Category Archives: Optical Attenuators

Guide to Optical Attenuators

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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 www.fs.com.

How to Test the Sensitivity of a Fiber Optic Receiver by using an Optical Attenuator

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Knowing how to test the sensitivity of a fiber optic receiver is an important skill. A fiber optic receiver provides optimal performance when the optical input power is within a certain range. But how do you test the receiver to see if it will provide optimal performance at the lowest optical input powers? One way is to use Optical Attenuators, such as bulkhead attenuators. Typically only a couple of values are required to complete your testing. This process involves three steps shown as following.

  1. Measure the optical output power of the fiber optic transmitter with the power meter. Remember that industry standards define transmitter optical output power and receiver optical input power for a particular network standard. If you are testing a 100BASE-FX receiver, you should be using a 100BASE-FX transmitter. The optical output power of the transmitter should be within the range defined by the manufacturer’s data sheet.
  2. Connect the transmitter to the receiver and verify proper operation at the maximum optical output power that the transmitter can provide. You need to test the receiver at the minimum optical input power that the receiver can accept while still providing optimal performance. To do this, you need to obtain the lowest optical input power level value from the manufacturer’s data sheet.
  3. Calculate the attenuation level required for the test. For example: The transmitter’s optical output power is -17 dBm and the minimum optical power level for the receiver is -33 dBm. The difference between them is 16 dB. You would use a 16 dB bulkhead attenuator at the input of the receiver and retest the receiver. If the receiver still operates properly, it’s within specifications.

Note: The optical loss is not considered about in the example above. Suppose that the transmitter is located 10 km from the receiver and the loss for the whole optical fiber link (including interconnections) is 6 dB, then you should use a 10 dB bulkhead attenuator rather than the 16 dB one for your test.

10dB Bulkhead Attenuator

This article source is from fiberopticshare blog.