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What You Need to Know About Insertion Loss and Return Loss?

Author Yana

Date 06/27/2024

Learn about insertion loss (IL) and return loss (RL) in fiber optic communication, the differences between insertion loss vs. return loss, factors affecting them, and ways to minimize loss for improved network performance.

In fiber optic communication, insertion loss and return loss are two important metrics for evaluating the quality of termination between some fiber optic devices, such as fiber connectors, fiber optic cables, pigtails and so on. This article will detail the definitions, the differences between insertion loss vs. return loss, the factors that affect them, and ways to reduce return loss (RL) and insertion loss (IL).


What is Insertion Loss and Return Loss in Optical Fiber?


Insertion Loss Meaning

Insertion loss (often abbreviated as IL) mainly measures light lost between two fixed points in an optical fiber. It is the loss of optical power due to the intervention of optical devices in the fiber optic link of an optical communication system. The unit of insertion loss is dB. The lower the IL value, the better the optical performance. For example, if you have two fiber optic patch cords and one of their connectors has an insertion loss of 0.1 dB, and the other has an insertion loss of 0.5 dB, it is recommended that you use the fiber optic cable with an insertion loss of 0.1 dB, which will better ensure your network's transmission performance.


Return Loss Explained

When a fiber optic signal enters or leaves an optical device component (e.g., a fiber optic connector), discontinuities and impedance mismatches will result in reflections or echoes, and the power loss of the reflected or returned signal is known as the return loss (RL for short). Insertion loss is mainly measured when the optical link encounters the loss of the resultant signal value, while the RL is a measurement of the optical link encounters the component access to the reflected signal loss value. The return loss formula is as follows:


Return Loss = 10*log (incident power/reflected power) in +dB


Typically, a higher RL indicates a better quality fiber optic connection because less optical power returned means less signal loss.


Insertion Loss vs. Return Loss: What are the Differences?


Here's the table showing the differences between insertion loss and return loss:


Parameter Insertion Loss (IL) Return Loss (RL)
Standard Measure Lower is better Higher is better 
Impact on Network Reduces signal strength, affects transmission quality Causes interference and noise, reduces signal quality 
Measurement Method Using light sources and power meters Using Optical Time Domain Reflectometers (OTDRs)


What Factors Affect Poor Insertion Loss and Return Loss?


Quality and Cleanliness of Fiber End Faces

Scratches, pits, cracks, particle contamination, and other defects on the end face of an optical fiber can directly affect its performance. These defects cause the surface of the fiber to be uneven, which results in scattering and reflection of the optical signal as it passes through the connector or splice. In this case, the optical signal cannot be transmitted efficiently from one fiber to another, resulting in increased IL and decreased RL.

Broken Fiber and Incorrect Insertion

Fiber breaks cause discontinuities in the optical signal path, and even if the broken fiber fragment can guide some of the optical signals through, the tiny gaps and irregular surfaces at the breaks can seriously affect the efficiency of signal transmission. In this case, the optical signal will be scattered and reflected when it passes through the fracture area, resulting in significant attenuation of the signal strength and thus increasing the IL. At the same time, due to irregular reflections at the break, the RL also deteriorates, and the signal reflected to the light source increases, further affecting the communication quality.


Poor mating is also one of the main causes of high insertion loss and low return loss. When fiber optic connectors are poorly mated or inaccurately butted, the transmission path of the optical signal will be offset and gapped, resulting in partial loss or reflection of the signal. This not only increases the insertion loss but also makes the return loss worse because a poorly spliced connector causes more of the optical signal to be reflected to the source, increasing interference and noise and affecting overall network performance.


Overbent Fiber Radius

Optical fibers are flexible, and you can bend them to suit the installation environment. However, excessive bending can result in significant optical loss and may even directly damage the fiber. 


Excessive bending of an optical fiber causes the optical signal to be refracted and scattered at the bend, thereby increasing the insertion loss (IL). At the same time, small bends and irregular reflections at the bend also increase return loss (RL), affecting the quality and reliability of signal transmission. Excessive bending may also lead to micro-cracks or breaks in the fiber, further degrading the performance of the fiber.


How to Minimize the Loss of Fiber Connectors?


Use High-quality Optical Fiber Connectors

There are many kinds of patch cords on the market according to connector types, such as LC fiber optical patch cords, SC optical cables, MTP fiber cables, etc.  In addition to determining the type of connector you need, you also need to make sure that the connector you purchase is of high quality. High-quality connector materials and precise manufacturing processes ensure efficient transmission of optical signals, reducing losses and improving the overall performance of the network. Choose reliable manufacturers and brands to ensure the quality of your connectors. QSFPTEK's attention to detail and high-quality construction of every fiber connector ensure reliable, uninterrupted data transmission. QSFPTEK is a manufacturer you can trust. 

Keep Fiber Cable Connectors Clean

Dust, oil, and other contaminants can increase connector loss and cause signal degradation. Regularly use professional cleaning tools and methods, such as fiber optic cleaning pens, dust-free cloths, and fiber optic cleaning solutions, to ensure that the connector end faces are clean. The connector end face should be carefully inspected and cleaned before each connection to prevent contaminants from affecting the transmission of optical signals. During the use of fiber optic connectors, you should avoid touching the connector end face with your hands and cover its protective cap when not in use to prevent dust from entering. 


Use Factory-terminated Cabling

Factory-terminated cables are fiber optic connectors installed and tested during manufacturing by specialized equipment and technicians. This ensures that each connector achieves optimal mating and reduces potential errors that may occur during manual installation. The use of factory terminated cables not only improves the quality of connector installation, but also significantly reduces insertion loss and return loss, improving the performance and reliability of the entire fiber optic network.



In summary, insertion loss and return loss are key parameters of fiber optic systems. Minimizing insertion loss (IL) and maximizing return loss (RL) is essential to ensure efficient signal transmission and reduce signal attenuation. Keeping connectors clean, avoiding damage, and using factory pre-terminated cables maximizes network performance and reliability, guaranteeing efficient signal transmission and reducing interference.


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