An fiber attenuator uses a segment of attenuating fiber interposed in the optical path. The attenuating fiber is produced by using a solution doping technique to introduce transition or rare earth elements into the fiber’s core. The dopant reduces the transmission of the fiber. The degree of attenuation depends upon the material used as the dopant, the dopant level, and length of the attenuation segment. In a specific embodiment, an optical attenuator is provided having a first and second signal carrying optical fibers and an attenuating fiber segment, each of which has a core, a cladding substantially coaxial with the core, and a substantially planar end face. The attenuating fiber segment is fusion spliced between the first and second signal carrying optical fibers. In a second embodiment a portion of the cladding of the attenuating fiber is chemically etched.
The power reduction are done by such means as absorption, reflection, diffusion, deflection, and dispersion, etc. Attenuators usually works by absorbing the light, like sunglasses absorb the extra light energy. Attenuators typically have a working wavelength range in which they absorb the light energy equally. They should not reflect the light since that could cause unwanted back reflection in the fiber system. Or by scattering the light such as an air gap. Another type of attenuator utilizes a length of high-loss optical fiber, that operates upon its input optical signal power level in such a way that its output signal power level is less than the input level.
Optical attenuators can take a number of different forms and are typically classified as fixed or variable attenuators.
Fixed Attenuators Fixed attenuators have a fixed optical power reduction number, expressed in dB, such as 1dB, 5dB, 10dB, etc. A -3dB attenuator should reduce intensity of the output by 3 dB. Their applications include telecommunication networks, optical fiber test facility, Local Area Network(LAN) and CATV systems.
Fixed value attenuators are composed of two big groups: In-line type and connector type (or build out style). In-line type looks like a plain fiber patch cable, it has a fiber cable terminated with two connectors which you can specify types.
Connector type attenuator looks like a bulk head fiber connector, with a male connector interface on one end and a female interface connector on the opposite end. The connector style is typically fabricated with either air gap attenuation or doped fiber attenuation. It mates to regular connectors of the same type such as FC, ST, SC and LC. The female to female fixed attenuators work like a regular adapter. But instead of minimizing insertion loss, it purposely adds some attenuation. The male to female fixed attenuators work as fiber connectors, you can just plug in your existing fiber connector to its female side.
Variable Attenuators, the attenuation level can be adjusted, such as from 0.5 dB to 20dB, or even 50dB. Some variable attenuators have very fine resolution, such as 0.1dB, or even 0.01dB. This is critical for accurate testing. For precise testing purposes, engineers have also designed instrument type variable attenuators. These instrument type attenuators have high attenuation ranges, such as from 0.5 dB to 70dB. Variable attenuators are general used for testing and measurement, but they also have a wide usage in EDFAs for equalizing the light power among different channels.
The female to female variable attenuators are adjustable by turning a nut in the middle. The nut adjusts the air gap in the middle to achieve different attenuation levels. The in-line patch cable type variable attenuators work as regular patch cables, but your can adjust its attenuation level by turning the screw.
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