What Is a Fiber Optic Attenuator?
Fiber optic attenuators or optical attenuators are devices that can either reduce or increase the power of optical signals.
The light that travels through the optical fiber carries important information at what can be ultra-long distances. For that data to reach its final destination without any errors, the system has to receive the signal at the optimal optical attenuation level.
Too much light can result in the saturation of the fiber optic receiver. Too little power will lead to noise interfering with the signal. Having either too much or too little power can result in a high Bit Error Rate (BER), which is the number of bit errors per unit of time.
Here is where optical attenuators come in: they help achieve optimal power levels and ensure the best system performance.
Multi-mode fiber optic systems typically do not need attenuators. For the most part, multi-mode sources — including Vertical-Cavity Surface-Emitting Lasers (VCSELs) — do not support a strong enough power output to be able to saturate receivers.
Single-mode systems, however, often require fiber optic attenuators to adjust the power level during transmission. That is especially true in the case of long-haul Dense Wavelength Division Multiplexing (DWDM) network links.
How Do Fiber Optic Attenuators Work?
Power reduction can be achieved through a number of methods. These include absorption, deflection, diffraction, diffusion, dispersion, reflection, scattering, and more.
Most optical attenuators achieve power reduction by absorption, similar to how sunglasses absorb light.
An optical attenuator will normally have a working wavelength range in which it is able to absorb all light energy equally. What the attenuator should not be doing, however, is scattering or reflecting the light in an air gap. That might cause undesired back reflection in the fiber optic system.
In addition, some attenuator types use the length of a high-loss optical fiber to adjust the input level of the signal power so that it is higher than the output level.
In any case, the end result is to keep the power level within the range of the receiver’s detector.
The manufacture of attenuating fiber involves the introduction of rare or transition elements into the core of the fiber using a solution-doping technique. It is the dopant that reduces fiber transmission.
The degree of attenuation itself depends on the dopant material and level, as well as the length of the attenuation segment.
Different Types of Fiber Optic Attenuators
There are four main types of fiber optic attenuators. Which one would work best for you depends on your goals and individual system needs, as well as on your existing infrastructure.
1. Fixed Optical Attenuators
Fixed optical attenuators may use either misaligned splices (also known as doped fibers) or total power. Both are reliable and relatively inexpensive.
Fixed attenuators further split into:
- Inline-style attenuators, which you can build into patch cables
- Build-out-style attenuators, or male-female adapters that you can add onto other cables
- Non-preferred attenuators, which tend to use reflective principles or gap loss
2. Loopback Optical Attenuators
Loopback attenuators are used for engineering, testing, and also at the burn-in stage of boards and other types of equipment.
3. Built-In Variable Optical Attenuators
Built-in attenuators may be either electrically or manually operated.
Manual devices can be used for one-time system setups and work in much the same way as fixed attenuators, whereas electrical attenuators can deliver adaptive power optimization.
4. Variable Optical Test Attenuators
These attenuators use a variable neutral density filter. They tend to be more expensive than other attenuator types but offer a number of advantages, including stability, insensitivity to mode and wavelength, and an extensive dynamic range.
Operators can control variable optical test attenuators manually or via a motor. The distinct advantage of motor control is that it makes it possible to run test sequences automatically.
Fiber Optic Attenuator Uses
Optical attenuators are used to test power level margins by temporarily adding a specified amount of signal loss. Alternatively, optical attenuators can help match receiver and transmitter levels, in which case they are installed permanently.
Fiber optic attenuators are used in various industries and for a wide range of purposes, including:
- Cable TV
- Optical sensors
- Instrument front panels
- Fiber optic patch panels
- Optical fiber test facilities
- Wide Area Networks (WAN)
- Local Area Networks (LAN)
- Telecommunication networks
- Liquid crystal variable attenuator (LCVA)
- Lithium niobate devices
… and more.
To learn more about the different applications of fiber optic attenuators, as well as if they are the solution you need, feel free to contact us today for an expert consultation. We would be more than happy to answer any questions you might have. If you need help choosing the right fiber optic attenuator for your project, our team can assist you with that too.