Let’s talk about core diameter mismatch defined Intrinsic losses in optical fiber : This type of losses are due to factors intrinsic to the nature of the fibres, such as geometric or optical parameters of the same. In a union of optical fibers, any difference between them will lead to this type of loss. We must make a distinction between joints of fibre singlemode and multimode fibers. In the former, these losses fall into losses by the radius of modal field mismatch. In the second case, you can talk of losses by mismatch of the numerical aperture, Core diameter mismatch and the refractive index of the core profile mismatch.
Single mode Fiber ( Unions of monomode fibers ) : In this type of unions inherent losses are determined by the mismatch of the modal field radio. The modal field is a concept associated with the diameter of modal field (MFD). The latter indicates the geometric distribution of the light is produced in the propagated mode (do not forget that there is talk of single-mode fibers). Thus, the differences between the radio of modal fibers involved in the union field translates into losses in the signal.
The expression that characterizes these losses is as follows:
where ?1 and ?2 are modal field of fibers transmitting and receiving radios.
Singlemode fibers used in most connectors have nuclei very small, usually with 9 to 10 µm in diameter, so that a single particle of dust or smoke can block an important transmission zone and increase significantly the loss.
A poor fiber-core alignments are the main causes of loss of link when connecting two fibers using a joint. Another source of loss of important link is the difference in optical properties. If spliced fibers have diameters of different core or cladding they may increase the coupling losses, this is called core mismatch.
Core diameter mismatch definition: Unions of multimode fibers In this type of unions inherent losses are determined by the mismatch of the numerical aperture, the mismatch of the diameter of the nucleus, and the mismatch of the profile of the refractive index of the core of the fibers. Any disagreement between these magnitudes in the fibres involved in the union will cause a loss of power in the signal. Expressions that model these losses are presented below:
Losses by the numerical aperture mismatch:
Mismatch of the numerical aperture
where AN1 and AN2 represent numerical openings of transmitting and receiving fibers respectively.
Losses due to mismatch of the diameter of the core:
Mismatch of the diameter of the core
where F1 and F2 represent the diameter of the nucleus of the fibers transmitting and receiving respectively.
Profile mismatch losses:
The refractive index of the core profile mismatch
where a1 and a2 are profiles of transmitting and receiving fibers respectively.