Guide to Optical Attenuators

Attenuators Overview

An optical attenuator, or fiber optic attenuator, is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The optical attenuators can have a tuning control to set the level of attenuation into a range of selectable values (variable optical attenuators), or can introduce a fixed level of attenuation (fixed optical attenuators).

Variable optical attenuators are normally used for testing and measurement. Also they could be used in EDFAs (erbium doped fiber amplifier) for equalizing the light power among separate channels. Fixed optical attenuators have fixed values specified in decibels. The attenuation is expressed in dB and its value cannot be varied. It is ideal for attenuating single-mode fiber connectors in various applications.

Why Use Optical Attenuators?

Optical attenuators is a critical component of any fiber optic network. Using an attenuator, the transmission signal into the dynamic range of the receiver could be adjusted. This increases the life span of the optical equipment and ultimately provides a clearer transmission signal. Moreover, the utilization of optical attenuators could assure the linear behaviour of optical fiber receivers avoiding optical power overloading. At the same time, it is able to balance the optical power into passive optical network branches and can make measurements on an optical telecommunication system.

How Optical Attenuators Work?

Optical attenuators usually work by absorbing the light, like sunglasses absorb the extra light energy. Typically, they have a working wavelength range in which they absorb the light energy equally. However, they should not reflect the light since that could cause unwanted back reflection in the fiber system. 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.

Application of Optical Attenuators

Optical attenuators are commonly used in fiber optic communications. They could be used to test power level margins by temporarily adding a calibrated amount of signal loss, or installed permanently to properly match transmitter and receiver levels.

One of the important applications of optical attenuators is channel balancing in WDMs (wavelength division multiplexing). As illustrated in the following picture, an eight channel wavelength multiplexed signal from a trunk line is demultiplexed into individual signals. The signals are of different intensities, and need to be balanced to avoid saturating any of the receivers. So each channel is sent through a corresponding port on an eight channel MEMS (micro-electro-mechanical systems) VOA (variable optical attenuator). The signal strength through the optical attenuator outputs is monitored by a control circuit. If the output signal gets too high or too low, the corresponding optical attenuator is adjusted to bring the light level to the correct range.

optical attenuator in WDM network

As stated above, an optical attenuator is used to reduce the power level when there is too much light deliver through a fiber optic receiver. It is used to adjust optical signal levels thereby increasing network flexibility and providing management of optical power. If you are looking for an optical attenuator, Fiberstore is a primary option. It has many different fixed optical attenuators and variable optical attenuators including fixed LC/APC fiber optic attenuator, fixed SC/UPC fiber optic attenuator, BVA610 optical variable attenuator(0-60dB), etc. For more information, you can visit

DO You Know Variable Optical Attenuator?

Optical Attenuator is one part of passive optical components. It’s widely used in fiber optic communications to reduce optical fiber power at a certain level. Variable optical attenuator is one of optical attenuator. Now I would like to introduce some basic knowledge of variable optical attenuator in this blog.

what is Variable Optical Attenuator?

Variable Optical Attenuator (VOA) is a double window (1310/1550nm) of passive optical components. Variable optical attenuator could continually and variably attenuate the light intensity in the optical fiber transmission. 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 the variable optical attenuator (VOA), technicians could verify the power margin received by testing the fiber optic link power budget. Fiber optic VOA can help the user vary the light power injected from a light source into the optical fiber.

VOA type

Principle of Variable Optical Attenuator

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.

Built-in Variable Optical Attenuator

Variable optical attenuator may be either manually or electrically controlled. A manual device is useful for one-time set up a system, and is a near-equivalent to a fixed attenuator, and may be referred to as an “adjustable attenuator”. In contrast, an electrically controlled attenuator can provide adaptive power optimization.

Attributes of merit for electrically controlled devices, include speed of response and avoiding degradation of the transmitted signal. Dynamic range is usually quite restricted, and power feedback may mean that long term stability is a relatively minor issue. Speed of response is a particularly major issue in dynamically reconfigurable systems, where a delay of one millionth of a second can be expected to result in the loss of large amounts of transmitted data. Typical technologies employed for high speed response include LCD, or Lithium niobate devices.

With this blog, we have learnt the basic knowledge of variable optical attenuator.  It is necessary to use in fiber optical communications. Fiberstore is a professional supplier of fiber optic communication solution. Variable optical attenuator is just one of PON(passive optical network) components. For more information about variable optical attenuator, welcome to visit our website or contact us over

Understanding Optical Attenuators

Optical fiber attenuators are used to reduce the power level of optical signal, either in free space or in an optical fiber. They are often used in optical communication systems where the optical signal is too strong and needs to be reduced, in which the attenuation, also called transmission loss, helps with the long-distance transmission of digital signals.

Optical attenuators can take a number of different forms and are typically classified as fixed or VOA attenuator. Fixed attenuators can be broken down into either build out style or incorporated into a patch cord. The build out variety is a small (~ 1.25 inch long) attenuator with a male connector interface on one end and a female interface connector on the opposite end. The build out style is typically fabricated with either air gap attenuation or doped fiber attenuation.

Fiber optic attenuators can be designed to use with various types of fiber optic connectors. Commonly used fiber optic attenuators are the female to male type, which is also called a plug fiber attenuator. Another type inline fiber optic attenuator is designed with a piece of fiber optic cable at any length and connectors are installed as the customers request. Fixed value fiber optic attenuators can reduce the optical light power at a fixed level, for example, a 10dB SC fiber optic attenuator will reduce the optical power 10dB and utilize a SC male to female attenuator. Variable fiber optic attenuators are with adjustable attenuation range. There are also attenuation fiber optic patch cables available, their function is the same as attenuators and are used inline.

Variable Attenuator (or ajustable fiber optic attenuator) is a need to provide different under construction decline. The reduction of precision devices for a wide variety of fiber optic transmission lines to carry out scheduled, the amount of light intensity attenuation. There are also handheld variable fiber optic attenuators which are used as test equipment.

Typical attenuation values are between 3 and 20 dB. It is used in optical systems where the optical power from a source is too high for the test equipment in use. Fixed plug type fiber attenuator provides a connector plug (male) and an adapter socket (female) to connect between fiber patch cord and fiber adapter. Fixed plug type optical attenuator introduces an in-line fixed loss that will reduce the source power to an acceptable detection level. The attenuation level should be stable with temperature and wavelength for a stable reliable system.

An optical 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 the 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.

Wide range variable & inline fiber optic attenuator and the inline fiber optic attenuator are with more accurate attenuation compared with traditional connector type fiber optic attenuators. Variable optical attenuators from FiberStore are specifically designed for use in DWDM networks with individual channel source elements such as add drop multiplexer.

Application of Optical Add-Drop Multiplexer

What’s the Optical Add-drop Multiplexer?

The optical add-drop multiplexers (OADM) are used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks. An OADM may be considered to be a specific type of cross connect cabinet.

A traditional OADM consists of three stages: an optical demultiplexer, and optical multiplexers, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

Principles of OADM technology

General OADM node can use four port model (Figure 1) to represent, includes three basic functions: Drop required wavelength signal, Add rumored signal to other wavelengths pass through unaffected. OADM specific network process is as follows: WDM signal coming from the line contains mangy wavelength signals into OADM’s “MainInput” side, according to business required, from many wavelength signals to selectively retrieved from the end (Drop) output desired wavelength signal, relative to the end from the Add the wavelength of the input signal to be transmitted. While the other has nothing to do with the local wavelength channels directly through the OADM, and rumored signals multiplexed together, the line output from the OADM (Main Output) Output.

OADM node technical classification

Optical drop multiplexer network technologies can be divided into two types, fixed optical drop multiplexer (Fixed OADM, FOADM) and reconfigurable optical drop multiplexer (Reconfigurable OADM, ROADM).

Fixed Optical Drop Multiplexer (FOADM)

FOADM to filter as the main component, and its function is fixed to join or retrieve certain light wavelengths. General common FOADM can be divided into three types, namely Thin Film Filter type (TFF type), Fiber Bragg Grating (FBG type) and integrated planar Arrayed Waveguide Gratings (AWG type).


Thin Film Filter (TFF FOADM)

TFF FOADM using thin film between the filtering effect of the different refractive index.

Fiber Bragg Grating (FBG FOADM)

FBG FOADM use of fiber Bragg grating filtering effect, with two circulator can become FOADM.

Arrayed Waveguide Gratings (AWG FOADM)

AWG FOADM gererally used in semiconductor fabrication processes, the integration of different refractive index material is formed on a flat substrate in a planar waveguide, when different wavelength light source is incident through the couping after the import side, due to take a different path length, while the different phase delay caused by different wavelengths and thus produce certain wavelengths in the export side to form a constructive or destructive interference, making waves in the export side, the different wavelengths will follow the design on a different channel to reach, and thus achieve FOADM function.

Reconfigurable Optical Add/Drop Multiplexer (ROADM)

ROADM can always be adjusted with the distribution network to add and drop wavelength, which reconstruct the network resource allocation, the flexibility to meet the requires of modern urban network, so a flexible ROADM features, plus optical switch substantial advantage, making the current fastest growing ROADM based optical switches based ROADM (switch based OADM). ROADM mainly be the optical switch, multiplexer and demultiplexer composed, Switch-based OADM, mainly divided into Wavelength independent switch array and wavelength selection switch.

Wavelength independent switch array

Type 1: Wavelength independent switch array

Wavelength selective switch

Type 2: Wavelength selective switch

All kinds of optical drop multiplexer performance comparison

optical drop multiplexer performance

OADM network applications

WDM ROADM optical fiber suitable for different network environments

OADM network applications

OADM in the metropolitan network development tendency

1. Arbitrary choice must be retrieved, adding wavelength, the wavelength can take advantage of the limited resources, the node can be retrieved with the need to do to join the adjustment of the signal wavelength, and has a remote control functions. This can provide dynamic reconfiguration of optical communications network capable ROADM will be connected to the backbone network critical devices. And FOADM is used for wavelength demand network access will be smaller parts to reduce costs. Furthermore, ROADM use to all kinds of Tunable Laser, unable Filter, or wavelength selective optical switches and other components.

2. Must be able to convert incompatible wavelength suitable for the backbone network will be transmitted wavelengths. Therefore, OADM be combined with wavelength conversioin Transponder or other functional components.

3. Must be able to compensate for the node to make acquisistion, adding such action energy loss. Therefore, OADM optical amplifiers must be combined with functional components.

4. Wavelength signals related specifications, such as: the signal to noise ratio (S/N), the energy balance between the signal wavelength, etc., are required to meet network requirements. Therefore must be combined OADM variable optical attenuators (VOA), dispersion compensation module (DCM) and other components.