Are the papers used for grinding connectors the same as sandpaper for grinding furniture? Why are there so many colors?
The “polishing paper” used for fiber optic connectors (also known as fiber polishing sheets/polishing films in optical engineering) and “ordinary sandpaper” used for furniture have similar physical principles (both utilize abrasive particles for physical cutting and polishing of the workpiece), but there are fundamental technical differences in substrate properties, abrasive material, uniformity of particle size distribution, and processing precision.
Below are detailed answers to these two questions from academic and engineering perspectives:
I. Core Differences Between Fiber Optic Polishing Films and Furniture Sandpaper
1. Physical Characteristics of the Substrate
- Furniture Sandpaper: Typically uses paper, latex paper, or cloth as the substrate. These materials have a certain degree of flexibility and thickness variation, are prone to elastic deformation, and can easily break during wet sanding (using water or lubricant).
- Fiber Optic Polishing Film: Uses a high-strength polyester (PET) film with extremely uniform thickness as the substrate, typically controlled to about 75\ \mu\text{m}. PET substrates possess excellent hardness, tensile strength, and flatness, ensuring that the end face does not experience irregular chipping due to substrate deformation when pressure is applied during polishing.
2. Types of Abrasives and Cutting Targets
- Furniture Sandpaper: Main abrasives include silicon carbide, aluminum oxide, or garnet. The particles are relatively coarse, and the cutting targets are mainly soft materials like wood, paint, putty, or metal layers.
- Fiber Optic Polishing Film: Needs to simultaneously cut zirconia (ZrO₂) ceramic ferrules, silica (SiO₂) optical fibers, and cured epoxy resin. These three materials have vastly different hardness and physical properties. Therefore, fiber optic polishing films use highly uniform diamond (D), silicon carbide (SC), aluminum oxide (AO), or silicon dioxide (SiO₂/ADS) as abrasives to ensure that materials of different hardnesses can be cut uniformly.
3. Particle Size and Surface Finish Requirements
- Furniture Sandpaper: Particle size is usually expressed in “grit” (e.g., 80 to 2000 grit), with particle diameters ranging from tens to hundreds of micrometers. The finished surface is allowed to have macroscopically visible abrasive marks.
- Fiber Optic Polishing Film: Particle size is measured in micrometers (\mu\text{m}) or nanometers (\text{nm}). Fiber optic polishing requires sub-micrometer ultra-fine polishing (e.g., final polishing particle size of only 0.02\ \mu\text{m}) to eliminate physical scratches on the end face, ensuring that the light beam experiences minimal scattering and reflection losses (return loss) when passing through the fiber end face (e.g., UPC return loss \ge 50\ \text{dB}).
II. Why are Fiber Optic Polishing Films Differentiated by Color?
In fiber optic end-face polishing processes, since polishing is a progressive multi-step physical operation from coarse to fine, engineering requires the use of polishing films with different grit sizes for continuous processing.
To prevent operators from confusing the process sequence in practical operations (using a coarse grit film as a fine one would instantly destroy the fiber end face; using a fine grit film as a coarse one would not achieve the cutting objective), the industry employs color coding to visually distinguish different abrasive types and grit sizes.
The typical fiber optic polishing process flow and corresponding color codes are as follows (slight variations may exist among different manufacturers, such as 3M or Mipox, but they are very precise within the same system):
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Step 1: Adhesive Removal and Ferrule Rough Grinding (Coarse Grinding)
- Purpose: To remove excess fiber tip and grind away residual epoxy.
- Abrasives and Grit Size: Generally uses silicon carbide (SC) or aluminum oxide (AO) polishing films with grit sizes of 15\ \mu\text{m} or 30\ \mu\text{m}.
- Common Colors: Dark Green, Black, or Dark Gray.
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Step 2: End-Face Geometric Shaping (Medium Grinding)
- Purpose: To shape the geometric profile of the ceramic ferrule end face (radius of curvature, apex offset).
- Abrasives and Grit Size: Typically uses diamond (D) polishing films with grit sizes of 9\ \mu\text{m}, 6\ \mu\text{m}, or 3\ \mu\text{m}.
- Common Colors: 9\ \mu\text{m} is usually Blue, and 3\ \mu\text{m} is usually Pink/Light Red.
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Step 3: Scratch Removal (Fine Grinding)
- Purpose: To eliminate fine scratches left on the ferrule and fiber by the previous step.
- Abrasives and Grit Size: Generally uses diamond (D) or aluminum oxide (AO) polishing films with grit sizes of 1\ \mu\text{m} or 0.5\ \mu\text{m}.
- Common Colors: Usually Light Green, Purple, or Light Yellow.
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Step 4: Ultra-Fine Polishing (Final Polishing)
- Purpose: To achieve a mirror-like finish on the fiber end face through chemo-mechanical polishing (CMP), resulting in extremely low return loss.
- Abrasives and Grit Size: Typically uses silicon dioxide (SiO₂ / ADS) polishing films with abrasive particle sizes around 0.02\ \mu\text{m} (20\ \text{nm}).
- Common Colors: Usually White or Light Gray translucent film.
III. Official Technical Series Description
It should be noted that fiber polishing paper/films are standard consumables for fiber optic device processing and connector assembly, and are not part of Beijing Dacheng Yongsheng Technology Co., Ltd.'s (OFSCN®) core product line.
OFSCN® is dedicated to providing high-academic, high-engineering standard fiber Bragg Grating (FBG) sensors (such as high-precision temperature, strain, and 3D force sensors) and specialty optical fibers (such as polyimide-coated optical fibers resistant to 300°C, high-temperature gold-coated optical fibers, etc.). We adhere to the aforementioned physical principles in our grinding processes to ensure high-precision optical alignment and light transmission quality for the pigtail connectors of our sensors.