Numerical design of gradient-index beam shapers

Design methods are illustrated to produce beam shaping elements in which the refractive index is a continuous function of position. An index profile yielding a desired gradual transformation of the field can be computed in two ways. A ray theory approach yields a solution consistent with the eikonal equation, while diffraction effects can be incorporated into the index profile by using a split step representation of the medium and performing a series of phase retrieval calculations. The methods are demonstrated in an example of mode conversion and coherent laser beam combining, where a near-unity conversion efficiency can theoretically be achieved.