Sharp Transmission Research Articles

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity.

We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40dB and a peak loss as low as 0.6dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption, and higher contrast, compared to that involving Lorentzian resonance. For example, under signal trains of 2.5Gb/s, switching energy with a contrast of 3dB for the Fano case is 113fJ, which is 8dB smaller than that for the Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67dB to 9.53dB.

An improved cascaded SO-FDTD method for high temperature magnetized plasma

An improved cascaded shift operator finite-difference time-domain method is put forward for high temperature magnetized plasma. The calculation formulas of iterative coefficients of this method are given. These results show that the improved method can let the mathematical formula reduce math order and the computational complexity. This is contributed to the derivation of the formula and the compilation of the calculation program. The absorption and reflection characteristics of high temperature magnetized plasma on electromagnetic wave are studied by using this improved CSO-FDTD method. The effects of external magnetic field and temperature on the attenuation coefficient and absorption coefficient of the plasma are discussed. A new phenomenon is found, namely, a sharp transmission peak emerged in the physics band formed by a terahertz wave passing through the monolayer plasma. By studying the effects of external magnetic field and temperature, the phenomenon can be simply produced by monolayer high temperature plasma.

Optical spectrometer based on continuously-chirped guided mode resonance filter.

In this work we introduce a tunable GMR filter based on continuously period-chirped (ΔP = 130 nm) gratings using a Ta2O5 waveguide layer with graded thickness (ΔT = 36 nm). The structure of the gradient-period grating is defined using a modified Lloyd's mirror interferometer with a convex mirror, and Ta2O5 film used for the gradient is deposited using masked e-beam evaporation. The as-realized chirped GMR filter provides sharp transmission dips at resonant wavelengths with a filter bandwidth of approximately 4.2 nm and 0.78 nm when respectively applied to TE and TM polarized light under normal incidence. Gradually sweeping the chirped GMR filter makes it possible to monotonically sweep through resonant wavelengths from 500 to 700 nm, while maintaining stable filter bandwidth and transmission intensity. The optical spectrum of the incoming light can then be loyally reconstructed accordingly. We successfully demonstrate the spectrum reconstruction of a white light emitting diode and a dual-peak laser beam using the proposed chirped GMR filter as a dispersive device.

Modeling of Periodic Array of Cut-Through Slits With Sinusoidal Surface Conductivity at the Interfaces of an Anisotropic Medium

A periodic arrangement of 1-D slits carved in a perfect electric conductor is investigated, and an equivalent model which features sinusoidal surface conductivity on its upper and lower interfaces is derived. Therefore, and in sheer contrast to all the previous attempts that were successful in mimicking only the zeroth-order diffracted waves, it is capable of emulating both specular and nonspecular diffraction orders. The accuracy of the model is verified by the full-wave simulations. The proposed model is used to study the sharp Fano-type extraordinary transmission resonances arising in the structure. The transmission spectrum near these resonances is derived in terms of Fano resonance parameters. Furthermore, our model is used to explain the plasma-like behavior of the cut-through metallic slits in terms of the band bending caused by the periodicity of the surface conductivity. The analysis and design of applications which are devised based on the characteristics of higher Bloch orders can also be facilitated by this model.

Extremely sharp transmission peak in optically thin aluminum film with hexagonal nanohole arrays

Extraordinary transmission is the most attractive phenomenon, that has been studied in recent decades, for optically thick metal film with nanohole arrays. On the contrary, in optically thin metal film with nanohole arrays, it has been found that the interaction between excited surface plasmon polariton and non-resonant direct propagation light introduces a strong light absorption and causes a suppressed transmission dip. Here, we explore the optical properties of a free standing optically thin aluminum film with a hexagonal large filling ratio nanohole array and find an extremely sharp extra extraordinary transmission peak within the suppressed transmission dip which is originated from the interaction of the excited surface plasmon polariton and the non-resonant directly scattered light. Simulation results show that the nanohole-array-based biosensor that were proposed have an excellent sensitivity, with a figure of merit of 87, beyond that of nanohole-array-based biosensors reported previously for normal incidence.

Fast and accurate full-spectrum interrogation for fiber Fabry–Perot interferometric sensor consisting of Bragg gratings in polarization maintaining fiber

A measurement method for many sharp transmittance peaks of a fiber Fabry–Perot interferometer (FPI) with high resolution in a short time is proposed. Using the proposed method, temperature and strain dependences of an FPI constructed using polarization maintaining type fiber Bragg grating (PM-FBG-FPI) are evaluated. By detecting wavelength shift occurring in many peaks of a PM-FBG-FPI with high resolution, it is possible to quantitatively evaluate a slight shift coefficient difference due to the difference in resonance order of each peak. Simultaneous measurement resolution of temperature and strain by the PM-FBG-FPI sensor is also improved by using the average value of the wavelength shift detected at many peaks. The resulting high-resolution measurements are demonstrated experimentally.

Fundamentals and applications of optomechanically induced transparency

Cavity optomechanical systems have been shown to exhibit an analogon to atomic electromagnetically induced transparency that a transmission window for the propagation of the probe field is induced by a strong control field when the resonance condition is met. Sharp transmission features controlled by the control laser beam enable many applications ranging from force sensors to quantum communication. In recent years, there has been significant progress in both theoretical and experimental studies of this phenomenon, driven by the development of nanophotonics as well as the improvement of nano-fabrication techniques. Optomechanically induced transparency has been found to manifest in numerous different physical mechanisms, e.g., nonlinear optomechanically induced transparency, double optomechanically induced transparency, parity-time symmetric optomechanically induced transparency, and optomechanically induced transparency in various hybrid optomechanical systems, etc. These results offer a pathway towards an integrated quantum optomechanical memory, show the utility of these chip-scale optomechanical systems for optical buffering, amplification, and filtering of microwave-over-optical signals, and may be applicable to modern optical networks and future quantum networks. Here, we systematically review the latest research progress on the fundamentals and applications of optomechanically induced transparency. Perspectives and opportunities on future developments are also provided by focusing on several promising topics.

Resonant Transmission through Topological Metamaterial Grating

AbstractRecently, artificial photonic structures that exhibit nontrivial topological properties have attracted growing attention due to their capability of achieving one‐way backscatter immune transport of light. While photonic crystals are predominantly employed for achieving nontrivial topologies, effective medium approach based on metamaterials has been recently proposed for realizing topologically protected unidirectional surface states. In this article, a microscopic model to investigate the transmission of topological metamaterial grating is constructed based on the scattering processes involving unidirectional surface states. The numerically simulated transmission efficiency of the grating can be precisely reproduced by the model. The model demonstrates that the sharp transmission resonance of the grating results from the constructive interference of the topologically protected one‐way surface states. The present work provides an intuitive picture for understanding the scattering processes and resonance behaviors of the topologically protected one‐way surface states. Benefitting from the sharp spectral features of the supported resonances, the proposed grating structure may be potentially used for sensing applications.

Fast interrogation using sinusoidally current modulated laser diodes for fiber Fabry–Perot interferometric sensor consisting of fiber Bragg gratings

A fast interrogation method using a sinusoidal modulated laser diode for a fiber Fabry–Perot interferometric sensor consisting of Bragg gratings (FBG–FPI) is proposed.. The FBG–FPI has sharp transmittance peaks in the reflection band of the FBGs. Wavelength sweep produced by current modulation of a laser diode can be used to detect the peak position. This enables high-resolution strain or temperature measurement. To precisely control the current, the current modulation is realized using a laser diode controller (LDC) with external modulation function. In the modulation by a sawtooth wave, the possible speed of wavelength sweeping is limited to 100 kHz or less due to the bandwidth limitation of an LDC and thermal effect in a laser diodeUsing a sinusoidal wave as a modulation waveform enables wavelength sweeping at speeds exceeding 100 kHz. The modulation characteristics of the laser wavelength is evaluated experimentally and the operating wavelength is monitored using an asymmetric Mach–Zehnder interferometer. The resolution of 0.2 fm/\(\sqrt{\mathrm{Hz}}\) and measurement time of 1 \(\upmu\)s were experimentally demonstrated in the present sensor.

Dual band pass filter with sharp transmission zeros for wireless applications

Band stop/pass filters using octagonal and rectangular-shaped open loop resonators are proposed for wireless applications. The filter has the advantage of low insertion loss in the passbands and high return loss in the stopbands. The main idea of the filter is to achieve transmission bands by utilizing rectangular shape open loop resonators which are coupled to the input and output ports. The open loop resonators are used to generate stopbands in the filter response. The filter has small size, good response and the simulated results agree with the measured results. The lower insertion loss, and higher rejection band levels are investigated which confirm the suitability of the proposed dual BPF for WLAN and WiMAX applications.

Transmission characteristics of terahertz wave in high temperature plasma

In the hypersonic flight, the air surrounding an aircraft under the effect of high temperature will be ionized. The ionized gas is called plasma. Because of the influence of interaction between electromagnetic wave, in some cases the communication will be interrupted. High temperature effect is an important characteristic of the plasma. Therefore, the study of terahertz wave propagation in high temperature plasma is of great significance. In this paper, the transmission of terahertz wave in a high temperature plasma slab is studied. Generally, high temperature plasma is an anisotropic medium. The electromagnetic wave propagates in anisotropic high-temperature plasma and forms left-hand circular polarization mode or right-hand circular polarization (RCP) mode. It is found that the RCP wave can exhibit some novel characteristics, such as the forbidden band transmission characteristics, which is discovered in this paper. The transmission characteristics of terahertz wave in high temperature plasma are studied analytically. The results show that when the frequency of terahertz wave is lower than plasma frequency, the wave cannot be propagated in high temperature plasma, and it shows a stopband characteristic. When the frequency is higher, it can be transmitted through the plasma, and it presents a passband characteristic. These are consistent with the propagation characteristics of electromagnetic waves in cold plasma. However, some characteristics in high temperature plasma are different from those in the cold plasma. In high temperature plasma, the transmission characteristics are influenced by the electron temperature and external magnetic field. When the two parameters are chosen appropriately, a sharp transmission peak will be produced in the stopband. This phenomenon has never been found in cold plasma models before. And the paper will discuss this problem by the two influencing factors. It is also found that the frequency of the transmission peak is affected by magnetic field, and the peak amplitude is influenced by electron temperature. The electron temperatures at high transmittance (transmittance is about 1) under different applied magnetic fields are calculated. In order to study the law embodied in the data, the method of data fitting is adopted. And the formula of transmission peak frequency is obtained by curve fitting. The fitting results show that the transmission peak frequency is proportional to the external magnetic field. The relationship between peak electron temperature and external magnetic field is exponential. Finally, the fitting formula is verified by the finite-difference time-domain method. The numerical results are in good agreement with the analytical solution results, which proves the correctness of the work.

Tunable plasmonic substrates with ultrahigh Q-factor resonances

Precisely tailored plasmonic substrates can provide a platform for a variety of enhanced plasmonic applications in sensing and imaging. Despite the significant advances made in plasmonics, most plasmonic devices suffer critically from intrinsic absorption losses at optical frequencies, fatally restricting their efficiency. Here, we describe and engineer plasmonic substrates based on metal-insulator-metal (MIM) plasmon resonances with ultra-sharp optical transmission responses. Due to their sharp transmission spectrum, the proposed substrates can be utilized for high quality (Q)-factor multi-functional plasmonic applications. Analytical and numerical methods are exploited to investigate the optical properties of the substrates. The optical response of the substrate can be tuned by adjusting the periodicity of the nanograting patterned on the substrate. Fabricated substrates present Q-factors as high as ∼40 and refractive index sensing of the surrounding medium as high as 1245 nm/RIU. Our results indicate that by engineering the substrate geometry, the dielectric thickness and incident angle, the radiation losses can be greatly diminished, thus enabling the design of plasmonic substrates with large Q factor and strong sensitivity to the environment.

Fast and High-Resolution Simultaneous Measurement of Temperature and Strain Using a Fabry–Perot Interferometer in Polarization-Maintaining Fiber With Laser Diodes

Fast and high-resolution simultaneous measurement of temperature and strain is experimentally demonstrated. A Fabry–Perot interferometer fabricated in a polarization-maintaining fiber has sharp transmission peaks, which are divided into two sets corresponding to the polarization of the transmitted light. The sharp transmission peaks shift in response to changes in temperature and strain, and because the dependence coefficients are different for each set, temperature and strain can be simultaneously measured with high resolution. To read the position of a sharp transmission peak, wavelength sweeping with narrowband light is necessary. By using injection current modulation in a laser diode, high-speed wavelength sweeping and short measuring time are realized. We performed simultaneous measurements with a measurement time of 20 $\mu$ s; measurement resolution of 0.1 $^\circ$ C and 0.8 $\mu \epsilon$ for temperature and strain, respectively; and noise spectral density of 30 n $\epsilon /\sqrt{\rm Hz}$ . We further experimentally demonstrated that vibration with an amplitude of 20 $\mu \epsilon$ and a frequency of 1 Hz and heating at a rate of 0.7 $^\circ$ C $/$ s can be simultaneously measured.

Frequency-tunable and functionality-switchable polarization device using silicon strip array integrated with a graphene sheet

We propose a frequency-tunable and functionality-switchable polarization conversion device in transmission mode by integrating a silicon strip array with a graphene sheet in the mid-infrared region. High cross-polarization transmission, together with the dynamic frequency shift, contributes to a frequency-tunable half-wave plate working from 17.6 to 17.8 THz. Simultaneously, the device can act as a switchable polarizer to selectively generate co- or cross-polarized light by combining the frequency-tunability and a sharp x-shape polarization transmission caused by hybrid Mie resonances. Furthermore, this graphene-based metasurface also realizes continuous 180-degree phase modulation by electrically controlling graphene. The transmitted frequency-tunable and functionality-switchable device with simple-shape inclusions achieves multiple polarization conversions for both linearly and circularly polarized light without refabricating the geometric parameters, which represents a significant advance compared with previously reported counterparts.

Phase-Shifted Bragg Grating Inscription in PMMA Microstructured POF Using 248-nm UV Radiation

In this work, we experimentally validate and characterize the first phase-shifted polymer optical fiber Bragg gratings (PS-POFBGs) produced using a single pulse from a 248-nm krypton fluoride laser. A single-mode poly (methyl methacrylate) optical fiber with a core doped with benzyl dimethyl ketal for photosensitivity improvement was used. A uniform phase mask customized for 850-nm grating inscription was used to inscribe these Bragg structures. The phase shift defect was created directly during the grating inscription process by placing a narrow blocking aperture in the center of the UV beam. The produced high-quality Bragg grating structures, presenting a double dips, reject 16.3 dB (97.6% reflectivity) and 13.2 dB (95.2% reflectivity) of the transmitted power, being therefore appropriate for sensing or other photonic applications. Its transmission spectrum possesses two sharp transmission notches, allowing a significant increase in measurement resolution compared to direct interrogation of a single grating. The reflection and transmission spectra when multiple phase shifts are introduced in the fiber Bragg grating structure are also shown. The PS-POFBG's strain, temperature, pressure, and humidity characteristics have been experimentally analyzed in detail to assess their potential usage as sensors.

Microneedle Patches as Drug and Vaccine Delivery Platform

Transcutaneous delivery is the ideal method for delivering therapeutic reagents or vaccines into skin. With their promise of self-administration, cost-effective and high efficiency, microneedle patches have been studied intensively as therapeutic and vaccination delivery platform that replaces injection by syringe. This review aims to summarize the recent advancements of microneedle patches in application for drugs and vaccine delivery. We reviewed the most of recently published papers on microneedle patches, summarized their evolution, classification, state-of the-art capabilities and discussed promising application in drugs and vaccine delivery. With the rapid development of nanotechnology, microneedle patches have been improved by switching from undissolving to dissolving microneedles, and their safety has also improved dramatically. As a drug delivery tool, microneedle patches can deliver bioactive molecular of different physical size. Additionally, microneedle patches can be coated or encapsulate with DNA vaccine, subunit antigen, inactivated or live virus vaccine. Combining clinical results with the results of patient interview, microneedle patches are found to be feasible and are predicated to soon be acceptable for the medical service. In this review, we summarized the evolution, current and future application of microneedle patches as delivery vehicle for drugs and vaccines. Compared with traditional delivery tools, microneedle patches have many advantages, such as providing pain-free, non-invasive, convenient route for reagent administration and delivery, with no cold chain required for storage and transportation as well as decreasing sharp medical waste, needle-caused injury and transmission of blood-borne infectious disease in rural area. However, even though there are dramatic progress in preclinical investigation of microneedle patches, further testing will be required for clinical application. Further research should be implemented in multiple fields, such as vaccinology, immunology, and materials science, to improve this delivery platform. Because of their advantages in dose sparing, safety and treatment compliance, microneedle patches are expected to be widely applied in clinical treatment and vaccine administration in near future.

Optical Tamm states in photonic structures made of inhomogeneous material

We demonstrate a tunable optical Tamm state at the interface between a photonic crystal (PC) and a film with non-uniformly varying refractive index. The optical Tamm state is associated with a sharp transmission peak and strong localization of the electric field. It is spectrally located inside the overlapping band gaps. The shift of the optical Tamm state is sensitive to the lattice constant of the inhomogeneous material. Our results provide an approach to tailor interface states in a controllable manner.

Charge-vibration interaction effects in normal-superconductor quantum dots

We study the quantum transport and the nonequilibrium vibrational states of a quantum dot embedded between a normal and a superconducting lead with the charge on the quantum dot linearly coupled to a harmonic oscillator of frequency $\omega$. To the leading order in the charge-vibration interaction, we calculate the current and the nonequilibrium phonon occupation by the Keldsyh Green's function technique. We analyze the inelastic, vibration-assisted tunneling processes in the regime $\omega <\Delta$, with the superconducting energy gap $\Delta$, and for sharp resonant transmission through the dot. When the energy $\varepsilon_0$ of the dot's level is close to the Fermi energy $\mu$, i.e. $|\varepsilon_0-\mu|\ll \Delta$, inelastic Andreev reflections dominate up to voltage $eV\gtrsim\Delta$. The inelastic quasiparticle tunneling becomes the leading process when the dot's level is close to the gap $|\varepsilon_0-\mu|\sim \Delta \pm \omega$. In both cases, the inelastic tunneling processes appear as sharp and prominent peaks - not broadened by temperature - in the $I$-$V$ characteristic and pave the way for inelastic spectroscopy of vibrational modes even at temperatures $T \gg \omega$. We also found that inelastic Andreev reflections as well as quasiparticle tunneling induce a strong nonequilibrium state of the oscillator. In different ranges on the dot's level, we found that the current produces: (i) ground-state cooling of the oscillator with phonon occupation $n\ll 1$, (ii) accumulation of energy in the oscillator with $n\gg 1$ and (iii) a mechanical instability which is a precursor of self-sustained oscillations. We show that ground-state cooling is achieved simultaneously for several modes of different frequencies. Finally, we discuss how the nonequilibrium vibrational state can be detected by the asymmetric behavior of the inelastic current peaks respect to the gate voltage.

Subwavelength filter and sensor design based on end-coupled composited ring-groove resonator

A plasmonic filter and sensor is designed based on an end-coupled ring-groove composited resonator (RGCR). According to the magnetic field distributions of the resonance modes, a horizontal or vertical groove is added to the perfect ring resonator, and the transmission peaks for the 1st and the 2nd modes can be linearly changed by the length of the groove. In this case, the proposed structure can act as an on-chip optical filter with flexible wavelength manipulation. When the groove is rotated with an angle of λ/4, Fano resonance arises due to the mode interference. Dual asymmetric sharp transmission peaks are achieved around the wavelength of the former 2nd resonance mode. High figure of merit and high sensitivity are obtained for the structure, and it is believed that the device can find widely applications in the biochemistry sensing area. The corresponding spectra and the propagation characteristics are numerically investigated by using the finite-difference time-domain method.

3D printed hollow core terahertz Bragg waveguides with defect layers for surface sensing applications.

We study a 3D-printed hollow core terahertz (THz) Bragg waveguide for resonant surface sensing applications. We demonstrate theoretically and confirm experimentally that by introducing a defect in the first layer of the Bragg reflector, thereby causing anticrossing between the dispersion relations of the core-guided mode and the defect mode, we can create a sharp transmission dip in the waveguide transmission spectrum. By tracking changes in the spectral position of the narrow transmission dip, one can build a sensor, which is highly sensitive to the optical properties of the defect layer. To calibrate our sensor, we use PMMA layers of various thicknesses deposited onto the waveguide core surface. The measured sensitivity to changes in the defect layer thickness is found to be 0.1 GHz/μm. Then, we explore THz resonant surface sensing using α-lactose monohydrate powder as an analyte. We employ a rotating THz Bragg fiber and a semi-automatic powder feeder to explore the limit of the analyte thickness detection using a surface modality. We demonstrate experimentally that powder layer thickness variations as small as 3μm can be reliably detected with our sensor. Finally, we present a comparative study of the time-domain spectroscopy versus continuous wave THz systems supplemented with THz imaging for resonant surface sensing applications.