Investigating orbital angular momentum modes in multimode interference waveguides and revealing their mode conversion property

Abstract Orbital angular momentum (OAM) modes of light have aroused a widespread interest in quantum and classical communications.Their various integrated photonics applications require devices and circuits for miniaturization, improved performance, andadvanced performance. Accordingly, in this work, the propagation of OAM modes in multimode interference (MMI) waveguidesas the basic elements in many integrated optical devices is studied to utilize their benefits in integrated OAM applications.OAM modes shape the field-splitting and OAM-maintaining images at the specific lengths of an MMI waveguide. As the mosteffective parameters on the properties of these generated images, width of the MMI waveguide, topological charge (l) and waistradius of the OAM modes are investigated. Power overlap integral (POI) and mode purity are used to evaluate the quality ofimages. The investigations show that the images produced in wider waveguides are purer (up to 92.43%). Furthermore, for thehigher order of OAM modes (|l| > 1), the higher values of POI could be achievable by enlarging the width of the waveguides (up to 93.93% for l = ±6 and 81.6% for l = ±7). It is also demonstrated that mode conversion between even order of OAM modeswith opposite topological charges can occur at OAM-maintaining length of the MMI waveguides which is the most outstandingachievement of this survey for optical communication systems.