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Submarine distributed acoustic sensing cables record seafloor strain with striking spatial variability whose physical origin is not immediately obvious. By explicitly partitioning the recorded wavefield into ocean‐wave, Scholte‐wave, and teleseismic Rayleigh‐wave components, we show that these amplitude variations are not random but encode systematic modulation by seabed properties. Softer sediment intervals consistently amplify all wavefield components, whereas harder patches suppress them. Numerical simulations reproduce this behavior and reveal frequency‐ and mode‐dependent amplitude modulation controlled by surface‐wave sensitivity kernels confined to a shallow fraction of a wavelength. In this sense, the seabed acts as an elastic modulator governing how external energy, from ocean‐wave pressure to teleseismic arrivals, is converted into measurable strain on the cable. Amplitude information therefore provides a direct, spatially resolved proxy for near‐surface seabed stiffness. Additionally, undoing this seabed‐induced modulation is a necessary first step for quantitative analysis of other processes, such as wind forcing and microseism generation.

Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar-induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements. We developed an instrument to measure leaf-level gas exchange simultaneously with pulse-amplitude modulation (PAM) and spectrally resolved fluorescence over the same field of view – allowing us to investigate the relationships between active and passive fluorescence with photosynthesis. Strongly correlated, slope-dependent relationships were observed between measured spectra across all wavelengths (Fλ , 670–850 nm) and PAM fluorescence parameters under a range of actinic light intensities (steady-state fluorescence yields, F t) and saturation pulses (maximal fluorescence yields, F m). Our results suggest that this method can accurately reproduce the full Chl emission spectra – capturing the spectral dynamics associated with changes in the yields of fluorescence, photochemical (ΦPSII), and nonphotochemical quenching (NPQ). We discuss how this method may establish a link between photosynthetic capacity and the mechanistic drivers of wavelength-specific fluorescence emission during changes in environmental conditions (light, temperature, humidity). Our emphasis is on future research directions linking spectral fluorescence to photosynthesis, ΦPSII, and NPQ.

Reconfigurable intelligent surface (RIS)-aided index modulation (IM) shows great potential for next-generation wireless communications. Nevertheless, obtaining channel state information (CSI) for RIS-based IM incurs high pilot overhead, particularly for multi-domain IM. In this paper, we integrate orthogonal frequency division multiplexing into RIS-aided differential reflecting modulation (DRM) communications, introducing the differential reflecting frequency modulation (DRFM) system. In DRFM, information bits are jointly conveyed through the activation permutations of reflecting patterns, grouped carriers, and constellation symbols. The transmitter combines the differentially coded reflecting-time block and the time–frequency block using the Kronecker product. This allows DRFM to operate without relying on CSI at the transmitter, RIS, or receiver. Moreover, we design a novel high-rate quadrature amplitude modulation (QAM) scheme for DRFM. Compared to PSK-based DRFM, this QAM scheme can boost either the throughput or the performance of DRFM. Simulation results illustrate the superiority of the DRFM system, along with an acceptable SNR penalty, compared to non-differential modulation with coherent detection. At the same spectral efficiency, the proposed QAM-aided DRFM outperforms schemes using traditional PSK, amplitude phase shift keying (APSK), and star-QAM constellation modulations.

In this paper, the theoretical bit error rate (BER) of N -level pulse amplitude modulation (PAM- N ) and M -ary quadrature amplitude modulation ( M -QAM) have been studied and compared under different scenarios, including (i) PAM with intensity modulation with direct detection (IM/DD) and field modulation with detection (FMD) (including coherent detection and single-sideband modulation with direct detection (SSB-DD)), and (ii) QAM with coherent detection and SSB-DD. Considering the relationship between the symbol spacing and signal-to-noise ratio (SNR), we provide the mathematical BER equations, including the optical signal-to-noise ratio (OSNR) and carrier-to-signal power ratio (CSPR), especially for PAM signals. To verify the validity of our theoretical expressions for SSB systems, transmissions with 224-Gb/s SSB-PAM4/16QAM signals using the Kramers-Kronig (KK) receiver were implemented on a unified optical system platform. The simulation results agreed well with theoretical calculations both in back-to-back (BtB) and 120-km transmission scenarios, which showed that the BER evaluation methods can serve as a theoretical guidance and system assessment criteria for SSB scenarios.

High-speed optical receivers are crucial in modern optical communication systems. While complex photonic integrated circuits (PICs) are widely employed to harness the full degrees of freedom (DOFs) of light for efficient data transmission, their waveguide nature inherently constrains two-dimensional spatial scaling to accommodate a large number of optical signals in parallel. Here we present a scalable optical receiver platform that fully exploits the high spatial parallelism and ultrabroad bandwidth of light, while leveraging all DOFs—intensity, phase, and polarization. Our solution integrates a thin metasurface, composed of silicon nanoposts, with ultrafast membrane photodetectors on a compact chip. The metasurface provides all the functionalities of conventional PICs for normal-incident spatially parallelized light, enabling high-speed detection of optical signals in various modulation formats, including simultaneous detection of 320-gigabit-per-second four-channel four-level pulse amplitude modulation (PAM4) signals and coherent detection of 240-gigabit-per-second 64-ary quadrature amplitude modulation (64QAM) signals. The authors present a scalable optical receiver platform that integrates a functional metasurface and ultrafast membrane InGaAs photodetector array on a compact chip. Detection of high-speed signals at up to 320 Gbit/s is experimentally demonstrated.

Frequency modulation (FM)-to-amplitude modulation (AM) conversion is an important factor that affects the time–power curve of inertial confinement fusion (ICF) high-power laser facilities. This conversion can impact uniform compression and increase the risk of damage to optics. However, the dispersive grating used in the smoothing by spectral dispersion technology will introduce a temporal delay and can spatially smooth the target. The combined effect of the dispersive grating and the focusing lens is equivalent to a Gaussian low-pass filter, which is equivalent to 8 GHz bandwidth and can reduce the intensity modulation on the target to below 5% with 0.3 nm @ 3 GHz + 20 GHz spectrum phase modulation. The results play an important role in the testing and evaluating of the FM-to-AM on the final optics and the target, which is beneficial for comprehensively evaluating the load capacity of the facility and isentropic compression experiment for ICF.

This article adopts direct numerical simulation method to study concave cavity flow with high Reynolds number, and explores the influence of outer region structure on inner region turbulence of concave cavity flow, as well as the mechanism of coherent structure in the near wall region of concave cavity flow. This article finds that the superposition and amplitude modulation effects of separated flow are weaker than those in smooth wall turbulence. At different positions within the concave cavity, the superposition effect in the reattachment zone is the strongest, while the superposition effect in the separation zone is the weakest, indicating that flow separation prevents large-scale structures from outer region penetrating into the near wall region. The amplitude modulation effect of the reattachment point is the strongest, which is related to the strong adverse pressure gradient of the reattachment point.

A novel hybrid pulse width modulation (PWM) and pulse amplitude modulation (PAM) (HPP) driving method is proposed for improving the low gray-level expression of a micro light-emitting diode (µLED) display. At the high and middle gray-levels, PWM is adopted in order to suppress the wavelength shift of µLEDs. At the low gray-level, PAM is applied when the emission time and current of µLEDs simultaneously decrease. The HPP driving method is simulated by using a simplified p-type low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT)-based µLED pixel circuit. HPP driving exhibits stable PWM and PAM operations. Furthermore, HPP driving guarantees a data voltage range approximately 14 times larger than PWM driving, thus resulting in a robust operation with a maximum error rate of 3.83% under data signal distortion. Consequently, the µLED pixel circuit adopting HPP driving improves the low gray-level expression and demonstrates a robust circuit operation.

Internet of Things (IoT) enables the inter-connectivity of different “things” using which wide range of items and devices can communicate with each other and their external environment. 5G technology offers enhanced quality of service with high-data transmission rates, which necessitates the implementation of IoT in 5G architecture. Free space optics (FSO) is considered as a promising technology that can offer high-speed information transmission links and therefore is an optimal choice for wireless networks to satisfy the full potential of 5G technology offering 100 Gbit/s or more speed. By implementing 5G features in IoT, the coverage area and performance of IoT will be enhanced using high-speed FSO links. This work proposes the development of high-speed long-reach FSO link for the implementation of 5G and IoT. We investigate a long-haul, single-channel polarization division multiplexed 16-level quadrature amplitude modulation (PDM-16-QAM) based FSO link at 160 Gbit/s incorporating digital signal processing with coherent detection at the receiver terminal. The results show that the proposed system demonstrates a good bit error rate performance under different weather conditions. The proposed system can be deployed for high-speed, long-haul, spectral efficient, robust information transmission links in future 5G wireless networks under dynamic weather conditions.

The significance of a cryptograph method lies in its ability to provide high fidelity, high security, and large capacity. The emergence of metasurface-empowered cryptography offers a promising alternative due to its unparalleled wavefront modulation capabilities and easy integration with traditional schemes. However, the majority of reported strategies suffer from limited capacity as a result of restricted independent information channels. In this study, we present a novel method of cryptography that utilizes a dual-band complex-amplitude meta-hologram. The method allows for the encoding of 2 different patterns by combining a modified visual secret-sharing scheme (VSS) and a one-time-pad private key. The use of complex-amplitude modulation and the modified VSS enhances the quality and fidelity of the decrypted results. Moreover, the transmission of the private key through a separate mechanism can greatly heighten the security, and different patterns can be generated simply by altering the private key. To demonstrate the feasibility of our approach, we design, fabricate, and characterize a meta-hologram prototype. The measured results are in good agreement with the numerical ones and the design objectives. Our proposed strategy offers high security, ultra-capacity, and high fidelity, making it highly promising for applications in information encryption and anti-counterfeiting.