Abstract
The objective of this work is to develop a near-infrared laser device capable of emitting orbital angular momentum (OAM) light. The prototyped device must be suitable for compact, energy-saving optical communication applications. Integrated OAM lasers would revolutionize high capacity data transmission over any telecommunication network environment as OAM light can be guided and transmitted through kilometers of optical fibers as well as propagated in free space and underwater.
Several methods for generating OAM light, employing various complex monolithic and hybrid integration methods have been demonstrated. In this work, micro-scale integrated spiral phase plates (SPPs) are chosen to convert the laser beam output into an OAM mode. The concept and design fundamentals of SPPs are discussed, followed by the SPP fabrication process and their implementation in a high-speed communication setup, and integration with a semiconductor laser.
Spiral phase plates are fabricated by the novel direct laser writing that provides the possibility to rapidly prototype three-dimensional photonic structures via a two-photon polymerization process. After the fabrication, SPPs are used in a fine-tuned free-space optical experimental setup that requires high-precision inter-component adjustment capability to test the high-speed OAM communication system and analyze the quality of OAM modes, reporting high-purity OAM beams at data rates up to 1.8 Gbit/s – limited by the avalanche photodetector (APD) frequency response. The fabricated 20‑µm-diameter SPPs were the smallest reported in the literature to date for optical characterization.
A proof-of-concept monolithic light-emitting arrays as a highly integrated OAM laser source is further proposed for telecommunications and other applications. SPP-integrated 940‑nm vertical-cavity surface-emitting laser (VCSEL) array chips are developed that are relatively low-cost, small footprint, and manufacturable in high volumes. SPPs with topological charge modulus values from 1 to 3 are fabricated on the VCSEL arrays, demonstrating OAM modal purities up to ~65%. The experimentally evaluated data rates in the OAM setup showed consistently stable links up to 2.0 Gbit/s with a bit error ratio of $\sim1.6\times10^{-8}$ (APD-limited). The challenges of SPP-laser integration are summarized, and it is concluded that wide-spread adoption of OAM is limited by the availability of practical integrated solutions for OAM generation and detection.
Brief Biography
Edgars Stegenburgs is a Ph.D. candidate in Electrical and Computer Engineering (ECE) at the KAUST Photonics Laboratory. He received an M.Sc. degree in ECE from KAUST in 2016 and a B.Sc. degree in Physics from the University of Latvia in 2014. He has served as the Vice President of the OSA-KAUST Student Chapter, and he is a student member of OSA, IEEE, and SPIE professional associations. His primary research interests include the design, fabrication, and characterization of optoelectronic semiconductor devices, including lasers, LEDs, photodetectors, and novel structures, for solid-state lighting, telecommunication, and integrated photonics applications. Before joining KAUST, he worked in the Laser Centre of the University of Latvia as a natural sciences laboratory assistant under the supervision of Dr. Aigars Ekers in the Laser-manipulation Laboratory, focusing on light-matter interaction, manipulation of light, and laser cooling of atoms.