An optical attenuator is a passive device that is used to reduce the power level of an optical signal. Optical attenuators are generally used in single-mode long-haul applications to prevent optical overload at the receiver.
According to the different types of port of optical attenuator, it can be divided into several categories: SC fiber optic attenuator, LC fiber optic attenuator, FC fiber optic attenuator, ST optical attenuator. Different types of fiber optic attenuator used in different places, LC optical attenuator commonly used on the router, FC optical attenuator is on the distribution frame to use most, for 10 base – F connection, the connector is usually ST type.
The types of attenuators generally used are fixed, stepwise variable, and continuously variable. Fixed attenuators are designed to have an unchanging level of attenuation. They can theoretically be designed to provide any amount of attenuation that is desired. The output signal is attenuated relative to the input signal. Fixed attenuators are typically used for single-mode applications. A stepwise variable attenuator is a device that changes the attenuation of the signal in known steps such as 0.1dB, 0.5dB, or 1dB. The stepwise attenuator may be used in applications dealing with multiple optical power sources for example, if there are three inputs available, there may be a need to attenuate the signal at a different level for each of the inputs. Conversely, the stepwise attenuator may also be used in situations where the input signal is steady, yet the output requirements change depending on the device that the signal is output to. The stepwise attenuator should be used in applications where the inputs, outputs, and operational configurations are known. A continuously variable attenuator is an attenuator that can be changed on demand. These attenuators generally have a device in place that allows the attenuation of the signal to change as required. A continuously fiber optic variable attenuator is used in uncontrolled environments where the input characteristics and/or output needs continually change. This allows the operator to adjust the attenuator to accommodate the changes required quickly and precisely without any interruption to the circuit.
Now that we have looked at Types of Attenuators, we will discuss principles of Optical Attenuators. Optical attenuators use several different principles in order to accomplish the desired power reduction. Attenuators may use the gap-loss, absorptive, or reflective technique to achieve the desired signal loss. The types of attenuators generally used are fixed, stepwise variable, and continuously variable.
The principle of gap-loss is used in optical attenuators to reduce the optical power level by inserting the device in the fiber path using an in-line configuration. Gap-loss attenuators are used to prevent the saturation of the receiver and are placed close to the transmitter. Gap-loss attenuators use a longitudinal gap between two optical fibers so that the optical signal passed from one optical fiber to another is attenuated. This principle allows the light from the transmitting optical fiber to spread out as it leaves the optical fiber. The farther away the gap-loss attenuator is placed from the transmitter,the less effective the attenuator is, and the desired loss will not be obtained. The absorptive principle, or absorption, accounts for a percentage of power loss in optical fiber. This loss is realized because of imperfections in the optical fiber that absorb optical energy and convert it to heat. The reflective principle, or scattering, accounts for the majority of power loss in optical fiber and again is due to imperfections in the optical fiber, which in this case cause the signal to scatter. The scattered light causes interference in the optical fiber, thereby reducing the amount of transmitted and/or received light.
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