Abstract
Orbital angular momentum (OAM) multiplexing has emerged as an important method to increase the communication capacities in future optical information technologies. In this work, we demonstrate a silicon integrated OAM (de)multiplexer with a very simple structure. By simply tapping the evanescent wave of two different whispering gallery modes rotating inside a multimodal micro-ring resonator, four in-plane waveguide modes are converted to four free-space vector OAM beams with high mode purity. We further demonstrate chip-to-chip OAM multiplexing transmission using a pair of silicon devices, which shows low-level mode crosstalk and favorable link performance.
Highlights
Spatial degree of freedom has attracted much attention for multiplexing information channel in addition to the time, wavelength and polarization dimensions [1]
There have been several approached to the use of orbital angular momentum (OAM) mode basis for mode-division multiplexing (MDM) communications in optical fibre
The device parameters of themultiplexer are carefully designed using finite difference time-domain (FDTD) method to make the resonances of TE0 and TE1 whispering gallery modes (WGMs) coincide at the target wavelength λc, as shown in Fig. 2(a).The two access waveguides are configured in a so-called “pulley-coupling” scheme [18,19,20], in which the waveguides wrap around the micro-ring resonator to form bent directional couplers (see Fig. 1(a))
Summary
Spatial degree of freedom has attracted much attention for multiplexing information channel in addition to the time, wavelength and polarization dimensions [1]. A more elegant solution is based on a device referred to as an OAM mode sorter [9,10,11], which can be used to (de)multiplex OAM modes with low crosstalk, and more importantly, does not experience the 1/N insertion loss that occurs during cascaded beam splitting It still relies on large-scale (bulk) optical elements, which are vulnerable to even tiny changes in alignment. To achieve good device performance, coupling through the micro-ring must be designed to minimize the power that is coupled to the undesired WGM mode as well as to minimize the insertion loss for the desired mode This can be done by optimizing the coupling gap and the bending angle of the bent directional couplers. According to the principle of reciprocity, this device can be used as a demultiplexer (DEMUX) that receives 4 specific OAM states and separates them into different waveguides according to their phase structures [23]
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