What is the knowledge of fiber connector insertion loss
As we all know, optical fiber connectors are widely used in optical fiber transmission lines, optical fiber distribution frames, optical fiber test instruments and meters. So, do you know what are the key points of the insertion loss of fiber optic connectors? Let's go and understand them together.
1, the concept of insertion loss
(1) Definition of insertion loss (IL) of optical fiber connector: where P1 is the output optical power and P0 is the input optical power. The insertion loss unit is dB.
(2) Test method for insertion loss of optical fiber connectors
There are generally three methods for testing the insertion loss of optical fiber connectors: the reference method, the replacement method, and the standard jumper comparison method. Because in mass production, the insertion loss test must be fast, accurate, and non-destructive. Therefore, most manufacturers now use the third method, which is the standard jumper comparison method.
When the single-mode fiber pigtail is less than 50M and the multi-mode fiber pigtail is less than 10M, the loss of the pigtail itself can be ignored. The measured data at this time is the insertion loss of the 3 terminals relative to the standard connector. To customers. When the single-mode fiber pigtail is greater than 50M and the multi-mode fiber pigtail is greater than 10M, the fiber's own loss value should be subtracted from the measured loss value.
Repeatability refers to the range of change in insertion loss of the same pair of plugs after multiple insertions and removals in the same adapter. The unit is expressed in dB. Repeatability should generally be less than 0.1dB.
Because the insertion loss of the optical fiber connector is measured by the standard jumper comparison method, its value is a relative value. Therefore, in any docking, the actual insertion loss value is likely to be greater than the value measured by the standard jumper comparison method, and different connectors and different adapters will have different effects. Therefore, there is an indicator requirement of interchangeability. Connector interchangeability refers to the range of change in insertion loss between different plugs or different adapters. It should generally be less than 0.2dB.
2, the main factor of insertion loss of optical fiber connector
(1) Loss caused by mismatch of fiber structure parameters (different core diameters, different numerical apertures, different refractive index distributions, and other reasons).
(2) Core alignment error (core misalignment loss)
的 The loss due to lateral misalignment of the core is called misalignment loss. It is an important cause of insertion loss.
In the formula, d, a, and w are lateral dislocation, core radius, and mode field diameter, respectively.
的 The misalignment loss of the multimode graded fiber in the steady mode distribution is:
When single-mode fiber is connected, when the mode field distribution is approximated by Gauss, its misalignment loss is:
There are many reasons for this type of loss. It mainly includes the core / clad concentricity of the optical fiber, the concentricity of the ferrule, and the parameters of the test adapter are not ideal. The effects of the above factors on insertion loss are also related to external devices.
(3) End-face shape and gap loss
The reason for this loss is mainly because the physical parameters of the end face of the optical fiber connector are not ideal, which results in non-planar direct contact between the two end faces of the connected optical fiber, leaving a gap or non-planar contact. It is inferred from the relevant formula that as long as the end face gap is controlled within 1um, this loss can be ignored.
Of course, there are many factors that affect the insertion loss in addition to the above three types, such as: dimensional fit of external devices, end face tilt, and Fresnel reflection on the end face.
3. Elements of production process control
(1) Ferrule quality
Is mainly the inner diameter and concentricity of the ferrule. For multimode fiber optic connectors, the ferrule concentricity is required to be less than 3um, and for single mode fiber optic connectors, the ferrule concentricity is required to be less than 1um. The concentricity of the ferrule, the physical parameters of the ground end face, and the fit dimensions of the external components will ultimately affect the concentricity of the core / ferrule, and eventually lead to the occurrence of misalignment loss.
(2) level of grinding
The criterion for measuring the quality of grinding depends on its end face and its physical parameters. There are three main physical parameters: curvature radius, spherical eccentricity, and optical fiber depression. For the APC type connector, it also includes two parameters: end face angle (inclined 8 degrees) and bond angle deviation. These parameters can all affect the insertion loss. The IEC has made clear requirements for these parameters, and has specific specifications. To do this, a stable-performance grinder is essential. Most of the quality problems generated during the production of optical fiber connectors are directly or indirectly related to the stability of the grinder.
There are many reasons for the radon loss. It mainly includes the core / clad concentricity of the optical fiber, the concentricity of the ferrule, and the parameters of the test adapter are not ideal. The influence of the above several factors on the insertion loss is also related to the dimensional fit of the external device, the loss caused by the shape of the end face and the gap. The reason for this loss is mainly because the physical parameters of the end faces of the optical fiber connector are not ideal, which results in non-planar direct contact between the two end faces of the connected optical fibers, but with a certain gap or non-planar contact. It is inferred from the relevant formula that as long as the end face gap is controlled within 1um, this loss can be ignored.
(3) Outer part size fit
The dimensional fit of the external components will directly affect the repeatability and interchangeability of the connector. Especially for the APC type connector, if the dimensional fit is not ideal, its interchangeability and repeatability may exceed 0.1dB or worse.
4. Testing control elements
(1) Accurate and reliable testing equipment
In order to make the test data accurate and reliable, accurate and stable test equipment will provide a reliable guarantee for this.
(2) Standard connector
Standard connector is a set of precision manufactured or selected connectors. It includes two parts: standard jumper and standard adapter. The insertion loss of an optical fiber connector is actually its loss relative to a standard test line, so the indicators (optical parameters and physical parameters) of the standard test line must be strictly controlled. Similarly, the indicator of the adapter must be controlled strictly according to the principle of selecting a standard adapter. In this way, the test results will reflect the true quality of the tested connector to the greatest extent possible. Therefore, the key to the accuracy and reliability of the test is the control of the standard test line and the standard adapter.
(3) End face cleanliness
Because the outer diameter of the fiber is only 125um, and the light passing part is smaller, the single-mode fiber is only about 9um, and the multi-mode fiber is 50um and 62.5um, so the cleanliness of the fiber end face is very high. Be sure to clean the end face of the fiber before the test to ensure that the end face is highly clean, so that the test results can be accurate and reliable. If cleaning is not possible at one time, you can clean more times.
5. Repeatability and interchangeability
(1) Factors affecting repeatability
Mainly the mechanical fit size. If the mating size is good, the same docking state can be reproduced each time the plug is inserted and removed, and the test results will not change greatly. In addition, the quality of the adapter will also affect the repeatability.
(2) Factors affecting interchangeability
因素 All the factors in the third part, namely the quality of the ferrule, the level of grinding, and the fit size of the external components, will affect the interchangeability, so the importance of these indicators is even more prominent.
The above is all the knowledge about the insertion loss of the optical fiber connector. The optical fiber connector has excellent performance and outstanding role, and its application range will not only achieve the connection of the optical fiber. I believe that in the near future, the stage of the optical fiber connector It will be broader.