Variable Optical Attenuator
Comparing to the fixed optical attenuator, variable optical attenuator has the function that attenuation can be adjusted as demand. There are two types of optical variable attenuators—these are known as the stepwise variable attenuator and the continuously variable attenuator. Here we are going to introduce different kinds of variable optical attenuator how to achieve the attenuation.
1. Gap-loss variable optical attenuator
The transmission of light in the optic fiber is restricted by the law of total reflection, it can not scatter out and will keep the light energy in a stable status. But if there is a gas between the two fibers, the light will scatter, hence cause the light loss. This is the working principle of gap-loss variable optical attenuator. The attenuation value is different with different gap interval.
Adjust the interval through a mechanical mechanism, then attenuation is adjusted. The attenuation range is 0~30db.
The advantage of gap-loss attenuator is easy to produce, not require advanced technology, small size, low cost. But it will cause reflection, so it will not work well when then fiber system requires no or low reflection.
2. Absorptive variable optical attenuator
The optical polished neutral absorption glass can also be used to produce optical attenuators. According to the light absorption characteristics of the material, the flake or strip-shaped neutral dark glass can attenuate the light intensity when placed on the light path. A single piece of light-absorbing glass can be used to produce a fixed attenuator. Multiple pieces of sheet-shaped absorption glass can be made into a stepwise adjustable attenuator through wheel disc conversion, while the strip-shaped absorption glass can be made into a continuous adjustable attenuator by continuous displacement.
The light-absorbing glass can be fixed and adjustable. However, the development of this attenuator requires optical collimator, high coupling of input and output, and high precision debugging equipment and supporting parts. The manufacturing cost is high.
3. Blocking type variable optical attenuator
The light-blocking element is blocked between two collimators to realize the attenuation of optical power. The light-blocking element can be sheet or conical, and the conical one can be pushed by rotation, while the sheet one needs to be pushed horizontally or by a certain mechanical structure. The light-blocking attenuator can be made into an optical fiber adapter structure or on-line structure.