Showing papers in "Journal of The Optical Society of America B-optical Physics in 2020"

Roadmap to free space optics

Abstract: With the ever-increasing demand for data and the radio frequency spectrum becoming congested, free space optics (FSO) may find a niche for situations where fiber is too expensive or too difficult to install. FSO is a cross-disciplinary field that draws from radio and fiber communication, astronomy, and even quantum optics, and it has seen major advances over the last three decades. In this tutorial-style review, we provide a broad overview of many of the important topics required to design, develop, and research the next generation of FSO technology.

Unidirectional ultrabroadband and wide-angle absorption in graphene-embedded photonic crystals with the cascading structure comprising the Octonacci sequence

Abstract: Using the transfer matrix method, a unidirectional absorber with an ultrabroadband absorption bandwidth and angular stability is realized in the graphene-embedded photonic crystals (GPCs) arranged by the cascading structure formed with the periodic sequence and the quasi-periodic Octonacci sequence in the terahertz regime. As a result, the surface conductivity of the graphene sheet can be modulated via the chemical potential, and the characteristics of the proposed absorber are tunable. Compared to the structure spliced by the diverse periodic sequences, the relative absorption bandwidth of the proposed composite construction is up to 94.53%, which far outweighs that of the periodic one. We compare the Octonacci sequence, the Fibonacci sequence, and the Thue–Morse sequence, and the calculated results reveal the advantage of the Octonacci sequence in the expansion of the absorption bandwidth. Under the optimization of the related parameters, the incident wave is primarily reflected in the forward propagation and absorbed in a wide range of θ under the TM mode in backward propagation, which shows the splendid unidirectionality and angular stability. The impacts of the chemical potential, structural thicknesses, and stack numbers on the absorption properties are also investigated in detail. Additionally, the impedance match theory and the interference field theory are introduced to explain the intrinsic absorption mechanism of the presented GPCs. In short, the unidirectional broadband and angle-insensitive absorber has extensive application prospects in optical sensing, optical filtering, photodetection, and solar energy collection.

Fabrication of magnesium metallic nanoparticles by liquid-assisted laser ablation

Abstract: Magnesium metallic nanoparticles have been synthesized using the pulsed laser ablation in liquid media technique (PLAL) in the range of 20–30 nm by varying the laser ablation time. During the laser ablation process, the laser-induced breakdown spectroscopy (LIBS) technique is used to investigate the physicochemical properties as laser-induced Mg plasma in terms of spectral line intensities and their plasma parameters (ne and Te). The X-ray diffraction technique and UV-visible technique show that the produced samples have a crystalline structure, and as the laser ablation time increases, the value of the absorption peak shifts to lower wavelengths and the average particle decreases, respectively. The use of the PLAL technique shows the capability to produce a metallic structure based on purging the solution by molecular nitrogen. The use of the LIBS technique shows a good and fast tool for detecting their particle sizes and the differentiation between the metallic form and its oxide structure.

Broadband metamaterial-based near-infrared absorber using an array of uniformly placed gold resonators

Abstract: Solar absorbers are designed for absorbing visible, infrared, and ultraviolet frequencies. Most of the absorbers designed so far have been for absorbing visible frequencies, and there is a strong need for designing infrared absorbers and ultraviolet absorbers. We present a broadband near-infrared absorber using metamaterial gold resonators. The gold resonators are uniformly placed over the SiO2 substrate in different patterns. All of these patterns’ solar absorbers are analyzed, and the results are presented in the form of reflection, transmission, absorption, electric field, permittivity, permeability, and refractive index. The parameter physical size is also varied, and results are observed in terms of reflection, absorption, and transmission. The optimized design is also obtained by analyzing all the design results. Comparative tables are also presented for all of these designs. The results are obtained for the near-infrared frequency range of 155 THz to 425 THz. The proposed uniform metamaterial absorber is applicable in photovoltaic applications and energy harvesting applications.

Quantum electrodynamics in modern optics and photonics: tutorial

Abstract: One of the key frameworks for developing the theory of light–matter interactions in modern optics and photonics is quantum electrodynamics (QED). Contrasting with semiclassical theory, which depicts electromagnetic radiation as a classical wave, QED representations of quantized light fully embrace the concept of the photon. This tutorial review is a broad guide to cutting-edge applications of QED, providing an outline of its underlying foundation and an examination of its role in photon science. Alongside the full quantum methods, it is shown how significant distinctions can be drawn when compared to semiclassical approaches. Clear advantages in outcome arise in the predictive capacity and physical insights afforded by QED methods, which favors its adoption over other formulations of radiation–matter interaction.

Ultrathin, polarization-insensitive multi-band absorbers based on graphene metasurface with THz sensing application

Abstract: This article presents multi-band plasmonic absorbers based on a graphene array at terahertz frequencies The absorbers are made of a very simple structure including a graphene disk array printed on the top surface of a dielectric spacer backed by a metallic ground plane Multi-band performance is achieved with more than 90% absorption in the 1–8 THz frequency range by exciting surface plasmon polaritons of graphene It is shown that the resonance frequencies of the proposed absorber can be tuned by varying the chemical potential between 08–1 eV for a triple-band absorber and 07–09 eV for a quad-band one, while keeping more than 80% absorption The results obtained by means of full-wave simulation are verified with the results obtained by the analytical circuit model The proposed absorbers are polarization-insensitive and provide stable absorption performance for both of the TE and TM polarizations As an application, we designed a refractive index sensor based on the triple-band absorber The results verify that the absorption bands are sensitive to the variations of the refractive index of the coating layer

Hyperbolic metamaterial for the Tamm plasmon polariton application

Abstract: The possibility of using a hyperbolic metamaterial to form conventional and epsilon-near-zero Tamm plasmon polaritons in the near-infrared and visible spectral ranges is demonstrated. The spectral properties of the hyperbolic metamaterial are investigated in the framework of the effective medium theory and confirmed by the transfer matrix method. It is found that at the oblique incidence of light onto a structure, the I-type hyperbolic metamaterial can be implemented, while II-type cannot. The sensitivity of the epsilon-near-zero wavelength to the variation in the angle of light incidence for TE and TM waves is demonstrated. It is shown that both the high-quality and broadband Tamm plasmon polaritons are excited in the investigated structures.

Ground-state cooling of a magnomechanical resonator induced by magnetic damping

Abstract: Quantum manipulation of mechanical resonators has been widely applied in fundamental physics and quantum information processing. Among them, cooling a mechanical system to its quantum ground state is regarded as a key step. In this work, we propose a scheme that can realize ground-state cooling of the resonator in a cavity magnomechanical system. The system consists of a microwave cavity and a small ferromagnetic sphere, in which phonon–magnon coupling and cavity photon–magnon coupling can be achieved via magnetostrictive interaction and magnetic dipole interaction, respectively. Within experimentally feasible parameters, we demonstrate that the extra magnetic damping can be utilized to achieve ground-state cooling of the magnomechanical resonator via an effective dark-mode interaction. The magnomechanical cooling mainly comes from the magnon–phonon interaction terms. We further illustrate that optimal cooling can be obtained by adjusting the external magnetic field.

High-dimensional cryptography with spatial modes of light: tutorial

Abstract: Fast and secure sharing of information is among the prime concerns of almost any communication system While commonly used cryptographic algorithms cannot provide unconditional security, high-dimensional (HD) quantum key distribution (QKD) offers an exceptional means to this end Here, we provide a tutorial to demonstrate that HD QKD protocols can be implemented in an effective way using optical elements that are known to most optics labs We use spatial modes of light as our HD basis and show how to simulate QKD experiments with bright classical light, fostering its easy implementation for a more general audience including industry laboratories or laboratory classes in university teaching and in advanced laboratories for validation purposes In particular, we use orbital angular momentum Bessel–Gaussian modes for our HD QKD demonstration to illustrate and highlight the benefits of using spatial modes as their natural Schmidt basis and self-healing feature

Research on photonic crystal fiber based on a surface plasmon resonance sensor with segmented silver-titanium dioxide film

Abstract: A photonic crystal fiber based on a surface plasmon resonance sensor coated with segmented silver-titanium dioxide (${\rm Ag} \text{-} {{\rm TiO}_2}$Ag-TiO2) film is proposed for microfluid refractive index sensing. The sensing properties of the designed sensor are analyzed numerically by the full-vectorial finite element method. The results display that the wavelength sensitivity can be tuned by the thickness of the ${{\rm TiO}_2}$TiO2 film and segmented number and angle of the ${\rm Ag} \text{-} {{\rm TiO}_2}$Ag-TiO2 film. It is observed that an average sensitivity of 6329 nm/RIU for refractive indexes ranging from 1.330 to 1.360, and a maximum wavelength sensitivity of 10600 nm/RIU with a high wavelength resolution of ${9.43} \times {{10}^{ - 6}}\;{\rm RIU}$9.43×10−6RIU, can be achieved in the sensing range of 1.350 to 1.355. In addition, it also shows a maximum amplitude sensitivity of ${633.4001}\;{{\rm RIU}^{ - 1}}$633.4001RIU−1, and the maximum figure of merit is 303 with ${n_a}$na varying from 1.330 to 1.360, which can be applied to the field of chemical and biological analysis.

Multiband terahertz absorbers using T-shaped slot-patterned graphene and its complementary structure

Abstract: A dual-band absorber using monolayer periodically T-shaped slot-patterned graphene at terahertz frequencies is presented. By changing the dimensions or Fermi levels of the T-shaped slot-patterned graphene, both of the two absorption bands will be adjusted. The absorber has the characteristics of polarization independence and incident angle insensitivity. Also, its complementary structure, i.e., using periodically T-shaped strip-patterned graphene, is investigated to design another dual-band absorber. Moreover, two triband absorbers are studied through periodically loading four more T-shaped slots and complementary strips in square graphene lattices, respectively. This paper provides a significant paradigm for designing different graphene-based absorbers with multiple absorption bands.

Highly sensitive temperature sensor based on cascaded HiBi-FLMs with the Vernier effect

Abstract: We propose and experimentally demonstrate a highly sensitive temperature sensor based on cascaded high birefringence fiber loop mirrors (HiBi-FLMs) with the Vernier effect. The two HiBi-FLMs have almost the same free spectrum range (FSR), which can be regarded as two scales of different periods of an optical Vernier-scale, and act as the fixed part and the sliding part, respectively. A Gauss fitting algorithm is introduced to fit the Vernier spectrum envelope to accurately trace the spectral shift of the envelope. The temperature sensitivity and temperature resolution of the cascaded configuration are much larger than those of the individual HiBi-FLMs due to the Vernier effect. The experimental result shows that the temperature sensitivity of the proposed sensor can be improved from −1.723nm/∘C (single HiBi-FLM) to −43nm/∘C (cascaded configuration) by employing the Vernier effect, and the temperature resolution is enhanced from ±0.029∘C to ±0.001162∘C. The amplification factors for temperature sensitivity and temperature resolution are both 24.96, which shows good agreement with the theoretical predictions. The proposed sensor with huge temperature sensitivity, high resolution, and simple configuration may be a promising candidate for some applications that need precise temperature control.

Multipass cells: 1D numerical model and investigation of spatio-spectral couplings at high nonlinearity

Abstract: Multipass cells (MPCs) are used nowadays as nonlinear tools to perform spectral broadening and temporal manipulation of laser pulses while maintaining a good spatial quality and spatio-spectral homogeneity. However, intensive 3D nonlinear spatio-temporal simulations are required to fully capture the physics associated with pulse propagation inside these systems. In addition, the limitations of such a scheme are still under investigation. In this study, we first establish a 1D model as a useful design tool to predict the temporal and spectral properties of the output pulse for nearly Gaussian beams, in a wide range of cavity configurations and nonlinearity levels. This model allows us to drastically reduce the computation time associated with MPC design. The validity of the 1D model is first checked by comparing it to 3D simulations. The results of the 1D model are then compared with experimental data collected from a near-concentric gas-filled multipass cell presenting a high level of nonlinearity, enabling the observation of wave breaking. In a second part, we experimentally characterize the spatio-spectral profile at the output of this experimental setup, both with an imaging spectrometer and with a complete 3D characterization method known as INSIGHT. The results show that gas-filled multipass cells can be used at peak power levels close to the critical power without inducing significant spatio-spectral couplings in intensity or phase.

Photonic nanojets generated by single microspheres of various sizes illuminated by resonant and non-resonant focused Gaussian beams of different waists

Abstract: We report theoretical simulations on the photonic nanojet (PNJ) of single dielectric microspheres of various sizes illuminated by focused Gaussian beams (FGBs), using analytical theory developed by Gouesbet et al. based on the Bromwich formalism. The radius of the microsphere ($R$R) is varied from 1 to 45 µm. The effect of the beam waist (${\omega _0}$ω0) on characteristic parameters such as maximum electric field enhancement (${\eta _{\rm max}}$ηmax) of the PNJ, the focal length of the microsphere ($f$f), effective length, and width of the PNJ is studied in detail. The effect of the refractive index of the microsphere (${n_p}$np) and $R$R on the ${\eta _{\rm max}}$ηmax for different values of ${\omega _0}$ω0 is studied. The dependence of (i) the $f$f value on $R$R and (ii) the ${\eta _{\rm max}}$ηmax value on $\lambda $λ is investigated systematically.

Design of a near-infrared plasmonic gas sensor based on graphene nanogratings

Abstract: In this work, a gas sensor based on the plasmonic double-layer graphene nanograting (GNG) structure with an enhanced figure of merit (FoM) is presented in the near-infrared region. This structure includes double periodic graphene nanoribbon arrays, separated by a dielectric. The wavelength interrogation method is employed to accurately investigate the behavior of the proposed structure for various physical and geometrical parameters, including the array pitch, graphene nanoribbon width, refractive index of the intermediate dielectric between the GNGs, and the chemical potential of the graphene. A sharp dip is achieved by the guided-mode resonance between the two GNG layers, due to their near-field coupling. For the optimized design, obtained sensitivity and FoM are 430.91 nm/RIU and 174.68RIU−1, respectively, when the finite-element method is used for the simulations. The high FoM is a result of the field enhancement at the edges of the graphene nanoribbons, as well as the narrow resonance linewidth achieved by the sharp transmission dip. In addition to the high performance and FoM, the structure is robust to the misalignment of two GNG layers, offering a solution for practical gas sensing applications. To the best of our knowledge, the proposed GNG-based structure enjoys a boosted FoM compared to the previously proposed integrated gas sensors, as well as a practically feasible design for fabrication.

Optimizing optical trap stiffness for Rayleigh particles with an Airy array beam

Abstract: Airy array beams are attractive for optical manipulation of particles owing to their non-diffraction and auto-focusing properties. An Airy array beam is composed of $ N $N Airy beams that accelerate mutually and symmetrically in opposite directions, for different ballistics trajectories, i.e., with different initial launch angles. Based on this, we investigate the optical force distribution acting on Rayleigh particles. Results show that it is possible to obtain greater stability for optical trapping by increasing the number of beams in the array. Also, the intensity focal point and gradient and scattering force of the array on Rayleigh particles can be controlled through a launch angle parameter.

Spectrally selective filter design for passive radiative cooling

Abstract: Radiative cooling is potentially one of the most innovative approaches to reducing energy density in buildings and industry, as well as achieving higher levels of energy efficiency. Several studies have reported the design of spectrally selective layered structures for daytime passive radiative cooling. However, a comprehensive design of such systems requires the spectral behavior of different materials and radiative heat transfer mechanisms to be addressed together. Here, we introduce a design methodology for daytime passive radiative cooling with thin film filters which accounts for the spectral tailoring at the visible and infrared spectrum. The major difference of this method is that it does not require a predefined target ideal emittance. The results show that higher cooling powers are possible compared to the previously reported thin-film structures, which were designed from a purely spectral perspective. The underlying mechanisms of the resulting spectral profiles, which give rise to improved performance, are investigated by wave impedance analysis. Cooling powers up to ${100}\,{{\rm W/m}^2}$100W/m2 are obtained with seven layers on Ag. The findings of this study indicate that structures with better performance in terms of cooling powers and temperature reduction rates can be obtained following the procedure discussed.

Surface plasmon resonance-based silicon dual-core photonic crystal fiber polarization beam splitter at the mid-infrared spectral region

Abstract: In this paper, a novel silicon dual-core photonic crystal fiber (Si-DC-PCF) polarization beam splitter (PBS) based on the surface plasmon resonance effect is proposed The mode-coupling characteristics between the X- and Y-polarized even and odd modes and surface plasmon polariton mode are analyzed by using the finite-element method and coupled-mode theory The influences of the structure parameters of the Si-DC-PCF on the coupling length and coupling length ratio are investigated The normalized output power of the X- and Y-polarized modes in cores A and B and the corresponding extinction ratio are also discussed By optimizing the structure parameters of the Si-DC-PCF, the PBS length of 192 µm and bandwidth of 830 and 730 nm in cores A and B are achieved It is believed that the proposed Si-DC-PCF PBS can find important applications in mid-infrared laser and sensing systems

High-sensitivity spectroscopic gas sensor using optimized H1 photonic crystal microcavities

Abstract: An optimized H1 photonic crystal (PhC) microcavity with a high quality factor (Q), small mode volume, wide measurement range, and high sensitivity is proposed, and its possibility in spectroscopic gas sensing is theoretically demonstrated. In the proposed structure, we have taken advantage of the air holes surrounding the defect region to optimize the resonance characteristics so as to detect the target gas, which is required for designing miniaturized spectroscopic gas sensors. By fine-tuning the structural parameters of several ring air holes surrounding the defect region, the results show that the sensitivity can be up to 3303 nm/RIU, along with a high Q of 104 and a detection limit as low as 10−4 RIU for gas sensing. Also, it is theoretically verified that the optimized H1 PhC microcavity has the ability to maintain RI sensitivity over a wide RI range of gases, enabling detection of He, N2, CO2, C2H2, and C3H8 gases. The main feature of this structure is that the enhanced electrical field is strongly localized in the defect region for any gas sample due to a small mode volume. Therefore, these findings provide useful design rules for applications involving compact and tunable spectroscopic gas sensor devices with high Q and sensitivity.

Coupled-mode theory for microresonators with quadratic nonlinearity

Abstract: We use Maxwell’s equations to derive several models describing the interaction of the multi-mode fundamental field and its second harmonic in a ring microresonator with quadratic nonlinearity and quasi-phase-matching We demonstrate how multi-mode three-wave mixing sums entering nonlinear polarization response can be calculated via Fourier transforms of products of the field envelopes Quasi-phase-matching gratings with arbitrary profiles are incorporated seamlessly into our models We also introduce several levels of approximations that allow us to account for dispersion of nonlinear coefficients and demonstrate how coupled-mode equations can be reduced to the envelope Lugiato–Lefever-like equations with self-steepening terms An estimate for the χ(2) induced cascaded Kerr nonlinearity, in the regime of imperfect phase-matching, puts it above the intrinsic Kerr effect by several orders of magnitude

Performance analysis of an efficient and stable perovskite solar cell and a comparative study of incorporating metal oxide transport layers

Abstract: As poor stability is the primary constraint for the commercialization of perovskite solar cells, improving stability has been the primary focus of recent research works regarding solar cells that make use of perovskite materials. Different metal oxide transport layers are being used with the aim of fabricating stable perovskite solar cells. A stable and efficient solar cell with both metal oxide transport layers (ZnO and NiOX) and a perovskite (methyl ammonium lead iodide) absorber layer is simulated in this work, and a comparison of performance parameters is made with other transport layers from the literature. The issue of optimization regarding the thickness of the absorber layer and the doping concentration in the absorber and transport layers has been addressed, and the effect of defect concentration at the interface has been investigated. Optimum performance is achieved with an absorber layer of thickness 800 nm. Linear grading is also introduced in the absorber layer by varying the concentration of different halides, which increases the efficiency by approximately 8% owing to the increase in the short circuit current density.

Measuring the nonlinear optical properties of indium tin oxide thin film using femtosecond laser pulses

Abstract: We have investigated the nonlinear optical properties of indium tin oxide (ITO) thin film coated on soda–lime glass substrate using the z-scan technique. With 100 fs laser pulses, the nonlinear absorption coefficient and nonlinear refractive index are measured at different excitation wavelengths and at different incident intensities. The nonlinear optical absorption shows a competition between saturable absorption and reverse saturable absorption at the different excitation wavelengths and incident intensities. A transition from saturable to reverse saturable absorption was observed with increasing excitation wavelengths. The measured nonlinear refractive index was found to be dependent on wavelength with a maximum value of 5.34×10−12cm2/W at wavelength of 900 nm.

Quantum-enhanced balanced detection for ultrasensitive transmission measurement

Abstract: Balanced detection is a popular method to cancel out the effect of laser intensity noise in optical measurements and spectroscopy. However, the signal-to-noise ratio (SNR) that can be achieved with balanced detection is constrained by the standard quantum limit (SQL). Here, we propose quantum-enhanced balanced detection (QBD), which allows us to improve the SNR beyond the SQL to realize ultrasensitive transmission measurement. In QBD, squeezed vacuum is injected to one of the input ports of a beamsplitter (BS) used in balanced detection to produce a pair of light waves whose shot noises are entangled with each other. Compared with previous quantum-enhanced measurement methods, QBD is advantageous because it can handle a higher optical power without sacrificing the degree of sensitivity enhancement. We present the theory of QBD and discuss the effects of the splitting ratio of the BS and the optical loss caused by the sample under test. We also describe the application of QBD to the sensitivity enhancement of molecular vibrational imaging based on stimulated Raman scattering microscopy.

Reflective photonic hook achieved by a dielectric-coated concave hemicylindrical mirror

Abstract: In this study, we propose a new design of a dielectric-coated concave hemicylindrical mirror for efficient generation of a reflective photonic hook (PH). Numerical approaches based on the finite-difference time-domain technique are used to investigate the physical mechanism of reflective PH formation. The field intensity distributions and photonic fluxes near the concave mirror are analyzed for working in the reflection mode. The asymmetric vortexes of Poynting vectors cause the reflective PH with a large bending angle. By changing the refractive index of the dielectric film, the shape and curvature of the reflective PH can be efficiently adjusted. Moreover, the narrow waist of the reflective PH is obtained beyond half of the incident wavelength. This compact dielectric-coated concave mirror has proven its practicability for integrated photonic circuits in the reflection mode.

Teleporting quantum Fisher information for even and odd coherent states

Abstract: We present a scheme for implementing a quantum teleportation process using the Jaynes–Cummings model. For this, we study the interaction between an excited state of a two-level atom and a single electromagnetic field in a superposition of coherent states. The resulting entangled state may be considered as a good quantum channel for quantum teleportation protocol. By controlling the interaction field parameters inside the cavity, the average fidelity of the teleported state may be maximized. However, the weight and phase parameters in the teleported states are estimated by using quantum Fisher information. It allows one to show that the sensitivity of the teleported states fluctuates between maximum and minimum bounds for large numbers of photons. Evaluating different quantities of quantum entanglement, average fidelity, and the amount of quantum Fisher information shows that the odd coherent states are usually larger than those obtained using even coherent states.

Integrable all-optical NOT gate using nonlinear photonic crystal MZI for photonic integrated circuit

Abstract: A silicon photonic crystal (PhC)-based nonlinear Mach–Zehnder interferometer (NMZI) is used to design a new model for an all-optical NOT gate. The nonlinear arm of the NMZI is considered to be made of a slotted-PhC waveguide, where the slot is filled with silicon nanocrystal ($ {\rm SiNC}/{{\rm SiO}_2} $SiNC/SiO2) material. The high nonlinearity of the $ {\rm SiNC}/{{\rm SiO}_2} $SiNC/SiO2 and low group velocity of the PhC make it possible to attain a significant phase shift in low-power high-frequency pulses traveling through the nonlinear arm. A control wave is utilized to increase the phase shift by the cross-phase modulation phenomenon. A complete study on the phase variation is performed by varying various parameters such as powers and pulse widths of the probe and control signal. The study is used to determine the length of the nonlinear arm to calculate the transfer characteristic of the device. The transfer characteristic shows a successful inversion operation in the power range of 28–60 mW for a pulse width of 3 ps. The overall dimension of the device is found as $ \approx {112} \times {7}\,\,\unicode{x00B5}{\rm m^2} $≈112×7µm2. Tolerances of the device performance under fabrication imperfections are analyzed by allowing random variations in the positions and the radii of the holes. This study reveals that the inversion characteristic is sustained, even for the significant fabrication imperfections.

Experimental study on a high-sensitivity optical fiber sensor in wide-range refractive index detection

Abstract: A novel plasmonic sensor based on a photonic crystal fiber has been fabricated. Experimental results show that 2 cm is an optimal fiber length of the sensor for refractive index monitoring. It is found that the average wavelength sensitivity and the resolution of the proposed sensor are 4000 nm/RIU and 2.5×10−5RIU in the wind range of 1.3333–1.4035, respectively. In addition, this paper presents a set of operation flat roofs that is used in the side-polished fiber technique. Moreover, two effective methods of coating silver film are discussed in detail. The research in this paper has enlightening significance for exploring new optical fiber sensing technology and will open a new design methodology for optical fiber sensors.

Strong coupling between excitons and guided modes in WS 2 -based nanostructures

Abstract: Transition-metal dichalcogenides (TMDCs) exhibit great potential in light–matter interaction due to their semiconducting nature and remarkable excitonic properties. Here a simple guided resonance structure is proposed to numerically investigate and realize dual-band light absorption exploiting the guided mode resonance (GMR) in the system and the robust exciton in the $ {{\rm WS}_2} $WS2 monolayer. The dispersive GMR can strongly interact with the nondispersive exciton state by tuning the incident angle, resulting in remarkable Rabi splitting and the emergence of two hybrid polariton bands. The strong GMR–exciton coupling behavior can be well described by the classic oscillator model. The influence of the geometrical parameters on the spectral response is investigated. In addition, we also find that the Rabi splitting is strongly affected by the position of the $ {{\rm WS}_2} $WS2 monolayer in the dielectric slab. Our findings provide a simple route for realization of hybrid light–TMDCs interactions, which may inspire related studies on compact, scalable, and easy-to-fabricate TMDC-based devices.

Generation of narrowband counterpropagating polarization-entangled photon pairs based on thin-film lithium niobate on insulator

Abstract: We propose a scheme for the generation of counterpropagating polarization-entangled photon pairs from a periodically poled lithium niobate on insulator waveguide. The waveguide is designed to enable a special dispersion relationship between the TM00 and TE00 modes that allows two concurrent counterpropagating quasi-phase-matching type-II spontaneous parametric downconversion processes with a single reciprocal wave vector. Due to the counterpropagating phase-matching geometry, the source has a narrow bandwidth in the order of several gigahertz. The compact source opens up a new method for integrated photonic technologies.

Sub-surface modifications in silicon with ultra-short pulsed lasers above 2 µm

Abstract: Nonlinear optical phenomena in silicon such as self-focusing and multi-photon absorption are strongly dependent on the wavelength, energy, and duration of the exciting pulse, especially for wavelengths >2µm. We investigate the sub-surface modification of silicon using ultra-short pulsed lasers at wavelengths in the range of 1950–2400 nm, at a pulse duration between 2 and 10 ps and pulse energy varying from 1 µJ to 1 mJ. We perform numerical simulations and experiments using fiber-based lasers built in-house that operate in this wavelength range for the surface and sub-surface processing of Si-wafers. The results are compared to the literature data at 1550 nm. Due to a dip in the nonlinear absorption spectrum and a peak in the spectrum of the third-order nonlinearity, the wavelengths between 2000 and 2200 nm prove to be more favorable for creating sub-surface modifications in silicon. This is the case even though those wavelengths do not allow as tight focusing as those at 1550 nm. This is compensated for by an increased self-focusing due to the nonlinear Kerr-effect around 2100 nm at high light intensities, characteristic for ultra-short pulses.