In order to provide high quality fiber jumper to customers, manufacturers conduct a series of tests during the design and manufacturing process. These fiber jumper tests are critical for any type of fiber network. Not only suppliers, but also end users need to be aware of these fiber jumper tests in order to better judge the quality of fiber jumper and ensure the feasibility of their application. Four types of tests will be presented: 3D testing, insertion loss (IL) testing and return loss (RL) testing, and end face testing. Generally, the fiber jumpers that have passed these four tests are of good quality and can be used with confidence by end users.
3D testing: Guarantee of high quality connector ends
3D testing is a key test to ensure the performance of fiber connectors. In the production of fiber jumper components, the supplier will use a 3D interferometer (an optical interferometry instrument) to check the fiber connector end face and strictly control the connector end face size. The 3D test mainly measures the radius of curvature, apex offset, and fiber height. Details are as follows:
Radius of curvature
The radius of curvature refers to the radius from the axis of the core to the end face, as shown below, which is the curve radius of the end face of the ferrule. The curvature radius of the end face of the high-quality fiber jumper connector should be controlled within a certain range. The radius of curvature is too small to put more pressure on the fiber, while the radius of curvature is too large to put pressure on the fiber, resulting in air gap between the connector and the end face of the fiber (that is, air gap). Whether the radius of curvature is too large or too small will result in light scattering or insufficient physical contact to ensure optimal transmission performance. Only the proper radius of curvature ensures the correct pressure and the best transmission performance.
Shift of vertices
Vertex offset refers to the distance between the highest point of the end curve of the grinding and polishing insert and the axis of the fiber core. This is a key term in the polishing process, and imprecise polishing can lead to vertex offset.
In the technical standard, the vertex offset of the fiber jumper is generally required to be ≤50μm. If the tip offset is large, an air gap will form, which will result in higher insertion loss (IL) and return loss (RL) of the fiber jumper. In an ideal case, the apex offset of PC and UPC fiber connectors is almost zero, because they make the ferring end face perpendicular to the polished surface and the vertex coincides with the core axis during the polishing process. However, for the APC type fiber connector, the end face is at an Angle of 8 degrees from the fiber axis and is not completely perpendicular. More information about PC/UPC/APC can be found in Choosing Which Connector: PC vs UPC vs APC? .
Fiber height
The fiber height is the distance from the end face of the fiber to the core section, that is, the extension height of the fiber core to the end face of the ferrule. Similarly, the fiber height must not be too low or too high. If the height of the fiber is too high, it will increase the pressure in the fiber when docking the two fiber connectors, thus damaging the fiber; If the fiber height is too low, a gap will be created when docking the two fiber connectors, resulting in increased insertion loss. This must be avoided for transmissions with strict insertion loss requirements.
Different polishing methods and types of fiber jumper using 3D interferometer test values will be different, but the test fiber jumper should meet or exceed the industry recognized end geometry size standard.
IL and RL tests: Critical tests for optical deployment
Insertion loss (IL) refers to the loss of signal power due to the insertion of a device somewhere in the transmission system. Return loss (RL) is the power loss caused by partial signal reflection back to the signal source during transmission due to the discontinuity of the transmission link. For more information on insertion loss and return loss definitions, please visit "Brief Analysis of Fiber connector Insertion loss and return loss".
It is very important to test insertion loss and return loss in both manufacturing and installation processes. For the cable provider, the insertion loss and return loss of the supplied fiber jumper should meet the corresponding standards. For example, the TIA standard clearly specifies that the maximum insertion loss of the fiber jumper is 0.75dB (that is, the maximum acceptable value). For most fiber jump-wires on the market, the normal range of insertion loss is between 0.3dB and 0.5dB, and some low insertion loss ranges from 0.15dB to 0.2dB. For fiber manufacturers, it is common to use insertion loss testers and return loss testers to check that they are within normal limits so that end users can receive qualified products.
For the end user, in addition to using the insertion loss and return loss values presented in the product specification sheet as a reference to design the fiber link and select other equipment or components, they can also test themselves if the test tools are available. This helps installers quickly troubleshoot and identify faulty system components. Optical time-domain reflectometry (OTDR) and optical frequency domain reflectometry (OFDR) are commonly used to measure the echo insertion loss.
End face test: ensure end face cleanliness and smoothness
The so-called fiber cleaning actually refers to the cleaning of the end face of the fiber connector. Whether it was 40 years ago or today, fiber connector end face cleaning is an essential step in fiber maintenance. The manufacturer will usually use the fiber end face detector to conduct an end face inspection to confirm whether the fiber connector end face is contaminated, scratched, or cracked. For fiber engineers, fiber cleaning tools (such as fiber cleaning pens, cassette cleaning boxes, etc.) are usually used to clean the fiber end face during wiring to ensure no contamination.
Why do end face tests? Because having a good fiber connector end face is the basic condition to ensure a high-quality fiber connection. If there are contaminants (such as dust, etc.) or abrasions or even deformation on the end face of the fiber connector, it will increase the return loss, and may even permanently damage the fiber connector, resulting in unusable. In addition, dust between the end faces can scratch the surface and cause air gaps or fiber cores to fail to align, thereby reducing the quality of optical signal transmission. Since these contaminants cannot be identified with the naked eye, if the end face is not tested and cleaned, it will contamize the socket connected to it. Therefore, even if the supplier has tested and cleaned the end face of the fiber connector before shipment, it is necessary to clean the end face before and after inserting and pulling the fiber connector. At the same time, if it will not be used again for a while, it needs to be covered with a dust cap.
Summary
In summary, the fiber optic industry has improved the quality of fiber connectors by exploring the key parameters that need to be measured, and industry associations and committees have been working to define manufacturing standards for fiber quality assurance. If the fiber jumper passes the above four tests, and the test results meet the standard, then they will help achieve high-quality optical signal transmission. For the end user, it is necessary to check that the vendor has performed these tests and can provide the relevant test reports to confirm that the parameter values are in the correct range.
