2024-03-01
In order to ensure the provision of high-quality fiber optic patch cords to customers, manufacturers conduct a series of tests during the design and production processes. These tests are crucial for any type of fiber optic network. It's important not only for suppliers but also for end-users to understand these tests to better assess the quality of fiber optic patch cords and ensure the reliability of their applications. This article will introduce four key tests: 3D testing, Insertion Loss (IL) testing, Return Loss (RL) testing, and End-face testing. Through these four tests, the quality of fiber optic patch cords can be effectively validated, providing peace of mind for end-users.
3D testing is a critical validation of fiber optic connector performance. During the production of fiber optic patch cord assemblies, suppliers employ 3D interferometers to inspect connector end-faces, rigorously controlling their dimensions. This test primarily measures curvature radius, apex offset, and fiber height. Details are as follows:
Curvature Radius:
The curvature radius refers to the radius from the core axis to the end-face, representing the curvature radius of the ferrule end-face. For high-quality fiber optic patch cord connectors, the curvature radius should be controlled within a certain range. If it is too small, it will exert excessive pressure on the fiber, while if it is too large, it may not apply enough pressure, potentially causing gaps between the connector and the fiber end-face. Both excessively small and excessively large curvature radii will affect transmission performance. Only an appropriate curvature radius can ensure optimal transmission performance and connection quality.
Apex Offset:
Apex offset refers to the distance from the highest point of the polished ferrule end-face curve to the axis of the fiber core. This metric is crucial during the polishing process, as imprecise polishing can result in apex offset.
According to technical standards, the apex offset of fiber optic patch cords should generally be maintained at ≤50μm. Larger apex offset may lead to the formation of gaps, thereby increasing insertion loss (IL) and return loss (RL). Ideally, the apex offset for PC and UPC type fiber optic connectors is almost zero because they align the ferrule end-face perpendicular to the polishing surface during the polishing process, ensuring alignment with the fiber core axis. In contrast, APC type fiber optic connectors have an end-face angled at 8 degrees to the fiber axis, rather than being completely perpendicular.
Fiber Height:
Fiber height refers to the distance from the fiber end-face to the ferrule cross-section, which is the extension height from the fiber core to the ferrule end-face. Similarly, the fiber height should not be too low or too high. If the fiber height is too high, it may increase pressure inside the fiber when connecting two fiber optic connectors, leading to fiber damage. If the fiber height is too low, it may create gaps during connection, increasing insertion loss. This is a situation that must be avoided, especially for transmissions with strict requirements on insertion loss.
While the values obtained from testing fiber optic patch cords with a 3D interferometer may vary depending on different polishing methods and types, all tested fiber optic patch cords should meet or exceed industry-recognized end-face geometry standards. Below is a summary of the geometric requirements for MTP single-mode fiber optic connector end-faces based on IEC / PAS 61755-3-31 and IEC / PAS 61755-3-32:
Fiber Curvature Radius（RF）
Insertion Loss (IL) refers to the loss of signal power caused by the insertion of a component into the transmission system. Return Loss (RL) is the power loss resulting from the reflection of some signal back to the signal source due to the discontinuity of the transmission link. For more information on the definitions of insertion loss and return loss, please visit "An Analysis of Fiber Optic Connector Insertion Loss and Return Loss."
During manufacturing and installation, IL and RL testing are crucial. Fiber optic patch cords provided by cable suppliers should comply with relevant standards. For instance, TIA standards specify a maximum insertion loss of 0.75dB for fiber optic patch cords. The insertion loss of most fiber optic patch cords in the market typically ranges from 0.3dB to 0.5dB, while some high-quality products can achieve as low as 0.15dB to 0.2dB. Fiber optic manufacturers usually utilize insertion loss testers and return loss testers to ensure product quality.
In addition to referring to insertion loss and return loss values in product specifications to design fiber optic links and select equipment, end-users can also perform self-testing using available tools. Optical Time Domain Reflectometers (OTDRs) and Optical Frequency Domain Reflectometers (OFDRs) are commonly used instruments for measuring return loss and insertion loss, helping installation personnel to quickly troubleshoot and identify faulty system components.
Fiber optic cleaning has always been about cleaning the end-faces of fiber optic connectors, whether in the past or present, it remains a necessary step in fiber maintenance. Manufacturers typically use fiber end-face inspection tools to inspect end-faces, ensuring there are no contaminants, scratches, or damages. Fiber optic engineers commonly use fiber cleaning tools (such as fiber cleaning pens, cassette-style cleaning boxes, etc.) during installations to ensure end-faces remain uncontaminated.
Why is end-face testing necessary? Because having well-maintained end-faces of fiber optic connectors is fundamental to ensuring high-quality connections. End-face contamination, scratches, or even deformities can increase return loss and may even permanently damage the connector, affecting its usability. Additionally, dust between end-faces can scratch surfaces, causing misalignment or misalignment of fiber cores, thereby reducing transmission quality. Since these contaminants are difficult to identify with the naked eye, without testing and cleaning end-faces, connectors can become contaminated every time they are plugged in. Therefore, even if the supplier has tested and cleaned the end-faces, it is necessary to clean them before each connector insertion and to protect the end-faces with dust caps when not in use.
In summary, the fiber optic industry improves the quality of fiber optic connectors by identifying key parameters, while industry organizations continually strive to establish manufacturing standards for fiber optic quality assurance. If fiber optic patch cords pass the four tests mentioned above and the results meet the standards, they will ensure high-quality optical signal transmission. End-users need to ensure that suppliers perform these tests and provide relevant test reports to confirm that the parameter values are within the correct range.
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