Pump Light Intensity Research Articles

Heterogeneous Random Laser with Switching Activity Visualized by Replica Symmetry Breaking Maps

In the past decade, complex networks of light emitters are proposed as novel platforms for photonic circuits and lab-on-chip active devices. Lasing networks made by connected multiple gain components and graphs of nanoscale random lasers (RLs) obtained from complex meshes of polymeric nanofibers are successful prototypes. However, in the reported research, mainly collective emission from a whole network of resonators is investigated, and only in a few cases, the emission from single points showing, although homogeneous and broad, spatial emission. In all cases, simultaneous activation of the miniaturized lasers is observed. Here, differently, we realize heterogeneous random lasers made of ribbon-like and highly porous fibers with evident RL action from separated micrometric domains that alternatively switch on and off by tuning the pumping light intensity. We visualize this novel effect by building for the first time replica symmetry breaking (RSB) maps of the emitting fibers with 2 {\mu}m spatial resolution. In addition, we calculate the spatial correlations of the laser regions showing clearly an average extension of 50 {\mu}m. The observed blinking effect is due to mode interaction along light guiding fibers and opens new avenues in the fabrication of flexible photonic networks with specific and adaptable activity.

Demonstration of rewritable hologram by using photo-induced optical nonlinearity in liquid crystals

The photo-responsive liquid crystals (LCs) close to the isotropic condition shows very large optical nonlinearity lasting for tens/hundreds of milliseconds after a pulse light illumination due to the flow-induced reorientation of liquid crystals. By optimizing the temperature and the pump light intensity, we succeeded to demonstrate various refractive index patterns due to this optical nonlinearity with a pattern illumination under a microscope. We demonstrated a rewritable hologram by using a computer generated hologram pattern on a photo-responsive LC.

Tunable Electro- and All-Optical Switch Based on Epsilon-Near-Zero Metasurface

A novel design of a tunable optical switch based on epsilon-near-zero (ENZ) metasurface is proposed, which can work as an electro-optical or an all-optical switch, and be tuned by gate-voltages, incident angles, and intensity of pump light. The result shows that the coupling of the ENZ mode and plasmon resonance lead to an obvious Rabi splitting which can be observed in the transmission spectrum. Numerical analysis also demonstrates that the coupling belongs to the ultra-strong coupling regime. The proposed design can achieve electro-optical switching with a large modulation depth of up to ∼ 17 dB, all-optical switching with an extinction ratio exceeding 5 dB and an ultrafast response time of 650 fs.

An ultrafast and low-power slow light tuning mechanism for compact aperture-coupled disk resonators**Project supported by the National Natural Science Foundation of China (Grant Nos. 11647122 and 61705064) and the Natural Science Foundation of Hubei Province, China (Grant Nos. 2018CFB672 and 2018CFB773).

An ultrafast and low-power slow light tuning mechanism based on plasmon-induced transparency (PIT) for two disk cavities aperture-coupled to a metal-dielectric-metal plasmonic waveguide system is investigated numerically and analytically. The optical Kerr effect is enhanced by the local electromagnetic field of surface plasmon polaritons, slow light, and graphene–Ag composite material structures with a large effective Kerr nonlinear coefficient. Through the dynamic adjustment of the frequency of the disk nanocavity, the group velocity is controlled between c/53.2 and c/15.1 with the pump light intensity increased from 0.41 MW/cm2 to 2.05 MW/cm2. Alternatively, through the dynamic adjustment of the propagation phase of the plasmonic waveguide, the group velocity is controlled between c/2.8 and c/14.8 with the pump light intensity increased from 5.88 MW/cm2 to 11.76 MW/cm2. The phase shift multiplication of the PIT effect is observed. Calculation results indicate that the entire structure is ultracompact and has a footprint of less than 0.8 μm2. An ultrafast responsive time in the order of 1 ps is reached due to the ultrafast carrier relaxation dynamics of graphene. All findings are comprehensively analyzed through finite-difference time-domain simulations and with a coupling-mode equation system. The results can serve as a reference for the design and fabrication of nanoscale integration photonic devices with low power consumption and ultrafast nonlinear responses.

Combined effect of pump-light intensity and modulation field on the performance of optically pumped magnetometers under zero-field parametric modulation

This paper investigates the performance optimization of optically pumped magnetometers under zero-field parametric modulation. Based on the analytical solutions of the Bloch equation, both longitudinal and transverse modulations are studied experimentally. To estimate the nonuniform polarization distribution of alkali-metal atoms in the vapor cell, an average pumping rate model is proposed. Furthermore, the accuracy of this model and the measurement of the transverse relaxation rate are verified via the agreement between experimental and theoretical values. The results indicate that optimal performance can be achieved by employing a suitable modulation field, the selection of which is related to the modulation index $u$ in the Bessel series and the pump-light intensity. Although both operating modes show similar responses to weak magnetic fields, their effects on pump-light intensity are different due to the means of detecting atomic polarization. An optimal value of the pump-light intensity on the response strength exists in longitudinal modulation. However, with regard to transverse modulation, the sensitivity under weak pump-light intensity is better. This research has far-reaching significance for cases when the parametric modulation is manipulated.

Simultaneous Determination of the Spin Polarizations of Noble-Gas and Alkali-Metal Atoms Based on the Dynamics of the Spin Ensembles

We demonstrate a method for simultaneously measuring the spin polarizations of noble-gas and alkali-metal atoms. Under a low magnetic field, the polarized alkali-metal and noble-gas spin ensembles exhibit novel dynamics in the self-compensation and resonance regimes, which can be used to measure the polarizations. We perform this method on a $\mathrm{K}$-$\mathrm{Rb}$-${}^{21}$$\mathrm{Ne}$ comagnetometer with various operation temperatures and pump-light intensities. The polarization of alkali-metal electrons from 0.245 to 0.964 and the polarization of noble-gas nuclear spins from 0.01 to 0.065 are measured with relative uncertainties less than $12.4\mathrm{%}$. The measured polarizations are consistent with the theoretical model and are also verified by the traditional polarization-measurement method.

Research on Temperature Sensor Using Rhodamine6G Film Coated Microstructure Optical Fiber

Temperature monitoring plays a key role in the kinetics of chemical reaction. In this paper, a sensitive dynamic temperature monitoring sensor based on the rhodamine6G (R6g) film coated anti-resonance fiber (ARF) is proposed. Because of the high thermo-dependent fluorescence intensity of R6g, the ARF coated with R6g film is highly sensitive to the temperature variation, forming the basis of our proposed temperature sensor application. To enhance the temperature monitoring performance and strengthen the florescence intensity, one of the ARF ends spliced a silica ball for reflecting the input signal, and the other end is inserted with two tapered multimode fiber (MMF), acting as bridges for the input of pump light and the output of signal light, respectively. The dual-peak reached the temperature resolution of $3.946\times 10^{-2}\,\,^{\circ }\text{C}$ and $3.991\times 10^{-3}\,\,^{\circ }\text{C}$ with linearity of 0.99914 and 0.99953 respectively. The experiment results show that the output fluorescence and pump light intensity decrease with the increasing temperature. These excellent characteristics demonstrate a highly sensitive dual-peak sensor for temperature calibration with wide potential applications, such as environmental monitoring, mine monitoring and other fields of chemical kinetics.

Three-output-channel photonic crystal splitter and switch based on nonlinear resonators and the self-collimation characteristics of a light beam.

Based on the nonlinear resonators and self-collimation characteristics of light beams, we designed an all-optical photonic crystal beam splitter and switch. The proposed device consists of an input waveguide and three output waveguides connected to different ring resonators. Three pump beams transmit through different resonators via the self-collimation effect, and eight output states are realized by altering the intensity of the pump light. The proposed device works at the wavelength of 1629.57 nm, and the pump wavelength is located at 1240.00 nm. The transmittance contrast between the "on" and "off" states reached a maximum value of 124.0 and a minimum of 17.6. The minimal pump light intensity required to implement the performance is only ${0.162}\,\,{\rm W/}\unicode{x00B5}{\rm m}^2$0.162W/µm2, while the maximal value is about ${0.497}\,\,{\rm W/}\unicode{x00B5}{\rm m}^2$0.497W/µm2. Due to the small size of our proposed device and also its insensitivity to the pump light beams' incident location and spatial width within a certain degree, it has great potential application value in all-optical communications.

A 2 × 1 all-optical multiplexer using Kerr nonlinear nano-plasmonic switch

In this paper, a novel surface plasmon polariton based 2 × 1 multiplexer, which is based on an adder module and an all-optical controllable nano-plasmonic switching module is presented. It is shown that by applying a pump light, the transmissions of the input signals into the output waveguide can be controlled. The operation of the proposed device is investigated through the use of coupled-mode theory and finite-difference time-domain method. In the proposed adder module, the transmissions of the input signals at the working wavelengths are about 0.7. Based on the simulation results, by applying a pump light intensity of 150 KW/cm2 the transmissions of input signals alter with the extinction ratio of 22.04 dB, which shows a significant switching effect. For a pump light intensity of 150 KW/cm2 the switching times of input signals are measured about 560 fs. It is expected that the proposed 2 × 1 multiplexer can be used in all-optical signal processing, nano-plasmonic circuits, communication, etc.

Strong Light-Field Driven Nanolasers.

Einstein established the quantum theory of radiation and paved the way for modern laser physics including single-photon absorption by charge carriers and finally pumping an active gain medium into population inversion. This can be easily understood in the particle picture of light. Using intense, ultrashort pulse lasers, multiphoton pumping of an active medium has been realized. In this nonlinear interaction regime, excitation and population inversion depend not only on the photon energy but also on the intensity of the incident pumping light, which can be still described solely by the particle picture of light. We demonstrate here that lowering significantly the pump photon energy further still enables population inversion and lasing in semiconductor nanowires. The extremely high electric field of the pump bends the bands and enables tunneling of electrons from the valence to the conduction band. In this regime, the light acts by the classical Coulomb force and population inversion is entirely due to the wave nature of electrons, thus the excitation becomes independent of the frequency but solely depends on the incident intensity of the pumping light.

Determination of Spin Polarization in Spin-Exchange Relaxation-Free Atomic Magnetometer Using Transient Response

A novel method to determine the spin polarization and its distribution for a spin-exchange relaxation-free (SERF) atomic magnetometer are proposed in this paper. The Larmor precession frequency is measured using the fast Fourier transform (FFT) analysis result of the transient response of the magnetometer under the excitation of a series of the step-changed magnetic field. The spin polarization is extracted from the slow-down factor of the precession frequency. The variation of the spin polarization with different pump light intensities and the distribution of the spin polarization along the direction of the pump light are analyzed, and the experimental results are well consistent with the theoretical predictions. The expanded uncertainties of the experimental results vary from 2% to 11% with the increase of the spin polarization and the reason for this variation is analyzed. The advantage of this method is that it allows the accurate measurement of the spin polarization in the pump beam direction within the SERF regime operating state, and it is unaffected by the large optical depth of the vapor cell.

Squeezed property of optical transistor based on cavity optomechanical system

All-optical diodes and all-optical transistors are the basis of all-optical logic devices. We study the quantum statistical properties of all-optical diodes based on cavity quantum electrodynamics (QED)<sup>[<xref ref-type="bibr" rid="b1">1</xref>]</sup>, and discuss the squeezed properties of the output light after passing through the diode when coherent light and squeezed light are incident. Here we extend our research to all-optical transistor, and take all-optical transistor based on cavity optomechanical system as the research object. By changing the intensity of classical pump light, the all-optical transistor can effectively control the output of the probe light and realize optical amplification. We discuss the squeezed properties of the output light of the all-optical transistor with squeezed light and coherent light as the probe light. Our results show that when the probe light is coherent, the output light remains coherent no matter whether it works in the amplified region, and is not squeezed. When the input probe light is amplitude squeezed light, the output light is still squeezed light in the light amplification region of all-optical transistor, but the squeezed properties are modulated by the input light squeezed properties and system parameters. When the squeezed angle of the input probe squeezed light is 0°, the minimum squeezed parameter S<sub>1</sub> of the output squeezed light decreases with the increase of the squeezed coefficient r of the input probe light, and the minimum value approaches to the squeezed limit of –0.25. But the change of squeezed angle of the input probe squeezed light changes has a great influence on the squeezed parameter S<sub>1,2</sub> of the output light, and the squeezed properties will disappear. Only when the squeezed angle is an integer multiple of π, will the squeezed properties of the output light be best. This result has a potential application value in quantum measurement, weak signal detection, and other fields.

Graphene-based spatial light modulator operating at near infrared spectral range

In this paper, a near infrared operating spatial light modulator is demonstrated, assembled in a way to combine the excellent photoconductivity of Ru-doped Bi12SiO20 (BSO:Ru) crystal, strong birefringence of liquid crystal (LC) and exceptionally high transparency and conductivity of graphene. A photo-alignment method instead of mechanical rubbing is used to simplify the fabrication procedure and to prevent detachment of the graphene layer from the substrate. The proposed device operates at low driving voltage (competitive to a reference device using ITO electrodes) moreover requires much less near infrared intensity for the light modulation. It is assumed the effect is due to the photo-induced space charge exchange between BSO:Ru and graphene allowing charge redistribution and optical doping effect resulting in a modulation of graphene’s properties. The voltage-dependent transmittance and phase retardation show high contrast ratio with the response time of ∼100 ms at 1064 nm. In addition, by projecting a video image through the proposed structure the response of modulated pump light intensity is demonstrated which supports device ability to work as near infrared optically addressed spatial light modulator (OASLM). The obtained performances reveal great potentials of graphene-based electro-optic devices for near infrared applications.

Pump wavelength-independent broadband terahertz generation from a nonlinear optical crystal.

In nonlinear optical (NLO) crystals, the selection of pump light wavelengths for the generation of terahertz (THz) waves is limited due to problems associated with coherence length, refractive index, and absorption by the crystal. Relaxation of this limitation would open up potential light sources for THz generation. One such solution, Cherenkov phase matching, removes the coherence length constraint. In this study, we attempted to generate THz waves from an NLO crystal using femtosecond pulses of various wavelengths. Specifically, 805-nm and 1560-nm femtosecond pulses were used to pump a prism-coupled LiNbO3 crystal. Broadband THz-wave generation and a THz-wave output proportional to the square of the pump light intensity were observed at both wavelengths. The generation of THz waves by prism-coupled Cherenkov phase matching was not limited by the wavelength of the pump light. Moreover, THz-wave generation at even greater intensities may be possible by optimizing the pump source and coupling to an NLO crystal.

Light controlled surface plasmon polaritons switch based on a gradient metal grating

A surface plasmon polaritons (SPPs) switch controlled by a pump light in the terahertz (THz) regime is designed. The switch is based on the surface slow-light technology. A gradient metal grating on a silicon (Si) layer is adopted to slow the SPP waves. By adjusting the grade of grating depths, the location of stopped waves can be tuned. By changing the intensity of pump light shining on the Si layer, the carrier density of Si layer can be modulated and thus the dielectric constant of Si layer. Then the SPPs can switched between two states: going through the structure or being stopped. The bandwidth of the captured surface wave can be effectively broaden by using this kind of depth gradient grating. This approach may provide a new method to design controllable SPPs devices.

Ultra-fast all-optical plasmon induced transparency in a metal–insulator–metal waveguide containing two Kerr nonlinear ring resonators

In this work, an ultra-fast all-optical plasmon induced transparency based on a metal–insulator–metal nanoplasmonic waveguide with two Kerr nonlinear ring resonators is studied. Two-dimensional simulations utilizing the finite-difference time-domain method are used to show an obvious optical bistability and significant switching mechanisms of the signal light by varying the pump-light intensity. The proposed all-optical switching based on plasmon induced transparency demonstrates femtosecond-scale feedback time (90 fs), meaning ultra-fast switching can be achieved. The presented all-optical switch may have potential significant applications in integrated optical circuits.

Influence of optical pumping on the transverse spin relaxation of Cs atoms in different ground-state hyperfine levels

The influence of optical pumping on the transverse spin relaxation of 133Cs atoms in different ground-state hyperfine levels is investigated. Transverse relaxation times for 133Cs atoms in the two ground-state hyperfine levels are detected separately under different intensities and frequencies of pump light, and a statistical model is adopted to analyze the experimental results. Theory and experiment show that optical pumping changes the populations of the two ground-state hyperfine levels, thereby influencing the transverse spin relaxation due to spin-exchange collisions. As a result, an unusual phenomenon that the transverse relaxation time for 133Cs atoms in the upper ground-state hyperfine level increases with the pump-light intensity is observed.

Ultra-fast all-optical plasmonic switching in near infra-red spectrum using a Kerr nonlinear ring resonator

In this paper, an all-optical plasmonic switch based on metal–insulator–metal (MIM) nanoplasmonic waveguide with a Kerr nonlinear ring resonator is introduced and studied. Two-dimensional simulations utilizing the finite-difference time-domain algorithm are used to demonstrate an apparent optical bistability and significant switching mechanisms (in enabled-low condition: T(ON/OFF) =21.9 and in enabled-high condition: T(ON/OFF) =24.9) of the signal light arisen by altering the pump-light intensity. The proposed all-optical switching demonstrates femtosecond-scale feedback time (90 fs) and then ultra-fast switching can be achieved. The offered all-optical switch may recognize potential significant applications in integrated optical circuits.

A nonlinear plasmonic waveguide based all-optical bidirectional switching

In this paper, an all-optical switching with a nanometer coupled ring resonator is demonstrated based on the nonlinear material. By adjusting the light intensity, we implement the resonance wavelength from 880 nm to 940 nm in the nonlinear material structure monocyclic. In the bidirectional switch structure, the center wavelength (i.e. 880 nm) is fixed. By changing the light intensity from I=0 to I=53.1MW∕cm2, the function of optical switching can be obtained. The results demonstrate that both the single-ring cavity and the T-shaped double-ring structure can realize the optical switching effect. This work takes advantage of the simple structure. The single-ring cavity plasmonic switches have many advantages, such as nanoscale size, low pumping light intensity, ultrafast response time (femtosecond level), etc. It is expected that the proposed all-optical integrated devices can be potentially applied in optical communication, signal processing, and signal sensing, etc.

Theoretical and experimental investigation of magnetic resonance on the Cs hyperfine structure

When the influence of hyperfine structure is ignored for atomic magnetometers, it will lead to considerable measuring errors in some cases. Considering the Cs hyperfine structure, an analytical form of magnetic resonance spectrum of the exciting-field frequency response is obtained through theoretical derivation, which is verified by the experiment. Based on the results of the experimental scheme, the optimal frequency and intensity of pump light for a Cs atomic magnetometer with well-resolved magnetic resonance spectrum are found. Additional applications in minimizing the measuring error of atomic magnetometers and the study of optical pumping are explored.