Modulation Depth Research Articles

Broadband terahertz modulation in symmetric gate-controlled graphene photonic crystals

Innovative research in terahertz (THz) communications is urgently needed to meet the evolving demands of the industry. In the past, the absence of optoelectronic devices made it difficult to control THz waves effectively. In this study, a symmetric gate-controlled graphene photonic crystal (PC) is proposed, which achieves a modulation depth (MD) of more than 99 %, an ultralow insertion loss (IL) of 0.08, and a wide operation bandwidth (BW) simultaneously. Additionally, even in graphene samples with low carrier mobilities, the high-performance MD can be achieved with acceptable IL in the broadband THz range. Furthermore, our proposed one-dimensional graphene PC system enhances manufacturing convenience. Through the adoption of the proposed symmetric structure, highly efficient THz communications can be achieved through photonic systems that utilize graphene.

Robust Edge States of Quasi-1D Material Ta2NiSe7 and Applications in Saturable Absorbers.

The helical edge states (ESs) protected by underlying Z2 topology in two-dimensional topological insulators (TIs) arouse upsurges in saturable absorptions thanks to the strong photon-electron coupling in ESs. However, limited TIs demonstrate clear signatures of topological ESs at liquid nitrogen temperatures, hindering the applications of such exotic quantum states. Here, we demonstrate the existence of one-dimensional (1D) ESs at the step edge of the quasi-1D material Ta2NiSe7 at 78 K by scanning tunneling microscopy. Such ESs are rather robust against the irregularity of the edges, suggesting a possible topological origin. The exfoliated Ta2NiSe7 flakes were used as saturable absorbers (SAs) in an Er-doped fiber laser, hosting a mode-locked pulse with a modulation depth of up to 52.6% and a short pulse duration of 225 fs, far outstripping existing TI-based SAs. This work demonstrates the existence of robust 1D ESs and the superior SA performance of Ta2NiSe7.

Performance study of an optical modulator based on a funnel-shaped waveguide with tip-plasma effect

Electro-optical modulators play a crucial role in the field of optical communications; high modulation depth and low loss are used to qualify optical modulators. In this study, the tip-plasmon effect was utilized to improve the optical mode confinement and achieve a significant enhancement of the optical-graphene coupling. The evaluated modulator demonstrates robust performance characteristics, exhibiting a modulation depth of up to 8.5 dB/µm while sustaining a transmission loss of 2.3 dB/µm. Furthermore, the modulator operates with an energy efficiency of 4.36 fJ/bit and achieves a modulation bandwidth of 293 GHz, assuming a modulation length of 20 µm.

Nonlinear optical response and application of indirect narrow-bandgap SbTe nanosheets

The nonlinear optical properties of antimony telluride (SbTe) crystal with indirect narrow bandgap are investigated, which exhibits superior performance for nonlinear laser modulation in the infrared band. The nonlinear optical coefficients of SbTe nanosheets are determined to be −3.3 cm/GW, −2.3 cm/GW, −1.9 cm/GW and the modulation depths are 5.5 %, 2.0 %, 1.5 % at 400 nm, 800 nm, 1064 nm, respectively. Based on the SbTe-SA, a Yb:GdScO3 laser centered at 1064 nm is achieved with 633 mW maximum output power, 56 fs pulse width and 104 MHz repetition rate. The damage threshold of the SbTe nanosheets is calculated to be exceed 338 GW/cm2, revealing the great potential in high-power laser modulation. This investigation marks the inaugural theoretical and experimental analysis of SbTe’s optical properties and its application in laser modulation, laying the groundwork for future research into indirect narrow-bandgap materials in laser technology.

Developmental trajectory and sex differences in auditory processing in a PTEN-deletion model of autism spectrum disorders

Autism Spectrum Disorders (ASD) encompass a wide array of debilitating symptoms, including severe sensory deficits and abnormal language development. Sensory deficits early in development may lead to broader symptomatology in adolescents and adults. The mechanistic links between ASD risk genes, sensory processing and language impairment are unclear. There is also a sex bias in ASD diagnosis and symptomatology. The current study aims to identify the developmental trajectory and genotype- and sex-dependent differences in auditory sensitivity and temporal processing in a Pten-deletion (phosphatase and tensin homolog missing on chromosome 10) mouse model of ASD. Auditory temporal processing is crucial for speech recognition and language development and deficits will cause language impairments. However, very little is known about the development of temporal processing in ASD animal models, and if there are sex differences. To address this major gap, we recorded epidural electroencephalography (EEG) signals from the frontal (FC) and auditory (AC) cortex in developing and adult Nse-cre PTEN mice, in which Pten is deleted in specific cortical layers (layers III-V) (PTEN conditional knock-out (cKO). We quantified resting EEG spectral power distribution, auditory event related potentials (ERP) and temporal processing from awake and freely moving male and female mice. Temporal processing is measured using a gap-in-noise-ASSR (auditory steady state response) stimulus paradigm. The experimental manipulation of gap duration and modulation depth allows us to measure cortical entrainment to rapid gaps in sounds. Temporal processing was quantified using inter-trial phase clustering (ITPC) values that account for phase consistency across trials. The results show genotype differences in resting power distribution in PTEN cKO mice throughout development. Male and female cKO mice have significantly increased beta power but decreased high frequency oscillations in the AC and FC. Both male and female PTEN cKO mice show diminished ITPC in their gap-ASSR responses in the AC and FC compared to control mice. Overall, deficits become more prominent in adult (p60) mice, with cKO mice having significantly increased sound evoked power and decreased ITPC compared to controls. While both male and female cKO mice demonstrated severe temporal processing deficits across development, female cKO mice showed increased hypersensitivity compared to males, reflected as increased N1 and P2 amplitudes. These data identify a number of novel sensory processing deficits in a PTEN-ASD mouse model that are present from an early age. Abnormal temporal processing and hypersensitive responses may contribute to abnormal development of language function in ASD.

An AI-assisted terahertz reconfigurable metamaterial in standard 180-nm CMOS

For large-scale terahertz (THz) reconfigurable metamaterials (RM), each unit element needs to be controlled by an independent voltage source. This leads to a huge solution space for control words to achieve the required RM performance specification. In this paper, we propose a fast AI-assisted control-word generation scheme to reduce the computation cost of electromagnetic (EM) simulations (Forward Model) and to speed up iterations for control word searches (Inverse Model). We demonstrate the effectiveness of our models by designing and fabricating a 12 × 9 RM array with a Bi-layer Bi-Split-Ring Resonator structure (B-BSRR) in standard 180 nm CMOS technology. The terahertz RM can be electrically reconfigured, providing active metamaterials with an amplitude modulation depth of around 0–1.7 dB at 0.49 THz. The results show that our Forward Model can predict the S-parameters between 100 GHz and 800 GHz with a mean absolute error of 0.61 dB. Our method is more than 200 times faster than traditional full-wave simulation methods. The Inverse Model can generate required control words within a 1.3 dB error margin in less than 200 iterations.

Ultranarrow and multiband perfect absorbers based on dual quasi-bound states in the continuum in near infrared

High quality factor (Q-factor) and multiband perfect absorbers are highly desired in light-harvesting efficiency related optical devices, yet they are always limited by conventional mechanisms like electromagnetically induced transparency, Tamm or plasmonic resonance. In this paper, through constructing the strong coupling between two guided-mode resonances in subwavelength gratings, we propose an ultranarrow and multiband perfect absorber based the dual-band quasi-bound states in the continuum (quasi-BIC) design in near infrared. Benefiting from its angle-dependent characteristic, the device can be straightforwardly utilized for light-switched lamps and optical sensors. Q-factor 8337 and the modulation depth 98.1% are realized while the insertion loss is only 0.07 dB. Compared with its conventional counterparts, the quasi-BIC based absorber enables an excellent hexa-frequency and ultranarrow asynchronous switch function. The quatary-band perfect absorption below 1 nm bandwidth can be applied to the optical sensor to detect four light signals with weak signal strength. This work provides a theoretical basis for multifunctional absorbers with high Q-factor, high modulation depth, and low insertion loss.

Multi-frequency and multi-functional optical switch based on dual plasmon-induced transparency

Research into multi-frequency and multi-functional optical switches for complex applications is pioneering territory. By employing a single-layer structure comprising three distinct graphene strips, we successfully created a dual-PIT effect through the destructive interference among two bright modes and a dark mode. The numerical simulations were corroborated by coupled mode theory, reflecting a high degree of consistency between the theory and the simulations. Remarkably, the modulation of the Fermi level in graphene metamaterials through gate voltage enabled the realization of asynchronous optical switches capable of operating at six, five, four, and three frequencies. Notably, the six-frequency switch exhibited an impressive modulation depth of 88.54% and an insertion loss of just 0.15 dB, highlighting its superior performance. This study lays a solid foundation for future multi-frequency and multi-functional optical switch designs, offering significant implications and practical applications.

Gold saturable metasurface for building a wavelength-tunable optical spiking neuron.

Plasmonic resonant metasurfaces have found many applications in nonlinear optics, such as harmonic generation, all-optical modulation, saturable absorption, etc. A saturable absorber, as a key device for pulsing emission, plays an important role in building passively Q-switched or mode-locked fiber lasers. Recently, excitable fiber lasers have attracted much attention in the area of neuromorphic photonics. In this work, a plasmonic metasurface consisting of periodic gold nanorods resonant near 1550 nm is designed and fabricated, which exhibits saturable absorption with a modulation depth of about 2.6%. The saturable metasurface is, for the first time, utilized in an excitable erbium-doped polarization-maintaining fiber laser, acting as a crucial nonlinear term for the dynamics of the optical spiking neuron. Compared to biological neurons, the artificial optical neuron possesses shorter a refractory period, faster pulse encoding capability, and changeable firing rate as a function of cavity length (up to 20 kHz in our experiment). In addition, the optical neuron is tunable in emission wavelength within the range from 1526.3 nm to 1568.2 nm, beneficial to wavelength-division multiplexing in photonic neural networks. The trial of the nonlinear plasmonic metasurface for an excitable laser could inspire new perspectives in constructing optical neurons and extend applications of metasurfaces from conventional nonlinear optics to neuromorphic computing.

Evaluating Changes in Adult Cochlear Implant Users' Brain and Behavior Following Auditory Training.

To describe the effects of two types of auditory training on both behavioral and physiological measures of auditory function in cochlear implant (CI) users, and to examine whether a relationship exists between the behavioral and objective outcome measures. This study involved two experiments, both of which used a within-subject design. Outcome measures included behavioral and cortical electrophysiological measures of auditory processing. In Experiment I, 8 CI users participated in a music-based auditory training. The training program included both short training sessions completed in the laboratory as well as a set of 12 training sessions that participants completed at home over the course of a month. As part of the training program, study participants listened to a range of different musical stimuli and were asked to discriminate stimuli that differed in pitch or timbre and to identify melodic changes. Performance was assessed before training and at three intervals during and after training was completed. In Experiment II, 20 CI users participated in a more focused auditory training task: the detection of spectral ripple modulation depth. Training consisted of a single 40-minute session that took place in the laboratory under the supervision of the investigators. Behavioral and physiologic measures of spectral ripple modulation depth detection were obtained immediately pre- and post-training. Data from both experiments were analyzed using mixed linear regressions, paired t tests, correlations, and descriptive statistics. In Experiment I, there was a significant improvement in behavioral measures of pitch discrimination after the study participants completed the laboratory and home-based training sessions. There was no significant effect of training on electrophysiologic measures of the auditory N1-P2 onset response and acoustic change complex (ACC). There were no significant relationships between electrophysiologic measures and behavioral outcomes after the month-long training. In Experiment II, there was no significant effect of training on the ACC, although there was a small but significant improvement in behavioral spectral ripple modulation depth thresholds after the short-term training. This study demonstrates that auditory training improves spectral cue perception in CI users, with significant perceptual gains observed despite cortical electrophysiological responses like the ACC not reliably predicting training benefits across short- and long-term interventions. Future research should further explore individual factors that may lead to greater benefit from auditory training, in addition to optimization of training protocols and outcome measures, as well as demonstrate the generalizability of these findings.

Few-layer NbTe2 nanosheets-based saturable absorber for generating 176 fs pulse at 1 μm in ultrafast fiber laser

Ultrafast fiber lasers play an increasingly vital role in diverse fields of science and industry. In this study, a novel NbTe2 nanosheet-based saturable absorber (SA) was prepared by using liquid phase exfoliation and flame brush technology for the first time. Using a twin balance measurement system, the nonlinear optical absorption property was checked. It was found that the fabricated NbTe2 nanosheets-based SA has excellent saturable absorption properties with a large modulation depth of 5.3 %, a very high saturation intensity of 1.11 GW/cm2, and a low non-saturation loss of 63.6 %. After inserting the NbTe2 nanosheets-based SA into a ring-cavity ytterbium-doped fiber laser (YDFL), a stable soliton mode-locking state was achieved. A 176-fs ultrafast soliton pulse train was successfully generated at 1029.76 nm with the repetition rater of 3.097 MHz. Thanks to the unique and very high saturation intensity of NbTe2 nanosheets, the proposed YDFL system achieved a maximum peak power of 96.3 kW and a single pulse energy of 14.09 nJ under 370 mW pump power. These findings indicate that NbTe2 nanosheets have great potential for generating ultra-short optical pulses with higher peak power in mode-locked fiber lasers.

Programmable Optical Encryption Based on Electrical-Field-Controlled Exciton-Trion Transitions in Monolayer WS2.

Optical encryption is receiving much attention with the rapid growth of information technology. Conventional optical encryption usually relies on specific configurations, such as metasurface-based holograms and structure colors, not meeting the requirements of increasing dynamic and programmable encryption. Here, we report a programmable optical encryption approach using WS2/SiO2/Au metal-oxide-semiconductor (MOS) devices, which is based on the electrical-field-controlled exciton-trion transitions in monolayer WS2. The modulation depth of the MOS device reflection amplitude up to 25% related to the excitons ensures the fidelity of information, and the decryption based on the near excitonic resonance assures security. With such devices, we successfully demonstrate their applications in real-time encryption of ASCII codes and visual images. For the latter, it can be implemented at the pixel level. The strategy shows significant potential for low-cost, low-energy-consumption, easily integrated, and high-security programmable optical encryptions.

Efficient Manipulation of Near‐Field Terahertz Waves: Individually Addressable Transmissive Meta‐Device

AbstractDue to the powerful capability in manipulating electromagnetic (EM) waves, digital coding and programmable metasurfaces have found vast application prospects across numerous areas such as next‐generation wireless communications and digital holography. Liquid crystals (LCs), as dielectric materials with significant birefringence effect over a wide frequency range, provide a cost‐effective solution for achieving the programmable metasurfaces and flexible EM manipulations, especially in the terahertz (THz) band. Different from the conventional 1D control and single functionality of transmissive LC‐based devices, here, a 16 × 16 addressable amplitude‐phase coding meta‐device is proposed to support for frequency multiplexing by using the film on glass (FOG) technology. Both numerical simulations and experimental results demonstrate that the meta‐atom exhibits an amplitude modulation depth over 90% and a phase tuning range ≈180° at two distinct frequencies, and hence the single meta‐device can provide multifunctional EM applications, including near‐field printing imaging, 3D THz energy convergence, and zero‐order Bessel beam generation. The proposed strategy paves a way for constructing highly integrated and high‐performance THz multifunctional information processing systems.

A Metamaterials-Based Absorber Used for Switch Applications with Dynamically Variable Bandwidth in Terahertz Regime.

A broadband absorber based on metamaterials of graphene and vanadium dioxide (VO2) is proposed and investigated in the terahertz (THz) regime, which can be used for switch applications with a dynamically variable bandwidth by electrically and thermally controlling the Fermi energy level of graphene and the conductivity of VO2, respectively. The proposed absorber turns 'on' from 1.5 to 5.4 THz, with the modulation depth reaching 97.1% and the absorptance exceeding 90% when the Fermi energy levels of graphene are set as 0.7 eV, and VO2 is in the metallic phase. On the contrary, the absorptance is close to zero and the absorber turns 'off' with the Fermi energy level setting at 0 eV and VO2 in the insulating phase. Furthermore, other four broadband absorption modes can be achieved utilizing the active materials graphene and VO2. The proposed terahertz absorber may benefit the areas of broadband switch, cloaking objects, THz communications and other applications.

Dual-band tunable electromagnetically induced transparency in vanadium dioxide-based miniaturized terahertz metasurfaces

A dual-band electromagnetically induced transparency (EIT) effect with high transmission amplitudes and polarization-insensitive characteristic is realized in vanadium dioxide (VO2)-based miniaturized terahertz metasurfaces. The unit cell comprises a metallic spiral (MS) structure, a small square metal frame (SMF2) structure, and a large square metal frame (SMF1) structure. Two transparent windows with the transmission amplitudes of 0.84 and 0.82 are obtained. The surface current distributions reveal that the dual-band EIT effect is created by the bright-bright-quasi-dark coupling mode. The two transparent windows achieve modulation depths of 45.2% and 42.7%, with maximum group delays of 3.24 ps and 3.17 ps, respectively. The proposed EIT metasurfaces exhibit an electric size of only 0.25λ0, which is considerably smaller than that of other dual-band EIT metasurfaces. The present study offers a novel approach to investigating multi-band EIT metasurfaces, with considerable promise for the development of multi-band communication devices.

A liquid optical memristor using photochromic effect and capillary effect

In the era of the Internet of Things, photonic neuromorphic computing presents a promising method for real-time, local processing of vast quantities of data. However, the rigidity of materials used in such devices can considerably impact performance and longevity when subjected to mechanical deformation. In this study, we introduce a liquid optical memristor (LOM) based on an organic-inorganic hybrid in a liquid state. This novel approach offers programmable optical properties and significant mechanical flexibility thanks to the robust photochromic and capillary effects. We have developed a LOM with a 24 dB cm−1 modulation depth and over 3-bit nonvolatile memory states. By controlling the droplet morphology to mimic a synapse-like shape, the LOM can withstand strains over 400% and endure misalignment and bending. Furthermore, our findings substantiate the application of LOM for photonic neuromorphic computing systems, yielding 100% accuracy in pattern recognition. The easily-integratable LOM paves the way for the creation of flexible and wearable photonic neuromorphic computing systems.

3985Utilizing EllipticalRingIMI-Plasmonic Waveguides, Nanomaterials in Nanophotonic Structure for All-Optical 2 × 1 Demultiplexer

In many industries, particularly electronics, photonic devices are indispensable. However, the diffraction limit and miniaturization are the two problems that have hampered the development of photonics devices. These problems are resolved by plasmonic devices, which enable nanophononics and nanodevices. One of the primary all-optical demultiplexer components utilized in an all-optical Athematic Logic Unit (ALU), which is regarded as the basic building block for all-optical computers, is a plasmonic demultiplexerThis paper provides a new design for an elliptical ring insulator-metal-insulator (IMI) plasmonic waveguide-based all-optical demultiplexer (Demux). The suggested device has a small footprint (300 nm × 250 nm) and works at a 1550 nm wavelength. Demux has a 0.5 transmission threshold between logic zero and logic one states. Transmission (T), extinction ratio (contrast ratio (CR)), modulation depth (MD), and insertion loss (IL) are the four metrics that best explain the performance of the plasmonic Demux. The suggested structural dimensions are outstanding and optimal based on the values of MD for Demux which is (95.87%). The device's maximum transmission efficiency is 56.84%. The suggested plasmonic Demux structure makes a substantial contribution to all-optical signal processing Nano-circuits and nano-photonics integrated circuits. Using COMSOL Multiphysics, wesimulate the proposed plasmonic Demux using the Finite Element Method (FEM).

Molecularization of Metasurfaces for Multifunctional Ultrafast All‐Optical Terahertz Waves

Hybrid metasurfaces incorporated by active materials hold great promise for state‐of‐the‐art terahertz functional devices. However, it is still a major challenge to achieve ultrafast, dynamic, and multifunctional effective control of THz waves via hybrid metasurfaces. Herein, a modulator consisting of split rings and cut‐wires is first demonstrated, with an amplitude of −35.6 dB at 0.524 THz. By embedding semiconductor silicon into specified locations to form a hybrid metasurface, the ultrastrong connectivity of the silicon bridges leads to rapid optical molecularization. Under photoexcitation, the frequency tuning range is 26.7%, the phase shifting reaches 357.5°, and the maximal modulation depth is 94.54%. Taking advantage of the rapid relaxation of photocarriers in the silicon bridges, the ultrafast frequency switching is within 1400 ps. More interestingly, by changing the positions of the silicon bridges, the frequency tuning range is further promoted to 60%, the phase shifting is 353.5°, the modulation depth of 100% is achieved, and the full recovery time is 1600 ps. Furthermore, the underlying mechanism of the ultrafast tuning process is elucidated. This work demonstrates the feasibility of all‐optical‐controlled hybrid metasurface to achieve multifunctional dynamic modulation of THz waves, which has tremendous potential for applications in optical switching, signal processing, and frequency conversion.

Electrically tunable third-harmonic generation using intersubband polaritonic metasurfaces

Nonlinear intersubband polaritonic metasurfaces, which integrate giant nonlinear responses derived from intersubband transitions of multiple quantum wells (MQWs) with plasmonic nanoresonators, not only facilitate efficient frequency conversion at pump intensities on the order of few tens of kW cm-2 but also enable electrical modulation of nonlinear responses at the individual meta-atom level and dynamic beam manipulation. The electrical modulation characteristics of the magnitude and phase of the nonlinear optical response are realized through Stark tuning of the resonant intersubband nonlinearity. In this study, we report, for the first time, experimental implementations of electrical modulation characteristics of mid-infrared third-harmonic generation (THG) using an intersubband polaritonic metasurface based on MQW with electrically tunable third-order nonlinear response. Experimentally, we achieved a 450% modulation depth of the THG signal, 86% suppression of zero-order THG diffraction tuning based on local phase tuning exceeding 180 degrees, and THG beam steering using phase gradients. Our work proposes a new route for electrically tunable flat nonlinear optical elements with versatile functionalities.

Six-state modulation method for improving the accuracy of fiber optic gyroscopes by reducing electrical crosstalk

Reducing the influence of electrical crosstalk is crucial for the development of fiber optic gyroscopes. We present a six-state modulation method that takes advantage of highly flexible modulation voltages to eliminate the correlation between the modulation voltage with a fixed phase delay and the demodulation sequence. Theoretical analysis indicates that our approach can eliminate the impact of crosstalk with a fixed phase delay at any modulation depth. Experimental measurements demonstrate that compared to the conventional four-state modulation method, the zero bias is reduced by about 0.3319°/h at the modulation depth of π/2 when our method is applied. Additionally, at the depths of π/2, 2π/3, and 7π/8, the bias instability is reduced by approximately 30%, and the angular random walk (ARW) is reduced by over 60%. The results confirm its effectiveness in decreasing electrical crosstalk, which holds profound implications for enhancing the accuracy of fiber optic gyroscopes.