Customer Guidance on Variable Optical Attenuators

Speaking of a variable optical attenuator (VOA), people may know something about it. But asked to define a variable optical attenuator, they hesitate, and some of them may say it is just a simple device to reduce the signal power. Few of them can tell you the importance and principle of a variable optical attenuator, let alone how to choose a good one for you. But now, you’ve got a chance to get all the answers in this post.

If you ask me to define a variable optical attenuator in a straightforward way, I would say it is a device that can incrementally adjust the power of the optical signal passing through it. A variable optical attenuator is a double window of passive optical components, which could continually and variably attenuate the light intensity in the optical fiber transmission. And the variable optical attenuator cable could help simulate distance or actual attenuation in the fiber optic testing work by inserting a calibrated attenuation into the link. By using a VOA, the light power injected from a light source can be adjusted into the optical fiber. To put it simply, a VOA is used to control the optical power in a fiber.

People may wonder that why we need such a device to reduce the power level of an optical signal. It is easy for people to believe that stronger signal power is always tend to be better for optical transmission. Yes, in most cases a strong signal intensity is beneficial and helpful. And we even invented a device called erbium doped fiber amplifier (EDFA) to boost the intensity of fiber optical signal. So it seems paradoxical to create a VOA. However, things are not as simple as we think. The truth is that too much light can overload a fiber optic receiver and degrade the bit error ratio (BER). To achieve the best BER, the light power must be reduced. Or in a multi-wavelength fiber optic system, you need to equalize the optical channel strength so that all the channels have similar power levels. That’s to say, the power of stronger channels need to be reduced to match lower power channels. Fiber optic attenuator is the ideal device to help solve these issues perfectly.

The power reduction is done by such means as absorption, reflection, diffusion, scattering, deflection, diffraction, and dispersion, etc. Variable optical attenuator usually works by absorbing the light, like sunglasses absorb the extra light energy. It typically gets 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. It operates upon its input optical signal power level in such a way that its output signal power level is less than the input level.

At FS, VOAs from our FMT( FS.COM multi-service transport) platform are equipped with MEMS technology to balance signals in a DWDM network. FS MEMS VOAs allow for the automated, fine-tune control of the attenuation level in an optical system. A MEMS mirror may be configured such that a beam from an input fiber bounces off the mirror and into an outer fiber. By slightly tilting the mirror, the input and output fibers are decoupled and the signal is attenuated.

As it has been mentioned before, Fiber-mart variable optical attenuators adopt MEMS technology and could continually and variably attenuate the light intensity in the optical fiber transmission and help simulate distance or actual attenuation in the fiber optic testing work. Also, as a part of our FMT system, the hot-swappable plug-in VOA cards only occupies 1 slot in the 1U/2U/4U chassis and online attenuation adjustment can be done to make business much safer. Fiber optical attenuators provided by FS are in a great variety, some of which are shown in the table below. These fiber optical attenuators have great performance in wavelength ranging from 1250nm to 1625nm, with attenuation range from 1dB to 30dB optional.

So far, we have known the important role and basic principle of variable optical attenuators in optical transmission. Fiber-mart can provide a wide range of fiber optic attenuators, offer modifications to existing products, create truly custom solutions, or integrate multiple variable optical attenuator components together to create an application specific solution. For more information, please contact us at www.fiber-mart.com.