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Optical signatures of the coupled spin-mechanics of a levitated magnetic microparticle

Vanessa Wachter, Victor Bittencourt, Shangran Xie, Sanchar Sharma, Nicolas Joly, Philip Russell, Florian Marquardt, and Silvia Viola-Kusminskiy

DOI: 10.1364/JOSAB.440562 Received 16 Aug 2021; Accepted 25 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: We propose a platform that combines the fields of cavity optomagnonics and levitated optomechanics in order to control and probe the coupled spin-mechanics of magnetic dielectric particles. We theoretically study the dynamics of a levitated Faraday-active dielectric microsphere serving as an optomagnonic cavity, placed in an external magnetic field and driven by an external laser. We find that the optically driven magnetization dynamics induces angular oscillations of the particle with low associated damping. Further, we show that the magnetization and angular motion dynamics can be probed via the power spectrum of the outgoing light. Namely, the characteristic frequencies attributed to the angular oscillations and the spin dynamics are imprinted in the light spectrum by two main resonance peaks. Additionally, we demonstrate that a ferromagnetic resonance setup with an oscillatory perpendicular magnetic field can enhance the resonance peak corresponding to the spin oscillations and induce fast rotations of the particle around its anisotropy axis.

Soliton Shedding from Airy Pulses in a Highly Dispersive and Nonlinear Medium

Deependra Gaur, Ankit Purohit, and Akhilesh Mishra

DOI: 10.1364/JOSAB.439424 Received 03 Aug 2021; Accepted 25 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: Soliton propagation, a result of the interplay between dispersion and nonlinearity, is possible at certain input pulse power. Soliton shedding from Airy pulse at low input pulse power is a challenge. We present a numerical investigation of the propagation of truncated Airy pulse in a highly dispersive and nonlinear medium by employing the split-step Fourier transform method and look, in particular, into the effects of fourth order dispersion (FOD) and cubic-quintic nonlinearity on pulse propagation. Presence of FOD cancels the Airy pulse’s self-acceleration along with eclipsing the oscillatory tail during propagation in the linear regime. In addition, soliton shedding is observed not only in the presence of negative FOD and cubic nonlinearity but also in the case of negative FOD and quintic nonlinearity, where the emergent soliton characteristics are influenced by the initial launch power. Moreover, the combined effect of group-velocity dispersion (GVD) and FOD on the Airy pulse dynamics is also explored.

All-glass hybrid fibers for dispersion management

Svetlana Aleshkina and Mikhail Likhachev

DOI: 10.1364/JOSAB.437891 Received 15 Jul 2021; Accepted 22 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: We present a review devoted to hybrid optical fibers, which combine the properties of conventional total internal reflection and anti-resonant fibers and enable dispersion control at wavelengths where the material dispersion of the fiber host optical glass is normal. We discuss the main principles of mode propagation in such structures and show the prospects for their practical application.

Specialty optical fibre fabrication: Preform manufacturing based on asymmetrical CO Laser heating

Taras Oriekhov, Clarissa Harvey, Korbinian Mühlberger, and Michael Fokine

DOI: 10.1364/JOSAB.438027 Received 16 Jul 2021; Accepted 22 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: Here, we present an innovative preform manufacturing technique for specialty optical fibres based on a carbon monoxide laser heating a rotating preform. The setup performance is evaluated with the aid of finite element modelling. The fabrication process is described in detail using silicon core preforms as a benchmark. The hybrid material nature of such a preform is addressed, together with the relevant characteristics, such as the difference in thermal conductivity and thermal expansion. Si-core preforms with a wide range of core sizes were manufactured, proving the viability of this system for the development specialty optical fibres based on novel materials.

Geometry-dependent two-photon absorption followed by free-carrier absorption in AlGaAs waveguides

Daniel Espinosa, Stephen Harrigan, Kashif Awan, Payman Rasekh, and Ksenia Dolgaleva

DOI: 10.1364/JOSAB.440293 Received 11 Aug 2021; Accepted 22 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: Nonlinear absorption can limit the efficiency of nonlinear optical devices. However, it can also be exploited for optical limiting or switching applications. Thus, characterization of nonlinear absorption in photonic devices is imperative for designing useful devices. This workuses the nonlinear transmittance technique to measure the two-photon absorption coefficients (α₂) of AlGaAs waveguides in the strip-loaded, nanowire, and half-core geometries in the wavelength range from 1480 to 1560 nm. The highest α₂ values of 2.4, 2.3, and 1.1 cm/GW were measuredat 1480 nm for a 0.8-nm-wide half-core, 0.6-nm-wide nanowire, and 0.9-nm-wide strip-loaded waveguides, respectively, with α₂ decreasing with increasing wavelength. The free-carrier absorption cross-section was also estimated from the nonlinear transmittance data to be around 2.2 × 10¨¹⁶ cm² for all three geometries. Our results contribute to a better understanding of the nonlinear absorption in heterostructure waveguides of different cross-sectional geometries. We discuss how the electric field distribution in the different layers of a heterostructure can lead to geometry-dependent effective two-photon absorption coefficients. More specifically, we pinpointthe third-order nonlinear confinement factor as a design parameter to estimate the strength of the effective nonlinear absorption, in addition to tailoring the bandgap energy by varying the material composition.

Critical Ambient Pressure and Critical Cooling Rate in Optomechanics of Electromagnetically Levitated Nanoparticles

Amir Jazayeri

DOI: 10.1364/JOSAB.439655 Received 03 Aug 2021; Accepted 21 Oct 2021; Posted 26 Oct 2021  View: PDF

Abstract: The concept of critical ambient pressure is introduced in this paper. The particle escapes from its trap when the ambient pressure becomes comparable with or smaller than a critical value, even if the particle motion is cooled by one of the feedback cooling (or cavity cooling) schemes realized so far. The critical ambient pressure may be so small that it is not a limiting factor in ground-state cooling, but critical feedback cooling rates, which are also introduced in this paper, are limiting factors. The particle escapes from its trap if any of the feedback cooling rates (corresponding to the components of the particle motion) becomes comparable with or larger than its critical value. Critical feedback cooling rate is different from the well-known manifestation of the measurement noise. The critical feedback cooling rate corresponding to a certain component of the particle motion is usually smaller than the optimum feedback cooling rate at which the standard quantum limit happens unless that component is cooled by the Coulomb force (instead of the optical gradient force). Also, given that the measurement noise for the z component of the particle motion is smaller than the measurement noises for the other two components (assuming that the beam illuminating the particle for photodetection propagates parallel to the z axis), the feedback scheme in which the z component of the particle motion is cooled by the Coulomb force has the best performance. This conclusion is in agreement with the experimental results published after writing the first version of this paper. The dependence of the critical ambient pressure, the critical feedback cooling rates, and the minimum achievable mean phonon numbers on the parameters of the system is derived in this paper, and can be verified experimentally. The insights into and the subtle points about the EM force (including the gradient force, radiation pressure, and recoil force), the EM force fluctuations, and the measurement noise that are presented in this paper are all of theoretical and practical importance, and might be useful in many systems besides those examined in this paper.

Nested non-concentric microring resonators with high-Q and large fabrication tolerance

Raktim Haldar, Sandeep Ummethala, Rajat Sinha, and Shailendra Varshney

DOI: 10.1364/JOSAB.430789 Received 05 May 2021; Accepted 21 Oct 2021; Posted 21 Oct 2021  View: PDF

Abstract: Microring resonators are the most sought optical components for realizing several on-chip functionalities that include sensing, data routing, and quantum photonic applications. Many of these applications demand a high-quality factor and large notch depth (higher extinction ratio), which can be achieved by critical coupling. However, the critical coupling is very sensitive to the fabrication accuracies and the thermal drift. Geometrical parameters of the resonators are generally swept to attain critical coupling, where a few designs can pass the critical coupling condition criteria. In this work, we propose a methodology to circumvent this vital issue. The proposed technique is based on coupled-resonator systems where two different microrings are embedded into a larger microring, referred as a non-concentric nested microring resonator (NN-MRR). The NN-MRR configuration relaxes the requirement of the critical coupling condition by 20% when the strip optical waveguide has either smooth or rough sidewalls. Numerical simulations reveal that unlike standard MRR, a high Q-factor (>105) and a large transmission notch depth >10 dB can be maintained irrespective of rings' coupling conditions for the nested MRRs. The most significant advantage of the proposed NN-MRR is compactness and enhanced coupling-relaxation. We believe that the nested MRR arrangement could be highly efficient for bio-sensing, nonlinear and quantum applications within a broad ambient temperature range. We have fabricated the NN-MRRs and experimentally demonstrated the theoretical and numerical findings.

Numerical simulation design of all-inorganic hole-transport-layer-free CsSnI3 (Sn-rich)/CsSnI3 perovskite efficient solar cells

Mengyying Jiang and Jiyu Tang

DOI: 10.1364/JOSAB.439672 Received 04 Aug 2021; Accepted 21 Oct 2021; Posted 21 Oct 2021  View: PDF

Abstract: As perovskite solar cell (PSC) technology is about to be commercialized, the use of toxic and organic material is still a problem. At the same time, hole-transport-layer-free (HTL-free) PSCs have received widespread attention given their simple structure and low manufacturing cost. In this study, we use the wxAMPS software to produce a simulation, using CsSnI3 (Sn-rich)/CsSnI3 all-perovskite as the absorption layer and carbon as the back electrode, as well as to propose a new inorganic HTL-free PSC. CsSnI3 is a narrow band material whose absorption range can be extended to the near-infrared spectral region; it also has very high hole mobility and so can be used as both the light absorption layer and the HTL. Compared with that of standard structure devices, the photoelectric conversion efficiency (PCE) of the PSC is better. When the perovskite layer thickness is 900 nm, the optimal PCE is 14.91%, the open-circuit voltage (Voc) is 0.81V, the short-circuit current (Jsc) is .77 mA/cm2, and the fill factor (FF) is 77.37%. Our research further found that CsSnI3 (Sn-rich) has the best PCE at 1018~1019 /cm3. When the electron transport layer (ETL) and the light absorption layer conduction band offset (CBO) is -0.2 eV, the PCE has an optimal value of 15.02%. Finally, by changing the light temperature, the PCE value of our study is between 12.07% and 16.61% under non-extreme work environments, and the results show that the device has good thermostability. This proves that the proposed all-inorganic HTL-free PSCs has broad prospects in future photovoltaic and optoelectronics applications and provides theoretical guidance for the manufacture of non-toxic and inorganic PSCs.

Unified model for spectral and temporal properties of quasi-CW fiber lasers

Wei Liu, Pengfei Ma, and Pu Zhou

DOI: 10.1364/JOSAB.439829 Received 09 Aug 2021; Accepted 20 Oct 2021; Posted 21 Oct 2021  View: PDF

Abstract: This paper discusses a unified theoretical approach to model the spectral and temporal properties of various quasi-continuous-wave (CW) fiber lasers. The unified spectral evolution model and temporal evolution model of quasi-CW fiber lasers are established through demonstrating the nonlinear propagation equations with gain coefficient, and analyzing the corresponding definite conditions and computation methods for effective simulations. Simulation results based on the two unified models are given to show their capacities and application scope in describing the basic spectral and temporal properties of typical quasi-CW fiber lasers involving single gain mechanism with simple structure. Furthermore, the two unified models could also be extended to analyze the spectral and temporal properties of quasi-CW fiber lasers involving hybrid gain mechanism or with composite structure. Overall, the unified spectral evolution model and temporal evolution model could provide a useful tool to describe and design the quasi-CW fiber lasers and quasi-CW fiber amplifiers.

Heralded Quantum-Entanglement Transfer Based onPhoton Absorption of Nitrogen-Vacancy Centers inDiamond

Yong Zhang and Zhong Ding

DOI: 10.1364/JOSAB.432827 Received 31 May 2021; Accepted 19 Oct 2021; Posted 19 Oct 2021  View: PDF

Abstract: As a kind of hybrid spin system, nitrogen-vacancy (NV) centers in diamond have shown great advantages in implementing quantum registers for quantum information processing (QIP). When scaling up quantum registers to quantum networks for long-distance quantum communication and distributed quantum computation, determining how to entangle two registers in distant nodes is a basic challenge in the absence of direct interactions. In this paper, we present a scheme for entangling two distant NV centers based on the special optical absorption and emission of NV centers. In this demonstration, we transfer the entanglement information of a pair of photons to nuclear spins in NV centers and create remote NV--NV entanglement mediated by entangled photons. We then explain how to extract the entangled information from NV centers to prepare on-demand entangled photons for optical quantum information processing. The strategy of entanglement transfer between spins and photons demonstrated herein may pave the way for an NV- center-based quantum network.

Physical factors affecting the propagation length of Bloch surface modes in one-dimensional photonic crystals

Francisco Villa, Jesus Gutiérrez Villarreal, Hector Perez Aguilar, and Jorge Gaspar-Armenta

DOI: 10.1364/JOSAB.440928 Received 20 Aug 2021; Accepted 17 Oct 2021; Posted 18 Oct 2021  View: PDF

Abstract: A detailed study of the propagation length of Bloch modes along the surface between a bulk medium and a one-dimensional photonic crystal is presented by considering different parameters like the number of periods composing the photonic crystal, absorption of materials, the leak of energy due to the intrinsic structure of the system and the roughness of involved surfaces that is inherently present depending on the manufacturing method and the materials itself. To analyze the influence of different factors affecting the propagation length we use essentially three different methods: the characteristic matrix for systems composed of smooth surfaces, along with the numerical fitting of a Lorentz curve around the resonance, the integral method based on the Green function for two-dimensional systems that include random rough surfaces, and the numerical analysis of the energy propagation along the surface when a Gaussian beam impinges on it.

Forward THz Wave Generation from Liquid Gallium in the Non-relativistic Regime

Kareem Garriga Francis, Yuqi Cao, Yiwen E, Fang Ling, Mervin Lim Pac Chong, and Xi-Cheng Zhang

DOI: 10.1364/JOSAB.435759 Received 02 Jul 2021; Accepted 17 Oct 2021; Posted 18 Oct 2021  View: PDF

Abstract: We characterize a terahertz (THz) source based on plasmain liquid Gallium. The dependence of the emitted THz pulseenergy on second order phase, pump pulse energy, andpolarization of the short laser pulse is evaluated. Our studysuggests that the THz emission mechanism is due to theponderomotive force and is aided by a direct-field driventerm. The proposed source and accompanying generationmechanism are studied under a previously unreported non-relativistic regime (1015 < I < 1018 W/cm2) for forwarddirected THz under a single pump excitation scheme.

A highly sensitive long-period fiber grating based biosensor inherently immune to temperature and strain

Krishnendu Dandapat and Saurabh Tripathi

DOI: 10.1364/JOSAB.437929 Received 15 Jul 2021; Accepted 16 Oct 2021; Posted 18 Oct 2021  View: PDF

Abstract: For two simultaneously varying external perturbation parameters, namely temperature and strain, we propose and theoretically demonstrate a novel scheme of developing inherently insensitive bio-sensors based on long period fiber gratings (LPFGs). The insensitivities have been respectively achieved by inherently nullifying (i) temperature induced phases of the core and cladding modes by judiciously adjusting the core dopants and their concentrations, and (ii) strain induced phase changes generated inside one LPFG with that inside the other LPFG by optimizing the grating parameters (grating period, strength and length). The resulted bio-sensor has ultra high overall bulk refractive index sensitivity of ∼3 μm/RIU for bio-samples (RI varying in the range of 1.33 to 1.34 RIU) and an affinity sensitivity of ∼1.4 nm/nm for bio-molecules (RI ∼1.45 RIU). Our study should find application in developing ultra sensitive, high precision bio/chemical sensors that are inherently immune to environmental temperature and strain variations.

Bidirectional Coupling of Diamond Emitters to Optical Nanowire: Tuneable and Efficient

Rajan Jha, Satyajit Murmu, and Avijit Kumar

DOI: 10.1364/JOSAB.439383 Received 02 Aug 2021; Accepted 16 Oct 2021; Posted 21 Oct 2021  View: PDF

Abstract: Negatively charged Nitrogen Vacancy (NV-) centers in diamond are required to be coupled to optical systems for various applications. A slowly varied tapered waveguide displays a near unity power transfer from an optical fiber to on-chip photonic devices. This physical situation refers to an adiabatic transition of photons from a highly effective confinement mode to a lower effective confinement mode or vice versa. Here, we report tunable bidirectional coupling with enhanced efficiency in a hybrid structure of elliptically-faceted (ELFA) diamond nanowire with NV- centers integrated to optical nanowire. Initiating from diabatic transition to adiabatic transition, corresponding to smaller length to longer wire length, respectively, coupling efficiency oscillates and asymptotically saturates to a maximum value. Our calculations indicate coupling efficiency of 85% and 84% for azimuthal and radial dipole configuration for the hybrid structure, respectively. The structure with optimum geometry provides similar coupling efficiency of ~81% for radial and azimuthal dipole configurations. By excitation of one of few dipoles placed strategically at various locations in the cylindrical region of the diamond nanowire will allow one to tune coupling efficiency in the two directions. Tailored size and tunable bidirectional coupling of ELFA diamond nanowire with enhanced efficiency will enable its wide-field applications including multi-scale quantum photonics devices.

Magnetic-field assisted laser ablation of silicon

Mareike Schäfer, Pavel Terekhin, Yiyun Kang, Garik Torosyan, Xavier Fargas, Steffen Hirtle, Baerbel Rethfeld, and Johannes Lhuillier

DOI: 10.1364/JOSAB.433104 Received 02 Jun 2021; Accepted 15 Oct 2021; Posted 15 Oct 2021  View: PDF

Abstract: Understanding and manipulation of the laser processing quality during the ablation of solids have crucial importance from fundamental and industrial perspectives. Here we have studied the effect of external magnetic field on the micro-material processing of silicon by ultrashort laser pulses. It was found experimentally that such a field directed along the laser beam improves the quality and efficiency of the material removal. Additionally, we observe that the formation of laser-induced periodic surface structures (LIPSS) in a multi-pulse regime is affected by the external magnetic field. Our results open a route towards efficient and controllable ultrafast laser micromachining.

Detection of virus particles by scattering field using three-dimensional polarization modulation imaging method

Baoheng Guo, Bin Ni, Xiao Jin, Heng Zhang, Hanwen Zhao, John Marsh, Lianping Hou, Lei Dong, Shanhu Li, Jichuan Xiong, and Xuefeng Liu

DOI: 10.1364/JOSAB.436357 Received 09 Jul 2021; Accepted 15 Oct 2021; Posted 15 Oct 2021  View: PDF

Abstract: Polarization parametric indirect microscopic imaging (PIMI) method, which employs a polarization modulated incidence illumination and fitting the far-field variation of polarization states of the scattered photons, is capable of direct identification of the sub-diffraction-scale structures and substances, such as the virus particles. However, in the present strategy, the optical elements which collect the scattered photons are nearly fixed above the sample, making the collected information relatively limited as the side-scattering photons are not fully utilized. To address this problem, we propose a 3D PIMI imaging method to maximize the collection of the scattering photons from different spatial directions, which can obtain more useful information and have great potential to retrieve 3D nano-features. As a proof-of-concept study, virus detection using such method is performed theoretically and experimentally. Results reveal that the virus particles can be detected and determined more distinctly thanks to the set of PIMI images from different spatial angles, showing notable superiority to the previous scheme where only a single PIMI image is derived from a fixed spatial direction. With the capability of acquiring more characteristics of the samples, such 3D PIMI method can be applied in many fields such as morphological characterization and bio-sensing.

Inner shell excitation by strong field laser rescattering: Optimal laser conditions for high energy recollision

Liam Kelley, Zach Germain, Evan Jones, David Miliken, and Barry Walker

DOI: 10.1364/JOSAB.440211 Received 12 Aug 2021; Accepted 12 Oct 2021; Posted 14 Oct 2021  View: PDF

Abstract: We address the challenge of finding the optimal laser intensity and wavelength to drive high energy, strong field rescattering and report the maximum yields of K- and L-shell hole creation. Surprisingly, our results show laser driven rescattering is able to create inner shell holes in all atoms from lithium to uranium with the interaction spanning from the deep IR to x-ray FEL sources. The calculated peak rescattering follows a simple scaling with the atomic number and laser wavelength. The results show it is possible to describe the ideal laser intensity and wavelength for a general high-energy laser rescattering processes.

Inhibition of stimulated Raman side-scattering with one-dimensional smoothing by spectral dispersion

Ning Kang, Huiya Liu, shenlei zhou, Yao Zhao, and An-Le Lei

DOI: 10.1364/JOSAB.435784 Received 01 Jul 2021; Accepted 12 Oct 2021; Posted 12 Oct 2021  View: PDF

Abstract: Smoothing by spectral dispersion (SSD) is a beam smoothing technology aiming at improving irradiance uniformity in laser inertial confinement fusion which has potential to suppress many kinds of laser-plasma instabilities. Different effectiveness of SSD on the suppression of instabilities were reported in previous works, suggesting SSD has different effects on different instabilities under various laser and plasma conditions. In this paper, inhibition of stimulated Raman side-scattering, deduced from the decrease of side-scattered light and hot electrons, in plastic plasmas at moderate laser intensity was observed in experiments with the application of one-dimensional SSD, the reason of which is deduced to be related to the suppression of filamentation. In contrast, two-plasmon decay and backward Raman scattering were not effectively suppressed by SSD in the experiments, the reason of which could be attributed to the limited modulation frequency and the directions of growth with respect to SSD induced rapid motion of laser spot.

Adiabaticity analysis of multimode optical fiber taper in phase space

Li Li and Xiuquan Ma

DOI: 10.1364/JOSAB.438638 Received 23 Jul 2021; Accepted 11 Oct 2021; Posted 11 Oct 2021  View: PDF

Abstract: We propose a new method to analyze the adiabaticity of highly multimode tapered waveguide. The propagation of the optical beam in the multimode fiber taper is calculated using Monte-Carlo ray tracing technique, then the corresponding phase space of the optical beam is obtained. Based on the analysis of etendue variation in phase space, the adiabaticity of the fiber taper is evaluated.

Dynamics of chirped Airy pulse in a dispersive medium with higher-order nonlinearity

Ankit Purohit, Deependra Gaur, and Akhilesh Mishra

DOI: 10.1364/JOSAB.439227 Received 30 Jul 2021; Accepted 11 Oct 2021; Posted 11 Oct 2021  View: PDF

Abstract: Chirp can control the dynamics of the Airy pulse, making it an essential factor in pulse manipulation. Finite energy chirped Airy pulse (FECAP) has potential applications in underwater optical communication and imaging. Hence, it's critical to study the propagation of FECAP. We present a numerical investigation of the propagation dynamics of a FECAP in a dispersive, and highly nonlinear medium. The nonlinearity under study includes self-phase modulation (SPM), self-steepening (SS), as well as intra-pulse Raman scattering (IRS) terms. We have observed soliton shedding and the chirp parameter is demonstrated to have a considerable impact on the pulse dynamics. In particular, the emergent soliton does not propagate in a straight path instead, depending on the sign of the chirp parameter, it delays or advances in the time. Furthermore, it has been established that the chirp can be employed as an alternate control parameter for the spectral manipulation. The results of our study may have implications in supercontinuum generation and for producing tunable sources.

Effects of optically biaxial anisotropy in orthogonal-circular polarization gratings operating in Raman-Nath to Bragg regime

Ryusei Momosaki, Moritsugu Sakamoto, Kohei Noda, Tomoyuki Sasaki, Takeya Sakai, Yukitoshi Hattori, Nobuhiro Kawatsuki, and Hiroshi Ono

DOI: 10.1364/JOSAB.442104 Received 31 Aug 2021; Accepted 11 Oct 2021; Posted 12 Oct 2021  View: PDF

Abstract: The incident angle dependence of the diffraction properties of orthogonal-circular polarization gratings (OCPGs) fabricated using a polymer liquid crystal exhibiting biaxial anisotropy have been investigated with the plane orthogonal to the surface of the OCPGs as the plane of incidence. It was found that a specific biaxial anisotropy reduces the incident angle dependence of optically thin OCPGs against the wavelength of the incident light, and is less effective on thick OCPGs. In addition, a method has also been proposed to determine the biaxial anisotropic shape that most reduces the incident angle dependence in thin OCPGs.

Semi-analytical model of the optical properties of a metasurface composed of nanofins

Jeck Borne, Denis Panneton, Michel Piche, and Simon Thibault

DOI: 10.1364/JOSAB.438125 Received 19 Jul 2021; Accepted 11 Oct 2021; Posted 11 Oct 2021  View: PDF

Abstract: We propose a method to evaluate the optical propagation properties of a dielectric non-resonant metasurface composed of rectangular nanofins. Our approach is based on a semi-analytical assessment of the effective indices to perform the guided vectorial propagation inside the nanostructure. The proposed model is an extension of the commonly used Pancharatnam-Berry model where the effect of the incidence angle can be satisfactorily accounted for. The model shows good agreement with numerical simulations and it can be inverted to give the nanofin rotation angle for a given output phase function. We show that the far-field distribution of a metalens predicted by our model is in good agreement with data from a simulation code.

Time-resolved imaging of CaF2 poly-crystal response following 355 nm nanosecond laser irradiation

Jiuling Meng, Tao Lü, Yong Jiang, and Rong Qiu

DOI: 10.1364/JOSAB.435806 Received 05 Jul 2021; Accepted 11 Oct 2021; Posted 19 Oct 2021  View: PDF

Abstract: The evolution of a 355 nm nanosecond laser-induced damage to CaF2 poly-crystals is investigated by using the time-resolved pump-probe shadowgraph technique. The damage morphologies of the front surface, rear surface, and interior of the CaF2 crystal are imaged by optical microscopy. When the rear surface is focused by one laser pulse throughout the front surface, three shock waves (SWs) and one SW are observed in the air beside the front and rear surfaces, respectively. When the laser energies are 40 mJ and 60 mJ, at delay time of 1000 ns the radii of SW fronts beside the front surface are 2569.8 µm and 2831.7 µm, while those beside the rear surface are 1012.9 µm and 1078.1 µm, respectively. The filamentary channels inside the CaF2 crystal have been established before the end of a laser pulse with energies of 25, 40, or 60 mJ. The average propagation velocities of SWs along the filamentary channel are approximately 8.2 µm/ns. The maximum diameters of channels can reach approximately 53 µm and 128 µm for 25 mJ energy and 40 mJ energy, respectively. Experimental results can help disclose the underlying damage mechanism of 355 nm nanosecond laser ablation of CaF2 poly-crystal.

Using multi-polar scattering and near-field plasmonic resonances to achieve optimal emission enhancement from quantum-emitters embedded in dielectric pillars

Faraz Inam and stefania castelletto

DOI: 10.1364/JOSAB.434605 Received 18 Jun 2021; Accepted 10 Oct 2021; Posted 11 Oct 2021  View: PDF

Abstract: Recently, high refractive index micro-pillars have been widely used for enhancing the fluorescence of quantum emitters (vacancy/defect centers) embedded within the pillar. However, the maximum observed enhancement from these pillars has been restricted to about an order of magnitude. Inside the dielectric pillars, the Purcell enhancement is restricted to around unity and the fluorescence enhancement results largely due the enhancement in the collection efficiency for dipole emission from inside the pillar as against a bulk substrate. Using multi-polar electromagnetic scattering resonances and near-field plasmonic field enhancement/confinement, here we report a simple metal-dielectric pillar resonator scheme for close to three-orders of magnitude fluorescence enhancement from embedded solid state vacancy-centers. The scheme comprises of a silver (Ag) cylinder fabricated on top of a silicon-carbide (SiC) dielectric pillar, with both the SiC and Ag cylinders having the same diameter. Selective dipole orientation relative to the metal-dielectric interface for emitters close to the SiC pillar's top surface leads to large Purcell enhancement of the dipole's emission. The Ag cylinder was found to function as an efficient resonator as well as an antenna, enhancing as well as directing a significant fraction of the dipole's emission into the far-field free-space.

Lowering Helstrom Bound with non-standard coherent states

Evaldo Curado, Sofiane Faci, Jean Pierre Gazeau, and Diego Noguera

DOI: 10.1364/JOSAB.428637 Received 10 May 2021; Accepted 08 Oct 2021; Posted 08 Oct 2021  View: PDF

Abstract: In quantum information processing, using a receiver device to differentiate between two nonorthogonal states leads to a quantum error probability. The minimum possible error is known as the Helstrom bound. In this work we study statistical aspects and quantum limits for states which generalize the Glauber-Sudarshan coherent states, like non-linear, Perelomov, Barut-Girardello, and (modified) Susskind-Glogower coherent states. For some of these, we show that the Helstrom bound can be significantly lowered and even vanish in specific regimes.

The role of the quintic terms in the stability of dissipative solitons of the complex Ginzburg-Landau equation

Jose Soto-Crespo and Nail Akhmediev

DOI: 10.1364/JOSAB.439531 Received 03 Aug 2021; Accepted 08 Oct 2021; Posted 08 Oct 2021  View: PDF

Abstract: We revisit the role of the quintic terms of the complex cubic-quintic Ginzburg-Landau equation in the generation of stable dissipative solitons. Using direct numerical simulations and a qualitative analysis we show that the presence of one of the two quintic terms is a sine qua non. However, this term is not necessarily the quintic gain saturation term as had been demonstrated by Moores (Opt. Commun. 96, 65 (1993)) but can be the higher-order (quintic) nonlinear refraction term. We prove that by numerically solving this equation and perform a qualitative analysis that shows that the negative soliton chirp, anomalous dispersion and the spectral filtering are the physical effects responsible for gain saturation in this case.

Method of characterising multicomponent spectrum of VCSEL in devices based on CPT effect

Sergey Kobtsev, Daba Radnatarov, and Valeriy Andryushkov

DOI: 10.1364/JOSAB.442253 Received 02 Sep 2021; Accepted 06 Oct 2021; Posted 08 Oct 2021  View: PDF

Abstract: We propose and experimentally demonstrate a method of spectral measurement of multicomponent radiation emitted by modulated vertical cavity surface-emitting laser relying on peculiarities of absorption in alkali metal vapour. The method consists in determination of the radiation spectrum (which is formed due to RF modulation of the injection current of a diode laser) from the dependence of transmittance of rubidium vapour upon the radiation wavelength. We show that the proposed method allows fairly precise measurement of the spectrum of multicomponent radiation used in devices based on the CPT effect when the frequency difference between the radiation components matches that between absorption lines of an alkali metal.

Machine learning techniques in the examination of the electron-positron pair creation process

C. Gong, Q. Charles Su, and Rainer Grobe

DOI: 10.1364/JOSAB.439484 Received 02 Aug 2021; Accepted 05 Oct 2021; Posted 08 Oct 2021  View: PDF

Abstract: We employ two machine learning techniques such as neural networks and genetic programming based symbolic regression to examine the dynamics of the electron-positron pair creation process with full space-time resolution inside the interaction zone of a supercritical electric field pulse. Both algorithms receive multiple sequences of partially-dressed electronic and positronic spatial probability densities as training data and exploit their features as a function of the dressing strength in order to predict each particle's spatial distribution inside the electric field. A linear combination of both predicted densities is then compared to the unambiguous total charge density, which contains also contributions associated with the independent vacuum polarization process. After its subtraction, the good match confirms the validity of the machine learning approach and lends some credibility to the validity of the predicted single-particle densities.

Producing Near-Zero-Index/Directivity-Tunable Metamaterials Using Transformation Optics

Reza Dehbashi

DOI: 10.1364/JOSAB.440769 Received 18 Aug 2021; Accepted 05 Oct 2021; Posted 20 Oct 2021  View: PDF

Abstract: In some literature [18], zero-index metamaterials are regarded as non-Transformation optics (TO) materials. In this paper, for the first time, new sets of transformation mapping functions are introduced to produce near-zero-index metamaterials, using TO. In addition, other than producing near-zero materials, it is shown that the proposed structures can be used in applications like radiators with highly tunable directivity when the parameters of the transformation functions are adjusted. In near-zero-index metamaterials, refractive index is near zero when either permittivity or permeability or both are near zero. The introduced mapping functions are applied to a desired space, then using Maxwell’s equations, the wave equation and consequently the wavenumber of the transformed space is obtained. From the wave equation, the obtained wavenumber is near-zero. Therefore, it is concluded that the transformed space is a near-zero-index material. The mapping is provided for open and enclosed spaces. At the end, a parametric numerical analysis is provided for various sets of obtained parameters for the introduced near-zero-index materials. From the analysis, it is shown that the proposed structures can be used as radiators with tunable directivity, as well.

Directional terahertz beam generation under interaction of intense femtosecond laser pulse with cluster jet

Alexei Balakin, Vladimir Gildenburg, Vyacheslav Gordienko, Nikolay Kuzechkin, Yiming Zhu, Peter Solyankin, Alexander Shkurinov, Ivan Pavlichenko, and Timur Semenov

DOI: 10.1364/JOSAB.438757 Received 26 Jul 2021; Accepted 05 Oct 2021; Posted 11 Oct 2021  View: PDF

Abstract: A supersonic jet consisting of atomic clusters of noble gases under the interaction with high-power femtosecond radiation allows control of radiation pattern and efficiency of generation of terahertz (THz) radiation. The laser filament formed in this jet is spatially defined by the shape of the jet. The concentration, spatial distribution and the size of the clusters influence the propagation of femtosecond laser pulse in it and the formation of THz pulse. We showed that a specially formed cluster jet allows to shape THz radiation with a high degree of directionality and increase its intensity by more than 10 times.

Tunneling times of single photons

Jan Gulla and Johannes Skaar

DOI: 10.1364/JOSAB.437386 Received 12 Jul 2021; Accepted 05 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: Although the group delay of classical pulses through a barrier may suggest superluminality, the information transfer is limited by the precursor which propagates at the vacuum light speed. Single photons, however, have infinite tails, and the question of causality becomes meaningless. We solve this problem by introducing strictly localized states close to single photons, which are examples of optical states produced by on-demand single-photon sources. These states can be arbitrarily close to single photons while demonstrating causality for their leading edge.

3D CFD modeling of flowing-gas Rb DPALs: effects of buffer gas composition and of ionization of high lying Rb states

Karol Waichman, Boris Barmashenko, and Salman Rosenwaks

DOI: 10.1364/JOSAB.441871 Received 30 Aug 2021; Accepted 05 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: A comprehensive three-dimensional modeling of flowing-gas Rb diode pumped alkali laser (DPAL) is carried out. The cases of He/CH4 and pure He buffer gases are investigated and the output power and optical efficiency calculated for various pump powers, mole fractions of methane, buffer gas pressures and flow velocities. The model considers the processes of excitation of high levels of Rb, ionization, ion-electron recombination and heating of electrons which affect the diffusion coefficient of Rb ions. Two types of Rb DPAL were studied: a low-power laboratory-scale device with pump power of several tens of W and a high-power multi-kilowatt laser. Efficient operation of the Rb laser using pure He as buffer gas can be achieved only in a large-scale laser with a pump beam cross-sectional area of several cm2. The calculated results for such a device were compared with those reported by A. Gavrielides et al [J. Opt. Soc. Am. B 35, 2202 (2018)], where a simplified three-level model based on one-dimensional gas dynamics approach was applied.

Tutorial on stochastic systems

Colin McKinstrie, Trevor Stirling, and Amr Helmy

DOI: 10.1364/JOSAB.439879 Received 09 Aug 2021; Accepted 04 Oct 2021; Posted 06 Oct 2021  View: PDF

Abstract: In this tutorial, three examples of stochastic systems are considered: A strongly-damped oscillator, a weakly-damped oscillator and an undamped oscillator (integrator) driven by noise. The evolution of these systems is characterized by the temporal correlation functions and spectral densities of their displacements, which are determined and discussed. Damped oscillators reach steady stochastic states. Their correlations are decreasing functions of the difference between the sample times and their spectra have peaks near their resonance frequencies. An undamped oscillator never reaches a steady state. Its energy increases with time and its spectrum is sharply peaked at low frequencies. The required mathematical methods and physical concepts are explained on a just-in-time basis, and some theoretical pitfalls are mentioned. The insights one gains from studies of oscillators can be applied to a wide variety of physical systems, such as atom and semiconductor lasers, which will be discussed in a subsequent tutorial.

Dispersion properties of plasmonic sub-wavelength elliptical wires wrapped with graphene

Mauro Cuevas and Ricardo Depine

DOI: 10.1364/JOSAB.438019 Received 19 Jul 2021; Accepted 04 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: One fundamental motivation to know the dispersive, or frequency dependent characteristics of localized surface plasmos (LSPs) supported by elliptical shaped particles wrapped with graphene sheet, as well as their scattering characteristics when these elliptical LSPs are excited, is related with the design of plasmonic structures capable to manipulate light at sub-wavelength scale. The anisotropy imposed by the ellipse eccentricity can be used as a geometrical tool for controlling plasmonic resonances. Unlike metallic case, where the multipolar eigenmodes are independent of each others, we find that the induced current on graphene boundary couples multipolar eigenmodes with the same parity. In the long wavelength limit, a recursive relation equation for LSPs in term of the ellipse eccentricity parameter is derived and explicit solutions at lowest order are presented. In this approximation, we obtain analytical expressions for both the anisotropic polarizability tensor elements and the scattered power when LSPs are excited by plane wave incidence.

Optimal spin- and planar-quantum squeezing in superpositions of spin coherent states

Richard Birrittella Jr., Jason Ziskind, Edwin Hach, Paul Alsing, and Christopher Gerry

DOI: 10.1364/JOSAB.433743 Received 09 Jun 2021; Accepted 03 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: We investigate the presence of spin- and planar- squeezing in generalized superpositions of atomic (or spin) coherent states (ACS). Spin-squeezing has been shown to be a useful tool in determining the presence of entanglement in multipartite systems, such as collections of two-level atoms, as well as being an indication of reduced projection noise and sub-shot-noise limited phase uncertainty in Ramsey spectroscopy, suitable for measuring phases $\phi\sim 0$. On the other hand, planar-squeezed states display reduced projection noise in two directions simultaneously and have been shown to lead to enhanced metrological precision in measuring phases without the need for explicit prior knowledge of the phase value. In this paper, we show that the generalized superposition state can be parametrized to display both spin-squeezing along all orthogonal axes and planar-squeezing along all orthogonal planes for all values of $J>1/2$. We close with an application of the maximally spin- and planar-squeezed states to quantum metrology.

Investigation of strontium titanate spherical shell supported terahertz all-dielectric metamaterials

Jin Leng, Jun Peng, Guangqing Wang, Xiaoyong He, Fangting Lin, and Feng Liu

DOI: 10.1364/JOSAB.435225 Received 25 Jun 2021; Accepted 03 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: Based on the strontium titanate (SrTiO3, STO) spherical shell all-dielectric metamaterials (ADMs) structure, the tunable propagation characteristics have been systematically studied, taking into account the effects of structural geometrical parameters, temperatures, and graphene Fermi levels. The results indicate that STO-ADMs exhibit excellent thermally and electrically tunable performance, e. g. when the temperatures rise from 77 K to 400 K, the resonant frequency and amplitude modulation depths (MDs) of the reflection dip reach 61.93% and 93.42%, and the absorptions are tunable in the range of 0.7995-0.9017. Moreover, when the temperature is 77 K, the ultra-wideband reflection with reflectivity up to 98% and bandwidth of 1.0 THz is obtained. Additionally, the amplitude MD of the reflection dip reaches 99.89% when the Fermi levels of graphene change from 0.1 eV to 1.0 eV, and the absorptions of the STO-ADMs increase from 0.8352 to 0.9953. These results provide a guide for understanding the resonance mechanisms of ADMs based on STO and for the future designing of multifunctional THz devices.

Ultrafast Nonlinear Optical Properties of Orthorhombic YbFeO₃ Thin Film

Anshu Gaur, MAHAMAD AHAMAD MOHIDDON, and Venugopal Rao Soma

DOI: 10.1364/JOSAB.431976 Received 20 May 2021; Accepted 02 Oct 2021; Posted 05 Oct 2021  View: PDF

Abstract: Tuning the extent of magnetization in rare earth orthoferrites (RFeO3) by ultrashort laser pulses is one of the emerging interest of new technologies. This has opened up the need of studying light intensity dependent [nonlinear (NL)] optical properties of orthoferrites. The present work reports the results from femtosecond NL optical characterization studies of YbFeO3 thin film by the standard Z-scan technique in open and closed aperture configurations. The thin film sample deposited on quartz substrate is irradiated with ~50 femtosecond laser pulses of different input powers. YbFeO3 exhibited reverse saturable absorption (RSA) characteristics at the excitation wavelengths of 600 and 800 nm. The observed NLA characteristics are associated to the electronic excitation between Fe3+ d-orbitals and charge transfer transition from O p-orbital to Fe3+ d-orbitals. The NL parameters are estimated using the coupled absorption model for simultaneous linear and two-photon absorption (2PA) developed previously by our group and are found comparable to that of the many other mixed oxide materials such as (Ba,Sr)TiO3. The NL coefficients are correlated with linear absorption at 2PA wavelengths and with theoretical 2PA model based on parabolic and non-parabolic band structures reported in literature.

High Performance Plasmonically Enhanced Graphene Photodetector for Near-Infrared Wavelengths

Somayeh Yousefi, Maryam pourmahyabadi, and Ali Rostami

DOI: 10.1364/JOSAB.438124 Received 21 Jul 2021; Accepted 29 Sep 2021; Posted 29 Sep 2021  View: PDF

Abstract: Graphene is a very attractive material for applications in optoelectronic devices such as photodetectors because of fast response and broadband absorption. However, the weak absorption of graphene layer limits the performance of the graphene-based photodetectors. To this end, a high responsivity graphene-based plasmonic photodetector, operating over a wide optical wavelength range is presented in this paper. In order to enhance the light absorption efficiency and consequently to improve the responsivity of the photodetector, a graphene layer and a specific plasmonic nanostructure is combined. The numerical simulation results revealed that nearly perfect light absorption is achieved at the wavelength of 1550nm for the proposed structure. The circuit model of the structure is presented based on transmission line theory whose results are in very good agreement with the numerical simulation results. Also, the high responsivity of 513mA/W and the bandwidth of 47GHz are achieved for this scheme.

Simultaneous nonlinear wavelength and mode conversion for high-brightness blue sources

Robert Lindberg, Xiao Liu, Andrius Zukauskas, Siddharth Ramachandran, and Valdas Pasiskevicius

DOI: 10.1364/JOSAB.436188 Received 06 Jul 2021; Accepted 26 Sep 2021; Posted 28 Sep 2021  View: PDF

Abstract: We investigate frequency doubling of focused Bessel-like higher order fiber modes in a one-dimensionally quasi-phase matched structured KTP crystal. A single higher-order fiber mode, LP₀¸₇, was generated at 971 nm using a fiber optical parametric amplifier pumped by sub-nanosecond pulses at 1064 nm. Frequency doubling to 485.5 nm was achieved with a maximum conversion efficiency of 48%, which produced a highly structured blue beam without any brightness improvement with respect to the fundamental beam. By optimizing the phase mismatch, we also experimentally demonstrate clean on-axis conversion –resulting from cascaded χ²:χ² processes, which is in good agreement with our numerical simulations, that give rise to brightness enhancement.

Tutorial on laser linewidths

Colin McKinstrie, Trevor Stirling, and Amr Helmy

DOI: 10.1364/JOSAB.439882 Received 09 Aug 2021; Accepted 14 Sep 2021; Posted 05 Oct 2021  View: PDF

Abstract: In this tutorial, the physical origins and mathematical analyses of laser linewidths are reviewed. The semi-classical model is based on an equation for the light-mode amplitude that includes random source terms, one term for each process that affects the amplitude (stimulated and spontaneous emission, stimulated absorption, and facet and material loss). Although the source terms are classical, their assigned strengths are consistent with the laws of quantum optics. Analysis of this equation shows that the laser linewidth is proportional to the sum of the (positive) source strengths for all gain and loss processes. Three-level and semiconductor lasers have broader linewidths than comparable four-level lasers, because stimulated absorption and the stimulated emission that compensates it both contribute to the linewidth.

Enhancement of 1532 nm emission in Ce3+, Er3+ co-doped Ca1.5Y1.5Al3.5Si1.5O12 performed by multichannel energy transfer

Haitao Wang, Yaoxiang Zhao, Siguo xiao, and Xiaoliang Yang

DOI: 10.1364/JOSAB.436294 Received 07 Jul 2021; Accepted 18 Aug 2021; Posted 12 Oct 2021  View: PDF

Abstract: Novel near-infrared emission material, Ce3+, Er3+ co-doped Ca1.5Y1.5Al3.5Si1.5O12 has been synthesized via high temperature solid state reaction method. The luminescence intensity of 1532 nm emission excited with 455 nm increases by 4.2 times after the introduction of Ce3+ ions, on account of Ce3+→Er3+ radiation-reabsorption energy transfer and nonradiative energy transfer sensitization as well as the 4I11/2(Er3+) + 2F5/2(Ce3+)→4I13/2(Er3+) + Ce3+(2F7/2) cross relaxation between Ce3+ and Er3+ ions. The result shows that the developed material is convenient to obtain near infrared emission of high efficiency using commercial blue GaN LED as pumping source.

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