Excess Loss for splicing MM 62.5 to MM 50 micron fibers
Technicians who are designing or installing an Optical Network should avoid using of different fibers in a link which having different MFD or Core Diameter .
We have to keep it in our mind that any deviation in MFD of single mode fibers or Core Diameter of MM fibers will result to an excess loss in the network .
In this article , we are trying to show how much extra loss will be added to the network by splicing two different multimode fibers to each other , say MM 62.5 to MM 50 micron .
When an Optical Fiber Network consists of two section one with MM62.5 and the other with MM 50 , regardless of the length of each section , a part of signal will be lost if MM62.5 be at the transmitter side and the MM50 at the receiver side .
We may compare it by dropping the water from the bulk to the hose . Pictures below will give a better idea about such problem :
Though by changing the location of transmitter and the receiver , such unpleasant case will not be happened but as the network will be mostly designed that both sending and receiving signals transmitted via the same fiber , so in any case excess loss will exist in the network .
The following table getting from FOA reports showing the approximate range of excess loss in dB for splicing two different type of MM fibers .
|Dimension Of Core/Clad||Transmission Side|
|Receiver Side||۵۰/۱۲۵||۰٫۹-۱٫۶ dB||۳٫۰-۴٫۶ dB||۴٫۷-۹٫۰ dB|
|۶۲٫۵/۱۲۵||–||۰٫۹ dB||۲٫۱-۴٫۱ dB|
By injection of optical signal to a Multimode fibers , different modes of propagation will be produced in them due their special construction as well as launching condition of the light source . MPD as an abbreviation to the Modal Power Distribution will determine that how many modes will be supported by the fiber . therefore the existing formula which calculating the excess loss in splicing dissimilar commercial SM fibers and the other special type of SM like DS or NZDS fibers will not be practically applicable for MM fibers .We are in the idea that values of excess loss due to mismatching of two MM fibers are more higher than what stated in FOA table . In order to be more closer to the real figures , one should study about modal distribution of optical signal in the fiber core as excess loss will entirely depending on such distribution profile . We did more investigated in the other documents and found out that Corning and Fluke data for excess loss in splicing MM62.5 to MM50 are between 3 to 5 dB which such values are more close to the reality figures .
With respect to the above reason , it is not recommended to splice MM 62.5 micron fibers to MM 50 , even technicians should be careful to use of the same dimension of MM fiber pigtail and patchcord as end termination to avoid unexpected excess loss .
If by any reason splicing of two dissimilar MM fibers is unavoidable , the highest amount of excess loss to be taken into consideration for loss budgeting of the network . Furthermore , effect of this high excess loss on the quality of transmission to be also measured and observed .
Afshan Cable Co.
Tehran – Iran