In optical fiber communication, insertion loss and return loss are two important indexes to evaluate the termination quality of some optical fiber devices, such as optical fiber connector, optical fiber patch cord, pigtail, etc.
What is insertion loss?
Insertion loss is the measurement of the loss of light between two fixed points in an optical fiber. It can be understood as the loss of optical power caused by the intervention of optical devices in the optical fiber link of optical communication system, the unit is dB. The smaller the insertion loss, the better the performance.
What is return loss?
When the optical fiber signal enters or leaves an optical component (such as optical fiber connector), discontinuity and impedance mismatch will lead to reflection or return. The power loss of the reflected or returned signal is called return loss (RL). The insertion loss is mainly to measure the result signal value when the optical link encounters the loss, while the return loss is to measure the reflection signal loss value when the optical link encounters the component access.
The return loss value is expressed as dB, which is usually negative, so the greater the return loss value, the better. The typical specification range is -15 to -60 dB. According to the industry standard, the return loss of ultra PC polished optical fiber connector should be greater than 50dB, and the return loss of bevel polished optical fiber connector is usually greater than 60dB. PC type shall be greater than 40dB. For multimode fiber, the typical RL value is between 20 and 40 dB.
What are the influencing factors?
1. End face quality and cleanliness
Defects (scratches, pits, cracks) and particle contamination of fiber end face will directly affect the performance of the connector, resulting in poor IL / RL. Even the tiny dust particles on the 5 Î¼m single-mode core may eventually block the optical signal, resulting in signal loss.
2. The optical fiber is broken and poorly inserted
Sometimes, although the fiber has broken, it can still guide light through, which will also lead to poor IL or RL. APC connector is connected with PC connector, one is inclined 8 Â° One is the grinding angle of the micro arc surface, which may cause light to pass through in a short time, but at the same time, it will also cause large insertion loss and low return loss, which may also cause the two fiber end faces can not be precisely butted, so that light can not pass through normally.
3. Exceeding bending radius
Optical fiber can be bent, but bending too much will cause a significant increase in optical loss, and may directly lead to damage. Therefore, it is recommended to keep the radius as large as possible when the optical fiber needs to be coiled. The general advice is not to exceed 10 times the diameter of the jacket. Therefore, the maximum bending radius is 20 mm for the jumper with 2 mm outer jacket.
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