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What Is Insertion Loss & Return Loss For Fiber Optical Components?

Views: 0     Author: Site Editor     Publish Time: 2022-08-01      Origin: Site

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In optical fiber communication, insertion loss (IL) and return loss(RL) are two important parameters to evaluate the interface quality between some optical fiber components, like fiber patch cables, optical spitters, pigtails, fiber connectors, optical adapters, attenuators, etc.

Insertion Loss

What is Insertion Loss?

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

Formula: IL=-10 lg (Pout /Pin). Pout is the output optical power, and Pin is the input optical power.

The lower the insertion loss, the better the performance. For example, an insertion loss of 0.3dB is better than 0.5dB. In general, the difference in attenuation between soldered and manual connections (less than 0.1 dB) will be less than the difference in attenuation between fiber optic connectors. Recommended maximum dB loss for fiber optic cabling in data centers: 15dB for LC multimode optical connectors, 15dB for LC singlemode optical connectors, 20dB for MPO/MTP multimode optical connectors, and 30dB for MPO/MTP singlemode optical connectors.

What is return loss?

Discontinuities and impedance mismatches can cause reflections or echoes when fiber optic signals enter or leave optical components such as fiber optic connectors. The power loss of the reflected or returning signal is called return loss (RL). Insertion loss is mainly the measurement of the resulting signal value when the optical link encounters loss, while return loss is the measurement of the reflected signal loss value when the optical link encounters component access.

Formula: RL=-10 lg (P0/P1), where P0 represents the reflected optical power, and P1 represents the input optical power.

The return loss value is expressed in dB and is usually a negative number, so the higher the return loss value, the better. Typical parameters range from -15 to -60 dB. According to industry standards, the return loss of UPC polished fiber connectors should be greater than 50dB, the return loss of APC polished fiber connectors is usually greater than 60dB, and the return loss of PC type polished connectors must be greater than 40dB. For multimode fiber, typical RL values are between 20 and 40 dB.

What are the influencing factors?

1. End face quality and cleanliness

Fiber end face defects (scratches, pits, cracks) and particle contamination directly affect connector performance, resulting in poor IL/RL. Even tiny dust particles on a 5-micron single-mode fiber core can eventually block the optical signal, causing signal loss.

2. Optical fiber breakage and poor plugging

There are times when the fiber is broken but is still able to guide light through, which will also result in poor IL or RL. As mentioned in the picture at the beginning of the article, the APC connector is connected to the PC connector, one is an angle of 8°, and the other is the grinding angle of the micro-arc surface. When the two are connected, light may pass in a short time. But at the same time, it will also cause a large insertion loss and a very low return loss, which may also cause the two fiber end faces to be unable to be precisely butted, so that the light cannot pass normally.

3. Exceed the bending radius

Fibers can be bent, but bending too hard can cause a significant increase in optical loss, or direct damage. Therefore, in cases where a coiled fiber is required, it is recommended to keep the radius as large as possible. The general recommendation is not to exceed 10 times the diameter of the jacket. Therefore, for a jumper with a jacket of 2mm, the maximum bend radius is 20mm.

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