The performance of the connector directly affects the quality of optical transmission. Therefore, in order to ensure the efficient transmission of optical fiber link signals, two key optical performance indicators, insertion loss (Insertion Loss) and return loss (Return Loss), are usually used to evaluate it. This article will focus on the main factors affecting the two types of loss and how to optimize them.
The concept of insertion loss and return loss
What is insertion loss?
In the field of telecommunications, insertion loss refers to the loss of signal power caused by the insertion of a device somewhere in the transmission system, usually referred to as attenuation, and is used to represent the ratio of the output optical power of the port to the input optical power, in decibels (dB) as the unit. Obviously, lower insertion loss values indicate better insertion loss performance.
What is Return Loss?
Return loss refers to the power loss caused by the reflection of part of the signal back to the signal source due to the discontinuity of the transmission link. This discontinuity could be a mismatch with the termination load, or a device plugged into the line. Return loss is easily misunderstood as the loss caused by the echo. In fact, it refers to the loss of the echo itself, that is, the greater the loss of the echo, the smaller the echo. It represents the ratio of the reflected wave power at the transmission line port to the incident wave power, in decibels, and is generally a positive value. Therefore, the higher the absolute value of return loss, the smaller the amount of reflection, and the greater the signal power transmission, that is, the higher the RL value, the better the performance of the fiber optic connector.
Factors Affecting Insertion Loss and Return Loss
The direct connection of a single optical fiber jumper is the most ideal optical fiber path, and the loss is the smallest at this time, that is, a direct-connected optical fiber without interference between A and B ends. Typically, however, fiber optic networks require connectors for modularity and path splitting. Therefore, the ideal low insertion loss and high return loss performance can be greatly compromised for the following three reasons.
End face quality and cleanliness
Obviously, fiber end-face defects such as scratches, pits, cracks, and particle contamination directly affect its performance, resulting in higher insertion loss and lower return loss. Any abnormality that prevents the transmission of optical signals between fibers will adversely affect these two losses.
End face cleanliness comparison
Connector Ferrule Alignment Deviation
The main function of the fiber optic connector is to quickly connect two optical fibers, ensure accurate alignment between the two fiber cores, realize the precise butt joint of the two fiber end faces, and maximize the optical power output from the transmitting fiber to the receiving fiber. In general, the smaller the ferrule hole diameter, the more centered the core. If the ferrule hole is not perfectly centered, the fiber core it contains will not be perfectly centered either. Therefore, when the cores are not precisely aligned, that is, when the centering position of the connector ferrule is deviated, both insertion loss and return loss will be greatly affected.
Two types of core alignment deviations
End Face Physical Contact Air Gap
The fiber optic connectors are fixed by an adapter, which is a physical connection, but not a real physical contact. There will be a gap between the contact end faces of the two connectors. Smaller end-face air gaps result in better insertion loss and return loss. Depending on the grinding method used for fiber optic connectors, the air gap between the end faces also changes. Typically, the typical insertion loss of optical fiber connectors using physical contact (PC), ultra-physical end face (UPC) and bevel physical contact (APC) grinding methods is less than 0.3 dB. Among them, the UPC connector has the lowest insertion loss due to the smallest air gap on the end face, and the APC connector can achieve the highest return loss among the three due to the use of a beveled fiber end face. Choosing the right fiber optic connector type can help you achieve better optical transmission quality.
PC vs UPC vs APC Grinding Method
How to optimize fiber optic connector loss?
The use of suitable 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:
· Make sure the fiber optic connector is clean before use. If contaminated, use suitable tools for cleaning.
· Avoid applying any undue stress to the fiber during use, and never bend the fiber beyond its maximum bend radius.
· Minimize bending, twisting, splicing, and coupling fiber jumpers, otherwise it may cause refraction of optical signals when passing through the fiber cladding. If coiling of fiber is required, a large coil radius should be maintained.
· Use factory terminated fiber optics. These terminations are performed under strict controls, often with manufacturer guarantees.
· Reasonable balance between power loss and fiber cost, using cheap and low-quality fiber may cause greater cost loss in the future.
Fiber is factory terminated. These terminations are performed under strict controls, often with manufacturer guarantees. Reasonable balance between power loss and fiber cost, using cheap and low-quality fiber may cause greater cost loss in the future.