Continuously Adjustable Cylindrical Vector and Vortex Beams by Programming Vortex Half-Wave Plates and Detection Based on Coaxial or Small-Angle Interference

Using an all-fiber mode selective coupler (MSC) at the visible band, here we experimentally demonstrate a generating and wavelength multiplexing scheme for the cylindrical vector (CV) and vortex beams (VBs). The proposed MSCs act as efficient mode converters to produce spectrally insensitive high-order modes (HOMs) at the wavelength ranging from 450 to 980 nm, which have broad operation bandwidth (more than 7 nm), high mode conversion efficiency (94%), and purity (98%), and low insert loss (below 0.5 dB). By adjusting the polarization state and the phase shift of linear polarization (LP)11 mode respectively, the donut-shaped CVs and circular-polarization VBs are achieved. The focused intensity distribution of the donut beam on the cross- and axial-sections is monitored by using a confocal system. The all-fiber solution of producing and multiplexing HOMs opens a new route for stimulated emission depletion microscopy applications.

The pulsed 1.7 µm vortex beams (VBs) has significant research prospects in the fields of imaging and material processing. We experimentally demonstrate the generation of sub-200 fs pulsed VBs at 1.7 µm based on a home-made mode-selective coupler (MSC). Through dispersion management technology in a thulium-doped fiber laser, the stable linearly polarized VBs pulse directly emitting from the cavity is measured to be 186 fs with central wavelength of 1721.2 nm. By controlling the linear superposition of LP11 modes, cylindrical vector beams (CVBs) can also be obtained. In addition, a variety of bound states pulsed VBs at 1.7 µm can also be observed. Our finding provides an effective way to generate ultrashort pulsed VBs and CVBs at 1.7 µm waveband.

We present a simple and convenient method to yield cylindrical vector (CV) beams and realize its polarization evolution on higher-order Poincaré sphere based on inhomogeneous birefringent metasurface. By means of local polarization transformation of the metasurface, it is possible to convert a light beam with homogeneous elliptical polarization into a vector beam with any desired polarization distribution. The Stokes parameters of the output light are measured to verify our scheme, which show well agreement with the theoretical prediction. Our method may provide a convenient way to generate CV beams, which is expected to have potential applications in encoding information and quantum computation.

The use of vortex laser beams has increased in various areas of optics and photonics, necessitating enhanced beam quality for wide usage. In the field of high-power lasers, a range of methods to implement vortex laser beams has been proposed. Nonetheless, enhancing beam quality becomes more challenging as the laser power increases. This study presents the successful implementation of a high-quality, high-intensity vortex laser beam exceeding 1020W/cm2—an essential advancement for enhancing the performance and applicability of high-power lasers. We achieved this by integrating a spiral phase mirror (SPM) with an orbital angular momentum of l=1, specially designed for the vortex beam, along with an adaptive optical system, into a 150-TW femtosecond Ti:sapphire laser. Importantly, SPM, featuring a modulation structure to correct for a 45° incidence angle, was utilized to produce the vortex beam. The adaptive optical system, comprising a Shack–Hartmann wavefront sensor and a deformable mirror, employed a feedback loop to correct wavefront aberrations distorting the vortex beam. Notably, the negligible difference between the Hartmanngrams of the Gaussian and vortex beams (l=1) allowed the Gaussian beam’s Hartmanngram to serve effectively as the input reference for wavefront correction, resulting in a successfully corrected vortex beam wavefront. Experimental results, both pre- and post-wavefront correction, were compared with simulation results obtained via field-tracing. The peak intensity of the focused high-quality vortex laser beam ultimately reached 1.8×1020W/cm2, exceeding previously reported experimental results. The results of this study could significantly contribute to the exploration of high-intensity angular momentum transfer in relativistic laser-plasma interactions.

Optical misalignment between transmitter and receiver leads to power loss and mode crosstalk in a mode division multiplexing (MDM) free-space optical (FSO) link. We report both numerical simulations and experimental results on the propagation performance of two typical vector beams, C-point polarization full Poincaré beams (FPB), and V-point polarization cylindrical vector beams (CVB), compared to homogeneous polarization scalar vortex beams (SVB) under optical misalignment. The FSO communication performance under misalignment using different transmit beams is evaluated in terms of power loss, mode crosstalk, power penalty, etc. Vector beams are shown to have superior misalignment tolerance compared to the corresponding SVBs, with the FPBs in particular being the most robust for small topological charges. At the same mode spacing, the CVBs have a larger misalignment tolerance, which causes the MDM-FSO communication systems with narrower mode spacing to have a smaller power penalty. Furthermore, moderately increasing the transmitted beam size could improve the system tolerance of lateral displacement while reducing that of tilt error.

In this work, the second harmonic (SH) of higher-order Poincaré sphere (HOPS) beam was introduced and demonstrated with two orthogonal 5%MgO:PPLN crystals. Based on the quasi-phase-matching technique, the vectorial coupled wave equations were derived to simulate the SH of HOPS beams through the two crystals, including the cylindrical vector beams (CVBs), elliptically polarized CVBs (EPCVBs), and circularly polarized vortex beams. Then, the experimental setup was established to reveal that the SH of CVBs and EPCVBs present the four-lobed structure and still exhibit vector characteristics. Meanwhile, the circularly polarized vortex beams become the linearly polarized vortex beams with double phase topology, confirming the conservation of orbital angular momentum. Moreover, the maximum SH conversion efficiency of CVBs, EPCVBs, and circularly polarized vortex beams can reach 25.3%, 23.4%, and 29.4%, respectively, which may be instructive for promoting the SH generation of vector vortex beams with high efficiency.

A 1645 nm end-pumped dual-channel Er:YAG vector laser that could generate two cylindrical vector (CV) beams simultaneously with different polarization orders is demonstrated. The laser is designed in a two-arm structure, wherein each arm places a q-plate (QP) to introduce intra-cavity spin-orbital angular momentum conversion, leading to the oscillation of two various CV modes in two arms, and finally output along two directions, respectively. The favorable experimental results illustrate high power stability and polarization mode purity. Furthermore, an additional setup is built to demonstrate the potential of the proposed dual-channel CV laser in data transmission. By placing additional acousto-optic modulators, the output dual CV modes are encoded to represent different digital symbols and achieve successful data transmission in free space.

Traditional optics usually studies the uniform polarization state of light. Compared with uniform vector beams, non-uniform vector beams have more polarization information. Most of the research on generating cylindrical vector beams using metasurfaces focuses on generating transmitted beams using the geometric phase. However, the geometric phase requires the incident light to be circularly polarized, which limits the design freedom. Here, an all-dielectric reflective metasurface is designed to generate different output light according to the different polarization states of the incident light. By combining the two encoding arrangements of the dynamic phase and the geometric phase, the output light is a radial vector beam when the linearly polarized light is incident along the x-direction. Under the incidence of linearly polarized light along the y-direction, the generated output light is an azimuthal vector beam. Under the incidence of left-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of -1. Under the incidence of right-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of +1. The proposed reflective metasurface has potential applications in generating vector beams with high integration.

Beams with spatially‐varying polarization states have been the topic of much interest recently due to the unusual ways in which they can interact with matter. Cylindrical vector beams (CVBs) represent the most commonly used type and feature cylindrically‐symmetric polarization distributions. The optical systems employed thus far for their generation have usually only been able to produce a single CVB. To generate and observe multiple CVBs, bulky optical systems with stringent alignment tolerances have been needed. Here, a method to generate an array of CVBs using a single optical element, namely a transmission‐mode dielectric metasurface, is demonstrated. The incident light is split into an array of left and right‐handed circularly polarized vortex beams that superpose with a controllable phase difference. An array of CVBs with 12 channels over a broad wavelength range is experimentally demonstrated. This study's method produces a significant increase in the number of polarization channels compared to previous reports and solves the long‐standing challenge of unequal intensity distributions. It furthermore improves the flexibility of the vector field control by not only generating CVBs of different orders but also controlling their polarization rotation. This method may pave the way for applications in optical communications, laser machining, and optical trapping.

We propose a chip-integratable cylindrical vector (CV) beam generator by integrating six plasmonic split ring resonators (SRRs) on a planar photonic crystal (PPC) cavity. The employed PPC cavity is formed by cutting six adjacent air holes in the PPC center, which could generate a CV beam with azimuthally symmetric polarizations. By further integrating six SRRs on the structure defects of the PPC cavity, the polarizations of the CV beam could be tailored by controlling the opening angles of the SRRs, e.g., from azimuthal to radial symmetry. The mechanism is governed by the coupling between the resonance modes in SRRs and PPC cavity, which modifies the far-field radiation of the resonance mode of the PPC cavity with the SRR as the nano-antenna. The integration of SRRs also increases the coupling of the generated CV beam with the free-space optics, such as an objective lens, promising its further applications in optical communication, optical tweezer, imaging, etc.

Cylindrical vector beams (CVBs), characterized by their spatially non-uniform but rotationally symmetric polarization distributions, have garnered considerable attention due to their unique properties. In this Letter, we demonstrate the generation of cylindrical vector beams directly from a Yb-doped Mamyshev oscillator (MO). Both the radially and azimuthally polarized vector beams are achieved with a pulse duration of 3.6 ps and a pulse energy of 8.2 nJ at the repetition rate of 15.25 MHz. We also find that the filtered linearly polarized beam from the output CVBs can be homogeneously dechirped to 114 fs using the external grating pairs, indicating the potential intracavity pulse compression capability for the output CVBs. Simultaneously, ultrafast scalar Gaussian beams can also be obtained from another arm. These results can give insights into the experimental design and realization of high-energy and high-power structured (CVB or vortex) ultrashort lasers.

We present a method for achieving the cylindrical vector beams (CVBs) and optical vortex generation in a solid-core ring fiber (SCRF) by using an acoustically induced fiber grating (AIFG). Theoretical analysis shows that the SCRF can introduce a refractive index difference of ~10-5 between the first group of adjacent high-order degenerate vector modes. In the experiment, the transmission spectra of AIFG constructed with the SCRF depicts three separate resonance peaks with 3-dB bandwidth and resonance wavelength interval of 0.16 and 2.5 nm, respectively, revealing that the high-order degenerate vector modes have been effectively separated. On the basis of the separation of the degenerate vector mode, the CVBs and the ±1-order optical vortex are further experimentally generated at three separate wavelengths using the AIFG.

CVBs (cylindrical vector beams) are widely used in optical imaging, optical trapping, material processing, etc. In this study, based on mode-selective couplers and passive mode-locking fiber technology, a cylindrical vector fiber amplifier with an MOPA (master oscillator power amplifier) structure was developed. In the experiment, the pre-amp stage reached 19.87 mW output power and a CVB output with a mode purity greater than 97%. The measured beam quality factor was M2 = 2.1. The CVB output power obtained by the first-amp stage was 152.4 mW, and the mode purity was greater than 92%. The measured beam quality factor was M2 = 1.99. The internal inhomogeneity and external effects of the isotropic LMA (large-mode-area) fiber led to a decrease in beam quality and mode purity. After amplification, the gain of the fundamental mode was higher and the power was greater, resulting in a greatly reduced mode purity. This CVB fiber amplifier yielded important research value in expanding the applications of high-power fiber lasers.

A practical direct-view scheme for generating arbitrary high-order cylindrical vector (HCV) beams by cascading vortex half-wave plates (VHPs) is presented. The combination of odd number 2n-1 VHPs for n≥1 can realize (m2n-1-m2n-2+…+m1)-order CV beams, in which m is the order number of VHP and the corresponding subscript 2n-1 represents the arrangement number of VHPs, and the cascading of even number 2n ones can obtain (m2n-m2n-1+…+m2-m1)-order CV beams. All 1-12 order CV beams, including the high-order anti-vortex CV (ACV) beams, are generated only by selectively cascading the VHPs with m=1, 3 and 8. The polarization properties of the generated HCV beams are investigated by measuring the corresponding Stokes parameters. It is experimentally demonstrated that arbitrary HCV beams are effectively achieved by the proposed method. The order numbers of CV beams can be greatly expanded by cascading limited types of VHPs.

Cylindrical vector beams (CVBs), which possess polarization distribution of rotational symmetry on the transverse plane, can be developed in many optical technologies. Conventional methods to generate CVBs contain redundant interferometers or need to switch among diverse elements, thus being inconvenient in applications containing multiple CVBs. Here we provide a passive polarization-selective device to substitute interferometers and simplify generation setup. It is accomplished by reversing topological charges of orbital angular momentum based on a polarization-selective Gouy phase. In the process, tunable input light is the only condition to generate a CVB with arbitrary topological charges. To cover both azimuthal and radial parameters of CVBs, we express the mapping between scalar Laguerre–Gaussian light on a basic Poincaré sphere and CVB on a high-order Poincaré sphere. The proposed device simplifies the generation of CVBs enormously and thus has potential in integrated devices for both quantum and classic optical experiments.