A fiber optic attenuator is a passive device used to reduce the power level of an optical signal in free space or in an optical fiber. They come in various types such as fixed types, stepwise variables, and continuous variables.
Attenuators are often used when the signal reaching the receiver is too strong, possibly overloading the receiving element. This could be due to a mismatch between the transmitter/receiver, or because the media converter was designed for a much longer distance than is actually used. Sometimes an attenuator can also stress test a network link by gradually reducing the signal strength until the optical link fails, thereby determining the existing safety margin of the signal.
While fiber optic attenuators are typically used in SM (single-mode) circuits, since this is where more powerful lasers are used for long-distance transmission, multimode attenuators can also be used.
Male and Female Attenuators
The most common versions of attenuators are male-to-female, often called plugs or extensions. These drop-in attenuators only need to be installed on one end of the fiber optic cable to insert the fiber optic cable into the receiving equipment or panel.
There are also female-to-female (male) attenuators, typically used to install in patch panels or to join two fiber optic cables together. Variable attenuators are more expensive but useful for testing and can be adjusted from 1dB to 30dB.
Keep in mind that dB levels are a measure of signal strength and can sometimes be confusing. The graph below will give you an idea of the percentage of signal attenuation at a specific dB value.
Attenuator
Fiber optic attenuators are commonly used in two situations
The first situation is during power level testing. To test power level margins in fiber optic communication systems, optical attenuators are used to temporarily add a calibrated amount of signal loss. In the second case, optical attenuators are permanently installed in the fiber optic communication link to properly match the optical signal levels at the transmitter and receiver.
How many types of optical attenuators (OA) can you find
There are four different types of OA, which can take many different forms and are generally classified as fixed attenuators or variable attenuators. In addition, according to the type of connector, it can be divided into LC, SC, ST, FC, MU, E2000, etc.
1. Fixed attenuators: Fixed optical attenuators used in fiber optic systems can function using various principles. Preferred attenuators use doped fiber or misaligned splices or total power as both are reliable and inexpensive.
fixed attenuator
In-line attenuators are included with jumpers. Another built-in attenuator is a small male-female connector that can be added to other cables.
Non-preferred attenuators typically use gap loss or reflection principles. Such devices may be sensitive to damage caused by mode distribution, wavelength, contamination, vibration, temperature, power pulses, which may cause back reflections, which may cause signal dispersion, etc.
2. Loopback attenuators: Loopback fiber optic attenuators are designed for testing, engineering and burn-in stages of circuit boards or other equipment. SC/UPC, SC/APC, LC/UPC, LC/APC, MTRJ, MPO for singlemode applications.
3. Built-in variable attenuator: Built-in variable optical attenuator, which can be controlled manually or electrically. A manual unit can be used for a one-time setup of the system and is almost equivalent to a fixed attenuator and can be called a "tunable attenuator". In contrast, electronically controlled attenuators can provide adaptive power optimization.
Advantages of electronically controlled equipment include speed of response and avoidance of attenuation of transmitted signals. Dynamic range is usually very limited, and power feedback can mean that long-term stability is a relatively minor issue.
Responsiveness is a particularly important issue in dynamically reconfigurable systems, where delays in the order of millionths of a second can cause massive loss of transmitted data.
Typical technologies for high-speed response include liquid crystal variable attenuators (LCVA) or lithium niobate devices.
A class of built-in attenuators are technically no different than test attenuators except that they are packaged for rack mounting and have no test display.
4.Variable fiber optic attenuator: This type usually uses a variable neutral density filter. Despite the relatively high cost, the advantages of this arrangement are stability, wavelength insensitivity, mode insensitivity, and large dynamic range.
