When you buy optical fiber, the supplier hands you a spec sheet. Loss, NA, core diameter — the numbers look good. But once it's installed in your equipment, the performance may tell a different story. The problem? There's a gap between what's on the spec sheet and how the fiber actually performs. First: Check the End Face End-face quality is the most overlooked — and most performance-critical — factor. Poor end-face preparation shows up in three ways: scratches, chips, and contamination. Scratches increase scattering loss. Chips distort the output beam. Contamination absorbs light energy directly. In high-power applications, end-face defects can even trigger thermal damage and fiber failure. The test is simple: inspect the end face under a microscope. A good end face should be flat, smooth, free of scratches and chips. If a supplier can't provide an end-face inspection report, that's a red flag. Hecho Technology's medical laser fibers and quartz fiber products undergo end-face inspection before shipment to ensure output quality. Second: Check Bending Performance Fibers will bend in real-world use. But "bend tolerance" varies widely between fiber types. A straightforward test: wrap the fiber around a cylinder of known diameter and measure the output power change before and after bending. The smaller the change, the better the bend performance. Some fibers show low loss in a straight configuration — but bend them slightly, and loss spikes. In equipment with tight internal routing, this directly reduces transmission efficiency. G.657 bend-insensitive fiber is designed for exactly this problem — bend radius can be very small with minimal loss. Third: Check Batch Consistency This is the most overlooked factor — and the one that matters most for volume production. A single fiber testing well doesn't mean every fiber in a batch performs the same. If batch-to-batch consistency is poor, equipment calibration parameters need constant adjustment, and production line efficiency suffers. The test: ask the supplier for test data across multiple batches. If they only provide a "typical value," they don't have confidence in their consistency. Summary Spec sheet numbers are the starting point. What actually determines performance is end-face quality, bending behavior, and batch consistency. Hecho Technology has nearly two decades of experience in specialty fiber. Our quartz, glass, and plastic fibers all undergo end-face inspection and performance testing, with batch delivery and custom specifications available. If you have questions about fiber selection or quality evaluation, contact the Hecho technical team.