- The paper introduces a novel method that leverages momentum-space polarization vortices at BICs for efficient optical vortex generation.
- The technique simplifies fabrication and alignment by eliminating complex real-space resonators while achieving quasi-non-diffractive beam propagation.
- Experimental validation and theoretical modeling underscore its potential for long-distance optical communications and high-precision material processing.
Generating Optical Vortex Beams by Momentum-Space Polarization Vortices
The paper presents a novel approach for optical vortex (OV) generation, leveraging the unique characteristics of bound states in the continuum (BIC) in photonic crystal slabs. Optical vortices, which feature a spiral phase front and carry orbital angular momentum, have significant applications across numerous fields, including optical communications, micromanipulation, and quantum information. The method introduced in the paper stands apart by utilizing momentum-space polarization vortices, thus circumventing some of the practical challenges associated with real-space structures.
The authors explore the generation of OVs using photonic crystals with inherent topological structures in momentum space. Specifically, they focus on leveraging the Pancharatnam-Berry phase induced by polarization vortices centered at BICs to generate OVs. These polarization vortices arise naturally around BICs in two-dimensional photonic crystal slabs. This property allows for the simplification of OV generation since it obviates the need for complex, space-variant resonators in the real space.
Key findings of this work include the theoretical proposition and experimental realization of OVs through a novel class of generators that function in momentum space. Importantly, this means there is no tangible structure center to align with the incident beam, greatly easing both fabrication and alignment hurdles. The approach is versatile in that it can potentially generate any even-order OV as quasi-non-diffractive high-order Bessel beams. This significant feature presents practical advantages such as quasi-diffraction-free propagation.
The numerical results underscore the usefulness of the approach. In the experimental setup, transmission through a photonic crystal slab corresponds well with the theoretical predictions. Specifically, phase distribution measurements demonstrate topological charges that confirm the presence of winding behavior of polarization, validating the momentum-space topological nature of these modes.
Practical implications of this research are considerable. The generated beams' non-diffractive properties make them advantageous for long-distance communications and high-precision material processing. By operating in momentum space without a central reference for alignment, this method also offers robustness and ease of scalability across different wavelength ranges.
Theoretical impingements arise from expanding the application of momentum-space physics and topological photonics, enhancing understanding in both areas. The findings compliment studies in topological photonics by utilizing inherent topological characteristics to achieve novel beam profiles.
Future directions facilitated by this research include exploring further design variability, such as exploiting different symmetries to create higher-order vortices and investigating other materials suitable for various operational wavelengths. The methodology potentially extends to the design of compact laser systems exhibiting topological properties.
In summary, the presented work offers a robust method for OV generation through the understanding and manipulation of topological properties in momentum space, presenting a significant step forward in the efficiency and functionality of OV generation techniques.