GRIN lens: a new element for complex vectorial beam modulation

Abstract

Graded index (GRIN) lenses focus light through a radially symmetric refractive index profile. It is not widely appreciated that the ion-exchange process that creates the index profile also causes a radially symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here we show that this birefringence can be harnessed as a basis of a versatile and expandable vectorial state manipulator. Using standard GRIN lenses in cascade with other optical components, we generate various states, including full Poincare beams that also contain orbital angular momentum. The combination of highly-symmetrical graded refractive index and corresponding birefringence – which benefit from the mature technology of the ion-exchange process – permit precise, simultaneous, phase and polarization modulation, which – when combined in a cascade structure with other elements – forms the basis for several applications. The non-pixelated nature of the birefringence of the lens, optical efficiency of the lens, and complex geometric phase inside the lens may also benefit future applications such as precision beam generation and quantum manipulation. All of these complex vectorial beam manipulations are achieved using off-the-shelf, inexpensive, passive optical components.