Abstract
Compact vortex beam emitters have emerged as new light sources for novel applications in areas including spectroscopy, particle manipulation, and communications. Reported devices depend on linear optical phenomena and emit light in the near-infrared (IR) regime. Here, we propose and numerically evaluate a nonlinear vortex beam emitter that functions in the THz regime. The design utilizes a LiNbO3 microring, a Si microdisk, and an Au second-order top grating to convert waveguide-coupled IR light into a freely propagating THz beam via a difference-frequency generation. The output beam carries a topological charge that is tunable with input wavelengths. Three devices are evaluated in a test frequency range from 9 THz to 13.5 THz, and the topological charge can change from −2 to 4. A frequency shift accompanies the change in the topological charge, and its magnitude depends on the planar dimensions of the emitter.
Highlights
Light beams carrying orbital angular momentum (OAM), which are termed vortex or Laguerre–Gaussian light beams, have a helical phase front.[1]
We have demonstrated a THz vortex beam emitter via numerical simulation
The emitter consists of a LiNbO3 microring for difference-frequency generation, a Si microdisk for nearfield confinement of the generated THz, and an Au second-order top grating for the creation of a topological charge
Summary
Light beams carrying orbital angular momentum (OAM), which are termed vortex or Laguerre–Gaussian light beams, have a helical phase front.[1]. A unique property of the vortex light beams is that the topological charge can take a wide, theoretically unbounded range of integer and fractional numbers.[2] It allows for a wide variety of intriguing phase and intensity distributions that are unavailable to conventional Hermite–Gaussian light beams This property underpins a range of emerging applications including detection of magnetic excitation and enantiomers,[3,4] phase-contrast microscopy,[5] holographic optical manipulation,[6] and high-capacity optical data communications.[7,8]. The integration of photonics and THz research has witnessed the use of nano- and microstructures at every stage of THz generation, propagation, modulation, and detection.[20,21,22] This work demonstrates a new approach of the integration that allows for creating a tunable topological charge in the generation of THz light
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