As we all know, a fiber optic amplifier is often installed where optical signals are weak and need to be enlarged. But what if there is too much power level of an optical signal which should be reduced? To solve this issue, fiber optic attenuator comes into being. Fiber optic attenuator or optical attenuator is a passive device utilized to decrease the power rate of the optical signal either in free space or in an optical fiber without appreciably distort the waveform. This article will give an overview of optical attenuator to make you better understand it.
Many people may think that the bigger the optical signal, the better the performance. Actually, either too little or too much power can cause high bit error rates. Too much power can make the receiver amplifier saturate, while too little will cause noise problems as it interferes with the signal. For example, in DWDM system, multiple wavelength channels arriving at a node may pass through different paths and experience different losses, their powers need to be equalized before entering the optical amplifier to get flat since the gain of each channel depends on the power level of the other channels. So in this case, a fiber optic attenuator is required to control the power level of optical signals.
The power reduction is done by means such as absorption, reflection, diffusion, scattering, deflection, diffraction, and dispersion, etc. The fiber optic attenuator usually works by absorbing the light, like sunglasses absorb extra light energy. Using this working principle, fiber optic attenuators typically have a working wavelength range in which they absorb all light energy equally, and should not reflect the light or scatter the light in an air gap which could cause unwanted back reflection in the fiber system. This kind of principle is more popular in the design of optical attenuator, since it is simple and can effectively reduce the optical signal power. The following picture shows the absorptive principle of optical attenuator.
Optical attenuator is widely used in fiber optic communications, either to test power level margins by temporarily adding a calibrated amount of signal loss, or to be installed permanently to properly match the levels of a transmitter and a receiver. There are two commonly used types, including fixed attenuator and variable attenuator.
Fixed attenuator, as its name shows, is designed with an unchanging level of attenuation that is ideal for attenuating single-mode fiber connectors in various applications. It can be theoretically designed to provide any amount of attenuation that is desired and be set to deliver a precise power output. This type of optical attenuator is utilized in structure for two distinct types of services. On the first type, it is used to regulate the channels in order to set up a recognized level of signal. On the second type, this mechanism is used to match the impedance and also as a shield to avoid the contact with two different device. A LC fixed fiber optic attenuator is shown in the image below.
Different from fixed attenuator, variable attenuator can offer a wide range of attenuation values with flexible adjustment which is generally used for testing and measurement or equalizing the light power among different channels in EDFAs. This type of optical attenuator can be divided into stepwise variable attenuator and continuously variable attenuator. The former one can change the attenuation of the single in known steps such as 0.1 dB, 0.5 dB, or 1 dB, while the latter one can allow the operators to adjust the attenuator to accommodate the changes required quickly and precisely without any interruption to the circuit. Like fixed attenuator, both these two types of variable attenuators are available with regular connectors, like LC, SC or FC. Here is a LC to LC variable fiber optic attenuator.
As an indispensable passive optical component in WDM networks, fiber optic attenuator is designed to control the power level of optical signals more precisely. We have discussed the importance, working principle and commonly used types of fiber optic attenuator. Hope you can have a better understanding of it.