Gaussian Mode Research Articles

Security analysis for a mutually partially unbiased bases–based protocol

The recently proposed mutually partially unbiased bases (MPUB)–based protocol, which encodes with Laguerre–Gaussian modes and Hermite–Gaussian modes of the same mode order, can close the security loophole caused by state-dependent diffraction. However, its pessimistic security proof limits the performance, and some practical issues, such as finite-key size and imperfect sources, have not been considered. Here, we improve the key rates of the MPUB-based protocol by accurately estimating the phase error rate. Moreover, the effect of finite-key size and its performance when combined with the decoy state method are demonstrated. Our work broadens the application scope of the MPUB-based protocol, and thereby advances the development of high-dimensional quantum key distribution using spatial modes.

Study on 1.9 [formula omitted]m structured lasers based on Ince–Gaussian modes superposition with multi-modulation by different directions off-axis dual-end-pump

The double IGp,pe modes multi-modulation superposition evolution structured lasers output is realized, based on the proposed different directions off-axis dual-end-pumping Tm:YLF laser method. Under the modes orthogonal superposition, the theoretical simulation and experimental measurement results have a high degree of agreement, and the orthogonal superposition of double IGp,pe modes within 5 orders is realized, which proves that different order modes and optical field intensity ratio have the capability to modulate the formation of vortex array structured beams. When the low-order IGp,pe modes of the same order are orthogonally superimposed, the phenomenon of superposition of different phase differences occurs, which proves the possibility of modulating the superposition of IGp,pe modes by the phase difference. At the same time, it is found that the regular pattern output of high-order IGp,m modes (odd mode m ≤ 3 or even mode m ≤ 2) can be realized at different angles, which proves the ability of rotation angle to modulate the superposition of double IGp,pe modes. Finally, the 1.9μm Tm:YLF structure laser output with double IGp,pe modes multi-factor composite modulation superposition evolution within 10 orders is realized. When the 10-order double IG10,10e modes are superimposed, the output power exceeds 5.7 W, and the conversion efficiency is higher than 17.5%.

Analytical and numerical design of a hybrid Fabry-Perot plano-concave microcavity for hexagonal boron nitride.

An efficient single-photon emitter (SPE) should emit photons at a high rate into a well-defined spatio-temporal mode along with an accessible numerical aperture (NA) to increase the light extraction efficiency that is required for effective coupling into optical waveguides. Based on a previously developed experimental approach to fabricate hybrid Fabry–Perot microcavities (Ortiz-Huerta et al. Opt. Express 2018, 26, 33245), we managed to find analytical and finite-difference time-domain (FDTD) values for the, experimentally achievable, geometrical parameters of a hybrid plano-concave microcavity that enhances the spontaneous emission (i.e., Purcell enhancement) of color centers in two-dimensional (2D) hexagonal boron nitride (hBN) while simultaneously limiting the NA of the emitter. Paraxial approximation and a transfer matrix model are used to find the spotsize of the fundamental Gaussian mode and the resonant modes of our microcavity, respectively. A Purcell enhancement of 6 is found for a SPE (i.e., in-plane dipole) hosted by a 2D hBN layer inside the hybrid plano-concave microcavity.

Optical Transparency Induced by a Largely Purcell Enhanced Quantum Dot in a Polarization-Degenerate Cavity.

Optically active spin systems coupled to photonic cavities with high cooperativity can generate strong light-matter interactions, a key ingredient in quantum networks. However, obtaining high cooperativities for quantum information processing often involves the use of photonic crystal cavities that feature a poor optical access from the free space, especially to circularly polarized light required for the coherent control of the spin. Here, we demonstrate coupling with a cooperativity as high as 8 of an InAs/GaAs quantum dot to a fabricated bullseye cavity that provides nearly degenerate and Gaussian polarization modes for efficient optical accessing. We observe spontaneous emission lifetimes of the quantum dot as short as 80 ps (an ∼15 Purcell enhancement) and a ∼80% transparency of light reflected from the cavity. Leveraging the induced transparency for photon switching while coherently controlling the quantum dot spin could contribute to ongoing efforts of establishing quantum networks.

Fiber laser cutting of steel materials with twin spot beam-twin spot setting in kerf width direction

In laser cutting, the temperature distribution would have significant influence on cutting characteristics, and the intensity distribution of a laser beam has a possibility to improve the cutting quality. In this study, a fiber laser beam of Gaussian distribution was divided into two beams by a roof axicon lens, and the cutting characteristics were investigated by using the twin spot Gaussian beam setting in the kerf directions. The cutting experiment of a cold-rolled steel plate with a thickness of 3.2 mm was carried out by a 3 kW fiber laser with a nitrogen assist gas, and the Gaussian mode of 114 μm spot and the twin Gaussian mode of two 110 μm spots were used with the variation of power ratio in twin spot processing. At the exit side of kerf by the twin spot process, the width of the cutting front in the low intensity side became wider than that in the high intensity side, and the dross could be reduced in the low intensity side due to sufficient ejection of the molten metal from the front wall rather than the side wall of kerf. The twin spot process could reduce the dross height below 18 μm in the low intensity side, which is smaller than that by the single Gaussian beam process.

All-dielectric metalens for quasi-optical mode and polarization conversion.

Quasi-optical mode conversion technology plays a very important role in the development of high-power terahertz radiation sources. The ability of metamaterials to manipulate wave-front paves a new way in the field of quasi-optical mode conversion. In this paper, the approach for quasi-optical mode conversion by all-dielectric metalens and polarization conversion is proposed and investigated. Three metalens are designed to converter cylindrical waveguide TE01 mode to linear polarized (LP), left-hand circularly polarized (LHCP), and right-hand circularly polarized (RHCP) Gaussian beams at 350 GHz. Electromagnetic simulations show that the Gaussian mode contents of output waves from three metalens are all over 98% with high polarization contents. Furthermore, a metalens is designed for dual circularly polarized (DCP) which could convert cylindrical waveguide TE01 mode to LHCP and RHCP simultaneously. This work unveils the potential application for metalens in terahertz region.

Investigation of the Electron–Phonon Coupling in Dirac Semimetal PdTe2 via Temperature‐Dependent Raman Spectroscopy

Layered Palladium ditelluride (PdTe2) is an interesting noble‐transition‐metal dichalcogenide with high electrical and thermal conductivity, exhibiting superconductivity and a type‐II Dirac semimetallic phase due to the increased electron–phonon (e–ph) coupling. Herein, the e–ph coupling constant λ of E g (in‐plane) and A 1g (out‐of‐plane) modes in the exfoliated PdTe2 nanoflakes via temperature‐dependent Raman spectroscopy within the temperature range from 80 to 580 K is determined. Both E g mode with a Gaussian line shape and A 1g mode with a Breit–Wigner–Fano line shape show nonlinear frequency redshift and linewidth broadening with temperature. The extracted e–ph coupling constants are = 1.54 and = 0.55, respectively. The Raman results confirm that PdTe2 is a phonon‐mediated Bardeen–Cooper–Schrieffer superconductor.

Generation of collimated vortex gamma-rays from intense Poincaré beam–plasma interaction

We report on numerical calculations in which a multi-petawatt γ-ray beam is generated using a novel configuration based on fully structured light irradiating an overdense plasma waveguide. We analyze how the relativistic laser pulse efficiently confines and accelerates plasma electrons to GeV-scale energies and drives a quasi-static field that induces magneto-bremsstrahlung radiation. Multiphoton Compton scattering of electrons in the intense part of the laser also occurs although the radiated energy-density is comparatively lower. The emitted γ-rays carry orbital angular momentum, are highly collimated, and account for upwards of 15% of the incident field energy in one particular case. A comparison of the laser-to-particle angular momentum and energy transfer efficiencies is made between the cases of irradiation by a circularly polarized Laguerre–Gauss mode and one type of full Poincaré beam, and it is found that the latter yields an order-of-magnitude enhancement. The essential characteristics of the interaction are validated with three-dimensional particle-in-cell simulations that include quantum electrodynamical effects.

Laser Additive Manufacturing of Bulk Silicon Nitride Ceramic: Modeling versus Integral Transform Technique with Experimental Correlation

A semi-analytical-numerical solution is theorized to describe the laser additive manufacturing via laser-bulk ceramic interaction modeling. The Fourier heat equation was used to infer the thermal distribution within the ceramic sample. Appropriate boundary conditions, including convection and radiation, were applied to the bulk sample. It was irradiated with a Gaussian spatial continuous mode fiber laser (λ = 1.075 µm) while a Lambert-Beer law was assumed to describe the laser beam absorption. A close correlation between computational predictions versus experimental results was validated in the case of laser additive manufacturing of silicon nitride bulk ceramics. The thermal field value rises but stays confined within the irradiated zone due to heat propagation with an infinite speed, a characteristic of the Fourier heat equation. An inverse correlation was observed between the laser beam scanning speed and thermal distribution intensity. Whenever the laser scanning speed increases, photons interact with and transfer less energy to the sample, resulting in a lower thermal distribution intensity. This model could prove useful for the description and monitoring of low-intensity laser beam-ceramic processing.

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

The generation of a 33.7 W radially polarized output is demonstrated by way of double-pass amplification in a Ho:YAG thin-slab crystal. The amplifier system was seeded with the radially polarized output beam from a continuous-wave 13.2 W, 2.1 µm Ho:YAG rod laser, which exploited gain medium bifocusing and a ring-shaped pump spot to promote preferential lasing on the radially polarized Laguerre–Gaussian mode. By compensating for both the thermally induced stress birefringence in the thin-slab crystal and the Gouy phase shift resulting from astigmatic focusing of the 13.2 W seed, only marginal beam degradation was observed across the 95 W range of pump power into the amplifier.

Experimental demonstration of dynamic spatiotemporal structured beams that simultaneously exhibit two orbital angular momenta by combining multiple frequency lines, each carrying multiple Laguerre–Gaussian modes

In general, there are different, relatively independent forms of orbital angular momenta at a given propagation distance, which might exhibit different dynamic spatial characteristics. One type involves a beam with a helical phasefront that rotates around its own beam center, such as a Laguerre–Gaussian (LG) beam with an azimuthal index not equal to zero. The other one is a Gaussian-like beam dot that revolves around a central axis. Here, we experimentally demonstrate the generation of a dynamic spatiotemporal (ST) structured beam that simultaneously exhibits both rotation and revolution at a given propagation distance. Nine Kerr frequency comb lines are coherently combined, each carrying a designed superposition of multiple LG modes containing one unique ℓ value and multiple p values. Experimental results show that the mode purity of the reconstructed revolving and rotating LG30 beam is ∼89% when both the beam waist and revolving radius (R) are 0.4 mm. Moreover, we explore the effects of the number of frequency comb lines and the R value on the mode purity of the generated ST beam. Consequently, we find that a higher mode purity can be achieved by involving more frequency comb lines or reducing the R.

Ultra-long anti-diffracting beam volume imaging using a single-photon excitation microscope.

We studied a novel volumetric single-photon excitation microscope with an ultralong anti-diffracting (UAD) beam as illumination. Volumetric fluorescence image direct mapping showed that the axial imaging range of the UAD beam was approximately 14 times and 2 times that of conventional Gaussian and Airy beams, respectively, while maintaining a narrow lateral width. We compared the imaging capabilities of the Gaussian, Airy, and UAD modes through a strongly scattering environment mixed with fluorescent microspheres and agarose gel. Thick samples were scanned layer by layer in the Gaussian, Airy, and UAD modes, and then the three-dimensional structural information was projected onto a two-dimensional image. Benefiting from the longer focal length of the UAD beam, a deeper axial projection was provided, and the volume imaging speed was vastly increased. To demonstrate the performances of the UAD microscope, we performed dynamic volumetric imaging on the cardiovascular system of zebrafish labeled with green fluorescent proteins in the three modes and dynamically monitored substance transport in zebrafish blood vessels. In addition, the symmetrical curve trajectory of the UAD beam and the axial depth of the lateral position can be used for localization of micro-objects.

Performance analysis of 400 Gbit/s hybrid space division multiplexing‐polarization division multiplexing‐coherent detection‐orthogonal frequency division multiplexing‐based free‐space optics transmission system

SummaryA high‐capacity free‐space optics‐based terrestrial communication link using spectral‐efficient space division multiplexing and polarization division multiplexing techniques has been proposed in this research work. Orthogonal frequency division multiplexing with the use of coherent detection has been proposed for the transmission of quadrature amplitude modulated high‐speed signals. Eight independent 50‐Gbit/s data streams are transported by two orthogonal polarization states (X and Y) of four distinct Hermite–Gaussian spatial modes to increase the transmission rate of the link to 400 Gbit/s over a single channel. Through numerical simulations, we report feasible transportation of 400‐Gbit/s information at 10 km under clear weather with faithful performance. Further, the impact of atmospheric scintillation and fog weather has been evaluated using simulations. The results report that the maximum range reduces to 6 km under clear weather in the presence of strong atmospheric scintillation. Moreover, the maximum range of 2000, 1700, and 1300 m is reported for light, moderate, and heavy fog conditions respectively.

Mode division multiplexing free space optics system with 3D hybrid modulation under dust and fog

Mode division multiplexing (MDM) is an emerging information transmission technique in which multiple data signals can be transmitted simultaneously on different modes of a single wavelength laser beam over a free-space channel. MDM is a potential technique for the realization of high-speed spectral efficient communication links for future generations of wireless networks. We present a novel MDM-based free-space optics (FSO) system. The system integrates a 3D hybrid modulation scheme produced by combining carrier suppressed-non-return-to-zero (CSNRZ), differential quadrature phase-shift keying (DQPSK), and polarization shift keying (PolSK) modulation schemes for beyond 100 Gbps applications. Three unrelated 40 Gbps data signals are modulated and transmitted on one optical carrier utilizing three distinct signal properties: amplitude (CSNRZ), phase (DQPSK), and polarization state (PolSK). The proposed 3D modulation scheme offers a high-capacity system, where each channel transmits 4 Gbps as compared to 1 Gbps in the case of OOK modulation. MDM using distinct Hermite Gaussian modes: (HG00 and HG01) of a laser beam is incorporated to boost the spectral efficiency and information rates of the FSO link. The proposed 120 Gbps single-channel MDM-FSO link performance is examined under the impact of different levels of dust and fog environmental conditions using quality factors and received eye diagrams as the performance metrics. This system achieved optimal performances up to 1250 m (very light dust), 540 m (light dust), 170 m (moderate dust), 750 m (low fog), and 425 m (medium fog). In the worst-case scenario, the system manages to work up to a 67 m range in dense dust with a maximum attenuation of 297.38 dB/km and a 200 m distance in heavy fog with only 90 dB/km attenuation which is less than 1/3rd of the attenuation measured for dense dust event. In addition, our results and the case studies confirm that dust introduces greater signal attenuation than fog. Therefore, an encounter with a dust environment should be considered as the bottleneck issue for FSO links. The creative contribution of this paper is to put forward a bandwidth-efficient MDM-FSO-enabled B5G system that could be deployed in harsh and challenging locations at reduced visibility. This is expected to be further technically sustainable owing to the use of advanced 3D hybrid optical orthogonal modulation and therefore find use in implementing 5G and 6G cellular and data networks.

Wavefront Sensing with a Coupled Cavity for Torsion-Bar Antenna

Torsion-Bar Antenna (TOBA) is a ground-based gravitational wave detector using torsion pendulums. TOBA can detect intermediate-mass black hole binary mergers, gravitational wave stochastic background, and Newtonian noise, and is useful for earthquake early warning. A prototype detector Phase-III TOBA with 35 cm-scale pendulums is under development to demonstrate noise reduction. The target strain sensitivity is set to $1\times10^{-15}\,{/\sqrt{\rm Hz}}$ between 0.1 Hz--10 Hz. A new scheme of wavefront sensing with a coupled cavity was proposed to measure the pendulum rotation as low as $5\times10^{-16}\,{{\rm rad}/\sqrt{\rm Hz}}$ for Phase-III TOBA. In our method, an auxiliary cavity is used to enhance the first-order Hermite--Gaussian mode in a main cavity. Experimental demonstration is ongoing to confirm the feasibility of angular signal amplification and establish a method for locking a coupled cavity. We evaluated the performance of the coupled cavity and concluded that angular signal amplification would be feasible with this sensor. The coupled cavity was successfully locked to the resonance by the Pound--Drever--Hall technique with two modulation frequencies.

Vibroacoustic mitigation for a cylindrical shell coupling with an acoustic black hole plate using Gaussian expansion component mode synthesis

In this paper, we consider a composite cylindrical shell having an internal thin plate. When some ABHs are embedded on the interior floor, the vibration of the cylindrical shell and the sound power radiated from it are expected to be effectively mitigated. To characterize the built-up system, the Gaussian expansion method (GEM) is employed to carry out the modal parameters of the shell and the plate, respectively, where mode truncation is possible for model order reduction. Then the Gaussian expansion component mode synthesis (GECMS) method is developed to describe the final modes of the whole system. The accuracy of the GECMS is validated against reference finite element simulations. To manifest the coupling between the components, the modal participation factors of the shell and the ABH plate are carried out. Furthermore, the sound radiation model for the cylindrical shell is built, together with the non-negative intensity strategy for sound source localization. Results show that the vibration and the sound power level of the shell can be remarkably suppressed, thanks to the exceptional damping effect of the ABHs, especially when the excitation force locates on the ABH plate. The present study is dedicated to pushing the applications of the ABHs.

Fast oscillations of orbital angular momentum and Shannon entropy caused by radial numbers of structured vortex beams.

We address theoretical and experimental considerations of two-parameter excitation of each Hermite-Gaussian (HG) mode in composition of a structured Laguerre-Gaussian (sLG) beam. The complex amplitude of the sLG beam is shaped in such a way that the radial and azimuthal numbers of eigenmodes are entangled with each other. As a result, variations in the amplitude and phase parameters of mode excitation, although dramatically changing the intensity and phase patterns, do not change the structural stability of the beam. We reveal that the radial number of the sLG beam can cause fast oscillations of the orbital angular momentum and Shannon entropy, dramatically increasing the uncertainty of detecting the beam in some particular state. We found that despite the fast oscillations, the sLG beam has an invariant in the form of a module of the total topological charge (TC), with the exception of narrow intervals of the phase parameter, where the measurement error does not allow us to accurately measure the sign of the TC. The difference between the interpretation of informational entropy as a measure of uncertainty and a measure of information capacity is considered on the example of the measurement of Shannon entropy in the bases of LG and HG modes.

Post-Flood UAV-Based Free Space Optics Recovery Communications with Spatial Mode Diversity

The deployment of unmanned aerial vehicles (UAVs) for free space optical communications is an attractive solution for forwarding the vital health information of victims from a flood-stricken area to neighboring ground base stations during rescue operations. A critical challenge to this is maintaining an acceptable signal quality between the ground base station and UAV-based free space optics relay. This is largely unattainable due to rapid UAV propeller and body movements, which result in fluctuations in the beam alignment and frequent link failures. To address this issue, linearly polarized Laguerre–Gaussian modes were leveraged for spatial mode diversity to prevent link failures over a 400 m link. Spatial mode diversity successfully improved the bit error rate by 38% to 55%. This was due to a 10% to 19% increase in the predominant mode power from spatial mode diversity. The time-varying channel matrix indicated the presence of nonlinear deterministic chaos. This opens up new possibilities for research on state-space reconstruction of the channel matrix.

Colloquium : Geometric phases of light: Insights from fiber bundle theory

This Colloquium reviews the role of geometric phases in optics from the perspective of fiber bundle theory. The transformation of the polarization of light by discrete optical components illustrates many elements of the theoretical formalism, and an outlook is presented for the study and application of geometric phases in higher dimensions through analyses of higher order Gaussian modes and general vectorial fields.

Generation of spiral optical vortex with varying OAM for micro-manipulation

Since the confirmation of orbital angular momentum (OAM) decades ago, numerous studies have led to a new understanding of optical effects and various applications. Here we propose a concept of the spiral optical vortex (SOV) which contains multiple OAM modes from inside to outside along the spiral intensity field. Theoretically, by linking the azimuthal spiral phase with the beam radius, the SOV can be generated. The corresponding OAM spectrum of the SOV are analyzed theoretically and measured experimentally. We also demonstrate the evolution characteristics of the SOV over the propagation distance. The OAM components of the SOV have also been investigated and measured based on the fundamental Laguerre–Gaussian mode experimentally. The experiment results show that the micro-particle can be transmitted along with the spiral intensity distribution of the SOV to the center. This proposal may paves a new way in the generation of the spiral light field and stimulate new applications in light field modulation and microparticles manipulation.