If the polishing is crooked, will the two connectors still align?
In the manufacturing and use of fiber optic connectors, if the “grinding is crooked” during the polishing process, it will directly lead to a critical geometric parameter exceeding the standard in physics and optical engineering – Apex Offset.
Simply put: If the grinding is crooked, the two connectors cannot perfectly align and contact at the microscopic core level. This directly leads to severe degradation of optical performance.
Here is an in-depth analysis from the perspective of physical and engineering principles:
I. What is “Apex Offset”?
During the polishing of fiber optic connectors (such as the common FC/PC, FC/APC, etc.), the end face of the ferrule is ground into a tiny spherical shape:
- Ideal State: The highest point of this spherical surface (the “apex”) should fall precisely on the geometric center of the fiber core.
- Crooked Grinding State: If the grinding fixture is skewed, the pressure is uneven, or the process fails, the highest point of the spherical surface will deviate from the fiber core. This lateral distance between the highest point of the spherical surface and the geometric center of the fiber core is the Apex Offset.
II. What is the Impact of Crooked Grinding (Excessive Apex Offset) on Alignment and Performance?
The ceramic sleeves in adapters (flanges) primarily provide radial alignment (ensuring the outer cylindrical surfaces of the two ferrules are coaxial), but they cannot correct the axial contact deformation of the end faces.
When two crooked connectors are mated and locked in an adapter:
- Physical Contact (PC) Cannot Be Achieved:
The fundamental principle of fiber optic connector design relies on the slight elastic deformation of the ferrule end faces under spring pressure, enabling seamless “physical contact” between the two fiber cores. - Air Gap is Created:
If the connector is crooked (excessive apex offset), the highest points of the ferrule spherical surfaces (apexes) will be the first to contact and butt against each other, not the fiber cores. This leaves an extremely small gap (air gap) between the fiber cores. - Optical Performance Severely Degrades:
- Insertion Loss (IL) Significantly Increases: Light traveling from glass to air and then to glass causes severe scattering and Fresnel reflection, leading to substantial attenuation of the optical signal.
- Return Loss (RL) Drastically Decreases (Increased Reflection): Reflected light from the end face increases significantly. For high-precision Fiber Bragg Grating (FBG) sensing systems or Distributed Optical Fiber Sensing (OFDR) systems, this high-intensity reflection noise can directly interfere with wavelength demodulation, causing background noise in the system, or even preventing the demodulator from reading the signal correctly.
III. How Does the Industry Control This Metric?
To ensure reliable mating in various environments, high-quality fiber optic connectors must be tested for end-face geometric parameters using a 3D interferometer after polishing. Industry standards (such as Telcordia GR-326-CORE) typically require:
- Apex Offset: Must be \le 50\ \mu\text{m} (high-quality connectors usually require \le 30\ \mu\text{m} ).
- Radius of Curvature (ROC): Usually controlled within 10\ \text{mm} \le \text{ROC} \le 25\ \text{mm} .
- Fiber Height: The amount the fiber protrudes from or is recessed into the ferrule end face (Undercut / Protrusion) typically needs to be controlled within \pm 50\ \text{nm} to prevent damage to the fiber core or failure to make contact.
IV. Official Product Association
High-precision Fiber Bragg Grating sensors and high-temperature patch cords produced by Dacheng Yongsheng (OFSCN®), such as the OFSCN® 300℃ Fiber Optic Patch Cord, are equipped with FC/APC, FC/PC, and other fiber optic connectors that undergo high-standard polishing process control. This ensures that geometric indicators such as “Apex Offset” of the end faces fully meet the standards, thereby guaranteeing stable signal transmission in long-term high-temperature or harsh industrial environments.
