### Lensless Optical Encryption of Multilevel Digital Data Containers Using Spatially Incoherent Illumination

Author(s):

Cheremkhin, Pavel; Evtikhiev, Nikolay; Krasnov, Vitaly; Ryabcev, Ilya; Shifrina, Anna & Starikov, Rostislav

Abstract:

“The necessity of the correction of errors emerging during the optical encryption process ledto the extensive use of data containers such as QR codes. However, due to specifics of optical encryp-tion, QR codes are not very well suited for the task, which results in low error correction capabilitiesin optical experiments mainly due to easily breakable QR code’s service elements and byte datastructure. In this paper, we present optical implementation of information optical encryption systemutilizing new multilevel customizable digital data containers with high data density. The results ofoptical experiments demonstrate efficient error correction capabilities of the new data container.”

Publication: Applied Sciences
Issue/Year: Applied Sciences, Volume 12; Number 1; Pages 406; 2021
DOI: 10.3390/app12010406

### Recognizing fractional orbital angular momentum using feed forward neural network

Author(s):

Jing, Guoqing; Chen, Lizhen; Wang, Peipei; Xiong, Wenjie; Huang, Zebin; Liu, Junmin; Chen, Yu; Li, Ying; Fan, Dianyuan & Chen, Shuqing

Abstract:

“Fractional vortex beam (FVB) possessing helical phase can be applied in the shift-keying communication due to its fractional orbital angular momentum (FOAM) mode, which theoretically allows an infinite increase of the transmitted capacity. However, the discontinuity of spiral phase makes FVB more likely to be disturbed in turbulence environment, and the precise measurement of distorted FOAM modes is crucial for practical FOAM-based communication application. Here, we proposed a FOAM mode recognition method with feedforward neural network (FNN). Employing the diffraction preprocessing of a two-dimensional fork grating, the original optical features of FVBs can be extended along the far-field diffraction order, endowing FNN more feature information and saving calculation time, and enlarging the detection range to conjugate FOAM modes. The simulation results show that the 9-layer FNN can identify FOAM mode with interval of 0.1 with an accuracy of 99.1% under the turbulences of $$C^n_2=1×10^{–14}m^{–2/3}$$ and Δz=10m. Furthermore, we experimentally constructed a 102-ary FOAM shift-keying communication link to transmit gray image, and the signals are successfully demodulated by the FNN model with the pixel-error-rate of 0.07160. It is anticipated that the proposed FNN-based FOAM recognition method will break the limitation of precision measurement under turbulence environment in practical FOAM applications.”

Publication: Results in Physics
Issue/Year: Results in Physics, Volume 28; Pages 104619; 2021
DOI: 10.1016/j.rinp.2021.104619

### Experimental analysis of adaptive optics correction methods on the beam carrying orbital angular momentum mode through oceanic turbulence

Author(s):

Zhan, Haichao; Wang, Le; Wang, Wennai & Zhao, Shengmei

Abstract:

“In recent years, as the demand for underwater communication has increased, underwater wireless optical communication (UWOC) has attracted a lot of attentions. Meanwhile, orbital angular momentum (OAM) has been applied in UWOC system to increase communication link capacity. However, the aberrations caused by oceanic turbulence (OT) is unavoidable, which results in serious intermodal crosstalk. Usually, adaptive optics (AO) is used to compensate these distortion aberrations. In this work, we experimentally demonstrate the influence of the distortion caused by OT, and evaluate the performance of AO correction algorithms, including Shack-Hartmann (SH), Stochastic-Parallel-Gradient-Descent (SPGD) and Gerchberg-Saxton (GS) algorithms. During the experiment, OT is simulated by using improved random phase screen model. We discuss the influence of various parameters of OT, including relative strength of temperature and salinity, strength of OT , and propagation distance, on the compensation effect with and without correction algorithms. The results show that all the three AO algorithms have good compensation effect on the distortion caused by OT, and GS algorithm has a better capability than the other two algorithms. Additionally, when the iteration numbers is less than 100, the compensation effect of GS and SPGD algorithms becomes more obvious as the iteration numbers increases, and GS algorithm is superior to SPGD algorithm. This work is beneficial to aberration correction of OAM-based UWOC system.”

Publication: Optik
Issue/Year: Optik, Volume 240; Pages 166990; 2021
DOI: 10.1016/j.ijleo.2021.166990

### Quantum cryptography technique: A way to improve security challenges in mobile cloud computing (MCC)

Author(s):

Abidin, Shafiqul; Swami, Amit; Ramirez-As{‘{i}}s, Edwin; Alvarado-Tolentino, Joseph; Maurya, Rajesh Kumar & Hussain, Naziya

Abstract:

“Quantum cryptography concentrates on the solution of cryptography that is imperishable due to the reason of fortification of secrecy which is applied to the public key distribution of quantum. It is a very prominent technology in which 2 beings can securely communicate along with the sights belongings to quantum physics. However, on basis of classical level cryptography, the used encodes were bits for data. As quantum utilizes the photons or particles polarize ones for encoding the quantized property. This is presented in qubits as a unit. Transmissions depend directly on the inalienable mechanic’s law of quantum for security. This paper includes detailed insight into the three most used and appreciated quantum cryptography applications that are providing its domain-wide service in the field of mobile cloud computing. These services are (it) DARPA Network, (ii) IPSEC implementation, and (iii) the twisted light HD implementation along with quantum elements, key distribution, and protocols.”

Publication: Materials Today: Proceedings
Issue/Year: Materials Today: Proceedings, 2021
DOI: 10.1016/j.matpr.2021.05.593

### Orbital-Angular-Momentum-Controlled Hybrid Nanowire Circuit

Author(s):

Ren, Haoran; Wang, Xiaoxia; Li, Chenhao; He, Chenglin; Wang, Yixiong; Pan, Anlian & Maier, Stefan A.

Abstract:

“Plasmonic nanostructures can enable compact multiplexing of the orbital angular momentum (OAM) of light; however, strong dissipation of the highly localized OAM-distinct plasmonic fields in the near-field region hinders on-chip OAM transmission and processing. Superior transmission efficiency is offered by semiconductor nanowires sustaining highly confined optical modes, but only the polarization degree of freedom has been utilized for their selective excitation. Here we demonstrate that incident OAM beams can selectively excite single-crystalline cadmium sulfide (CdS) nanowires through coupling OAM-distinct plasmonic fields into nanowire waveguides for long-distance transportation. This allows us to build an OAM-controlled hybrid nanowire circuit for optical logic operations including AND and OR gates. In addition, this circuit enables the on-chip photoluminescence readout of OAM-encrypted information. Our results open exciting new avenues not only for nanowire photonics to develop OAM-controlled optical switches, logic gates, and modulators but also for OAM photonics to build ultracompact photonic circuits for information processing.”

Publication: Nano Letters
Issue/Year: Nano Letters, Volume 21; Number 14; Pages 6220–6227; 2021
DOI: 10.1021/acs.nanolett.1c01979

### Programmable 147 Tb/s (92 Gb/s xhspace0.167em16) optical wireless broadcasting system empowered by a single spatial light modulator and a modified RSS algorithm

Author(s):

You, Quan; Li, Chao; Xiao, Xi & Yu, Shaohua

Abstract:

“We have proposed and experimentally demonstrated a programmable multi-access-point optical wireless broadcasting system with ±15° field-of-view by employing a single spatial light modulator (SLM) and a modified rotated-splitting-SLM algorithm. The 16 access points are generated and arbitrarily distributed by the proposed continuous tunable broadcasting algorithm. The optical beams for each point carry 92-Gb/s PAM-4 optical signal and transmitted over 1 km standard single mode fiber and 1.2 m indoor free space distance, offering a total wireless capacity beyond 1.47 Tb/s. The measured results show that the proposed multi-access-points transmission system with ultra-high transmission capacity and reconfigurability can be used for future indoor wireless mobile networks.”

Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 13; Pages 19373; 2021
DOI: 10.1364/oe.428752

### Flexible rotation of transverse optical field for 2D self-accelerating beams with a designated trajectory

Author(s):

Li, Zongtao; Cao, Kai; Li, Jiasheng; Tang, Yong; Ding, Xinrui & Yu, Binhai

Abstract:

“Self-accelerating beams have the unusual ability to remain diffraction-free while undergo the transverse shift during the free-space propagation. We theoretically identify that the transverse optical field distribution of 2D self-accelerating beam is determined by the selection of the transverse Cartesian coordinates, when the caustic method is utilized for its trajectory design. Based on the coordinate-rotation method, we experimentally demonstrate a scheme to flexibly manipulate the rotation of transverse optical field for 2D self-accelerating beams under the condition of a designated trajectory. With this scheme, the transverse optical field can be rotated within a range of 90 degrees, especially when the trajectory of 2D self-accelerating beams needs to be maintained for free-space photonic interconnection.”

Issue/Year: Opto-Electronic Advances, Volume 4; Number 3; Pages 20002101–20002115; 2021
DOI: 10.29026/oea.2021.200021

### Non-diffracting and self-accelerating Bessel beams with on-demand tailored intensity profiles along arbitrary trajectories

Author(s):

Yan, Wenxiang; Gao, Yuan; Yuan, Zheng; Wang, Zhuang; Ren, Zhi-Cheng; Wang, Xi-Lin; Ding, Jianping & Wang, Hui-Tian

Abstract:

“Owing to their robustness against diffraction, Bessel beams (BBs) offer special advantages in various applications. To enhance their applicability, we present a method to generate self-accelerating zeroth-order BBs along predefined trajectories with tunable z-direction intensity profiles. The character of tunable direction intensity profiles in non-diffracting self-accelerating BBs potentially can attract interest in the regimes of particle manipulation, microfabrication, and free-space optical interconnects.”

Publication: Optics Letters
Issue/Year: Optics Letters, Volume 46; Number 7; Pages 1494; 2021
DOI: 10.1364/ol.418928

Author(s):

Na, Youngbin & Ko, Do-Kyeong

Abstract:

“Structured light with spatial degrees of freedom (DoF) is considered a potential solution to address the unprecedented demand for data traffic, but there is a limit to effectively improving the communication capacity by its integer quantization. We propose a data transmission system using fractional mode encoding and deep-learning decoding. Spatial modes of Bessel-Gaussian beams separated by fractional intervals are employed to represent 8-bit symbols. Data encoded by switching phase holograms is efficiently decoded by a deep-learning classifier that only requires the intensity profile of transmitted modes. Our results show that the trained model can simultaneously recognize two independent DoF without any mode sorter and precisely detect small differences between fractional modes. Moreover, the proposed scheme successfully achieves image transmission despite its densely packed mode space. This research will present a new approach to realizing higher data rates for advanced optical communication systems.”

Publication: Scientific Reports
Issue/Year: Scientific Reports, Volume 11; Number 1; 2021
DOI: 10.1038/s41598-021-82239-8

### Optical vortex with multi-fractional orders

Author(s):

Juntao Hu, Yuping Tai, Liuhao Zhu, Zixu Long, Miaomiao Tang, Hehe Li, Xinzhong Li and Yangjian Cai

Abstract:

“Recently, optical vortices (OVs) have attracted substantial attention because they can provide an additional degree of freedom, i.e., orbital angular momentum (OAM). It is well known that the fractional OV (FOV) is interpreted as a weighted superposition of a series of integer OVs containing different OAM states. However, methods for controlling the sampling interval of the OAM state decomposition and determining the selected sampling OAM state are lacking. To address this issue, in this Letter, we propose a FOV by inserting multiple fractional phase jumps into whole phase jumps (2π), termed as a multi-fractional OV (MFOV). The MFOV is a generalized FOV possessing three adjustable parameters, including the number of azimuthal phase periods (APPs), N; the number of whole phase jumps in an APP, K; and the fractional phase jump, α. The results show that the intensity and OAM of the MFOV are shaped into different polygons based on the APP number. Through OAM state decomposition and OAM entropy techniques, we find that the MFOV is constructed by sparse sampling of the OAM states, with the sampling interval equal to N. Moreover, the probability of each sampling state is determined by the parameter α, and the state order of the maximal probability is controlled by the parameter K, as K * N. This work presents a clear physical interpretation of the FOV, which deepens our understanding of the FOV and facilitates potential applications, especially for multiplexing technology in optical communication based on OAM.
This work was supported by the National Natural Science Foundation of China (NSFC) (Nos. 11974102, 11525418, 91750201, and 11974218), the Open Research Fund of State Key Laboratory of Transient Optics and Photonics, CAS (No. SKLST201901), the Innovation Group of Jinan under Grant No. 2018GXRC010, and the National key Research and Development Project of China (2019YFA0705000).”