People often wonder why you would intentionally set attenuation on a fiber-optic network when they see fiber optic attenuators. When testing optical fibers, attenuation is one of the key points you are looking for. You want your attenuation to be as low as possible so that you can adapt to the link budget you are trying to meet or beat.
For those who don’t know, attenuation refers to the amount of light or signal loss over a span or connection. When building a network, customers always want to cover the distance as much as possible, and sometimes they add a fiber amplifier to increase the signal to ensure that they reach the running fiber, so that a signal will reach every customer or where it is needed. Sometimes adding an amplifier will result in the use of a higher-power laser, and conversely, if the signal is only a short distance from your first position, it will cause the optical signal to be too strong when it hits the optical receiver.
It will either distort the signal or burn the optical receiver. This is where an attenuator that increases loss purposefully is useful and necessary. Many types of attenuators exist, and the attenuation levels are different so that the network can be perfectly balanced. Let us delve into the different types of fiber optic attenuators to give you a better understanding of the different methods that you can help create losses and potentially save your equipment costs.
1. Male and female optical attenuator
The most common optical attenuators I usually sell are male-to-female-style attenuators. These attenuators are used at the end of the wiring, usually plugged into the receiving end of the transmission. Some people call them inline attenuators because they plug directly into the switch and then plug in a patch cable. They increase at a rate of 1 decibel, and the attenuation level ranges from 1 decibel to 25 decibels. They have the four most common types of fiber optic connectors, including UPC and APC polishing.
Normally, the level of attenuation that is most suitable for the application is not known. Most customers will buy a dB level from 1 to 10. At work, the amount of attenuation required is different, so they have various attenuations, which becomes a “try until it works” process. This means if they are 5dB at first, but it is too big and the signal is turned off, you will know that you need less attenuation, and your next level will try 4dB. Repeat this process until the desired attenuation is reached.
2. Female-to-female optical attenuator
There are attenuators that allow you to plug two male connectors into each other. These are bulkhead-type female-to-female attenuators. They are often of a specific wavelength. Attenuation for the specified wavelength will only be known at 1310nm or 1550nm.
This style uses wavelength-sensitive neutral density filters to help achieve the proper attenuation level. When using this type, they have only four different dB levels. Take 5 as the unit, 5 10 15 or 20dB as the unit. Use this style when you know exactly the dB level that needs to be attenuated and the wavelength that needs to be attenuated.
3. Variable optical attenuator
Instead of getting several attenuators of different decibel levels, there are some other types of attenuators that allow you to change the amount of loss. One type is called variable optical attenuator. It has a device installed in the middle of the patch line, and you can turn a screw to change the attenuation. It has a range from 1dB to 20 dB and works at 1310nm and 1550nm wavelengths. It has a specific connector on each end. Turning the nut on the device helps to separate the connectors or helps to pull them back together. This will change the amount of loss in the system because the end faces of the connector have to be in contact to eliminate the loss.
The other type is an air gap attenuator. These only apply to ST and FC style connectors. This kind of optical fiber uses its name and places different levels of spatial air between a pair of mating optical fiber connectors. Air attenuators include the use of “washers” to cause attenuation by creating a distance between the end faces. The washing machine has different thicknesses to help change the amount of loss. There is no specific decibel level for this washer-type attenuator because at that point there are other factors that can affect the amount of loss. They do come in different colors to help you understand which one you tried during the test. Unlike the male and female attenuators, the gasket is placed on the light source or transmitter instead of the receiving end.
4. Passive optical attenuator
Another form of attenuator is called a passive attenuator. This is where you use a device to help attenuate the patch line that is already in place. For this type, we have two different options. One is the Clip-On attenuator, which can be used on a 3mm sheathed fiber, which can range from zero dB to 47dB at a wavelength of 1550nm. For a wavelength of 1310nm, the level will be from 0 to 21 dB.
When the Clip-On attenuator is placed on the fiber, it works by bending the fiber to generate the required loss. The device can be reused, once removed, it does not affect the performance of the optical fiber. Another one that falls into this category is a three-stage attenuator. This can only work at 1310nm wavelength. There are 3 different ranges, 2-7dB, 5-15dB and 5-20dB. The working principle of this device is to exceed the recommended bending radius of the optical fiber without introducing any back reflection.
As you can see, attenuators play a very important role in some networks. They may sound counterproductive because when you run, you are looking for the smallest amount of loss. The attenuator not only causes loss but also can help affect the signal and cause data loss on the link in a network with too much light passing through. Interestingly, a component that costs about $12 can have a huge impact on a higher-cost network.
