Input Light Intensity Research Articles

Studies on growth and characterization of (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate: a nonlinear optical material

Hydrazone compound (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate (DMABHBH) was synthesized and single crystals of DMABHBH were grown by solvent evaporation method at room temperature. Molecular structure of DMABHBH compound was confirmed by 1H and 13C nuclear magnetic resonance techniques. The presence of functional groups was confirmed by Fourier transform infrared and FT Raman spectral analyses. The X-ray crystal structure was elucidated at 173 K by single crystal X-ray diffraction and the results were compared with the corresponding values obtained at 298 K. The compound crystallizes in the chiral monoclinic space group P21. Mechanical stability of the grown crystals was estimated from the Vicker’s microhardness test. Powder second harmonic generation efficiency of DMABHBH is about 1.1 times that of potassium dihydrogen phosphate. DMABHBH is found to show optical limiting behavior at high input light intensities, the third order nonlinear optical absorption coefficient measured using open aperture Z-scan studies, is 0.95 × 10−11 m/W. Anti-bacterial activity was studied using the well and disc diffusion methods.

Unidirectional photonic circuit with a phase-change Fano resonator

We demonstrate that the integration of a phase-change material (PCM) in one of the two microresonators of a photonic metamolecule, coupled to a bus waveguide, can lead to unidirectional Fano resonances and to the emergence of a unidirectional transmission window. The phase change is caused by light-induced heating and is accompanied by an abrupt increase in the extinction coefficient of the PCM resonator. Due to the photonic circuit asymmetry, the critical value of the input light intensity triggering the phase change is strongly dependent on the input light direction. The latter determines the unidirectional nature of the emerging transmission window. This effect can be utilized in on-chip magnetic-free isolators and Q-switches.

Optical bistability in a low-photon-density regime

We give a microscopic description of the optical bistability, where the transmission coefficient has two different values as a function of input light intensity, and the system exhibits a discontinuous jump with a hysteresis loop. We developed an efficient numerical algorithm to treat the quantum master equation for hybridized systems of many photons and a large number of two-level atoms. By using this method, we characterize the bistability from the viewpoint of eigenmodes and eigenvalues of the time evolution operator of the quantum master equation. We investigate the optical bistability within the low photon-density regime, where the hybridization of photon and atom degrees of freedom occurs and the resonance spectrum has a double peak structure. We compared it with the standard optical bistability between the low photon-density regime and the high photon-density regime, where the photons can be treated as a classical electromagnetic field and the resonance spectrum has a single peak structure. We discuss the steady-state properties of the optical bistability: dependencies of the photon number density on the intensity and the double peak structure of the photon number distribution inside the bistable region. As for the dynamical properties, we find that the relaxation timescale shows an exponential growth with the system size, and reveal how the hysteresis loop of the optical bistability depends on the size of the system and the sweeping rate of the driving amplitude. Finally, by investigating the effects of detuning frequency of the input field, we clarify the characteristic properties of the present optical bistability within the low photon-density regime, which are qualitatively different from the standard optical bistable phenomena.

A New Material and Structures for Light-Emitting Thyristor Applications

We have demonstrated that GaInP materials with GaP and distributed Bragg reflector (DBR) structures can be applied in light-emitting thyristors (LEThs) and depleted optical thyristors (DOTs). The GaP epitaxial film greatly improved the current spreading, so that the brightness of LEThs was also greatly improved. The luminous intensity increased by 70% at an injection current of 250 mA with the GaP epitaxial film, compared to the LEThs without a GaP film. Moreover, the DBR structure played a role to prevent the emission light from being absorbed by the opaque GaAs substrate. The DBR structure can improve the droop efficiency, reduce the operation voltage, and maintain the wavelength at high-current operation. The luminous intensity of LEThs with the 18-pairs DBR structure increased by 71% at an injection current of 900 mA, compared to LETh with only three-pairs DBR and GaP window structure. It also showed nonlinear s-shaped ${I}$ – ${V}$ characteristics as a function of the input light intensity. The turn-on voltages were significantly reduced, from 5.36 to 1.66 V, as the external optical input intensity changed from dark to light with 300 mW. Under certain conditions, it also showed standard diode curve characteristics; as a result, the LETh can also be used as a DOTs.

Ultrafast and low-power plasmon-soliton switching based on two-dimensional MoS_2 nanostructure

The nonlinear propagation in a plasmonic nanostructure composed of two closely molybdenum disulfide (MoS2) sheets is investigated numerically using perturbation expansion of Maxwell’s equations. Because of the extraordinary nonlinear properties of monolayer MoS2, in particular significant Kerr effect, the production and propagation of dissipative plasmon-solitons in such a nanostructure is demonstrated. Considering the linear and nonlinear operation regimes, it is shown that by increasing the input light intensity, which leads to the appearance of the nonlinear correction terms in the MoS2 conductivity, the symmetry of such a coupler is breaking, and due to the change of the power coupling rate between two sheets, this nanostructure can operate as an all-optical nanoswitch. Compact dimensions and high nonlinearity of the proposed nanoswitch can provide us an ultrahigh-speed and low-power switching operation.

Photoresponsive Smart Coloration Electrochromic Supercapacitor.

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO3 -composite electrode that is capable of undergoing "smart" reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm2 C-1 and electrochemical performance with specific capacitance of 406.0 F g-1 , energy/power densities of 40.6-47.8 Wh kg-1 and 6.8-16.9 kW kg-1 . The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge-discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.

TYPE 1 & TYPE 2 OPTICAL LIMITING STUDIES IN DISPERSE ORANGE-25 DYE-DOPED PMMA-MA POLYMER FILMS USING CW LASER

Materials with exceptional third-order nonlinear optical properties are critical to the continuing development of photonics and electro-optical devices such as those used in optical communications, networking, the optical computation for signal processing, and data storage devices. The nonlinear optical material research is generally focussed on improving the efficiency of optical wavelength conversion, optical amplification, nonlinear absorption, refractive index changes etc. which are input light intensity dependent. During last few years, the organic dye-doped polymer films are getting more attention due to their advantages in fabricating optimum photonics devices. In this paper, we have studied the nonlinear optical properties like nonlinear absorption and nonlinear refraction of an azo dye Disperse Orange-25 (DO-25) doped in Polymethyl methacrylate-methacrylic acid (PMMA-MA) polymer matrix using open aperture and closed aperture Z-scan experimental methods for continuous wave (CW) laser input. The optical limiting properties of these films are also studied using Type 1 and Type 2 configurations at different input power using continuous wave (CW) laser beams of 532 nm wavelength.The nonlinear absorption coefficient, nonlinear refractive index, and saturated output power for type 1 and type 2 optical limiting are determined.

Novel “quasi-Bayer” micro-polarizer patterns for the division-of-focal-plane polarimeters

In this paper, we present two novel “quasi-Bayer” micro-polarizer (MP) patterns for the polarization imaging based on the division-of-focal-plane polarimeters (DoFP). Compared with the traditional equally-weighted MP pattern with four different micro-polarizers, the “quasi-Bayer” pattern requires less photo-lithography-based selective etching steps, leading to a significant reduction of the MP array's fabrication complexity. In addition, for the mainstream bilinear interpolation algorithm, the proposed “quasi-Bayer” pattern with three micro-polarizers exhibits the lowest mean square error (MSE) of 0.43%. Moreover, the “quasi-Bayer” patterns take advantages not only at the fixed illumination level, but also for different illumination levels. Reported experimental results validate the effectiveness of the “quasi-Bayer” patterns by varying the input light intensity from 13lx to 213lx.

Large enhancement of third-order nonlinear effects with a resonant all-dielectric metasurface

A novel low-profile nonlinear metasurface, consisting of a single-layer of all-dielectric material, is proposed and numerically investigated by a nonlinear full-wave finite-difference time-domain (FDTD) method. The proposed metasurface is transparent for low, and opaque for high values of incident light intensity. The metasurface design is broadly applicable to enhancement of intrinsic nonlinearities of any material with a sufficiently high refractive index contrast. We illustrate the ability of this design to enhance intrinsic nonlinear absorption of a transition metal oxide, vanadium pentoxide (V2O5), with resonant metasurface elements. The complex third-order nonlinear susceptibility (χ(3)) for V2O5, representing both nonlinear refraction and absorption is considered in FDTD simulations. Our design achieves high initial transparency (>90%) for low incident light intensity. An order of magnitude decrease in the required input light intensity threshold for nonlinear response of the metasurface is observed in comparison with an unpatterend film. The proposed all-dielectric metasurface in this work is ultrathin and easy to fabricate. We envision a number of applications of this design for thin film coatings that offer protection against high-power laser radiation.

All-optical high performance graphene-photonic crystal switch

The all-optical switch is realized based on nonlinear transmission changes in Fano resonance of 2D photonic crystals (PhC) which enhances the light intensity on the graphene in PhC; and in this study, the graphene layer is used as the nonlinear material. The refractive index change of graphene layer leads to a shift in the Fano resonance frequency due to the input light intensity through the Kerr nonlinear effect. Through finite-difference time-domain simulation, it is found that the high performance of all-optical switching can be achieved by the designed structure with a threshold pump intensity as low as MW/cm2. This structure is featured by optical bistability. The obtained results are applicable in micro optical integrated circuits for modulators, switches and logic elements for optical computation.

Phase transition in multimode nonlinear parity-time-symmetric waveguide couplers.

Parity-time-symmetric (-symmetric) optical waveguide couplers offer new possibilities for fast, ultracompact, configurable, all-optical signal processing. Here, we study nonlinear properties of finite-size multimode -symmetric couplers and predict the nonlinear oscillatory dynamics that can be controlled by three parameters: input light intensity, gain and loss amplitude, and input beam profile. Moreover, we show that this dynamics is driven by a transition triggered by nonlinearity in these structures, and we demonstrate that with the increase of the number of dimers in the system, the transition threshold decreases and converges to the value corresponding to an infinite array. Finally, we present a variety of periodic intensity patterns that can be formed in these couplers depending on the initial excitation.

Cooperative nonlinear grating sensitive to light intensity and photon correlation.

Utilizing dipole blockade of Rydberg excitations, we study an ensemble of stationary atoms driven into the four-level N configuration for achieving a new kind of electromagnetically induced grating in the presence of a traveling-wave and a standing-wave classical control fields. This grating shows cooperative optical nonlinearities as manifested by the sensitivity of output diffraction patterns to input light intensities (photon correlations) of a quantum probe field, promising then an essential opportunity for distinguishing weaker and stronger (bunched and anti-bunched) light fields.

Fabrication of Scalable Indoor Light Energy Harvester and Study for Agricultural IoT Applications

A scalable indoor light energy harvester was fabricated by microelectromechanical system (MEMS) and printing hybrid technology and evaluated for agricultural IoT applications under different environmental input power density conditions, such as outdoor farming under the sun, greenhouse farming under scattered lighting, and a plant factory under LEDs. We fabricated and evaluated a dye- sensitized-type solar cell (DSC) as a low cost and “scalable” optical harvester device. We developed a transparent conductive oxide (TCO)-less process with a honeycomb metal mesh substrate fabricated by MEMS technology. In terms of the electrical and optical properties, we achieved scalable harvester output power by cell area sizing. Second, we evaluated the dependence of the input power scalable characteristics on the input light intensity, spectrum distribution, and light inlet direction angle, because harvested environmental input power is unstable. The TiO2 fabrication relied on nanoimprint technology, which was designed for optical optimization and fabrication, and we confirmed that the harvesters are robust to a variety of environments. Finally, we studied optical energy harvesting applications for agricultural IoT systems. These scalable indoor light harvesters could be used in many applications and situations in smart agriculture.

An OTDR and Gratings Assisted Multifunctional Fiber Sensing System

We report a distributed multifunctional fiber sensing network based on weak-fiber Bragg gratings (WFBGs) and long period fiber grating (LPG) assisted OTDR system. The WFBGs are applied for temperature, strain, and vibration monitoring at key position, and the LPG is used as a linear filter in the system to convert the wavelength shift of WFBGs caused by environmental change into the power change. The simulation results show that it is possible to integrate more than 4472 WFBGs in the system when the reflectivity of WFBGs is less than {10}^{-5}. Besides, the back-Rayleigh scattering along the whole fiber can also be detected which makes distributed bend sensing possible. As an experimental demonstration, we have used three WFBGs UV-inscribed with 50-m interval at the end of a 2.6-km long fiber, which part was subjected for temperature, strain, and vibration sensing, respectively. The ratio of the intensity of output and input light is used for temperature and strain sensing, and the results show strain and temperature sensitivities are 4.2 \times {10}^{-4}{/\mu \varepsilon } and 5.9 \times {10}^{-3}{{/ {^{\circ }}\textrm {C}}} , respectively. Detection of multiple vibrations and single vibration with the broad frequency band up to 500 Hz are also achieved. In addition, distributed bend sensing which could be simultaneously realized in this system has been proposed.

Nonlinear tuning techniques of plasmonic nano-filters

In this paper, a fitting model to the propagation constant and the losses of Metal–Insulator–Metal (MIM) plasmonic waveguide is proposed. Using this model, the modal characteristics of MIM plasmonic waveguide can be solved directly without solving Maxwell's equations from scratch. As a consequence, the simulation time and the computational cost that are needed to predict the response of different plasmonic structures can be reduced significantly. This fitting model is used to develop a closed form model that describes the behavior of a plasmonic nano-filter. Easy and accurate mechanisms to tune the filter are investigated and analyzed. The filter tunability is based on using a nonlinear dielectric material with Pockels or Kerr effect. The tunability is achieved by applying an external voltage or through controlling the input light intensity. The proposed nano-filter supports both red and blue shift in the resonance response depending on the type of the used non-linear material. A new approach to control the input light intensity by applying an external voltage to a previous stage is investigated. Therefore, the filter tunability to a stage that has Kerr material can be achieved by applying voltage to a previous stage that has Pockels material. Using this method, the Kerr effect can be achieved electrically instead of varying the intensity of the input source. This technique enhances the ability of the device integration for on-chip applications. Tuning the resonance wavelength with high accuracy, minimum insertion loss and high quality factor is obtained using these approaches.

Converting one photon into two via four-wave mixing in optical fibers

Observing nonlinear optical quantum effects or implementing quantum information protocols using nonlinear optics requires moving to ever-smaller input light intensities. However, low light intensities generally mean weak optical nonlinearities, which are inadequate for many applications. Here we calculate the performance of four-wave mixing in various optical fibers for the case where one of the input beams is a single photon. We show that in tapered chalcogenide glass fibers (microwires) a single photon plus strong pump beam can produce a pair of photons with a probability of 0.1%, much higher than in previous work on bulk and wave-guided crystal sources. Such a photon converter could be useful for creating large entangled photon states, for performing a loophole-free test of Bell's inequalities, and for quantum communication.

All-optical sensitive phase shifting based on nonlinear out-of-plane coupling through 1-D slab photonic crystal with a layer of graphene.

We realize all-optical sensitive phase shifting based on nonlinear out-of-plane coupling to a slab waveguide through Fano resonance of a slab 1-D photonic crystal (PhC). We use a graphene layer as the nonlinear material and change its refractive index by the input light intensity through Kerr nonlinear effect to obtain a shift in the Fano resonance frequency. The Fano resonance and self-focusing effect lead to light-intensity enhancement on the graphene in the PhC, reinforcing the nonlinear effect of refractive index in the graphene. Through finite-difference time-domain simulation, we demonstrate that the phase changing sensitivity obtained can be 4 orders higher than that by a single graphene under the same input light intensity. Moreover the threshold pump intensity for all-optical sensitive phase shifting in the coupled light to the waveguide is as low as ~4 MW per square centimeter. The results are applicable in micro optical integrated circuits for phase shifters, phase modulators, power limiters, and phase logic elements for optical computation, digital phase shift keying in communication systems, and non-contact sensitive signal detectors.

Photoconductive response of strained silicon nanowires: A Monte Carlo study

Using Ensemble Monte Carlo simulations, the photocurrent in a 500 nm long strained [110] silicon nanowire with diameter of 3.1 nm is investigated. It was observed that a phototransistor based on this nanowire can have responsivities in the order of 21.3 mA/W for an input light wavelength of 532 nm and intensity of 0.25–2.5 kW/cm2. The super-unity slope of 1.2 in photo conductance versus input light intensity suggests that the nanowire has a photoconductive gain and highlights its advantage over germanium nanowires with sub-unity slope (0.77). The generated photocurrents are in the 0.1 nA–1 nA range. Density Functional Theory and Tight Binding methods were used for strain application and band structure calculation, respectively. Both longitudinal acoustic and optical phonons were included in the calculation of the carrier-phonon scattering events, which showed a two-order of magnitude stronger role for longitudinal optical phonons.

Photonic Sensing of Electrophysiological Activity for Wearable Applications

Photonic biosensors, featuring small size, lightweight, and remote sensing ability through optical fibers, show huge potential for wearable bioelectric applications. Electro-optic (EO) devices have high-input impedance and can achieve small-driving voltages, just what is required for a sensor targeting bioelectric activity monitoring. This paper proposes a multi-parameter bioelectric acquisition platform with a photonic sensor based on EO methods, and electronic circuitry for signal conditioning, filtering and amplification. The core sensing technology is based on a Lithium Niobate Mach-Zehnder interferometer modulator, which responds to the bioelectric signal by modulating the input light intensity. The photonic sensor performance was compared with standard acquisition systems. Results have shown that the developed sensor is reliable and allows multi-parameter acquisition with acceptable gain (from 1 to 4 mV/μV), sensitivity (minimum detected field of 20 μV), frequency content, and clinical relevance.

CMOS Tunable-Color Image Sensor With Dual-ADC Shot-Noise-Aware Dynamic Range Extension

A wide dynamic range CMOS tunable-color image sensor is presented. The sensor integrates an 8 × 8 array of tunable-color photogates which exploit the wavelength-dependent optical absorption properties of the polysilicon gate structure. An analysis is presented for the wide dynamic range asynchronous self-reset with residue readout architecture where photon shot noise is taken into consideration. An implementation of this architecture is presented where the (coarse) asynchronous self-reset operation and (line) residue analog-to-digital conversions are performed with separate in-pixel and off-pixel circuits, respectively, for a noise-optimized design. A prototype was fabricated in a standard 0.35 μm CMOS process and is validated in color light sensing which achieves SNRs of 24.3 dB and 28.5 dB in green and red light measurements, respectively, under a moderate input light intensity of 300 μW/cm2. The readout circuit achieves a measured dynamic range of 82 dB with a peak SNR of 46.2 dB under broadband illumination. The prototype has been integrated with a microfluidic device and experimentally validated in fluorescence contact imaging.