What is insertion loss and return loss of Patchcord?

- Nov 16, 2020-

What is insertion loss?

In the field of telecommunications, insertion loss refers to the loss of signal power due to the insertion of a device somewhere in the transmission system, usually refers to attenuation, used to express the ratio of the output optical power of the port to the input optical power, in decibels (dB) As a unit. Obviously, the lower the insertion loss value, the better the insertion loss performance.

What is return loss?

Return loss refers to the power loss that occurs when part of the signal is reflected back to the signal source due to the discontinuity of the transmission link. This discontinuity may be a mismatch with the terminal load, or a mismatch with the equipment inserted in the line. Return loss is easier to misunderstand as the loss caused by the return. In fact, it refers to the loss of the return itself, that is, the greater the loss of the return, the smaller the return. It represents the ratio of the reflected wave power at the port of the transmission line to the incident wave power in decibels, which is generally a positive value. Therefore, the higher the absolute value of the return loss, the smaller the reflection, and the greater the signal power transmission, that is, the higher the RL value, the better the performance of the optical fiber connector.

Factors affecting insertion loss and return loss

The direct connection of a single fiber jumper is the most ideal fiber path. At this time, the loss is the smallest, that is, a direct connection fiber without interference between the A and B ends. However, under normal circumstances, fiber optic networks require connectors to achieve modularity and path segmentation. Therefore, the ideal low insertion loss and high return loss performance will be greatly compromised for the following three reasons.

1.End face quality and cleanliness

Obviously, fiber end-face defects such as scratches, pits, cracks, and particle contamination will directly affect its performance, leading to higher insertion loss and lower return loss. Any abnormality that hinders the transmission of optical signals between optical fibers will have an adverse effect on these two losses.

2.Positioning deviation of connector ferrule

The main function of the optical fiber connector is to quickly connect two optical fibers, to ensure accurate alignment between the two cores, and to achieve precise butt connection of the two optical fiber end faces, so that the optical power output by the transmitting fiber can be coupled to the receiving fiber to the maximum. Generally, the smaller the diameter of the ferrule hole, the more centered the core position. If the ferrule hole is not completely centered, the core contained therein will naturally not be completely centered. Therefore, when the cores are not precisely aligned, that is, when the centering and positioning of the connector ferrule is deviated, the insertion loss and return loss will be greatly affected.

3.The end face physically contacts the air gap

The optical fiber connectors are fixed by adapters, which are physical connections, but if they are not in physical contact, there will be a gap between the contact end faces of the two connectors. The smaller the end air gap, the more ideal the insertion loss and return loss. The optical fiber connector uses different grinding methods, and the air gap between the end faces also changes. Under normal circumstances, the typical insertion loss of optical fiber connectors using physical contact (PC), super physical end face (UPC) and bevel physical contact (APC) grinding methods is less than 0.3 decibels. Among them, the UPC connector has the lowest insertion loss due to the smallest end face air gap, while the APC connector can achieve the highest return loss due to the use of beveled fiber end faces. Choosing the right type of fiber optic connector can help you achieve better optical transmission quality.

1.The use of appropriate high-quality fiber optic connectors helps to achieve long-term stable operation of high-speed transmission systems. Here are some tips to help optimize insertion loss and return loss:

2.Make sure the fiber connector is clean before use. If it is contaminated, use suitable tools for cleaning.

3.Avoid applying any improper pressure to the optical fiber during use, and do not bend the optical fiber beyond its maximum bending radius.

4.Minimize bending, coiling, splicing, and coupling fiber jumpers, otherwise it may cause refraction of optical signals when passing through the fiber cladding. If you need to coil the fiber, you should keep a large coil radius.

5.Use factory terminated fiber. These terminations are carried out under strict control and are usually guaranteed by the manufacturer.

6.Reasonably weigh the power loss and the cost of the optical fiber, and the use of cheap and inferior optical fiber may cause greater cost loss in the future.

7.Use factory terminated fiber. These terminations are carried out under strict control and are usually guaranteed by the manufacturer. Reasonably weigh the power loss and the cost of the optical fiber, and the use of cheap and inferior optical fiber may cause greater cost loss in the future.


Combining the two important optical indicators of insertion loss and return loss, it can more accurately evaluate the optical fiber transmission efficiency and performance, and judge whether there is impedance at the pins of the receiver and transmitter, as well as through holes, connectors and other discontinuities. lost pair.

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