The Importance of Optical Fiber Connector End-Face Geometry

Optical fiber connectors are fundamental components in modern communication networks, ensuring reliable signal transmission. The end-face geometry of these connectors plays a critical role in minimizing optical losses and ensuring long-term mechanical reliability. Standards such as IEC 61300-3-47, Basic test and measurement procedures for end face geometry of PC/APC spherically polished ferrules using interferometry, and a series of IEC 61755 standards covering angle polishing, ferrule geometry, materials, and other connector parts, provide precise guidelines for evaluating and maintaining optimal end-face geometry. This article explores the importance of key parameters—Radius of Curvature, Apex Offset, and Fiber Height—and methods to achieve high-quality end-face geometry.

 

Key Parameters of End-Face Geometry

1. Radius of Curvature

The Radius of Curvature (ROC) refers to the curvature of the connector’s ferrule end-face. This parameter is vital to ensure proper physical contact between mated connectors. The radius of curvature is defined as the 3D radius of the best fitting sphere over the defined fitting area.

A well-defined ROC ensures consistent and reliable optical performance by maintaining low insertion loss and return loss. It also prevents air gaps that can lead to signal degradation and reflection.

2. Apex Offset

To measure the apex offset, the high point or apex of the polished ferrule surface must be defined. Due to potential variations in the fiber itself, such as recesses or protrusions, the sphericity of the apex is considered. The apex offset is quantified as the distance from the highest point of the ferrule sphere to the center of the fiber core.

This parameter is essential for minimizing stress and ensuring uniform pressure distribution when connectors are mated. A properly controlled apex offset prevents misalignment, which could increase insertion loss and degrade mechanical performance.

3. Fiber Height

Fiber Height indicates the relative position of the fiber core compared to the surrounding ferrule surface. It can be either protruding (positive fiber height) or recessed (negative fiber height). Positive fiber height ensures sufficient contact pressure, reducing insertion loss. However, excessive protrusion or recession can cause mechanical damage or air gaps, affecting signal integrity. There are two possible ways to define fiber height, spherical height and planar height.

Spherical height refers to when the connector end face (both ferrule and fiber) forms a continuous sphere. It is measured as the difference in height between the fiber’s center and the theoretical height at the center sphere, based on the ferrule radius.

Planar height describes a scenario where the connector end face has a flat fiber in the middle of a spherical ferrule. It is defined as the height difference between the fiber’s center and the height at the center of the theoretical plane formed by connecting points on the ferrule. Planar height is commonly used to evaluate the fiber’s position after polishing.

 

 

 

 

 

 

Methods to Achieve High-Quality End-Face Geometry

Achieving high-quality end-face geometry requires precise manufacturing and inspection processes.

Polishing processes are critical to achieving desired ROC, apex offset, and fiber height. Automated polishing machines with controlled parameters ensure consistent results by using appropriate polishing films and sequences while maintaining controlled pressure, rotation speed, and duration. Inspection tools are equally important for ensuring compliance with IEC standards and identifying defects early. Interferometers can measure ROC, apex offset, and fiber height, while high-resolution microscopes detect scratches, pits, or debris.

Environmental controls are another key factor in maintaining high-quality end-face geometry. Contaminants and inconsistent environmental conditions can affect polishing and inspection results. Cleanroom environments minimize particulate contamination, while stable temperature and humidity during processing ensure consistent outcomes. Additionally, quality control protocols play a crucial role. Regular equipment calibration maintains measurement accuracy, and sample testing ensures batch compliance with standards.

 

Conclusión

The end-face geometry of optical fiber connectors significantly influences the performance and reliability of optical networks. Parameters such as Radius of Curvature, Apex Offset, and Fiber Height must be carefully controlled in accordance with IEC 61300-3-47 and IEC 61755 standards. By employing precision polishing techniques, advanced inspection tools, and stringent quality control measures, manufacturers can ensure superior connector performance and long-term network reliability. These efforts are essential to meet the growing demands of high-speed and high-capacity communication systems.

SENKO’s advancements in connector kit manufacturing and assembly processes have set a benchmark in the industry by enabling the production of connectors that exceed international standards. Through innovative designs, precision engineering, and cutting-edge technology, SENKO ensures exceptional end-face geometry that surpasses the stringent requirements of IEC standards. These advancements not only enhance the optical and mechanical performance of the connectors but also contribute to the overall reliability and efficiency of global communication networks.