Preparation of prefabricated bars
1. Materials and Structure:
Fiber optic is composed of a core layer (high refractive index) and a cladding layer (low refractive index), usually using silicon dioxide (SiO₂) as the base material, doped with germanium (Ge), fluorine (F), or boron (B) to adjust the refractive index.
Preparation method:
2. Chemical Vapor Deposition (CVD): Gas such as SiCl₄and GeCl₄is introduced into a quartz tube to deposit a core layer at high temperature, and then sintered into transparent glass.
3. External vapor deposition (OVD): SiO₂particles are deposited on the surface of a rotating target rod to form a porous preform, which is then sintered.
4. Vapor Axial Deposition (VAD): Deposition of materials along the axial direction of the target rod, suitable for manufacturing large-sized prefabricated rods.
Key point: Accurately control the doping concentration to achieve refractive index distribution and ensure material purity (impurities below ppb level).
Wire drawing process
1. Heating softening: The tip of the preform is heated to about 2000 ℃ in a high-temperature furnace (graphite resistance furnace/induction furnace) to soften it.
2. Wire drawing forming: speed control: traction speed reaches 10-50 meters per second, and real-time laser monitoring of diameter (125μm ±1μm) is used to feedback and adjust speed and temperature.
3. Cooling process: The pulled optical fiber is naturally cooled in the drawing tower to avoid internal stress.
4. Environmental control: A dust-free environment to prevent surface contamination and ensure the mechanical strength of optical fibers.
Coating process
1. One time coating: Apply UV cured acrylic resin with a thickness of about 250 μ m when the optical fiber is just formed, to protect the surface and reduce micro bending losses.
2. Secondary coating: adding nylon or polyimide layer to enhance mechanical strength and environmental resistance.
3. Curing technology: UV instant curing ensures uniform adhesion of the coating.
4 Quality Control
1. Geometric parameters: laser measured diameter, microscope detected core/cladding concentricity (deviation<0.5 μ m).
2. Optical performance: OTDR detects attenuation (≤ 0.2 dB)/ km@1550nm )Bandwidth and dispersion characteristics.
3. Mechanical performance: Tensile testing (tensile strength ≥ 100 kpsi), bending test to evaluate flexibility.
4. Environmental testing: Verify long-term stability under conditions such as high temperature and humidity, chemical corrosion, etc.
Five Environmental Protection and Cost Considerations
1. Waste gas treatment: Cl2 and GeCl₄ generated by CVD process need to be absorbed and treated with alkaline solution.
2. Cost factor: High purity materials and precision equipment drive up costs, but large-scale production (such as continuous drawing) can reduce unit prices.
3. Innovation direction: Developing low-cost dopants and improving drawing speed (such as ultra high speed drawing up to 2000m/min).
Technical Challenges and Solutions
1. Diameter fluctuation: The closed-loop control system adjusts the traction speed and furnace temperature in real-time.
2. Coating defects: high-precision coating molds and viscosity control technology.
3. Strength issue: Strictly control the environment to reduce surface defects, and protect the coating layer in a timely manner.
Summary
Fiber drawing manufacturing is a complex process that integrates material science, precision engineering, and optical technology. Its core lies in high-purity pre drawing