In fiber communication, insertion loss and return loss are two important indexes to evaluate the quality of end-to-end connection between some fiber components, such as fiber connector, fiber jumper, tail fiber, etc.

Insertion Loss is an Insertion Loss (IL for short), mainly a measure of the light lost between two fixed points in an optical fiber. It can be understood as the optical power loss caused by the intervention of optical devices in optical communication system fiber link, and the unit is dB.

Calculation formula: IL = -10 lg (Pout/Pin), Pout is the output optical power; Pin is the input optical power.

The smaller the value of insertion loss, for example, 0.3 dB is better than 0.5dB. In general, the attenuation difference between fusion and manual connections (less than 0.1 dB) will be smaller than the connection between fiber optic connectors. Recommended maximum dB losses for data center fiber wiring: LC multimode fiber connector maximum 15dB, LC single-mode connector maximum 15dB, MPO/MTP multimode fiber connector maximum 20dB, MPO/MTP single-mode fiber connector minimum 30dB.

When fiber signals enter or leave an optical device component (such as fiber connector), discontinuity and impedance mismatch will lead to reflection or echo, and the power Loss of reflected or returned signals, namely Return Loss and Return Loss (RL). Insertion loss is mainly used to measure the result signal value when the optical link encounters loss, while return loss is used to measure the reflected signal loss value when the optical link encounters component access.

Calculation formula: RL = -10 lg (P0 / P1), P0 represents reflected light power, P1 represents input light power.

The return loss is expressed as dB and is usually negative. Therefore, the larger the return loss is, the better. The typical specification range is -15 to -60dB. According to industry standards, the RETURN loss of Ultra PC polished fiber connectors should be greater than 50dB, and the return loss of bevel polished fiber connectors should be greater than 60dB. The PC type should be greater than 40dB. For multimode fibers, the typical RL value is between 20 and 40dB.

1. End face quality and cleanliness

Fiber end defects (scratches, pits, cracks) and particle contamination can directly affect connector performance, resulting in poor IL/RL. Even tiny dust particles on 5-micron single-mode cores can eventually clog light signals, causing signal loss.

2. Optical fiber is broken and poorly plugged

Sometimes an optical fiber is broken but still guides light through, which can lead to bad IL or RL. APC connector is connected to the PC connectors, one is inclined Angle 8 °, is a slightly curved grinding Angle, both of which are linked together in a short period of time may have light passing through, but at the same time can also cause a lot of low insertion loss and return loss, may also lead to two optical fiber end face cannot precision docking and make the light to pass.

3. Beyond the bending radius

Optical fibers can bend, but too much bending can lead to a significant increase in optical loss, which can lead directly to damage. Therefore, it is recommended to keep the radius as large as possible in the case of winding the fiber. The general recommendation is not to exceed 10 times the coat diameter. Therefore, for a jumper with a coat of 2mm, the maximum bending radius is 20mm.

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