Intensity Tuning Research Articles

Tunable polarization-insensitive multifocal metalens based on an inverse design framework.

Multifocal metalenses are effective elements for longitudinal light field modulation and have important applications in long-focal depth imaging and three-dimensional display. However, the forward design method is subject to destructive interference generated by phase discontinuity, and cannot achieve high-efficiency, tunable multifocal metalenses. Therefore, we propose an efficient and tunable inverse design framework based on the adjoint method and gradient strategy, transforming light field modulation into mathematical optimization of nonlinear constraints. As proof, a trifocal metalens based on the inverse design framework is proposed with a focusing efficiency of 41%, and the focal length deviation is less than 1 µm. Then, trifocal metalenses operating in the visible range with focusing efficiencies of more than 30% are designed to demonstrate the multi-wavelength optimization capability of the framework. Besides, we verified the tunable ability of the inverse design framework and achieved trifocal metalenses with a relative light intensity tuning range of 0.3-1 and a focal length interval tuning range of 20-60 µm, respectively. The inverse design framework avoids complex physical reasoning and prior knowledge in the design process and promotes the development of multifunctional photonic devices.

Monolithic back-end-of-line integration of phase change materials into foundry-manufactured silicon photonics

Monolithic integration of novel materials without modifying the existing photonic component library is crucial to advancing heterogeneous silicon photonic integrated circuits. Here we show the introduction of a silicon nitride etch stop layer at select areas, coupled with low-loss oxide trench, enabling incorporation of functional materials without compromising foundry-verified device reliability. As an illustration, two distinct chalcogenide phase change materials (PCMs) with remarkable nonvolatile modulation capabilities, namely Sb2Se3 and Ge2Sb2Se4Te1, were monolithic back-end-of-line integrated, offering compact phase and intensity tuning units with zero-static power consumption. By employing these building blocks, the phase error of a push-pull Mach–Zehnder interferometer optical switch could be reduced with a 48% peak power consumption reduction. Mirco-ring filters with >5-bit wavelength selective intensity modulation and waveguide-based >7-bit intensity-modulation broadband attenuators could also be achieved. This foundry-compatible platform could open up the possibility of integrating other excellent optoelectronic materials into future silicon photonic process design kits.

Intensity coupling characteristics of dual-longitudinal mode ring lasers with Ne dual-isotope.

The intensity coupling characteristics of Ne dual-isotope inflation and dual-longitudinal-mode operation ring lasers were investigated based on the Lamb theory. Considering the contribution of the Ne isotope system to the polarization of the gain medium and gain saturation effects, the frequency coupling effects were analyzed. Combined with the plasma dispersion function, the optical cavity length is 0.47 m, Ne20: Ne22= 0.53:0.47; the frequency spacing of the adjacent longitudinal mode is 640 MHz, and the intensity tuning curve of the ring laser is simulated. The alterations in the gain self-saturation and mutual saturation coefficients between the four frequencies generated via dual-longitudinal mode splitting are comprehensively discussed. Finally, a detection experiment for the intensity-tuning curve is designed to verify the theoretical analysis.

Computationally Efficient Scaled Clustering for Perceptually Invisible Image Intensity Tuning

Quality and information content of an image is a vital aspect affecting the performance of any artificial intelligence-related task. Improving the quality of an image while maintaining its color and naturalness in a very small time frame is a challenge. In this article, a computationally efficient scaled clustering-based contrast enhancement method is proposed for enhancing perceptually invisible images and preserving color and naturalness. Pixels in the image are grouped in clusters using the fuzzy c-means algorithm and are assigned membership to different clusters. Membership values of the pixels are modified and scaled up using the cluster centers. Based on these modified and scaled cluster memberships, the intensity level of the pixels is modified. The membership-based proportional modification of the intensity values in the scaled domain improves the color and information content of an image. It is scaled down to the original range of intensity levels, using linear scaling to obtain an enhanced image with better contrast and color information. The generated image is free from artifacts and is natural in appearance. The proposed method is simulated and tested on frequently used standard datasets. The simulation results and the average computation time of the proposed method are compared to some of the well-established conventional and latest techniques.

Evolution of a Gaussian pulse in negative index Kerr medium about threshold intensity: A numerical simulation

Temporal evolution of a pico-sec Gaussian pulse is numerically simulated in a representative intensity dependent negative index Kerr medium about a threshold intensity to study the effect of Kerr non-linearity on a propagating pulse, using the non-linear Schroedinger equation solved by split step Fourier method. Results are obtained for both dispersive and non-dispersive cases, that show the pulse to bear characteristics of a fundamental soliton. Moreover, the speed of the soliton i.e., the group velocity may be controlled by tuning the intensity of the pulse around the threshold. Overall, the analysis indicates prospect of an intensity dependent non-linear transmission material with the provision to control transmission speed through intensity tuning.

Integrated Phased Array for Scalable Vortex Beam Multiplexing

Orbital angular momentum (OAM) modes have low model interactions during fiber propagation at data center distances, and thus are suitable for ultra-high capacity systems at low digital signal processing. Generating OAM modes using free-space setups is useful for proof-of-concept experiments, but is not a scalable solution. We use an optical phased array (OPA) with two-dimensional antennas for on-chip circularly polarized OAM beam generation. Our previous work demonstrated an OAM multiplexer for lower-order modes. In this work, we demonstrate an OAM multiplexer that supports a record of 46 (23 per polarization) simultaneous spatial modes up to OAM order 11. We also improve the crosstalk performance of our multiplexer. We incorporate an intensity tuning capability that substantially improves the OAM quality by enabling a uniform power distribution across the antennas. The worst-case crosstalk for the supported OAM5 to OAM11 are found experimentally to be better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-12$</tex-math></inline-formula> dB, with OAM10 achieving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-17.2$</tex-math></inline-formula> dB.

Spectrally non-overlapping background noise disturbs echolocation via acoustic masking in the CF-FM bat, Hipposideros pratti

The environment noise may disturb animal behavior and echolocation via three potential mechanisms: acoustic masking, reduced attention and noise avoidance. Compared with the mechanisms of reduced attention and noise avoidance, acoustic masking is thought to occur only when the signal and background noise overlap spectrally and temporally. In this study, we investigated the effects of spectrally non-overlapping noise on echolocation pulses and electrophysiological responses of a constant frequency-frequency modulation (CF-FM) bat, Hipposideros pratti. We found that H. pratti called at higher intensities while keeping the CFs of their echolocation pulses consistent. Electrophysiological tests indicated that the noise could decrease auditory sensitivity and sharp intensity tuning, suggesting that spectrally non-overlapping noise imparts an acoustic masking effect. Because anthropogenic noises are usually concentrated at low frequencies and are spectrally non-overlapping with the bat's echolocation pulses, our results provide further evidence of negative consequences of anthropogenic noise. On this basis, we sound a warning against noise in the foraging habitats of echolocating bats.

Study of the Steady-State Operation of a Dual-Longitudinal-Mode and Self-Biasing Laser Gyroscope.

In order to stabilize the self-biasing state of a laser gyroscope, a dual-longitudinal-mode asymmetric frequency stabilization technique was studied. The special frequency stabilization is based on the accurate control of the intensity tuning curve in the prism ring laser. In this study, the effects of the ratio of the Ne isotopes, the inflation pressure, and the frequencies coupling on the intensity tuning curve in a laser gyro were examined. The profiles of the intensity tuning curve were simulated under the mixing ratios of Ne20 and Ne22 of 1:1 and 7:3, and the inflation pressures were 350 Pa, 400 Pa, and 450 Pa. The mixing ratio of Ne20 and Ne27 was dealt with similarly. The method for precisely adjusting the profiles of the intensity tuning curve was analyzed. The profiles were verified by experiments under different isotope ratios and pressures. Finally, based on a prism ring laser with an optical length of 0.47 m, the proposed frequency stabilization method was preliminarily verified.

Effects of background noise on auditory response characteristics of primary auditory cortex neurons in awake mice

To study the effects of different continuous background noises on auditory response characteristics of primary auditory cortex (A1) neurons in awake mice. We performed in vivo cell-attached recordings in layer 4 neurons of the A1 of awake mice to investigate how continuous background noises of different levels affected the intensity tuning, frequency tuning and time characteristics of individual A1 neurons. According to the intensity tuning characteristics and types of stimulation, 44 neurons were devided into 4 groups: monotonic-intensity group (20 monotonic neurons), nonmonotonic-intensity group (6 nonmonotonic neurons), monotonic-frequency group (25 monotonic neurons) and monotonic-latency group (15 monotonic neurons). The A1 neurons only had transient spike response within 10 to 40 ms after the onset of continuous wild-band noise stimulation. The noise intensity had no significant effects on the background firing rates of the A1 neurons (P>0.05). The increase of background noise resulted in a significant linear elevation of the intensity threshold of monotonic and nonmonotonic neurons for tone-evoked response (R2>0.90, P < 0.05). No significant difference was observed in the slopes of threshold changes between monotonic and nonmonotonic neurons (P>0.05). The best intensity of nonmonotonic neurons increased along with the intensity of the background noise, and the variation of the best intensity was positively correlated with the change of the threshold of the same neuron (r=0.944, P < 0.001). The frequency response bandwidth and the firing rate of the A1 neurons decreased as the noise intensity increased (P < 0.001), but the best frequency almost remained unchanged (P < 0.001). The increase of background noise intensity resulted in an increased first spike latency of the neurons to the same tone stimulus (P < 0.05) without affecting the time accuracy of the first action potential (P>0.05). The acoustic response threshold of the A1 neurons increases linearly with the increase of background noise intensity. An increased background noise leads to compressed frequency band-width, a decreased firing rate and a prolonged spike latency, but the frequency selectivity and the time accuracy of auditory response to the same noise remain stable.

Tuning of Optical Phonons in α-MoO3-VO2 Multilayers.

Merging the properties of VO2 and van der Waals (vdW) materials has given rise to novel tunable photonic devices. Despite recent studies on the effect of the phase change of VO2 on tuning near-field optical response of phonon polaritons in the infrared range, active tuning of optical phonons (OPhs) using far-field techniques has been scarce. Here, we investigate the tunability of OPhs of α-MoO3 in a multilayer structure with VO2. Our experiments show the frequency and intensity tuning of 2 cm-1 and 11% for OPhs in the [100] direction and 2 cm-1 and 28% for OPhs in the [010] crystal direction of α-MoO3. Using the effective medium theory and dielectric models of each layer, we verify these findings with simulations. We then use loss tangent analysis and remove the effect of the substrate to understand the origin of these spectral characteristics. We expect that these findings will assist in intelligently designing tunable photonic devices for infrared applications, such as tunable camouflage and radiative cooling devices.

Electrically Tunable Multifunctional Polarization-Dependent Metasurfaces Integrated with Liquid Crystals in the Visible Region.

Metasurfaces open up new avenues for designing planar optics, enabling compact dynamic metadevices. Numerous dynamic strategies have been proposed, among which liquid crystal (LC) based metasurfaces are expected due to the maturity of LC materials. However, existing schemes rarely exploit the polarization manipulation capabilities of metasurfaces and the limited performance hinders the development of practical addressable devices. Here, we demonstrate an electrically tunable multifunctional polarization-dependent metasurface integrated with LCs in the visible range. By a combination of the helicity-dependent metasurface and the birefringent LCs, continuous intensity tuning and switching of two helicity channels are realized. Electrically tunable mono- and multicolor switchable metaholograms and dynamic varifocal metalenses are demonstrated with a simple and performance-enhancing integration scheme. Further, electrically addressable dynamic metasurfaces are achieved. The proposed modulation and integration schemes pave the way for addressable dynamic metasurface devices in various applications, such as space light modulators, light detection and ranging systems, and holographic displays.

Constant Resting Frequency and Auditory Midbrain Neuronal Frequency Analysis of Hipposideros pratti in Background White Noise.

Acoustic communication signals are inevitably challenged by ambient noise. In response to noise, many animals adjust their calls to maintain signal detectability. However, the mechanisms by which the auditory system adapts to the adjusted pulses are unclear. Our previous study revealed that the echolocating bat, Hipposideros pratti, increased its pulse intensity in the presence of background white noise. In vivo single-neuron recording demonstrated that the auditory midbrain neurons tuned to the second harmonic (H2 neurons) increased their minimal threshold (MT) to a similar degree as the increment of pulse intensity in the presence of the background noise. Furthermore, the H2 neurons exhibited consistent spike rates at their best amplitudes and sharper intensity tuning with background white noise compared with silent conditions. The previous data indicated that sound intensity analysis by auditory midbrain neurons was adapted to the increased pulse intensity in the same noise condition. This study further examined the echolocation pulse frequency and frequency analysis of auditory midbrain neurons with noise conditions. The data revealed that H. pratti did not shift the resting frequency in the presence of background noise. The auditory midbrain neuronal frequency analysis highly linked to processing the resting frequency with the presence of noise by presenting the constant best frequency (BF), frequency sensitivity, and frequency selectivity. Thus, our results suggested that auditory midbrain neuronal responses in background white noise are adapted to process echolocation pulses in the noise conditions.

Unraveling the anomalous mechanoluminescence intensity change and pressure-induced red-shift for manganese-doped zinc sulfide

Mechanoluminescence (ML) has promising applications such as stress sensors and many other fields, which raises intensive research attention and enthusiasms in the past few decades. However, accurate characterizations of the ML process with high temporal and spectral resolution remain a considerable challenge for the current scientific community. Here, an advanced ML characterization system based on the dynamic diamond anvil cell (dDAC) is developed to achieve flexible modulations of ML performances. Upon compression, the ML spectra of manganese-doped zinc sulfide (ZnS:Mn) show a large red-shift (~45 nm) and a volcano-trend of the ML intensity, where the cumulative ML intensity is solely dependent on the pressure change. DFT calculations identify the coupling of Mn-doping and surface vacancies is playing a crucial role in contributing to the improvement of ML through the band offset. The suppression of the vacancies formation on the surface by the applied pressure over 4 GPa leads to the decreases of the ML intensity. This work provides a brand new ML color and intensity tuning strategy and offers a promising method to explore the ML mechanism.

Effective Electrochemical Modulation of SERS Intensity Assisted by Core-Shell Nanoparticles.

An effective and reversible tuning of the intensity of surface-enhanced Raman scattering (SERS) of nonelectroactive molecules at nonresonance conditions by electrochemical means has been developed on plasmonic molecular nanojunctions formed between Au@Ag core-shell nanoparticles (NPs) and a gold nanoelectrode (AuNE) modified with a self-assembled monolayer. The Au@Ag nanoparticle on nanoelectrode (NPoNE) structures are formed in situ by the electrochemical deposition of Ag on AuNPs adsorbed on the AuNE and can be monitored by both the electrochemical current and SERS signals. Instead of introducing molecular changes by the applied electrode potential, the highly effective SERS intensity tuning was achieved by the chemical composition transformation of the ultrathin Ag shell from metallic Ag to insulating AgCl. The electrode potential-induced electromagnetic enhancement (EME) tuning in the Au@Ag NPoNE structure has been confirmed by finite-difference time-domain simulations. Moreover, the specific Raman band associated with Ag-molecule interaction can also be tuned by the electrode potential. Therefore, we demonstrated that the electrode potential could effectively and reversibly modulate both EME and chemical enhancement in Au@Ag NPoNE structures.

Intensity-tunable terahertz radiation from tin selenide

Recently, the active controlled broadband terahertz (THz) emitter from semiconductor crystal has attracted considerable attention due to its field intensity tuning properties, which makes it a promising candidate for wide applications in THz photonics. A broadband THz wave radiation intensity by applying electric field control in an n-type semiconductor tin selenide (SnSe2) crystal had been reported. In addition, due to the weak phonon absorption of the material in the THz band, the resulting THz spectral range is up to 3.5 THz. With an applied voltage of −5 V, the actively modulated depth of THz intensity is up to 123%. Our work directly demonstrates that when the excited laser photon energy exceeds the material bandgap, photon drag effect would be the main mechanism of THz wave radiation rather than nonlinear effects. Owing to simple structure and high modulation depth, electrically controlled THz radiation, the SnSe2 crystal has great applications in generation and modulation devices in THz region.

Independent Luminescent Lifetime and Intensity Tuning of Upconversion Nanoparticles by Gradient Doping for Multiplexed Encoding.

Luminescent materials with engineered optical properties have been developed for multiplexed labeling detection, where encoding capacity plays a pivotal role in the efficiency. However, multi-dimensional optical identities are usually not independent which essentially hinder the practical encoding numbers to access theoretical capacity. In this work, we carefully studied the sensitizer gradient doping structure in near-infrared (NIR) excitable upconversion nanoparticles (UCNPs) and managed to achieve independent emission intensity and lifetime tuning. With the orthogonally tunability, it breaks the constraint of intensity (k) and lifetime (n) correlation and expands the practical encoding number to theoretical value as (k+1)n -1 in binary encoding. This method can also be combined with previous lifetime engineering as well to realize high level multiplexing.

Independent Luminescent Lifetime and Intensity Tuning of Upconversion Nanoparticles by Gradient Doping for Multiplexed Encoding

AbstractLuminescent materials with engineered optical properties have been developed for multiplexed labeling detection, where encoding capacity plays a pivotal role in the efficiency. However, multi‐dimensional optical identities are usually not independent which essentially hinder the practical encoding numbers to access theoretical capacity. In this work, we carefully studied the sensitizer gradient doping structure in near‐infrared (NIR) excitable upconversion nanoparticles (UCNPs) and managed to achieve independent emission intensity and lifetime tuning. With the orthogonally tunability, it breaks the constraint of intensity (k) and lifetime (n) correlation and expands the practical encoding number to theoretical value as (k+1)n−1 in binary encoding. This method can also be combined with previous lifetime engineering as well to realize high level multiplexing.

Intensity tuning of the edge states in the imperfect topological waveguides based on the photonic crystals with the $$C_{3}$$ point group symmetry

We explore the topological behavior of a two-dimensional honeycomb photonic crystal (2D HPC) based on the presence of double Dirac-cone connected the orbitals \(p\) and \(d\), due to the \(C_{6}\) point group symmetry. Removing the four-fold degeneracy between the bands at the Dirac point can be achieved by introducing three small dielectric rods near the bigger ones to realize the perturbed PCs with the \(C_{3}\) point group symmetry with different topological features. By proposing the unique structure involving two PCs with different topological effects, one may study the one-way light distribution along the local boundary in spite of the defects, cavities, and disorders. Moreover, we investigate the variation of the transmitted intensity values under different defect conditions and realize that the size, location and material type affect the transmitted light. In the other words, tunable intensity of the edge states can be achieved through adjusting the defects such that by decreasing the radius of rods, the intensity of the edge states can be decreased or by increasing their distance from the unit cell center, the intensity will be decreased too. Finally, topological rhombic resonator enables unidirectional filtering of guided mode. The fact that different light manipulation scenarios can be realized provides a unique aspect for topological photonic insulators.

Towards atom-scale spin-selective electron emitters based on strong-field Freeman resonant ionization

To produce electrons with well-defined spin via photoionization, realizing orbital-resolved ionization is the prerequisite due to spin-orbital coupling. In this paper, we numerically and experimentally demonstrate that the electrons emitted from two original energy degenerated orbitals ($j=3/2, m=1$ and $j=3/2, m=\ensuremath{-}1$) of Xe atoms can be well separated in the energy domain through selectively achieving Freeman resonance during strong-field ionization using a circularly polarized laser field. This orbital resolved Freeman resonant ionization leads to strong spin sensitivity without the need of fine laser frequency and intensity tuning. This result enables the production of high-degree spin-polarized electrons by energy gating, which provides a unique degree of freedom for advancing many promising applications.

The second harmonic neurons in auditory midbrain of Hipposideros pratti are more tolerant to background white noise

Although acoustic communication is inevitably influenced by noise, behaviorally relevant sounds are perceived reliably. The noise-tolerant and -invariant responses of auditory neurons are thought to be the underlying mechanism. So, it is reasonable to speculate that neurons with best frequency tuned to behaviorally relevant sounds will play important role in noise-tolerant perception. Echolocating bats live in groups and emit multiple harmonic signals and analyze the returning echoes to extract information about the target features, making them prone to deal with noise in their natural habitat. The echolocation signal of Hipposideros pratti usually contains 3–4 harmonics (H1H4), the second harmonic has the highest amplitude and is thought to play an essential role during echolocation behavior. Therefore, it is reasonable to propose that neurons tuned to the H2, named the H2 neurons, can be more noise-tolerant to background noise. Taking advantage of bat's stereotypical echolocation signal and single-cell recording, our present study showed that the minimal threshold increases (12.2 dB) of H2 neurons in the auditory midbrain were comparable to increase in bat's call intensity (14.2 dB) observed in 70 dB SPL white noise condition, indicating that the H2 neurons could work as background noise monitor. The H2 neurons had higher minimal thresholds and sharper frequency tuning, which enabled them to be more tolerant to background noise. Furthermore, the H2 neurons had consistent best amplitude spikes and sharper intensity tuning in background white noise condition than in silence. Taken together, these results suggest that the H2 neurons might account for noise-tolerant perception of behaviorally relevant sounds.