On-Chip Guiding of Higher-Order Orbital Angular Momentum Modes

Abstract

Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l-rotation symmetry can support the l-th order OAM mode. In order to mimic the rotational symmetry, we have proposed the waveguide structure of a cross-shaped core and designed a waveguide that can support OAM modes of ±1 and ±2 topological charges simultaneously at a wavelength of 1550 nm. Purity of the OAM modes guided in the designed waveguide has been assessed by numerically calculating their topological charges from the field distribution, which were close to the theoretical values. We also investigated the guiding of OAM modes of ±3 and ±4 topological charges in our proposed waveguide structure, which revealed the possibility of the separate guiding of those OAM modes with relatively lower purity.

Analysis of Bending-Induced Degradation of Orbital Angular Momentum Modes in Optical Fibers

“…where E even/odd represents a field profile of HE 21-even/odd , C e/o represent a power coupling ratio of HE 21-even/odd from a straight to a bend fibers, n bend,even/odd is an effective index of HE 21-even/odd in the bending region, and r b is a bending radius. To investigate the purity of the OAM mode after passing through a 90 • bending, we calculated a topological charge number from the field distribution of Equation 3 [16,17], which is plotted as a function of a bending radius in Figure 6. The VF and the RCF show serious OAM mode purity degradation for bending radii smaller than~15 and~45 mm, respectively.…”

Recent Advances in Generation and Detection of Orbital Angular Momentum Optical Beams—A Review

“…To implement such an operating principle, not only functional methods are important, but also the features of the chosen PIC platform. The most common integrated photonics platforms which are used for in-plane OAM applications are based on Siliconon-Insulator (SOI) [161][162][163][164] and Silicon Nitride (SiN x ) [165][166][167]. Because of the low cost, the high material strength of Si and CMOS compatibility, PICs based on the Si platform are particularly well suited as a medium for integrating with other components.…”

“…The normalized intensity distribution, normalized amplitude distribution, and phase mapping of the leading E-field component are shown in Figure 11a-f [166]. In [163] SAM and OAM of light in silicon channel WGs was studied, where OV beam carrying OAM represented by a superposition of the TE 01 and TE 10 modes. Due to the transverse confinement, the SAM and OAM of the OV fields are strongly coupled and the whole space of structure variables of the WG can be separated just into three regimes.…”

“…Anyway, in-plane operation using higher-order OAM modes is a competitive field. [163], mode n eff reliance on WG parameters (f) [163]. Furthermore, the same group discovered that an OAM mode directional coupler with fabricable dimensions might be difficult to achieve with a rectangular WG and presented an on-chip device based on the cross-shaped WG structure [164].…”

“… HG-similar mode field allocations in the WG ( a – d ) [ 163 ], WG configuration for concurrently managing l = ±1 OAM mode and l = ±2 OAM mode ( e ) [ 163 ], mode n eff reliance on WG parameters ( f ) [ 163 ]. …”