A fiber optic attenuator is a passive device used to reduce optical signal power levels in free space or fiber optics. They have various types of fixed types, stepwise variables and continuous variables.
Attenuators are usually used when the signal reaching the receiver is too strong, thus potentially overloading the receiving element. This could be due to a mismatch between the transmitter/receiver, or because the media converter is designed for a much longer distance than it is used for. Sometimes attenuators can also stress test network links by gradually reducing the signal strength until the optical link fails, thereby determining the existing safety margin of the signal.
Although fiber attenuators are commonly used in SM (single mode) circuits, since this is where stronger lasers are used for distance transmission, multimode attenuators are also available.
Male and female attenuators
The most common version of attenuators is male-to-female, often referred to as plug or extension. These plug-type attenuators are simply installed on one end of a fiber optic cable, allowing the fiber optic cable to be plugged into a receiving device or panel.
There are also female-to-female (male) attenuators, typically used to install in a patch panel or to connect two fiber optic cables together. Variable attenuators are more expensive but useful for testing and can be adjusted from 1dB to 30dB.
Remember that the dB rating is a measure of signal strength and can be confusing at times. The graph below will give you an idea of the percentage of signal attenuation at a specific dB value.
Attenuator
Fiber attenuators are commonly used in two situations
The first case is in a power level test. 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 of the transmitter and receiver.
How many types of optical attenuators (OA) you can find
There are four different types of OA, which can take many different forms and are usually classified as either fixed or variable attenuators. Also, according to the type of connectors, they can be divided into LC, SC, ST, FC, MU, E2000, etc.
1. Fixed attenuators: Fixed optical attenuators used in fiber optic systems may use various principles to function. Preferred attenuators use doped fibers 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 equipment may be sensitive to damage caused by mode distribution, wavelength, pollution, vibration, temperature, power bursts, may cause back reflections, 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 single mode applications.
3. Built-in variable attenuator: The built-in variable optical attenuator can be controlled manually or electrically. Manual devices can be used for one-time setup of the system and are almost equivalent to fixed attenuators and may be referred to as "adjustable attenuators". Instead, electronically controlled attenuators can provide adaptive power optimization.
Advantages of electronically controlled equipment include speed of response and avoidance of degradation of the transmitted signal. Dynamic range is often very limited, and power feedback can mean long-term stability is a relatively minor issue.
Responsiveness is a particularly major concern in dynamically reconfigurable systems, where a millionth of a second of delay can result in the loss of large amounts 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 is technically no different from test attenuators, except that they are packaged for rack mounting and have no test to show.
4. Variable fiber attenuators: This type usually uses variable neutral density filters. Despite the relatively high cost, the advantages of this arrangement are stability, wavelength insensitivity, mode insensitivity, and large dynamic range.
Other schemes, such as LCD, variable air gap, etc. have been tried over the years with limited success.
They can be manual or motor controlled. Motor control brings clear productivity benefits to the average user, as frequently used test sequences can be run automatically.
Attenuation calibration can be a real problem for fiber infrastructure. Users often want absolute port-to-port calibration. Also, since equipment is not always linear, calibration should generally be performed at multiple wavelengths and power levels. However, in practice many instruments do not provide these basic functions, presumably to keep costs down. The most accurate variable attenuator instruments have thousands of calibration points, resulting in excellent overall accuracy in use.
Since equipment is not always linear, calibration should generally be performed at multiple wavelengths and power levels.
In recent years, many technologies have emerged in the fabrication of variable optical attenuators, including mechanical VOA, magneto-optical VOA, LCD VOA, MEMS VOA, thermo-optical VOA, and acousto-optical VOA.
Test Automation: Test sequences using variable attenuators can be time-consuming. Therefore, automation may gain useful benefits. Both desktop and handheld devices are available.
How do fiber attenuators work?
Power reduction is accomplished by methods such as absorption, reflection, diffusion, scattering, reflection, diffraction and dispersion. Optical attenuators generally work by absorbing light in the same way that sunglasses absorb extra light energy. They generally have an operating wavelength range in which they absorb all light energy equally.
They should not reflect light in voids or scatter it, as this could cause unwanted back reflections in fiber optic systems. Another type of attenuator utilizes a length of high loss fiber that operates at its input optical signal power level such that its output signal power level is less than the input level.
Fiber attenuator performance:
Attenuation and insertion loss: The insertion loss and the attenuation of the optical attenuator are important indicators of the attenuation of the optical attenuator to the actual insertion loss and the added attenuation of the variable attenuator. There is a separate insertion indicator for high loss and good quality. The insertion loss of the variable attenuator can be 1.0dB or less. Generally speaking, the index of the ordinary variable attenuator is less than 2.5dB and can be used. The insertion loss when actually choosing an adjustable attenuator should be as low as possible.
Fiber Attenuator Accuracy: Attenuation accuracy is an important indicator of optical attenuators
A variable optical attenuator, usually a mechanical type, with an attenuation accuracy of ±0.1 times this amount. Its size depends on the processing degree of precision mechanical parts. Fixed optical attenuator with high attenuation precision. In general, the higher the attenuation accuracy, the higher the price. Return loss: an important indicator of the influence of system performance on the return loss of optical equipment parameters.
The role of retroreflective optical network systems is well known. The return loss of an optical attenuator is the light energy incident on the optical attenuator and the attenuator light energy incident along the road reflectance.
Now you can understand how fiber optic attenuators work and how important they are to fiber optic infrastructure.
