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.
<p>In this work, using investigation of odd order OAM modes in the two-dimensional MMI waveguides, a novel integrated optical OAM device is introduced to do mode conversion between beams carrying OAM with opposite topological charges. The proposed convertor is passive and the input and output ports can be swapped. The ability to produce high purity output mode (94% and 82% for OAM modes with <em>l</em>=±1 and <em>l</em>=±3, respectively), reciprocal behavior and compatibility with silicon on insulator technology are the remarkable features that make the proposed passive convertor utilizable in many classical and quantum communication systems. </p>
<p>In this work, using investigation of odd order OAM modes in the two-dimensional MMI waveguides, a novel integrated optical OAM device is introduced to do mode conversion between beams carrying OAM with opposite topological charges. The proposed convertor is passive and the input and output ports can be swapped. The ability to produce high purity output mode (94% and 82% for OAM modes with <em>l</em>=±1 and <em>l</em>=±3, respectively), reciprocal behavior and compatibility with silicon on insulator technology are the remarkable features that make the proposed passive convertor utilizable in many classical and quantum communication systems. </p>
Recently, the implementation of rectangular waveguides for generation and manipulation of orbital angular momentum (OAM) modes, has been developed to exploit the outstanding features of these modes in more complex integrated devices. Multimode interference (MMI) structures have been widely used in both one and two dimensions as the basic elements in many integrated optical devices like optical beam splitters, mode converters, couplers, wavelength-division (de)multiplexers, and switches. According to the various applications of OAM modes in quantum and classical communications, the study of their propagation properties in MMI waveguides is useful in order to facilitate the way into higher security and capacity systems. In this work, mode conversion between beams carrying OAM with opposite topological charges in the two-dimensional (2D) MMI waveguides is investigated. In this investigation, the OAM modes with odd topological charges are considered. Using the self-imaging properties of MMI structures, an integrated device including two MMI waveguides connected by phase shifters and linear waveguides is designed. The design procedure is performed for OAM modes with topological charge values of l=±1 and l=±3 using beam propagation method. The proposed device is passive with reciprocal behavior and has the output mode purity of 94% and 82% for beams carrying l=±1 and l=±3, respectively.
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