Orbital angular momentum vector modes (de)multiplexer based on multimode micro-ring

On-chip ultracompact multimode vortex beam emitter based on vertical modes

Free-space orbital angular momentum (OAM) communication is considered as one of the potential alternative on-chip optical interconnect solutions. The number of OAM modes determines the capacity of high-speed communication. However, existing integrated vortex beam emitters have a constraint relationship between the number of OAM modes and the emitter size, rendering it difficult to emit more OAM modes with a small-sized emitter. In view of the above, this study proposes an on-chip ultracompact multimode vortex beam emitter based on vertical modes, which permits more OAM modes without requiring an increase in the size of the emitter. Vertical modes in large-aspect-ratio waveguides are pointed out to enable multimode microrings with small radii because high-order vertical modes can maintain almost the same horizontal wave vector as that of the fundamental mode. Four-mode and five-mode vortex beam emitters with the same radius of 1.5 µm are designed and the effectiveness of these emitters is verified through simulation. Furthermore, a high-efficiency and low-crosstalk approach for high-order vertical mode coupling by varying the waveguide height is presented. This research not only promotes further integration of on-chip optical interconnection, but also provides a new strategy for optical waveguide mode selection in photonic integrated circuits design.

Compact and high Q-factor multimode racetrack ring resonator based on transformation optics

The ring resonator is a versatile and functional component in the silicon-based integrated optical circuit. Most of the previously reported ring resonators work in the single-mode case. With the rapid development of mode division multiplexing technology, a multimode ring resonator (MMRR) has been proposed and the usage beyond the limit of a conventional single mode ring resonator has been explored. However, the reported MMRRs are either large in size or low in quality factor. In this paper, we designed a compact silicon MMRR with a small bending radius of 15µm, in which the three lowest TE modes all have high Q-factors. For suppressing the mode loss and inter-mode crosstalk in MMRR, a multimode waveguide bend (MWB) with mode adiabatic evolution was designed based on transformation optics and waveguide shape optimization. The independent excitation of each order mode of the MMRR is realized by using bending directional coupler and asymmetric directional coupler. We successfully fabricated the device on a silicon-on-insulator (SOI) platform using simple one-step lithography. The measured loaded Q-factors of the three lowest TE modes are 5.9 × 10⁴, 4.5 × 10⁴, and 4.7 × 10⁴, respectively.

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

Herein, we have discussed three major methods which have been generally employed for the generation of optical beams with orbital angular momentum (OAM). These methods include the practice of diffractive optics elements (DOEs), metasurfaces (MSs), and photonic integrated circuits (PICs) for the production of in-plane and out-of-plane OAM. This topic has been significantly evolved as a result; these three methods have been further implemented efficiently by different novel approaches which are discussed as well. Furthermore, development in the OAM detection techniques has also been presented. We have tried our best to bring novel and up-to-date information to the readers on this interesting and widely investigated topic.

On-chip generation of the reconfigurable orbital angular momentum with high order

In this manuscript, the generation of an optical vortex beam with high order and reconfigurable orbital angular momentum (OAM) is studied. Multi-waveguide holographic gratings (MWHG) are deployed to generate OAM beams with high order. The generation of the OAM beam with an order l from +4 to +8 is demonstrated by numerical simulations, and the generated OAM order is manipulable and configurable by incident phase. The working bandwidths of the MWHG for different OAM orders are at the level of 40 nm. This work could provide valuable references for practical implementation of OAM in integrated optics.