Design of optical fibre coaxial couplers with arbitrary modal electric field

The authors analyse a method, which leads to an efficient and precise algorithm for synthesising coaxial, optical fibre couplers of arbitrary modal electric-field distributions. Their purpose is to design a fibre optic index profile supporting two preselected mode fields such that their interference transfers all the optical power spatially from the core region to a cladding part of the optical fibre completely. To deal with this problem, they apply inverse transmission-line techniques. Using the desired electric field, they work inversely and synthesise the appropriate refractive index profile of the couplers with excellent crosstalk. They envisage one can apply this technique to design fibre optic coaxial components acting as filters in sensing and numerous other applications.