How to Manage Fiber Optic Attenuation

Fiber optic attenuator is used in the fiber optic communications to reduce the optical fiber power at a certain level, the most commonly used type is female to male plug type fiber optic attenuator, it has the optical fiber connector at one side and the other side is a female type fiber optic adapter, fiber optic attenuator name is based on the connector type and the attenuation level.

 

The main limit to performance in optical fiber is attenuation. Optical fiber attenuation, commonly known as loss, refers to the weakening or degradation of the optical signal as it passes through the glass fiber over the total distance of the fiber. Insertion loss and back reflection are two tests that will enable a technician to correct attenuation problems on a fiber span.

 

Testing the fiber will show you where the weakened signals are located. Physical characteristics of the fibr, increased signal levels, amplification nonlinearity, inconsistent or ‘dirty’ connector end-faces as well as components on the fiber such as splices and connector terminations can all be a factor that can cause increased attenuation. Attenuation can be measured by using an Optical Power Meter and an Optical Light Source, or an Integrated Power Meter / Light Source for bidirectional testing, or an OTDR and a Handheld Power Meter. When testing large fiber counts, data storage and the ability to download the information to a computer, is essential.

 

Using any of the above mentioned test scenarios; the light source will send a continuous wave signal, which which simulates the operating wavelength of the emitter on the transmission equipment, down the fiber in question. At the far end of this fiber the power meter will be connected. The result of this test will be the loss of dB which is a relative reading and is equal to the transmitted power minus the received power. This test gives a numerical value for the power received. To obtain accurate loss measurements, a reference setting function must be available on the power meter. The setting of a reference requires a test jumper be connected to power meter, and also the light source and connected by a coupler. A reference reading is than taken, and than the power meter/light source are attached to the different ends of the cable under test. The resultant reading will be the loss or attenuation of the fiber under test only. Attenuation will differ depending on the direction in the fiber itself. Different results can be obtained when measuring from A to B and from B to A.

 

Back reflection (return loss) is the ratio of the light backscattered or reflected in the reverse direction of the forward direction of travel. Back reflection limits and/or degrades system performance. Unlike attenuation, which can be reduced by cleaning the connector interfaces etc., the effects of back reflection can only be resolved by re-polishing connector faces, or even changing the type of connector interfaces such as UPC or APC connector polishes.

 

While every effort should be made to keep attenuation to a minimum such as effective fusion splicing techniques, proper bend radius consideration, proper fiber end face maintenance techniques, etc., sometimes attenuation must be added to a circuit because the receiver on the network element cannot accept the signal level. An attenuator is a passive device used to reduce the amplitude of a light signal without significantly changing the waveform itself. Primarily there are five different configurations of attenuators and each configuration has its own strength.

 

Hybrid Attenuator Plug, (Male to Female) or The Opposing Ends are a Different Connector Type. The hybrid style is ideal for reducing the intensity of a signal just prior to going into a receiver. This type of attenuator is typically available with similar connector ends with male/female configurations. They can also be available with different connector types on each end as well. The high performance characteristics of this type of attenuator make it the perfect choice for DWDM systems, CATV, EDFA, with Instrumentation and other highly amplified systems, LAN and Telecommunication Networks and high-speed data-com.

 

Bulkhead Attenuator (Female to Female) The bulkhead style of attenuators are ideal when two male connectors need to be mated with a fixed attenuator. Many times you will find this type at the patch panel. This type of attenuator is ideal for applications where return loss is not as critical and price is a consideration.