Fiber cracks appeared after array fiber polishing

Fiber cracks after polishing are typically caused by mechanical stress, uneven pressure, contamination, or improper polishing procedures, and can be minimized with careful process control and inspection.

Causes of Fiber Cracks

Cracks in optical fibers often occur due to mechanical stress during polishing. Glass fibers are brittle and can fracture if subjected to tensile stress or localized pressure, especially if there are pre-existing flaws on the fiber surface . In fiber arrays, additional factors include:

• Impurities in polishing films or sandpaper that scratch or weaken the fiber surface .
• Uneven polishing pressure, where excessive local force can initiate microcracks .
• Contaminated or improperly concentrated polishing solutions, which can create abrasive effects or uneven material removal .
• Equipment vibration or unstable rotation speed, leading to inconsistent polishing and stress points .
• Insufficient or skipped polishing steps, which can leave surface irregularities that propagate into cracks .
• Fiber array not securely fixed, allowing movement during polishing and causing stress fractures .
• Differences in fiber material hardness, which can result in uneven wear and localized stress .

Consequences of Cracks

Cracks can propagate under mechanical or thermal stress, potentially leading to:

• Edge chips that interfere with connector mating.
• Increased insertion loss and reduced return loss.
• Reduced reliability and potential failure in high-power or sensitive optical systems .

Prevention and Optimization

To minimize fiber cracking during polishing:

1. Use high-quality, impurity-free polishing films and clean the polishing fixture before use .
2. Control polishing pressure stepwise: rough polishing (100–150 g) → fine polishing (50–80 g), and regularly calibrate equipment .
3. Use high-purity deionized water for polishing solutions and replace it for each batch .
4. Stabilize equipment with shock-absorbing bases and maintain consistent motor speed .
5. Follow a complete stepwise polishing process (rough → medium → fine) and adjust polishing time according to particle size .
6. Secure the fiber array using vacuum adsorption or epoxy resin curing, and add support blocks to prevent movement .
7. Inspect end-faces using magnified visual inspection or CCD-based fiber inspection scopes to detect cracks early .

Additional Recommendations

• For fragile or non-standard fibers, consider angle polishing or specialized holders to reduce stress during preparation .
• Avoid skipping cleaving or polishing steps, as incomplete preparation can leave micro-defects that evolve into cracks .
• Regularly maintain and replace polishing pads to ensure uniform material removal and prevent localized stress . By carefully controlling these factors, fiber cracks can be significantly reduced, ensuring high-quality end-faces and reliable optical performance.