We report, both in theory and experiment, on a novel kind of vortex symmetric Airy beam (VSAB) that exhibits elegant symmetric structure and autofocusing property. A general expression of the symmetric Airy beam (SAB) is derived first, and then VSAB is created by imposing a spiral phase into the initial SAB. Notably, we can tailor the structure and autofocusing behavior of VASB by embedding the vortex or vortices in an on or off-axis mode. Besides, multiple off-axis vortices projected into SAB are also investigated. This proposed VSAB will provide flexibility for optical manipulation and quantum communication.
Airy beam is a kind of wavepacket existing in the form of photons, electrons, and plasmonics. Well known as diffraction-free beam, optical Airy beam tends to accelerate in transverse space with a parabolic trajectory, and exhibits self-healing property when partially blocked. Those properties have attracted a great deal of research interests and applications. Circular Airy beam, exhibiting cylindrically symmetric intensity pattern and abruptly autofocusing characteristics in the linear media, is a variant of Airy-like wave. Optical vortex, on the other hand, is a kind of phase singularity. We present to shape the autofocusing Airy beam with a vortex phase structure, which was realized through the binary amplitude modulation with a digital micromirror device (DMD). Each mirror on the DMD could be electronically addressed to situate at either of the two solid positional states corresponding to on and off. Shaping the light into a specific mode requires the calculation of the amplitude pattern for display on the DMD. By reshaping individual DMD pixels into giant pixels, the complex field of the vortex Airy beam could be encoded with a super-pixel method. The propagation property of the vortex Airy beam was investigated through numerical simulation for different topological charges. Furthermore, the propagation characteristics of this beam in free space were verified and discussed through the experiments. We anticipate that the proposed vortex Airy beam in particle trapping, biological field and optical communications. This method with DMD can also be used to generate other beams with different characteristics.
The micromechanical digital micromirror device (DMD) performs as a spatial light modulator to shape the light wavefront. Different from the liquid crystal devices, which use the birefringence to modulate the light wave, the DMD regulates the wavefront through an amplitude modulation with the digitally controlled mirrors switched on and off. The advantages of such device are the fast speed, polarization insensitivity, and the broadband modulation ability. The fast switching ability for the DMD not only enables the shaping of static light mode, but also could dynamically compensate for the wavefront distortion due to scattering medium. We have employed such device to create the higher order modes, including the Laguerre-Gaussian, Hermite-Gaussian, as well as Mathieu modes. There exists another kind of beam with shape-preservation against propagation, and self-healing against obstacles. Representative modes are the Bessel modes, Airy modes, and the Pearcey modes. Since the DMD modulates the light intensity, a series of algorithms are developed to calculate proper amplitude hologram for shaping the light. The quasi-continuous gray scale images could imitate the continuous amplitude hologram, while the binary amplitude modulation is another means to create the modulation pattern for a steady light field. We demonstrate the generation of the non-diffracting beams with the binary amplitude modulation via the DMD, and successfully created the non-diffracting Bessel beam, Airy beam, and the Pearcey beam. We have characterized the non-diffracting modes through propagation measurements as well as the self-healing measurements.