Some applications require optical attenuators to control or limit the optical power on a fiber link. One example is wavelength division multiprocessing equipment, which uses fixed attenuator to allow a conventional transmitter to interoperable with many different physical layers. Other examples include fiber links in the cable television industry.Fixed attenuators can be expensive and must be incorporated into the design of the cable system; this means that duplex cables cannot be used if attenuation is required in only one path of duplex fiber link.Separation duplex connectors defeat the keying, which [prevents the connector from being improperly inserted into a receptacle or transceiver. The attenuators also provide an extra connection point in the link.Which must be cleaned and may be susceptible to mechanical vibration that will tend to dislodge connectors in data communication products.Instead of using fixed, placable attenuators, is impossible manufacture inline optical attenuators as part of the Hybrid Cables assembly.Several approaches can be used.
For multimode atenuators ,a short piece of single mode fiber can be spliced into the cable’s by controlling the alignment between the single mode fiber stub and the multimode cable on either side,as well as the lengthe of the stub various levels o f attenuation can be achieved ,the stub my be actively aligned during cable manufacturing ,then protected by an external sherathe or package to protec it from mechanical shock ,bibration ,and cable flexing ,similar effects can be achieved by deliberate misalignment of mulimode or sing-mode fiber susion splice. In most cases ,arbitrary attenuation values from 0.5lb to over20db can be achieved by with a tolerance of less than 0.5lb ,The resulting attenuated cables are quite robust ,and in many cases they serve a dual purpose since the application would have required jumper cable to adapt to different styles of optical connectors or connect with subtended equipment.
For additional applications in which optical power must be controlled, specialty Fiber Optic Cable are available with high attenuation that is flat over a certain spectral region.With so much design effort directed toward reducing the fiber attenuation to improve link budgets and distances, it can be simple to forget that optical fiber can just as easily be designed for extreme attenuation.using the saem precision controlled manufacturing techniques that consistently yiedl ow -loss fiber ,it is possible to dope the fiber in such a way that very consisten,high attenuation is provided over a wide range of operatin wavelengthes ,this can be an advantage in designing attenuatiors for wdm systems.As with the offset spliced cable attenuators, these fibers are usually more reliable and robust than conventional airgap attenuators.
They get the additional advantage that a controlled amount of attenuation can be chosen by simply cutting and splicing a desired length of the fiber.Short sections of high -attenuation fiber are also being incorporated into some types of fiber -optic components and are finding applications in optical test and measurement systems.Ti[tical fibers are available with attenuations ranging from 0.5db/meter to 30lb /meters in 0.5-db increments or from 0.25db/cm to 25lb /cm in 0.25-db increments.
