers can be stripped down to bare glass with the aid of a suitable thermal stripper.
The thermal stripper first softens the polymer coating with an electric heater and then strip off the coating just like a mechanical fiber stripper (with blades).
>> Chemical Fiber Stripping
Chemical stripping involves the use of an aggressive solvent to remove the polymer coating of the fiber. Chemical stripping is attractive since, unlike mechanical stripping, it does not require mechanical forces that cause defects on the fiber surface leading to strength and reliability degradation. Moreover, chemical stripping is effective for nearly all optical fibers, including polyimide coated and hard clad silica.
However, most of the chemicals are toxic, and some are even flammable. Thus chemical stripping does not lend itself to field splicing, but has been frequently employed in the laboratory or factory environments, especially when extremely high tensile strength and mechanical reliability is required.
Chemical stripping requires on the order of one minute of processing time, which is longer than mechanical or vaporization stripping techniques.
>> Vaporization Fiber Stripping
Some vaporization fiber stripping techniques have recently been developed. They are viable alternatives to chemical and mechanical stripping.
The acrylate coating material is removed from the fiber by high temperatures. Vaporization techniques are very fast, avoid dangerous solvents, minimize the amount of force applied to the fiber, minimize the amount of coating residue, and often maximize the surface quality of the resulting stripped fiber.
However, the hardware required for vaporizationbased fiber stripping is substantial, which precludes field splicing applications. Vaporization stripping techniques are well suited to automated splicing applications in a factory setting.