### Focal beam structuring by triple mixing of optical vortex lattices

Author(s):

Stoyanov, Lyubomir; Maleshkov, Georgi; Stefanov, Ivan; Paulus, Gerhard G. & Dreischuh, Alexander

Abstract:

“On-demand generation and reshaping of arrays of focused laser beams is highly desired in many areas of science and technology. In this work, we present a versatile approach for laser beam structuring in the focal plane of a lens by triple mixing of square and/or hexagonal optical vortex lattices (OVLs). In the artificial far field the input Gaussian beam is reshaped into ordered arrays of bright beams with flat phase profiles. This is remarkable, since the bright focal peaks are surrounded by hundreds of OVs with their dark cores and two-dimensional phase dislocations. Numerical simulations and experimental evidences for this are shown, including a broad discussion of some of the possible scenarios for such mixing: triple mixing of square-shaped OVLs, triple mixing of hexagonal OVLs, as well as the two combined cases of mixing square-hexagonal-hexagonal and square-square-hexagonal OVLs. The particular ordering of the input phase distributions of the OV lattices on the used spatial light modulators is found to affect the orientation of the structures ruled by the hexagonal OVL. Reliable control parameters for the creation of the desired focal beam structures are the respective lattice node spacings. The presented approach is flexible, easily realizable by using a single spatial light modulator, and thus accessible in many laboratories.”

Publication: Optical and Quantum Electronics
Issue/Year: Optical and Quantum Electronics, Volume 54; Number 1; 2021
DOI: 10.1007/s11082-021-03399-5

### 768-ary Laguerre-Gaussian-mode shift keying free-space optical communication based on convolutional neural networks

Author(s):

Luan, Haitao; Lin, Dajun; Li, Keyao; Meng, Weijia; Gu, Min & Fang, Xinyuan

Abstract:

“Beyond orbital angular momentum of Laguerre-Gaussian (LG) modes, the radial index can also be exploited as information channel in free-space optical (FSO) communication to extend the communication capacity, resulting in the LG- shift keying (LG-SK) FSO communications. However, the recognition of radial index is critical and tough when the superposed high-order LG modes are disturbed by the atmospheric turbulences (ATs). In this paper, the convolutional neural network (CNN) is utilized to recognize both the azimuthal and radial index of superposed LG modes. We experimentally demonstrate the application of CNN model in a 10-meter 768-ary LG-SK FSO communication system at the AT $$C^2_n= 10^{-14}m^{-\frac{2}{3}}$$. Based on the high recognition accuracy of the CNN model (>95%) in the scheme, a colorful image can be transmitted and the peak signal-to-noise ratio of the received image can exceed 35 dB. We anticipate that our results can stimulate further researches on the utilization of the potential applications of LG modes with non-zero radial index based on the artificial-intelligence-enhanced optoelectronic systems.”

Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 13; Pages 19807; 2021
DOI: 10.1364/oe.420176

### Reconfigurable generation of double-ring perfect vortex beam

Author(s):

Du, Yafei; Liu, Deming; Fu, Songnian; Wang, Yuncai & Qin, Yuwen

Abstract:

“Perfect vortex beam (PVB), whose ring radius is independent of its topological charge, play an important role in optical trapping and optical communication. Here, we experimentally demonstrate the reconfigurable double-ring PVB (DR-PVB) generation with independent manipulations of the amplitude, the radius, the width, and the topological charge for each ring. Based on complex amplitude modulation (CAM) with a phase-only spatial light modulator (SLM), we successfully verify the proposed DR-PVB generation scheme via the computer-generated hologram. Furthermore, we carry out a quantitative characterization for the generated DR-PVB, in terms of both the generation quality and the generation efficiency. The correlation coefficients of various reconfigurable DR-PVBs are above 0.8, together with the highest generation efficiency of 44%. We believe that, the proposed generation scheme of reconfigurable DR-PVB is desired for applications in both optical tweezers and orbital angular momentum (OAM) multiplexing.”

Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 11; Pages 17353; 2021
DOI: 10.1364/oe.424664

### Hologram generation via Hilbert transform

Author(s):

Tomoyoshi Shimobaba, Takashi Kakue, Yota Yamamoto, Ikuo Hoshi, Harutaka Shiomi, Takashi Nishitsuji, Naoki Takada, and Tomoyoshi Ito

Abstract:

“We propose an indirect method for generating a complex hologram and phase-only hologram from an amplitude hologram using the Hilbert transform. The Hilbert transform generates an imaginary part of complex amplitude from only an amplitude hologram, resulting in the reduction of the total computational complexity of complex and phase-only holograms. More importantly, the proposed method can reduce the hardware resources of dedicated hologram processors.”

Publication: OSA Continuum
Issue/Year: Vol. 3, Issue 6, pp. 1498-1503 (2020)
DOI: 10.1364/OSAC.395003

### Polarization nano-tomography of tightly focused light landscapes by self-assembled monolayers

Author(s):

Eileen Otte, Kemal Tekce, Sebastian Lamping, Bart Jan Ravoo and Cornelia Denz
Abstract:

“Recently, four-dimensional (4D) functional nano-materials have attracted considerable attention due to their impact in cutting-edge fields such as nano-(opto)electronics, -biotechnology or -biomedicine. Prominent optical functionalizations, representing the fourth dimension, require precisely tailored light fields for its optimal implementation. These fields need to be like-wise 4D, i.e., nano-structured in three-dimensional (3D) space while polarization embeds additional longitudinal components. Though a couple of approaches to realize 4D fields have been suggested, their breakthrough is impeded by a lack of appropriate analysis techniques. Combining molecular self-assembly, i.e., nano-chemistry, and nano-optics, we propose a polarization nano-tomography of respective fields using the functional material itself as a sensor. Our method allows a single-shot identification of non-paraxial light fields at nano-scale resolution without any data post-processing. We prove its functionality numerically and experimentally, elucidating its amplitude, phase and 3D polarization sensitivity. We analyze non-paraxial field properties, demonstrating our method’s capability and potential for next generation 4D materials.”

Publication: Nature Communications
Issue/Year: Nature Communications volume 10, Article number: 4308 (2019)
DOI: 10.1038/s41467-019-12127-3

### Three-dimensional vectorial multifocal arrays created by pseudo-period encoding

Author(s):

Tingting Zeng and Chenliang Chang and Zhaozhong Chen and Hui-Tian Wang and Jianping Ding

Abstract:

“Multifocal arrays have been attracting considerable attention recently owing to their potential applications in parallel optical tweezers, parallel single-molecule orientation determination, parallel recording and multifocal multiphoton microscopy. However, the generation of vectorial multifocal arrays with a tailorable structure and polarization state remains a great challenge, and reports on multifocal arrays have hitherto been restricted either to scalar focal spots without polarization versatility or to regular arrays with fixed spacing. In this work, we propose a specific pseudo-period encoding technique to create three-dimensional (3D) vectorial multifocal arrays with the ability to manipulate the position, polarization state and intensity of each focal spot. We experimentally validated the flexibility of our approach in the generation of 3D vectorial multiple spots with polarization multiplicity and position tunability.”

Publication: Journal of Optics
Issue/Year: Journal of Optics, Volume 20, Number 6
DOI: 10.1088/2040-8986/aac1de

### Demonstration of a vectorial optical field generator with adaptive close loop control

Author(s):

Jian Chen and Lingjiang Kong and Qiwen Zhan

Abstract:

“We experimentally demonstrate a vectorial optical field generator (VOF-Gen) with an adaptive close loop control. The close loop control capability is illustrated with the calibration of polarization modulation of the system. To calibrate the polarization ratio modulation, we generate 45° linearly polarized beam and make it propagate through a linear analyzer whose transmission axis is orthogonal to the incident beam. For the retardation calibration, circularly polarized beam is employed and a circular polarization analyzer with the opposite chirality is placed in front of the CCD as the detector. In both cases, the close loop control automatically changes the value of the corresponding calibration parameters in the pre-set ranges to generate the phase patterns applied to the spatial light modulators and records the intensity distribution of the output beam by the CCD camera. The optimized calibration parameters are determined corresponding to the minimum total intensity in each case. Several typical kinds of vectorial optical beams are created with and without the obtained calibration parameters, and the full Stokes parameter measurements are carried out to quantitatively analyze the polarization distribution of the generated beams. The comparisons among these results clearly show that the obtained calibration parameters could remarkably improve the accuracy of the polarization modulation of the VOF-Gen, especially for generating elliptically polarized beam with large ellipticity, indicating the significance of the presented close loop in enhancing the performance of the VOF-Gen.”

Publication: Review of Scientific Instruments
Issue/Year: Review of SCientific Instruments 88, 125111 (2017)
DOI: 10.1063/1.4999656

### Tailoring arbitrary hybrid Poincaré beams through a single hologram

Author(s):

Shiyao Fu and Yanwang Zhai and Tonglu Wang and Ci Yin and Chunqing Gao

Abstract:

“Hybrid Poincaré beams (HPBs) are a kind of structure field with anisotropic polarizations. Here, we demonstrate an approach to tailor HPBs with arbitrary states, through encoding a single hologram on a liquid-crystal display device along with a stable optical system. The state of the obtained HPB is determined only by the encoded holograms with special design, which means it is not necessary to adjust any optical elements or hardware when generating various HPB states. Moreover, perfect HPBs can also be generated through the proposed scheme. In the experiment, the obtained HPBs are analyzed through a polarizer and a special parameter S3/S0, showing good agreement with prediction. This work opens an insight in encoding single holograms for tailoring arbitrary HPBs and inspires various applications.”

Publication: Applied Physics Letters
Issue/Year: Applied Physics Letters Volume 111, Issue 21
DOI: 10.1063/1.5008954

### Tightly focused optical field with controllable photonic spin orientation

Author(s):

Jian Chen and Chenhao Wan and Ling Jiang Kong and Qiwen Zhan

Abstract:

“The spin angular momentum of photons offers a robust, scalable and highbandwidth toolbox for many promising applications based upon spin-controlled manipulations of light. In this work, we develop a method to achieve controllable photonic spin orientation within a diffraction limited optical focal spot produced by a high numerical aperture objective lens. The required pupil field is found analytically through reversing the radiation patterns from two electric dipoles located at the focal point of the lens with orthogonal oscillation directions and quadrature phase. The calculated pupil fields are experimentally generated with a vectorial optical field generator. The produced photonic spin orientations are quantitatively evaluated by their spin densities according to the tightly focused electric fields calculated by Richard-Wolf vectorial diffraction theory to demonstrate the validity and capability of the proposed technique.”

Publication: Optics Express
Issue/Year: Optics Express, Volume 25, Number 16 pp. 19517-19528 (2017)
DOI: 10.1364/OE.25.019517

### Characterization, design, and optimization of a two-pass twisted nematic liquid crystal spatial light modulator system for arbitrary complex modulation

Author(s):

A. J. Macfaden and T. D. Wilkinson

Abstract:

“Arbitrary two-dimensional complex modulation of an optical field is a powerful tool for coherent optical systems. No single spatial light modulator (SLM) offers true arbitrary complex modulation, but they can be combined in order to achieve this. In this work, two sides of a twisted nematic (TN) liquid crystal SLM are used sequentially to implement different arbitrary modulation schemes. In order to fully explore and exploit the rich modulation behavior offered by a TN device, a generalized Jones matrix approach is used. A method for in situ characterization of the SLM inside the two-pass system is demonstrated, where each side of the SLM is independently characterized. This characterization data is then used to design appropriate polarizer configurations to implement arbitrary complex modulation schemes (albeit without 100\% efficiency). Finally, an in situ optimization technique that corrects states by applying a translation in the complex plane is demonstrated. This technique can correct both for variations across the SLM and bulk changes in the SLM behavior due to the changing temperature.”