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Maintaining the s-polarization state of laser beams is important to achieve high modulation depth in a laser-interference-based super-resolution structured illumination microscope (SR-SIM). However, the imperfect optical components can depolarize the laser beams hence degenerating the modulation depth. Here, we first presented a direct measurement method designed to estimate the modulation depth more precisely by shifting illumination patterns with equal phase steps. This measurement method greatly reduces the dependence of modulation depths on the samples, and then developed a polarization optimization method to achieve high modulation depth at all orientations by actively and quantitatively compensating for the additional phase difference using a combination of waveplate and a liquid crystal variable retarder (LCVR). Experimental results demonstrate that our method can achieve illumination patterns with modulation depth higher than 0.94 at three orientations with only one LCVR voltage, which enables isotropic resolution improvement. [ABSTRACT FROM AUTHOR]

Steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) enable people to control external devices by focusing on repetitive visual stimuli (RVS). However, RVS can be visually annoying and cause user discomfort. To address this issue, this study proposes subtle flickering RVS to enhance visual comfort with SSVEP-based BCIs. Previous research on mitigating this discomfort has explored various stimuli characteristics, such as frequencies, colors, and patterns, but some studies are contradicting and have their limitations. This study investigates whether modulation depth (MD) can reduce user discomfort when using LCD-displayed stimuli. Specifically, MDs ranging from 1 down to 0.0125 and their effect on SSVEP response and BCI performance have been computed. Results demonstrate that stimuli with a 0.5 MD achieve accuracy and information-transfer rate (ITR) performance of 80.06% and 41.6 bpm which are at par with a baseline BCI having stimuli with a MD of 1, having 79.98% accuracy and 41.08 bpm ITR. These findings demonstrate that a lower flicker annoyance may be obtained with stimuli having a MD of 0.5. By reducing user discomfort, the proposed subtle flickering RVS can improve user experience without significant degradation in performance, potentially increasing the adoption and usability of SSVEP-based BCIs. [ABSTRACT FROM AUTHOR]

In this paper, we used the liquid phase stripping method to manufacture MoS2–SnSe2 heterojunction saturable absorber (SA). The scanning electron microscope, the atomic force microscope, and the Raman spectrometer were used to characterize the MoS2–SnSe2 heterojunction SA. The Q‐switched mode‐locked (QSML) Nd:GGG laser with MoS2–SnSe2 heterojunction SA was presented. The maximum output power of the QSML Nd:GGG laser was 236.4 mW with a repetition rate of 83.3 MHz and pulse width of 447 ps. In short, the MoS2–SnSe2 heterojunction nanosheets present excellent saturable absorption characteristics. [ABSTRACT FROM AUTHOR]

Historical documents are often severely damaged, making it impossible to open them manually without causing further damage. To address this challenge, computed tomography (CT) has emerged as a non-destructive method to explore the inside in a different way. However, the use of ionising radiation in CT scanning raises concerns about its impact on fragile historical documents. This study presents a methodology that uses a test object to conduct preliminary investigations to evaluate the capability of a CT scanner for digital preservation of historical documents. By assessing the feasibility and determining the setting parameters in advance, the X-ray exposure to historical documents can be minimised. For this purpose, a large dataset of inter-page distances was obtained from CT scans of a specially developed test object. The results obtained show a consistent correlation between the page-to-page distances and the derived modulation depths. This method offers great potential for assessing the separability of the pages of historical documents even before they are exposed to radiation for digitisation. Overall, this study helps to reduce the impact of X-ray radiation on sensitive historical documents during digitisation using CT, with the aim of preserving this fragile cultural heritage for future generations.

Compared with traditional methane sensors, metasurface methane sensors have advantages such as high sensitivity, stable performance, miniaturization, integration, and multi functional customizability. It better meets the application needs in complex environments such as coal mines. This paper proposes an all dielectric type metasurface methane sensor based on Fano resonance. The metasurface structure consists of periodic silicon nanostructures and SiO2 substrates, consisting of four square silicon ring nanostructures and a central silicon nanoblock. By changing the geometric parameters, the effect on the Fano resonance of the all dielectric metasurface structure is observed. The results show the following points. Considering the quality factor and modulation depth of the structure, the center distance of the square silicon ring should be 1000 nm, the inner edge length of the square silicon ring should be 100 nm, and the edge length of the silicon nanoblock should be 200 nm. At this time, the quality factor is 227.60, and the modulation depth is 99.98%, which is close to 100%. By coating methane gas sensing thin films within the metasurface structure to achieve sensing and detection functions, combined with the extremely narrow linewidth Fano resonance features and significant local field enhancement effect, high-precision detection of methane gas is achieved. The simulation results show that the sensitivity of the all dielectric metasurface sensor to methane volume fraction is −0.953 nm/%. The change in methane volume fraction is linearly related to the shift of the resonance peak, indicating good monitoring performance. The refractive index sensitivity of the all dielectric metasurface sensor is as high as 883.95 nm/RIU. The resonance peak offset is linearly related to the environmental refractive index increment, which can be used to detect changes in environmental refractive index.

ABSTRACT Purpose The inter-aural time difference (ITD) and inter-aural level difference (ILD) are important acoustic cues for horizontal localization and spatial release from masking. These cues are encoded based on inter-aural comparisons of tonotopically matched binaural inputs. Therefore, binaural coherence or the interaural spectro-temporal similarity is a pre-requisite for encoding ITD and ILD. The modulation depth of envelope is an important envelope characteristic that helps in encoding the envelope-ITD. However, inter-aural difference in modulation depth can result in reduced binaural coherence and poor representation of binaural cues as in the case with reverberation, noise and compression in cochlear implants and hearing aids. This study investigated the effect of inter-aural modulation depth difference on the ITD thresholds for an amplitude-modulated noise in normal hearing young adults. Methods An amplitude modulated high pass filtered noise with varying modulation depth differences was presented sequentially through headphones. In one ear, the modulation depth was retained at 90% and in the other ear it varied from 90% to 50%. The ITD thresholds for modulation frequencies of 8 Hz and 16 Hz were estimated as a function of the inter-aural modulation depth difference. Results The Friedman test findings revealed a statistically significant increase in the ITD threshold with an increase in the inter-aural modulation depth difference for 8 Hz and 16 Hz. Conclusion The results indicate that the inter-aural differences in the modulation depth negatively impact ITD perception for an amplitude-modulated high pass filtered noise.

The аrticle is devoted to the study of the possibility of creating an environmentally friendly source of radiation in the mid-infrared range of the spectrum. Chemical elements suitable for replacing mercury in the pulsed gas-discharge lamps plasma channel were theoretically analyzed. On the basis of a mathematical model, the effect of an additionally introduced component on the cesium vapor pressure and the thermal conductivity of the plasma-forming medium was revealed. In the paper, experimental studies confirming the technical solution validity for replacing mercury with rubidium were carried out, and practical recommendations were given on the weight ratios of the components introduced into the discharge. [ABSTRACT FROM AUTHOR]

In this paper, an electro-absorption modulator based on a hybrid plasmonic structure is designed and analyzed for wavelengths ranging from 1300 to 1800 nm and chemical potentials ranging from 0 to 0.65 eV for graphene. This modulator has a high modulation depth (19.9 dB/µm) in the broad wavelength range of 1300–1800 nm. The proposed modulator comprises three graphene layers and two Hexagonal Boron Nitride (h-BN) layers. Silver nano-ribbons are placed on the structure and inside the silicon layer. The silver nano-ribbons create a spatially confined plasmonic mode along its edge. The edge is covered by graphene sheets, which is isolated by a layer of h-BN. A silver nano-ribbon with sharp rectangular edges can serve as a guide for a spatially confined plasmonic mode. There are two edges involving in the presence of transverse electric field components that contribute to the interaction. Our results show a high amount of light confinement and surface plasmon polaritons. The proposed modulator has a 11.8 dB/µm modulation depth with 1.7 dB/µm loss at 1550 nm and a 19.9 dB/µm modulation depth with 2.9 dB/µm loss at 1300 nm. [ABSTRACT FROM AUTHOR]

Historical documents are often severely damaged, making it impossible to open them manually without causing further damage. To address this challenge, computed tomography (CT) has emerged as a non-destructive method to explore the inside in a different way. However, the use of ionising radiation in CT scanning raises concerns about its impact on fragile historical documents. This study presents a methodology that uses a test object to conduct preliminary investigations to evaluate the capability of a CT scanner for digital preservation of historical documents. By assessing the feasibility and determining the setting parameters in advance, the X-ray exposure to historical documents can be minimised. For this purpose, a large dataset of inter-page distances was obtained from CT scans of a specially developed test object. The results obtained show a consistent correlation between the page-to-page distances and the derived modulation depths. This method offers great potential for assessing the separability of the pages of historical documents even before they are exposed to radiation for digitisation. Overall, this study helps to reduce the impact of X-ray radiation on sensitive historical documents during digitisation using CT, with the aim of preserving this fragile cultural heritage for future generations. [ABSTRACT FROM AUTHOR]

In this work, the effect of SCH width on the modulation and distortion characteristics of tunnel injection transistor laserare analyzed. The rate equations of transistor laser are numerically solved using fourth order Runge Kutta method and the threshold current is found to reduce for increase in SCH width, in case of narrow SCH layer. A maximum modulation bandwidth of 21.8 GHz is predicted for aSCH width of 21 nm. However, at SCH width of 30 nm, a modulation depth of 0.44 is obtained, which is maximumcompared to other SCH widths. A minimum third order intermodulation distortion of − 39.6 dBc is obtained for SCH width of 21 nm. Further, anSFDR value of 79.6 dB Hz2/3 is observedfor the same width. Hence 21 nm SCH width is identified as an optimum value, which leads to minimum distortion and maximum bandwidth, for the TI-TL structure considered in this work. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A broadband plasmonic optical modulator based on a dual back-to-back U-shaped silicon waveguide and double layers of graphene has been investigated. The proposed structure is designed at TE mode over a range of wavelengths extending from 1.1 to 1.9 μm. By adjusting the geometry of the U-shaped structure, the modulator's performance has been tuned. Utilizing propagation loss, bandwidth, power consumption, and modulation depth, the proposed modulator's performance has been characterized. According to the results, at a wavelength of 1.55 μm, the loss, modulation depth, and small footprint read 0.0415 dB/μm, 0.6337 dB/μm, and (0.5 μm × 12.17 μm), respectively. Furthermore, the proposed modulator has a modulation bandwidth of about 151.7 GHz and a power consumption of 21.068 fJ/bit. [ABSTRACT FROM AUTHOR]

We propose a novel approach to obtain the ultra-narrowband, electrically switchable, and high-efficiency absorption in the monolayer graphene. The monolayer graphene is sandwiched between the silica substrate and a square array of silver nanospheres, which is covered by a very thick silica layer. The fundamental role of the thick silica cover layer is to homogenize the surrounding medium of the silver nanospheres, and thus efficiently exciting the lattice plasmon resonance. The lattice plasmon resonance arising from the coupling between the dipolar plasmon resonance of silver nanospheres and the zero-order diffraction wave at Wood anomaly can enhance the electromagnetic fields at the graphene surface, and thus greatly improve the near-infrared light absorption of the monolayer graphene with the maximum absorption efficiency up to 45%. Owing to the low radiation loss of the lattice plasmon resonance, the absorption linewidth of the monolayer graphene can be largely compressed to only several nanometers (3.2 nm ∼ 7.4 nm). Moreover, the absorption of the monolayer graphene in our proposed nanostructures has a nearly 100% modulation depth to exhibit an excellent switching property. Our work will be helpful for some graphene-based photoelectric devices.

All-optical terahertz (THz) modulators have received tremendous attention due to their significant role in developing future sixth-generation technology and all-optical networks. Herein, the THz modulation performance of the Bi2Te3/Si heterostructure is investigated via THz time-domain spectroscopy under the control of continuous wave lasers at 532 nm and 405 nm. Broadband-sensitive modulation is observed at 532 nm and 405 nm within the experimental frequency range from 0.8 to 2.4 THz. The modulation depth reaches 80% under the 532 nm laser illumination with a maximum power of 250 mW and 96% under 405 nm illumination with a high power of 550 mW. The mechanism of the largely enhanced modulation depth is attributed to the construction of a type-II Bi2Te3/Si heterostructure, which could promote photogenerated electron and hole separation and increase carrier density dramatically. This work proves that a high photon energy laser can also achieve high-efficiency modulation based on the Bi2Te3/Si heterostructure, and the UV-Visible control laser may be more suitable for designing advanced all-optical THz modulators with micro-level sizes. [ABSTRACT FROM AUTHOR]

A broadband plasmonic optical modulator based on a bowtie-shape waveguide and dual graphene layers has been investigated. The proposed structure is designed at TE mode over a range of wavelengths extending from 1100 to 1900 nm. The performance of the modulator has been tuned by adjusting the geometry of the bowtie structure. The proposed modulator's performance has been characterized using propagation loss, bandwidth, power consumption, and modulation depth. The obtained results show at a wavelength of 1.55 μm that the loss, modulation depth, and small footprint read 0.0257, 0.5829 dB/μm, and (0.5 × 12.17 μm), respectively. Additionally, the proposed modulator offers modulation bandwidth and power consumption of about 151.7 GHz and 32.919 fJ/bit, respectively. [ABSTRACT FROM AUTHOR]

In this study, a novel multilayer terahertz metamaterial with four graphene sub-structures is designed to achieve dynamically tunable triple plasmon-induced transparency (PIT) due to interference among bright-bright modes. Coupled mode theory (CMT) and finite-difference time-domain (FDTD) simulations show a high degree of consistency in their results. Interestingly, enhanced transmission dips are observed when various graphene structures couple with the two longitudinal graphene strips at the bottom layer. Based on the dynamic modulation characteristics of graphene, the metamaterial demonstrates seven-band optical switching capabilities, achieving modulation depths (MD) of 94.6%, 88.1%, 90.8%, 90.8%, 90.4%, 86.6%, and 87.5%. Additionally, the proposed graphene metamaterial also shows excellent slow-light effects, with a group index reaching up to 1034. This proposed terahertz metamaterial holds significant theoretical implications for the development of dynamically integrated terahertz optoelectronic devices. • A multilayer terahertz graphene metamaterial structure has been proposed for achieving dynamically tunable triple PIT. • The optical switching effect can be achieved by adjusting the Fermi energy level. • Enhanced transmission dips are observed when different graphene structures are coupled with two graphene strips. [ABSTRACT FROM AUTHOR]

In the ever-evolving landscape of wireless communication, innovations continue to push the boundaries of what's possible. One such ground-breaking advancement is the Four-Element Multiple-Input Multiple-Output (MIMO) antenna. This sophisticated technology combines the principles of antenna design with the power of MIMO to deliver unparalleled performance and efficiency in wireless communication systems. In this article, we explore the intricacies of the Four-Element MIMO antenna, its design principles, applications, and its transformative impact on the world of wireless connectivity. [ABSTRACT FROM AUTHOR]

In this research, a metamaterial structure composed of graphene sandwich structure is put forward to achieve triple plasmon-induced transparency. This phenomenon is generated by brightâ€"bright modes interaction in the proposed structure, and the results calculated though couple mode theory are consistent with the simulation ones using finite difference time domain method. In addition, the effects of graphene Fermi level and scattering rate on the transmission spectrum are also discussed. It is found that the five-fold switching effects are achieved with the modulation depths (MDs) of 92%, 91%, 95%, 90% and 94%, respectively. What is more, the different graphene strip can also be adjusted by changing Fermi levels to achieve the switching effects with the MDs of 98% and 97%. This model has the prospect to be applied in multi-functional modulators and optical switches in terahertz band. [ABSTRACT FROM AUTHOR]

In this paper, the liquid‐phase ultrasonic stripping preparation method was used to fabricate a TiS2 saturable absorber (SA). A Q‐switched Nd:YVO4 laser was demonstrated using the TiS2 SA. The modulation depth and saturation power intensity of TiS2 SA were 4.5% and 19.7 MW/cm2, respectively. The maximum output power was 322 mW under 4.5 W with T = 10%, and the corresponding conversion efficiency was 7.16%. The pulse width was 476 ns with a repetition rate of 72.4 kHz, and the corresponding single pulse energy was 4.45 μJ. Thus, TiS2 nanosheet is a suitable SA material for Q‐switched lasers. [ABSTRACT FROM AUTHOR]

Terahertz (THz) technology offers unparalleled opportunities in a wide variety of applications, ranging from imaging and spectroscopy to communications and quality control, where lack of efficient modulation devices poses a major bottleneck. Spatial modulation allows for dynamically encoding various spatial information into the THz wavefront by electrical or optical control. It plays a key role in single-pixel imaging, beam scanning and wavefront shaping. Although mature techniques from the microwave and optical band are not readily applicable when scaled to the THz band, the rise of metasurfaces and the advance of new materials do inspire new possibilities. In this review, we summarize the recent progress of THz spatial light modulators from the perspective of functional materials and analyze their modulation principles, specifications, applications and possible challenges. We envision new advances of this technique in the near future to promote THz applications in different fields. [ABSTRACT FROM AUTHOR]

In this study, all-optical OR, exclusive OR (XOR), NOR, XNOR, AND, NAND, and NOT logic gates using metal-insulator-metal (MIM) waveguides with a rectangular ring resonator are designed and analyzed. The structure has a silver plate with three input waveguides, one output waveguide, and a rectangular ring resonator. One of the input ports is used as a control port. The finite-difference time-domain (FDTD) method is utilized to obtain the optical spectrum of the proposed structures. To realize all-optical logic gate properties of the designed structures, optical signals with the same phase or different phases are passed through the waveguides. Transmission spectrum (T), contrast ratio (CR), and modulation depth (MD) parameters are obtained to determine the performances of all-optical logic gates. To determine the logic 1 (ON) and logic 0 (OFF) states of the output ports, the threshold transmission value is accepted as 0.23 for all-optical logic gates. For the proposed designs, the highest transmission, contrast ratio, and modulation depth values are 217%, 6.75 dB, and 100%, respectively. The structure also supports a data rate of 24 Tb/s. The designed optical logic gates have valuable features for developing high-performance optical devices. [Display omitted] • Design and analysis of all-optical OR, XOR, NOR, XNOR, AND, NAND, and NOT logic gates in the near-infrared regime. • The proposed structure has metal-insulator-metal waveguides and a rectangular ring resonator. • Maximum transmission is 217% at 836.8 nm. • The structure can support a data rate of 24 Tb/s. [ABSTRACT FROM AUTHOR]

The operation of a wind turbine (WT) is characterized by fluctuations in sound pressure amplitude associated with the passage of the propeller blade through the tower. Amplitude Modulation (AM) is one of the factors that contributes to the increased annoyance of wind turbine noise. The phenomenon of AM is currently the subject of research in many research centers around the world in the context of a parametric assessment of its impact on annoyance. Despite the development of many methods to measure the AM of a WT noise, there is no commonly accepted method. This paper discusses the most crucial factors that stimulate the phenomenon of AM and the implementation in the MATLAB environment of the algorithm to find the frequency and depth of AM proposed by the Amplitude Modulation Working Group (AMWG). The results of verification of the developed algorithm as well as the measurement results of the frequency and depth of modulation for two measurement samples of a 2 MW wind turbine are presented. [ABSTRACT FROM AUTHOR]

In order to solve the demodulation distortion caused by light intensity disturbance and modulation depth drift in traditional phase generated carrier (PGC) demodulation algorithm, an improved PGC demodulation algorithm based on fundamental wave mixing and differential self multiplication was adopted. And relevant theoretical analysis and simulation verification were carried out. The results show that the distortion caused by light intensity disturbance can be suppressed, and the demodulation efficiency can be improved at the same timeby using this algorithm. When the light intensity disturbance of 1.5rad ~3.5rad was introduced, the signal-to-noise and distortion ratio of nearly 30dB was obtained, which was 15dB higher than the traditional discrete cosine transform (PGC-DCM) algorithm. In addition, the dependence on modulation depth C can be eliminated, and the total harmonic distortion of less than 0.1% and the signal-to-noise ratio of 30dB can be achieved, which was nearly 10dB higher than the traditional algorithm, and the corresponding linearity was up to 99. 99%. It provides a new scheme for the demodulation of optical fiber interferometric sensor. [ABSTRACT FROM AUTHOR]

Electro-optic modulation with a constant modulation depth plays important roles in quantum metrology, microwave photonics, and optical precision measurement and sensing, etc. To compensate the continuous drift of the half-wave voltage and maintain the modulation depth, we incidentally generated a reference laser to make intermedia optical beatings with the carrier and +1st sideband, and tightly locked the carrier to sideband ratio by extracting the relative microwave power of those intermedia beat signals using a home-made electronic control module. Experiments of the short-term test for locking bandwidth, the anti-jamming capability, and the long-term stability were demonstrated. As is verified that, the locking bandwidth was estimated up to tens of kHz, and the anti-jamming capability was confirmed despite of a strong hair-dryer agitation. The long-term stability for the modulation depth stabilization showed that the peak-to-peak relative stability for 150-minute was 5.67 × 10−6, and the Allan deviation reached a minimum of 2.19 × 10−7 at an averaging time of 400 s, which is improved by more than four orders of magnitude compared with the open-loop regime. We believe the reported method as well as the designed module is versatile and potential to precision measurement and sensing applications badly requiring a stable modulation depth, such as atom interferometry, optical interferometry and lidar detection.

2D atomically thin graphdiyne oxide (GDYO) nanosheets (NSs) are synthesized, and their nonlinear modulation is investigated. Generally, improving the modulation depth (MD) of all‐optical modulation (AOM) requires a pump light with strong power, which limits the development of AOM technology in the design of low‐power loss devices. In this study, an AOM system based on spatial self‐phase modulation and spatial cross‐phase modulation methods is proposed using 2D GDYO NSs. The results reveal that 2D GDYO exhibits tunable nonlinearity and high stability, which is desirable for designing the AOM system. Because of the excellent optical properties of 2D GDYO, a large MD of >98% is achieved for the proposed AOM with a low power of pump light, which is higher than most AOMs currently reported. Thus, GDYO is an excellent modulation material in AOM, which improves the application prospects of carbon nanomaterials in all‐optical devices. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to suit the increasingly complex electromagnetism environment, multifunctional and continuously tunable terahertz device is becoming a research focus. In this paper, a frequency and amplitude tunable dual-band terahertz metamaterial absorber is proposed. Continuous tuning of absorption frequency and amplitude are completed by dynamic control of the conductivity of photosensitive silicon and the polarization angle, respectively. The tuning range of 55 GHz and amplitude modulation depth up to 100% are obtained. It can be concluded that the structure provides a new approach for the realization of future terahertz metamaterial absorbers possessing the characteristics of multifunction, portability, and intelligence. [ABSTRACT FROM AUTHOR]

We report on a novel effect of temperature-dependent modulation in graphene-supported metamaterials. The effect was observed during the theoretical analysis of a model graphene-supported electro-optical modulator having silicon dioxide (SiO2) or hafnium dioxide (HfO2) as a buffer dielectric layer. Comparative analysis of the two materials showed that they provide approximately the same maximum values for transmission and reflection modulation depths. However, in the case of a HfO2 buffer layer, a lower chemical potential of the graphene is required to achieve the maximum value. Moreover, theoretical calculations revealed that a lower gate voltage (up to 6.4 times) is required to be applied in the case of a HfO2 layer to achieve the same graphene chemical potential. The graphene layer was found to possesses high absorption (due to the additional resonance excitation) for some values of chemical potential and this effect is extremely temperature dependent. The discovered modulation effect was demonstrated to further increase the transmission modulation depth for the simple model structure up to 2.7 times (from 18.4% to 50.1%), while for the reflection modulation depth, this enhancement was equal to 2.2 times (from 24.4% to 52.8%). The novel modulation effect could easily be adopted and applied over a wide range of metadevices which would serve as a quick booster for the development of related research areas. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional nanomaterial, possess unique photoelectric properties that have potential application in designing optoelectronic devices. The tunable optical absorption is one of the most exciting properties that can be used to improve the performance of silicon modulators. However, the weak light–matter interaction caused by the size mismatch between the optical mode fields and graphene makes the graphene-on-silicon modulator (GOSM) has large footprint and high energy consumption, limiting the enhancement of modulation efficiency. Here, we propose a broadband GOSM with orthogonal hybrid plasmonic waveguides (HPWs) at near-infrared wavelengths. The orthogonal HPWs are designed to compress the interaction region of optical fields and enhance the light-graphene interaction. The results show that the GOSM has a modulation depth of 26.20 dB/μm, a footprint of 0.33 μm2, a 3 dB modulation bandwidth of 462.77 GHz, and energy consumption of 2.82 fJ/bit at 1.55 μm. Even working at a broad wavelength band ranging from 1.3 to 2 μm, the GOSM also has a modulation depth of over 8.58 dB/μm and energy consumption of below 4.97 fJ/bit. It is anticipated that with the excellent modulation performance, this GOSM may have great potential in broadband integrated modulators, on-chip optical communications and interconnects, etc.

All-optical terahertz (THz) modulators have received tremendous attention due to their significant role in developing future sixth-generation technology and all-optical networks. Herein, the THz modulation performance of the Bi2Te3/Si heterostructure is investigated via THz time-domain spectroscopy under the control of continuous wave lasers at 532 nm and 405 nm. Broadband-sensitive modulation is observed at 532 nm and 405 nm within the experimental frequency range from 0.8 to 2.4 THz. The modulation depth reaches 80% under the 532 nm laser illumination with a maximum power of 250 mW and 96% under 405 nm illumination with a high power of 550 mW. The mechanism of the largely enhanced modulation depth is attributed to the construction of a type-II Bi2Te3/Si heterostructure, which could promote photogenerated electron and hole separation and increase carrier density dramatically. This work proves that a high photon energy laser can also achieve high-efficiency modulation based on the Bi2Te3/Si heterostructure, and the UV-Visible control laser may be more suitable for designing advanced all-optical THz modulators with micro-level sizes.

Temporal modulations in the envelope of acoustic waveforms at rates around 4 Hz constitute a strong acoustic cue in speech and other natural sounds. It is often assumed that the ascending auditory pathway is increasingly sensitive to slow amplitude modulation (AM), but sensitivity to AM is typically considered separately for individual stages of the auditory system. Here, we used blood oxygen level dependent (BOLD) fMRI in twenty human subjects (10 male) to measure sensitivity of regional neural activity in the auditory system to 4 Hz temporal modulations. Participants were exposed to AM noise stimuli varying parametrically in modulation depth to characterize modulation-depth effects on BOLD responses. A Bayesian hierarchical modeling approach was used to model potentially nonlinear relations between AM depth and group-level BOLD responses in auditory regions of interest (ROIs). Sound stimulation activated the auditory brainstem and cortex structures in single subjects. BOLD responses to noise exposure in core and belt auditory cortices scaled positively with modulation depth. This finding was corroborated by whole-brain cluster-level inference. Sensitivity to AM depth variations was particularly pronounced in the Heschl's gyrus but also found in higher-order auditory cortical regions. None of the sound-responsive subcortical auditory structures showed a BOLD response profile that reflected the parametric variation in AM depth. The results are compatible with the notion that early auditory cortical regions play a key role in processing low-rate modulation content of sounds in the human auditory system.

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we discuss the quality of holograms based on the calculation of the modulation depth. It's shown that the terahertz (THz) pulsed vortex beams play a vital role in holography filed, where two lasers with frequency difference have used. The THz vortex beams give new regions of larger frequency detuning and an important value of the modulation depth and fringe contrast (MDFC ratio) for obtaining the best holograms contrary to the Gaussian beams for which the best holograms are realized for small frequency detuning. The particular cases such as, Gaussian beam and single cycle pulses are deduced from our result. Numerical simulations are also presented to study the dependence of the MDFC ratio on the frequency detuning for THz vortex beams and Gaussian beams. This research could be beneficial in holographic interferometry, and it will firmly establish as a tool for scientific and engineering studies. [ABSTRACT FROM AUTHOR]

Electro-optic modulation with a constant modulation depth plays important roles in quantum metrology, microwave photonics, and optical precision measurement and sensing, etc. To compensate the continuous drift of the half-wave voltage and maintain the modulation depth, we incidentally generated a reference laser to make intermedia optical beatings with the carrier and +1st sideband, and tightly locked the carrier to sideband ratio by extracting the relative microwave power of those intermedia beat signals using a home-made electronic control module. Experiments of the short-term test for locking bandwidth, the anti-jamming capability, and the long-term stability were demonstrated. As is verified that, the locking bandwidth was estimated up to tens of kHz, and the anti-jamming capability was confirmed despite of a strong hair-dryer agitation. The long-term stability for the modulation depth stabilization showed that the peak-to-peak relative stability for 150-minute was 5.67 × 10−6, and the Allan deviation reached a minimum of 2.19 × 10−7 at an averaging time of 400 s, which is improved by more than four orders of magnitude compared with the open-loop regime. We believe the reported method as well as the designed module is versatile and potential to precision measurement and sensing applications badly requiring a stable modulation depth, such as atom interferometry, optical interferometry and lidar detection. [ABSTRACT FROM AUTHOR]

In tunable diode laser absorption spectroscopy (TDLAS), the wavelength modulation spectroscopy (WMS) is widely employed. However, when measuring the gas concentration with the second harmonic signal, errors will occur and the inversion accuracy will be reduced, because the change of the modulation depth will lead to the change of the second harmonic peak value, and the value of modulation depth cannot be calculated directly in the absence of gas component. To improve the inversion accuracy of WMS technology, we calibrate the modulation depth and take it as a parameter to the concentration inversion model. In this article, the relationship between the modulation depth and the valley spacing of the second harmonic is first derived, and used to calibrate the modulation depth in the measurement; then, an improved concentration inversion model is established by adding the calibrated modulation depth to the traditional model. Through simulations in Simulink and gas concentration measurement experiments with carbon monoxide (CO), the effectiveness of modulation depth calibration using valley spacing and the accuracy of the improved model are verified. The gas concentration measurement error of the improved model (relative error -5) is reduced by nearly one order of magnitude compared to the traditional model without calibration of the modulation depth (relative error -4). The correction method of modulation depth in this article does not need the priori information of the gas component, and the improved model produces a better determination of gas concentration immune to the variations of modulation depth, which is important for field measurements especially those with large environmental variations.

In this paper, we discuss the quality of holograms generated by two-femtosecond laser pulses of two different colors based on the interference and holography processes by the calculation of the modulation depth. Some numerical simulations for the two Higher-order sh- and ch-Gaussian temporal profiles (shnGTP and chnGTP) are investigated. These simulations show that, when two lasers with a very large frequency detuning are used, the considered profiles exhibit more precise results and give new frequency detuning zones that allow a very significant value of the modulation depth to fringe contrast (MDFC) ratio to obtain the best hologram compared to Gaussian profile. The proposed theory will be a good basis for the development of some new experiments on holographic interferometry and it will certainly be very useful for the specialists using these femtosecond laser pulses. [ABSTRACT FROM AUTHOR]

In this paper, an optical modulator based on the hybrid structure is designed and analyzed in the wavelength range of 1.3 µm–1.8 µm. In this work, the proposed modulator consists of graphene, Molybdenum disulfide ( MoS 2 ), and Hexagonal Boron Nitride (h-BN) layers with Si layer on SiO 2 substrate. The Si layer on SiO 2 substrate has created a waveguide in the middle of the structure. Our investigations show that the strong coupling in this intermediate waveguide increases the light interaction with graphene, and finally increases the modulation depth (MD) of proposed modulator. In our proposed modulator, at telecommunication wavelength of 1.55 µm, the modulation depth equals 0.2 dB/µm, and the loss rate is 0.2 dB/µm. The highest modulation depth is 0.58 dB/µm, with loss of 0.58 dB/µm and occurs at wavelength of 1.8 µm. [ABSTRACT FROM AUTHOR]

A high-power light-emitting diode (LED) panel-lamp connected in series with a low-complexity modulation circuit using metal–oxide–semiconductor field-effect transistor (MOSFET) is proposed for an indoor visible-light communication system. The MOSFET modulation circuit consists of a high-speed MOSFET and a shunt resistor, in which the MOSFET gives a variable load driven by the data bit stream and the shunt resistor can tune the modulation depth of the transmitter. In addition, only focusing optical lens is employed in the receiver but no collimation optical lens is adopted in the transmitter to increase the working area. Although the largest data rate is limited to 2 Mbps, the longitudinal communication distances is as long as 6 m; moreover, the maximum horizontal distance is up to 5 m (~ 78.5 m2 in area) along with 3 m in longitudinal distance at the data rates of 1 Mbps. Compared with the traditional Bias-Tee configuration, the proposed MOSFET configuration leads to a lower data rate but a higher modulation depth as well as much larger working area. To the best of our knowledge, this is the largest working area at such a high data rate with on–off-keying using a single LED luminary without collimation optical lens. The system has the inherent ability to realize pulse amplitude modulation (PAM). The 4-PAM is demonstrated to double the data rates. [ABSTRACT FROM AUTHOR]