Vortex mode transformation interferometry

Abstract

Whilst many techniques exist for generation of an optical vortex, there remains a need for new devices and methods that can also provide vortex generation with higher powers, greater flexibility of wavelength, and generation beyond the lowest-order Laguerre-Gaussian LG01 mode to address a broader range of practical applications. This work reveals how an all-mirror based interferometric mode transformation system can provide these properties including revealing, for the first time, the generation of a much richer set of vortex mode patterns than might have been thought possible previously. A new developed theoretical formulation, confirmed with excellent agreement by experimental demonstrations in an imbalanced Sagnac interferometer, shows interferometric transformation is possible for all orders of Laguerre-Gaussian LG0l modes into a rich set of high quality higher-order vortex and vortex superposition. The interferometric approach is shown to be configurable to increase or decrease vorticity. The new mathematical formulation provides the ability to perform a full modal power analysis of both the mode-transformed transmitted vortex and the complementary reflected beam at the Sagnac beamsplitter (BS) port. A discussion is made on the origin of the orbital angular momentum transferred to the vortex output from the Sagnac BS.