Early Posting

Accepted papers to appear in an upcoming issue

Optica Publishing Group posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Dominated mode switching and nanoparticle detection at exceptional points

Zijie Wang, Xiaobei Zhang, Qi Zhang, Yiqi Chen, Yang Wang, Yang Yu, Yong Yang, and Tingyun Wang

DOI: 10.1364/JOSAB.473350 Received 22 Aug 2022; Accepted 22 Nov 2022; Posted 22 Nov 2022  View: PDF

Abstract: We present a theoretical investigation of dominated mode switching and nanoparticle detection at wavelength of 2 μm, which utilizes coupled whispering gallery mode (WGM) resonators operating at exceptional points (EPs). The simulations show that, with assists of gain and loss, the system can be steered to operate at EPs by adjusting the nanoparticles introduced backscattering. The unbalanced contributions of clockwise and counterclockwise mode can be observed when system approaches to EPs, and the dominated mode is switchable by transiting system from one EP to another. Owning to the square root topology of EPs, the enhanced frequency splitting can be obtained when system subjected to a perturbation, which results in a more than 5 times sensitivity enhancement compared with a traditional sensor. Furthermore, simulation also reveals that an increased gain-loss contrast of resonators contributes to an enhanced frequency splitting, and thus a higher sensitivity enhancement factor. Our investigations validate the feasibility of WGM resonator operating at EPs for unidirectional laser emitting and nanoparticle sensing.

Asymmetric Resonant Light Absorption in Chloroplast Microstructure

Pavel Pankin, Aleksandr Shabanov, Dmitrii Maksimov, Stepan Nabol, Daniil Buzin, Aleksey Krasnov, Gavriil Romanenko, Vitaly Sutormin, Vladimir Gunyakov, Fyodor Zelenov, Albert Masyugin, Vladimir Vyatkin, Ivan Nemtsev, Mikhail Volochaev, Stepan Vetrov, and Ivan Timofeev

DOI: 10.1364/JOSAB.477110 Received 30 Sep 2022; Accepted 20 Nov 2022; Posted 21 Nov 2022  View: PDF

Abstract: It is shown that, in the chloroplast periodic structure with adefect, the resonant absorption of light can be implemented. It isfound that the resonant light absorption depends significantly onthe position of a defect. In terms of the absorption of light energy,an asymmetric resonator is more efficient than a symmetric one.

Flat Bands and Quasi-Bound States in the Continuum in a Photonic Moiré Lattice

Ran Hao, Ibrahim Nasidi, and Erping Li

DOI: 10.1364/JOSAB.475563 Received 12 Sep 2022; Accepted 16 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: This paper proposes flat bands and quasi-bound states in the continuum (BIC) in a moiré lattice. In addition to the inter-layer coupling and small rotation angle, we show that the inter-node coupling at a large constant rotation angle in a single-layer moiré lattice can be controlled to obtain moiré flat bands. Unlike any flat bands reported in lattices such as kagome, rhombus, Lieb, and stub, we show that moiré lattice exhibit both singular and non-singular flat bands simultaneously. We investigate the flat band’s eigenmodes to confirm their flatness and assess their singularity. The robustness of the flat bands to variation of background permittivity is studied. Moreover, by further controlling the inter-node distance, the moiré flat band states change to a bound state at a non-zero wave-vector. The quasi-BIC exhibit an ultra-high quality factor of 2.7142e+6 , ultra-low mode volume of 0.214318μm3 and very narrow linewidth centered at 350.54THz . We show the capability of the quasi-BIC for lasing and nanocavity applications. Our results show that a single-layer photonic moiré lattice provides a suitable platform to explore fundamental phenomena related to flat band systems.

Design and modeling of quantum emitters embedded in dynamically tunable devices coupled with nano-antennas at visible wavelengths

Achiles da Mota and Hossein Mosallaei

DOI: 10.1364/JOSAB.476746 Received 28 Sep 2022; Accepted 15 Nov 2022; Posted 16 Nov 2022  View: PDF

Abstract: Gated tunable materials-based devices have proven efficient structures to dynamically control quantum emitters' (QEs) photonic density of states (PDoS). The active permittivity control enabled by these materials allows controlling the coupling and dissipation of evanescent modes radiated by the QE, hence controlling the emission parameters. In this sense, we propose here the design and optimization of a plasmonic device coupled with nano-antennas capable of dynamically manipulating the QEs emission at visible wavelengths using a thin gated doped TiN layer. We explore the use of metallic cubic and bowtie antennas and study their unique characteristics related to enhancing the QE's emission. For the nano-antenna geometrical parameters optimization, we propose a discrete-dipole-approximation (DDA) method to accurately calculate all the radiation parameters of a QE embedded in a layered medium coupled to a nano-antenna. This technique allows calculating the decay behavior of QEs arbitrarily distributed, which is only feasible with knowledge of the Purcell factor and quantum efficiency mapped for all possible positions, which is easily achieved with the proposed model. We show that by employing the proposed DDA, the time required for optimizing and building those maps to evaluate the device's response is drastically reduced (98%) compared to conventional numerical techniques. Using the DDA to optimize the antenna allowed the device's quantum efficiency to be enhanced from 1.8% (no nano-antenna) to 8% and 10.5% using the cubic and bowtie nano-antenna, respectively. In addition, the nano-antenna helps decrease the QE lifetime by a factor of approximately 2, allowing faster modulation speeds. Finally, our modeling and findings can be used to pave the way for the design of new gated optical modulators coupled with nano-antennas for applications that require amplitude modulation.

Theoretical analysis of quantum key distribution systems when integrated with a DWDM optical transport network

Irina Vorontsova, Roman Goncharov, Angelina Tarabrina, Fedor Kiselev, and Vladimir Egorov

DOI: 10.1364/JOSAB.469933 Received 07 Jul 2022; Accepted 12 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: A theoretical research and numerical simulation of the noise influence caused by spontaneous Raman scattering, four-wave mixing, and linear channel crosstalk on the performance of QKD systems was conducted. Three types of QKD systems were considered: coherent one-way (COW) QKD protocol, subcarrier-wave (SCW) QKD system, and continuous-variable (CV) QKD integrated with classical DWDM channels. We calculate the secure key generation rate for the systems mentioned addressing different channel allocation schemes (i.e., configurations). A uniform DWDM grid is considered with quantum channel located in C-band and O-band (at 1310 nm) of a telecommunication window. The systems' performance is analyzed in terms of the maximal achievable distance values. Configurations for the further analysis and investigation are chosen optimally, i.e., their maximal achievable distances are the best.

Bidirectional remote hyperstate preparation under commonquantum control using hyperentanglement

Cao Bich and Nguyen Ba An

DOI: 10.1364/JOSAB.471680 Received 26 Jul 2022; Accepted 11 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: In this paper, we propose a new protocol enabling two distantparties to prepare for each other a photon hyperstate encoded at the sametime in both polarization and spatial-mode degrees of freedom. Thebidirectional remote hyperstate preparation is demanded so that it isremotely controllable by a common supervisor. Such task appears possible byusing a shared quantum channel made of five photons entangled simultaneouslyin the two corresponding degrees of freedom, the so-calledhyperentanglement. We first design a near-deterministic scheme to produce arelevant five-photon hyperentanagled state to be served as the workingnonlocal channel and then present our protocol for controlled bidirectionalremote hyperstate preparation which always succeeds.

Fast Metasurface Hybrid Lens Design using a Semi-Analytical Model

Alexandre Cléroux Cuillerier, Jeck Borne, and Simon Thibault

DOI: 10.1364/JOSAB.468691 Received 23 Jun 2022; Accepted 10 Nov 2022; Posted 14 Nov 2022  View: PDF

Abstract: We propose a new method for integrating metasurfaces in optical design using semi-analytical modelling of dielectric nanostructures. The latter computes the output phase of an electric field incident on the metasurface, allowing their use with ray-tracing software. This tool provides a method to use metasurfaces in optical systems while using built-in optimization processes to avoid time-consuming computation. To demonstrate the applicability and versatility of our method, we present variations of a triplet composed of refractive elements and a metasurface. For each of the systems, similar optical performances are achieved. Our unique and innovative approach to joining metasurfaces and ray tracing has the potential to promote the design of innovative systems by exploiting the richness of metasurfaces and the functionality of conventional lens design software.

Unidirectional efficient hybrid coupler for integrated single-photon sources

Miaomiao Xu, Tingting Zhai, Zhaohua Tian, Xuewen Chen, and Rafael Salas-Montiel

DOI: 10.1364/JOSAB.473664 Received 19 Aug 2022; Accepted 09 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: Hybrid integrated quantum photonic circuits possess the potential to scale up the number of quantum nodes with distributed quantum-information-processing units at affordable resources. One of the key requirements is to achieve high-efficiency and unidirectional coupling of single quantum emitters into the low loss dielectric photonic waveguide modes. Plasmonic waveguides have the capability to have high coupling efficiency due to enhanced light-matter interactions. However, they suffer from significant propagation losses. Here we design and numerically demonstrate an on-chip hybrid plasmonic-photonic integrated single-photon source that enhances the emission rate of quantum emitters and possess unidirectional emission to a waveguide with high coupling efficiency. Currently, the emission rate of the single emitter is enhanced by a factor of 20 and the coupling efficiency from the single emitter into the photonic circuit exceeds 70%. The integrated hybrid single-photon source could find applications in quantum information technologies.

A PCF Sensor Coated with Au-Graphene /Mxene for Low Refractive Index and Wide Detection Range Detection

Yuhang Wu, Tao Shen, Feng Yue, Chi Liu, Xin Liu, and Shaofeng Wang

DOI: 10.1364/JOSAB.469247 Received 29 Jun 2022; Accepted 09 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: A photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) for detecting low refractive index (RI) and wide detection range is proposed and analyzed by full vector finite element method. The PCF is designed as a polishing construction and contains three different sizes of air holes. The Au and protective layer are coated on the grinding and polishing surface. The unique physical structure enables the sensor to detect trace substances. The sensor works in the near-infrared and mid-infrared bands. When Au-Graphene is used, the refractive index (RI) detection range is 1.11-1.31, the maximum wavelength sensitivity is 18600 nm/RIU, the maximum resolution is 5.38×10-6, and the linearity reaches 0.990 . At the same time, MXene(2D-Ti3C2) is applied to PCF-SPR sensor for the first time. When Au-MXene is used, the refractive index (RI) detection range is 1.25-1.32, the maximum wavelength sensitivity is improved to 22000 nm/RIU, and the maximum resolution is 4.55×10-6. Because of its high sensitivity and wide detection range at low refractive index, this sensor provides a promising method for drug detection, water pollution monitoring, aerosol concentration and optical film detection.

Graphene-based integrated plasmonic sensor with application in biomolecules detection

Vahid Ahmadi, Mohammad Javad Haji Najafi Chemerkouh, Bita Saadatmand, and Seyyedeh Mehri Hamidi

DOI: 10.1364/JOSAB.472734 Received 08 Aug 2022; Accepted 08 Nov 2022; Posted 10 Nov 2022  View: PDF

Abstract: Despite the existence of many techniques for detecting biomolecules, many efforts are being made to improve their performance. One of the new fields that have attracted the attention of researchers is the use of graphene-based surface plasmon resonance (SPR), a real-time and label-free technique. In this paper, to excite surface plasmon resonance, we use a low-cost one-dimensional grating extracted from DVD without any lithography process for phase matching. In addition, to improve the performance of the graphene-based SPR sensors after describing the plasmonic response, we use the surface plasmon enhanced by ellipsometric modeling as a strong and sensitive characterization method. The study of the delta parameter leads to a significant improvement in sensitivity and minimum detectable concentration. The response of the delta parameter to variation in miRNA-21 concentration indicates that a slight change in miRNA-21 concentration, about 30 fM, leads to a significant change in phase or the delta parameter; as a result, the proposed method can be used to measure the very small concentration of biomolecules. The results show that if appropriate complementary bioreceptors for the target’s biomolecules are used, the proposed sensor is attractive for use in biodetection.

Ultrabroadband second harmonic generation based on dispersion-engineered LNOI waveguide

Chi Zhang, XIAOHUI TIAN, Hua-Ying Liu, Jiachen Duan, Kunpeng Jia, Zhenda Xie, and Shining Zhu

DOI: 10.1364/JOSAB.469916 Received 06 Jul 2022; Accepted 07 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: Second harmonic generation (SHG) is widely used for wavelength conversions in various applications including multi-wavelength laser, imaging and ultrafast optics. However, it remains a long-standing challenge to achieve both broad SHG bandwidth and high efficiency due to the medium dispersion. Here, we propose an ultrabroadband efficient SHG in lithium niobate on insulator (LNOI) platform by dispersion engineering. The geometric shape of waveguide cross-section is carefully designed to minimize the first- and second-order dispersion of lithium niobate, which is feasible for current fabrication technique. Thanks to the flattened dispersion, record-high bandwidth-length product (Δλ·L) of 2444 μm² is achieved in a periodically poled 1.64-cm-long LNOI waveguide. The bandwidth is broadened by over 140 times compared to conventional LNOI ridge waveguide, without sacrificing absolute SHG efficiency. Such scheme can also be generalized to SHG waveguides in other material platforms. Our results provide a new strategy for dispersion engineering, and may be helpful for applications including frequency doubling, supercontinuum generation and optical frequency comb.

Analysis of infrared nanojets with self-focusing nonlinearities

RAGIB SHAKIL RAFI and Alessandro Salandrino

DOI: 10.1364/JOSAB.471456 Received 25 Jul 2022; Accepted 07 Nov 2022; Posted 07 Nov 2022  View: PDF

Abstract: We present a numerical study of the linear and nonlinear diffraction and focusing properties of dielectric metasurfaces consisting of silicon microcylinder arrays resting on a silicon substrate. Upon diffraction, such structures lead to the formation of near–field intensity profiles that are reminiscent of photonic nanojets and propagate in a similar fashion. The generation and propagation of these photonic jets was analyzed under high intensity mid–infrared illumination conditions for which the third order optical nonlinearity of silicon leads to pronounced self–focusing effects. The illumination wavelength of 3388nm was selected to be below the two–photon absorption edge. Our results indicate that the Kerr nonlinear effect enhances light concentration throughout the generated photonic jet with an increase in intensity of about 20% compared to the linear regime for the power levels considered in this work. In all cases, the transverse beamwidth remains subwavelength, and the nonlinear effect reduces the full width half maximum (FWHM) size by 100 nm for both electric field intensity and longitudinal Poynting vector.

2D Spot Size Converter Using Multilevel Asymmetric Coupler MAC Structure for Si Photonics Planar Technology

Salwa El-Sabban and Diaa Khalil

DOI: 10.1364/JOSAB.474004 Received 24 Aug 2022; Accepted 06 Nov 2022; Posted 08 Nov 2022  View: PDF

Abstract: In this work, we present a new architecture for the design of integrated optical spot size converter using planar technology. The proposed architecture is based on the use of multilevel planar structures without using vertical tapers. The function of the vertical taper is replaced by a horizontal taper and a Multilevel Asymmetric Coupler MAC structure. The proposed technique is applied for the coupling between a single mode fiber of core diameter 8.2 m to a Silica over silicon waveguide with 2 m x 4 m cross section with a coupling efficiency greater than 98% without the need of a vertical coupler. The coupling transformation of the spot of the standard Si photonics waveguide with 500 nm x 220 nm to the fundamental mode of a waveguide of 1 m x 1 m is also demonstrated with a coupling efficiency greater than 92%. This technique gives a very high flexibility in the coupling between different waveguides with different cross sections.

Time evolution characteristics of spectrum and temperature of lightning discharge plasma

Hong Deng, Ping Yuan, Tingting An, Ruibin Wan, Xin Huang, Wangsheng Wang, Guorong Liu, Jun Jiang, and Xueqiang Gou

DOI: 10.1364/JOSAB.475278 Received 08 Sep 2022; Accepted 03 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: Temperature is one of the crucial parameters reflecting the energy and current transfer characteristics in lightning discharge plasma channel. According to the spectra of six lightning return strokes discharge recorded simultaneously by two high-speed slit-less spectrographs with different time resolutions, the spectral intensity and temperature evolution of the plasma channels over time was quantitatively analyzed. The spectral characteristics show that the ionic line intensity decayed rapidly with time as the current declined, while the atomic line intensity decreased more slowly. Additionally, it is found that the ionic lines existed for much longer time than previously reported values, up to hundreds of microseconds in the spectra of continuing current process. It further indicates that the ionic line intensities are associated with the discharge currents and that their radiation mechanism is closely related to the collision excitation under the action of strong currents. The temperature calculated by the ionic lines can reflect the thermodynamic properties of the current-carrying channel. The temperature calculated using atomic lines is significantly lower than that calculated by the ionic lines in the same spectrum. The radiation mechanism for majority of the atomic lines differs from that of the ionic lines. During the continuing current, the channel temperatures calculated by both ionic lines and atomic lines showed a similar evolution feature which declined slowly or even basically unchanged. This property reflects the persistent heating effect of the current.

Discrete Talbot effect in reciprocal and nonreciprocal dimer lattices

Kaiyun Zhan, Xinyue Kang, Qian Zhang, Qixuan Chen, Tingjun Zhao, Lichao Dou, and Bing Liu

DOI: 10.1364/JOSAB.476207 Received 21 Sep 2022; Accepted 03 Nov 2022; Posted 03 Nov 2022  View: PDF

Abstract: We investigate the Talbot self-imaging in one-dimensional discrete dimer lattice, where the source of non-Hermiticity derives not from gain and loss but from anisotropic couplings. The conditions that guarantee the existence of Talbot effect in discrete dimer lattice are defined. It is shown that Talbot self-imaging effect is possible in both reciprocal (Hermitian) and nonreciprocal (non-Hermitian) dimer lattices when the period of input pattern is chosen as a finite set of periodicities (N = 1, 2, 3, 4 for reciprocal lattice and N = 1, 2 for nonreciprocal lattice). Unlike the PT-symmetric Talbot effect in discrete lattice, where the self-imaging with conserved total energy occurs during propagation, here the total energy of the field exhibits oscillatory behavior in the Talbot process for the nonreciprocal dimer lattices. The Talbot distance can be controlled by adjusting the lattice coupling and anisotropic coupling coefficients. Our results can be extended to other photonic superlattice with arbitrary number of sites in each unit cell.

Isotope selective three-step photoionization of 174Yb

Manda Suryanarayana and Manda Sankari

DOI: 10.1364/JOSAB.476224 Received 30 Sep 2022; Accepted 03 Nov 2022; Posted 04 Nov 2022  View: PDF

Abstract: A three-step photoionization scheme has been theoretically studied for the laser isotope separation of 174Yb from natural Yb using density matrix formalism. The effects of bandwidth and peak power density of lasers; Doppler broadening, number density of atoms on the degree of enrichment and production rate have been studied and the optimum conditions for the efficient separation of 174Yb have been derived. It has been shown that it is possible to enrich 174Yb isotope up to ~90% using lasers with a bandwidth of 500 MHz with a production rate up to 48 mg / hour. On the whole, the system required for the laser isotope separation of 174Yb is much simpler than that is required for the separation of any of the 176Lu, 177Lu and 176Yb isotopes. One gram of enriched isotope mixture upon irradiation in widely available low flux reactors produces 107 doses (7.4 GBq each) of 175Yb radionuclide for PRRT with 98.6% radionuclidic purity. It is envisaged that the production of 175Yb isotope through this route will be economical and widely available to the public at large as PRRT drug for cancer therapy.

Modelling of mode-locked fibre lasers and amplifiers with accurate saturable gain evaluation

Bhaswar Dutta Gupta, Ian Hendry, Stanley Tang, Thibaud Berthelot, Paul Du Teilleul, Solenn Cozic, Samuel Poulain, Miro Erkintalo, and Claude Aguergaray

DOI: 10.1364/JOSAB.476097 Received 19 Sep 2022; Accepted 27 Oct 2022; Posted 27 Oct 2022  View: PDF

Abstract: We present a numerical model for mode-locked lasers and ultrafast nonlinear amplifiers in which the saturated gain profile along active fibres are judiciously computed using experimental pump powers as input. This eliminates the need for approximating the gain profile by using small-signal gain coefficient and saturation energy to simulate pulse propagation in active fibres. Our model shows good agreement with experiments involving mode-locked cavities at 1 μm with silica glass host doped with Ytterbium ions. Accurate results are also obtained for continuous wave and mode-locked laser cavities around 2.8 μm which uses ZBLAN fibre doped with Erbium ions. In the case of Er:ZBLAN fibre, we use the model to show regions of stable mode-locking delivering single pulse as output and how the spectral width changes with variation in doping concentration and fibre lengths. Our model enables accurate numerical modelling of mode-locked fibre lasers and ultrafast amplifiers, and can be useful in guiding the design of new architectures, understand the complex intracavity laser dynamics, or optimise device output.

Enhanced higher order modulational instability in Parity-Time symmetric Fiber Bragg Grating system with modified saturable nonlinearity

P Mohanraj, Paramananda Padhi, and R Sivakumar

DOI: 10.1364/JOSAB.471171 Received 20 Jul 2022; Accepted 27 Oct 2022; Posted 02 Nov 2022  View: PDF

Abstract: With the use of cubic, quintic, and septic nonlinearities, we will demonstrate the influence of modified nonlinear saturation on modulational instability (MI) in a nonlinear complex parity-time (PT) symmetric fibre Bragg grating (FBG) structure. Using a modified coupled nonlinear Schrodinger equation and linear stability analysis, we were able to develop a dispersion relation for instability gain spectra in a complicated PT-symmetric system. Our main aim is to examine the MI in non-Kerr nonlinearities with nonlinear saturation in three different PT-symmetric regimes: below threshold point, at threshold point (breaking point), and above threshold point. The occurrence of MI is discovered to be problematic at the PT-symmetry threshold point in a standard FBG structure (A.K.Sharma 2014), but MI can exist in the normal group velocity dispersion domain when the modified nonlinear saturation effect is used. With the help of a modified form of saturable nonlinearity, we discovered that MI can exist in all three regimes in a complex PT-symmetric FBG structure. In anomalous group velocity dispersion alone, we discovered bi-stability behavior in a PT-symmetric FBG structure with higher order saturable nonlinearity. In the presence of modified nonlinear saturation effect and higher-order non-Kerr nonlinearities, we found a novel type of dynamics in the PT-symmetry FBG structure. All alterations in the photonic device bandgap are a direct result of changes in the medium's refractive index caused by the interaction of PT-symmetric potential with superior nonlinearity such as cubic-quintic-septic and modified form of nonlinear saturation. As a result, we provide new approaches for generating and managing the MI in a complex PT-symmetric FBG structure under the influence of the modified nonlinear saturation effect in this paper.

Quantum signatures in a quadratic optomechanical heat engine with an atom in a tapered trap

Mohsen Izadyari, Mehmet Öncü, kadir durak, and Ozgur Mustecaplioglu

DOI: 10.1364/JOSAB.472901 Received 11 Aug 2022; Accepted 24 Oct 2022; Posted 02 Nov 2022  View: PDF

Abstract: We investigate how quantum signatures can emerge in a single atom heat engine consisting of an atom confined in a tapered trap and subject to hot and cold thermal reservoirs. A similar system was realized experimentally in Ref. [1]. We model such a system using a quadratic optomechanical model and identify an effective Otto cycle in the system’s dynamics. We compare the engine’s performance in the quantum and classical regimes by evaluating the power dissipated.We find that lowering the temperature is insufficient to make the single atom engine of Ref. [1] a genuine quantum-enhanced heat engine. We show that it is necessary to make the trap more asymmetric and confined to ensure that quantum correlations cause an enhancement in the poweroutput.

Effect of the linear potential on the RIFS of Airy pulses

Li Mengjiao and Wang yan

DOI: 10.1364/JOSAB.468903 Received 24 Jun 2022; Accepted 22 Oct 2022; Posted 26 Oct 2022  View: PDF

Abstract: The dynamics of finite energy Airy pulse (FEAP) under the nonlinear Schrödinger equation with the higher-order effects, including third-order dispersive (TOD), self-steepening (SS), Raman scattering and in presence of the linear potential is investigated. The linear potential, which can control the trajectory of FEAP and leads to a monotonous spectrum shift has been introduced as a unique technique to manipulate the RIFS of the FEAP. The results show that the TOD and SS coefficients have a limited impact on the RIFS of the pulse. The RIFS is adjusted effectively with the linear potential and can be enhanced obviously with the increase of the linear potential strength.

Polarized grating transition radiation from a 2D photonic crystal

Daria Sergeeva, Damir Garaev, and Alexey Tishchenko

DOI: 10.1364/JOSAB.471124 Received 20 Jul 2022; Accepted 21 Oct 2022; Posted 26 Oct 2022  View: PDF

Abstract: Transition radiation (TR) is widely used as a radiation source in a wide spectral range, from THz to X-rays. Conventional flat surfaces are usually used, but with the development of applications using microscopically structured surfaces, periodic surface structures are beginning to be studied. The periodicity of the surface dramatically changes the characteristics of TR, so this type of radiation received its own name: grating transition radiation (GTR). In this work, we investigate the polarization properties of GTR from a two-dimensional photonic crystal consisting of small particles arranged in a flat lattice (a 2D photonic crystal slab). We show theoretically that the polarization properties of GTR differ significantly from those of the kindred types of radiation: conventional TR and Smith-Purcell radiation. Since we found that the asymptotic behavior depending on the electrons velocity for GTR and classical TR diverges, we performed homogenization and show that the results for GTR after homogenization are in perfect agreement with those for classical TR. This means that different dependence on the electrons velocity for TR from a slab and for GTR from a 2D photonic crystal slab is caused by the fundamental difference between a conventional slab and a 2D photonic crystal due to its microscopic structure. The constructed theory contains the coordinates of the particles the photonic crystal consists of, which allows considering structures of finite size, both symmetrical and asymmetric. For asymmetric targets, the polarization of the radiation proves to be very sensitive to the electrons trajectory. This sensibility of polarization characteristics opens up good opportunities for studying fine fundamental effects connected with the electron trajectory, such as the effect of quantum nature of free electrons which manifests itself in the properties of radiation generated by free electrons. Also, the obtained results may find application in the design of compact sources of polarized radiation based on microscopically structured surfaces.

Dual-functional polarization converter of all-dielectric metasurface with chiral L-type meta-atom

YiXing Song, Jianing Zhai, Shuang Huo, Yong Zeng, and X Sun

DOI: 10.1364/JOSAB.472101 Received 11 Aug 2022; Accepted 21 Oct 2022; Posted 28 Oct 2022  View: PDF

Abstract: We propose a dual-function metasurface with chiral double L-type silicon meta-atom that works in the near-infrared band. On the one hand, the designed metasurface can achieve the function of quarter-wave plate (QWP) in the wavelength of 1660nm1840nm, and convert y-linearly polarization (YLP) light into right-hand circularly polarization (RCP) light. The polarization conversion ratio (PCR) is above 90% up to 98% and the ellipticity of the transmitted light is 0.91.0. On the other hand, for the wavelength 1497nm the designed structure can also convert LP in any direction to left-hand circularly polarization (LCP) light by using circular dichroism of chiral structures. And the PCR is above 99%, the ellipticity of the transmitted light is approximately equal to -1. Moreover, when incident in the opposite direction, the wave plate can convert LP to RCP light. At present, the all-dielectric metasurface has important application potential in the polarization conversion and photonic integration.

Statistical parameters of femtosecond laser pulse post-filament propagation on 65m air path with localized optical turbulence

Dmitry Apeksimov, Andrey Bulygin, Yuri Geints, Andrey Kabanov, Elena Khoroshaeva, and alexei petrov

DOI: 10.1364/JOSAB.473298 Received 16 Aug 2022; Accepted 18 Oct 2022; Posted 19 Oct 2022  View: PDF

Abstract: High-power femtosecond laser radiation propagates nonlinearly in air exhibiting pulse self-focusing and strong multiphoton medium ionization, which leads to the spatial fragmentation of laser pulse into highly-localized light channels commonly called the filaments. The filaments are characterized by high optical intensity, reduced (even zero) angular spreading and can contain laser plasma or be plasmaless (postfilaments). The presence of optical turbulence on the propagation path dramatically changes pulse filamentation dynamics and in some cases causes pulse fragmentation enhancement and collapse arrest. For the first time to our knowledge, we experimentally and theoretically investigate the transverse profile of Ti:sapphire femtosecond laser radiation nonlinearly propagating a 65 m air path to the region of postfilament evolution after passing through an artificial localized air turbulence. We show that when a turbulent layer is placed before the filamentation region, the average number of high-intensive local fluence maxima (“hot points”) in pulse profile as well as their sizes grow as the turbulence strength increases, and then saturates at some levels. On the contrary, the deposition of a turbulent screen within the filamentation region has almost no effect on both the number and the average diameter of the postfilaments.

Near-Perfect Ultra-Broadband Metal-Free Ultrathin THz Absorber

GAURAV VARSHNEY, Ravi Gupta, and Ajay Sharma

DOI: 10.1364/JOSAB.469203 Received 30 Jun 2022; Accepted 14 Oct 2022; Posted 02 Nov 2022  View: PDF

Abstract: An ultrathin metal-free terahertz (THz) absorber is implemented and numerically analyzed. The absorber structure with rectangular graphite resonator is designed to operate with the fundamental magnetic resonance in the lower ang higher order magnetic resonance in the upper band. Carving the slots in the graphite resonator converts the magnetic resonance into the electric resonance at the upper frequency and merges both the resonance spectra. The proposed absorber provides the near-perfect flat broadband absorption more than 99% in the frequency range 7.28-11.21 THz. Furthermore, the absorber provides the absorption more than 90% and 80% in the frequency range 6.26-13.05 THz and 5.69-14.25 THz, respectively. The absorber structure utilizes a graphite-based resonator and back-reflecting plane and provides the polarization insensitive response with the allowed incidence angle of more than 20° with the absorption more than 99%. The absorber response is validated through transmission line method-based equivalent electrical circuit. Moreover, the reliability of the implemented absorber for its usage in electromagnetic shields and stealth applications is calculated in terms of shielding effectiveness which remains high in range of 50 to 250 dB.

Compressed Sensing in Photonics: A Tutorial

Velat Kilic, Trac Tran, and Mark Foster

DOI: 10.1364/JOSAB.469865 Received 12 Jul 2022; Accepted 04 Oct 2022; Posted 07 Oct 2022  View: PDF

Abstract: Traditional optical imaging and sensing methods capture signals of interest by direct sampling in the domain of interest such as by forming images on pixelated camera sensors or by regular temporal sampling of a waveform. These methods are indispensable in our daily lives and for many scientific disciplines such as microscopy in biology and spectroscopy in chemistry. Using these approaches, sampling constraints and their impact on the bounds on signal fidelity are well understood through the Nyquist-Shannon sampling theorem. However, the problems of modern science require ever increasing amounts of data at unprecedented temporal and spatial scales and resolutions, which challenges the limits of traditional sensing. The increased availability of computational power combined with recent strides in signal processing promise to surpass many of the problems associated with traditional sensing methods through computational imaging and sensing methods. Within the realm of computational sensing, compressed sensing, in particular, has enabled the capture of signals with lower sampling resources than traditionally required by the Nyquist-Shannon sampling theorem. In this tutorial, we focus on the operation and impact of such sub-Nyquist sampling schemes through the use of compressed sensing in photonic sensing and imaging systems. Emphasis is placed on intuition but mathematical results are derived or cited where appropriate. Finally, we highlight several applications in macroscopic imaging, microscopy, spectroscopy, hyperspectral imaging, endoscopy, optical coherence tomography, ultrahigh-speed imaging and RF (radio frequency) sensing.