dB In Experiment Research Articles

Twelve-channel LAN wavelength-division multiplexer on lithium niobate.

A twelve-channel local-area-network (LAN) wavelength-division multiplexing (LWDM) filter is proposed and demonstrated with a uniform channel spacing of 4.5 nm (800 GHz) in the O-band of 1270-1330 nm by using x-cut lithium-niobate-on-insulator (LNOI) photonic waveguides for the first time. The present LWDM filter consists of twelve single-channel bandpass filters based on multimode waveguide gratings (MWGs) assisted with a TE0/TE1 mode (de)multiplexer. In particular, two stages of MWGs in cascade are introduced for each single-channel bandpass filter, in order to achieve high sidelobe suppression ratios, thus reducing interchannel crosstalk. For the fabricated twelve-channel LWDM filter, all the channels have very excellent box-like spectral responses with low excess losses of ∼0.6 dB, broad 1-dB bandwidths of ∼2.9-3.4 nm (which is close to 75 % of the channel spacing), and ultra-low interchannel crosstalk of <-40 dB in experiments. In addition, the present device is highly tolerant to the random variations of the etching depth (±20 nm) and the grating waveguide width (±20 nm) of the LNOI photonic waveguides, showing great potential for high-capacity WDM systems.

Spin-decoupled meta-coupler empowered multiplexing and multifunction of guided wave radiation

Employing couplers to convert guided waves into free-space modes and flexibly control their wavefront is one of the key technologies in chip-integrated displays and communications. Traditional couplers are mainly composed of gratings, which have limitations in footprint, bandwidth, as well as controllability. Though the resonant/geometric metasurface newly emerges as a promising interface for bridging guided waves with free-space ones, it either relies on complex optimizations of multiple parameters, or is subject to the locked phase response of opposite spins, both of which hinder the functional diversity and practical multiplexing capability. Here, we propose and experimentally demonstrate an alternative with a spin-decoupled meta-coupler, simultaneously integrating triple functions of guided wave radiation, polarization demultiplexing, and dual-channel wavefront manipulation into a single device. By endowing polarization-dependent functionalities into a pure geometric metasurface, the out-coupled left-handed and right-handed circular polarization guided waves intelligently identify the predesigned phase modulation and reconstruct desired wavefronts, like bifocal focusing and holography multiplexing, with a polarization extinction ratio over 13.4 dB in experiments. We envision that the robust, broadband, and multifunctional meta-coupler could pave a way for the development of versatile multiplexed waveguide-based devices.

A receiver-optimized total focusing method for detectability enhancement of small defects in coarse grained materials

The identification and localization of small defects are among the main objectives of ultrasonic non-destructive testing (NDT). In particular, the inspection of polycrystalline materials remains a challenge due to ultrasonic attenuation and backscatter noise caused by grain scattering. An adaptive ultrasonic array imaging algorithm is proposed in this paper, which is capable of enhancing the signal-to-noise ratio (SNR) of small subwavelength defects. The proposed approach adopts an iterative optimization procedure based on sequential backward selection, and is termed receiver optimized total focusing method (ROTFM). ROTFM is formulated in a baseline subtraction (BS) setting, and it is shown to achieve higher defect SNRs compared to TFM results obtained by directly applying the BS method to measured array data. More importantly, the performance of the proposed ROTFM is robust to time and spatial misalignments, and hence, it alleviates the need for complex compensation schemes when performing imaging computations. Compared to conventional TFM, ROTFM achieved an average SNR improvement of 3.41 dB and 6.05 dB in experiments for four test defects (cracks and holes of sizes 0.5 mm and 1 mm) at the frequencies of 5 MHz and 7 MHz, respectively.

C- and O-Band Dual-Polarization Fiber-to-Chip Grating Couplers for Silicon Nitride Photonics.

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

A high-Q acoustic filter based on programable electromechanical Fano resonance

Fano resonance with a sharp and ultra-narrow asymmetrical spectral profile is formed by interfering a background mode by a local mode, which is widely found in numerous physical areas and serves as a bedrock for architecting functional metamaterials and constructing selective filters for physical waves. However, it requires subtle geometries and accurate mechanical properties for generating a local resonance to realize Fano resonance at a desired frequency, which challenges its widely applications. Here, we report an electromechanical Fano resonance delivered by an electromechanical diaphragm shunted by a multiple-branch resonant circuit (SEMD). The local resonance of the SEMD is induced by the electrical circuit, which removes the constraints of subtle geometries and mechanical properties design and allows digitally programing the Fano resonance through coding MOSFET switches to select a preset circuit branch. A Lumped theoretical model is used to analyze circuit effects, with verification by experiments in a one-dimensional waveguide, showing programing of three key parameters, the frequency, Q factor and extinction ratio (ER), of the electromechanical Fano resonance. The frequency of perfect sound absorption (null reflection) digitally assigned in a frequency range of [158.5 Hz 1486.75 Hz] is experimentally demonstrated, equivalent to a wavelength-to-thickness ratio range of [31.6 0.30], regarding the equivalent thickness of the SEMD. The Q factor of the SEMD, indexing the selectivity, can be tuned up to 145 in experiments and over 6000 theoretically, giving the half-bandwidth less than 0.2 Hz. The extinction ratio (ER) reaches 30 dB in experiments whereas 60 dB in predictions which means the circuit can totally change the acoustic response of the mechanical diaphragm. Due to features of real-time programmability, broadband tunability and mechanical properties and geometries independence, the SEMD with an electromechanical Fano resonance would be a superior platform to fulfill the envisaged manipulation of acoustics waves in a digital manner.

The effect of visual speech information on linguistic release from masking.

Listeners often experience challenges understanding a person (target) in the presence of competing talkers (maskers). This difficulty reduces with the availability of visual speech information (VSI; lip movements, degree of mouth opening) and during linguistic release from masking (LRM; masking decreases with dissimilar language maskers). We investigate whether and how LRM occurs with VSI. We presented English targets with either Dutch or English maskers in audio-only and audiovisual conditions to 62 American English participants. The signal-to-noise ratio (SNR) was easy at 0 audio-only and -8 dB audiovisual in Experiment 1 and hard at -8 and -16 dB in Experiment 2 to assess the effects of modality on LRM across the same and different SNRs. We found LRM in the audiovisual condition for all SNRs and in audio-only for -8 dB, demonstrating reliable LRM for audiovisual conditions. Results also revealed that LRM is modulated by modality with larger LRM in audio-only indicating that introducing VSI weakens LRM. Furthermore, participants showed higher performance for Dutch maskers compared to English maskers with and without VSI. This establishes that listeners use both VSI and dissimilar language maskers to overcome masking. Our study shows that LRM persists in the audiovisual modality and its strength depends on the modality.

Ultra-compact lithium niobate microcavity electro-optic modulator beyond 110 GHz

A lithium-niobate-on-insulator (LNOI) electro-optic (EO) modulator based on a 2 × 2 FP-cavity was designed and realized with an ultra-compact footprint and an ultra-high bandwidth. A comprehensive analysis on the present LNOI FP-cavity modulator was conducted to reveal the dependence of modulation bandwidth and modulation efficiency on the cavity Q-factor and the operation wavelength detuning to the resonance. In particular, the 2 × 2 FP cavity was designed to achieve an optimal Q factor by reducing the reflectivity of reflectors and the cavity length, thus reducing the photon lifetime in the cavity . An ultra-short effective cavity length of only∼ 50 µm was achieved for the designed LNOI FP-cavity modulator, with itsfootprint being as compact as ∼ 4 × 500 µm2. It was demonstrated theoretically that the modulation bandwidth could be improved significantly to be over 200 GHz by utilizing the peaking enhancement effect. The fabricated device exhibited an excess loss of ∼ 1 dB and an extinction ratio of ∼ 20 dB in experiments, while the measured 3-dB bandwidth was higher than 110 GHz (beyond the maximal range of the facilities in experiments). Up till now, to our best knowledge, this has been the first LNOI microcavity modulator with a bandwidth higher than 110 GHz. Finally, high-quality eye-diagrams of 100 Gbps on-off keying (OOK) and 140 Gbps 4-pulse amplitude modulation (PAM4) signals were demonstrated experimentally, and the energy consumption for the OOK signals was as low as 4.5 fJ/bit.

Subwavelength dichroic demultiplexer based on double Fabry-Perot cavities.

Plasmonic demultiplexers hold promise for the realization of the subwavelength and high-splitting ratio dichroic splitter and have a wide range of applications from optical communication, and manipulation to ultrafast data treatment. However, this vision has not been realized for a long time due to lacking the suitable splitting structure design, which limits its further development of integrated photonic circuits. Here, we demonstrate a plasmonic demultiplexer with subwavelength feature size (0.54 µm) and broadband spectral (620-870 nm) range, and high-splitting ratio (17 dB in experiments and 20 dB in calculations). It consists of two adjacent Fabry-Perot cavities (covered by PMMA polymer) and coupling gratings, which are integrated with the Au waveguide. The relatively simple double cavities design of our device has a simple theoretical analysis and fabrication process. Our work has relevance for various optical applications, such as multiple wavelength photodetectors and optical multichannel interconnects.

Broadband Sound Absorption and Energy Harvesting by a Graded Array of Helmholtz Resonators

In both experiment and simulation, we demonstrate a graded array of Helmholtz resonators (HRs) with cross-linked polypropylene (IXPP) ferroelectret films on the inner walls of cavities, which can realize both sound absorption and energy harvesting within 300–800 Hz. This dual-function graded array contains nine HRs with different sizes, which can offer a broadband working frequency and absorb part of acoustic energy. The unique ability of IXPP ferroelectret films can be used to efficiently harvest sound energy during resonant performances. An electric circuit is designed for collecting electrical signals of each branch individually. The average values of sound absorption coefficient and output power are about 0.81 and 1.43 nW in the range of 300–800 Hz with an input sound pressure level (SPL) of 100 dB in experiment, respectively. Our results enrich the fundamental techniques of both sound absorption and acoustic energy harvesting (AEH), which can pave a way for designing acoustic device in the field of sound absorption and energy conversion for future engineering application.

Deep-learning-enabled high-performance full-field direct detection with dispersion diversity.

Data center interconnects require cost-effective photonic integrated optical transceivers to meet the ever-increasing capacity demands. Compared with a coherent transmission system, a complex-valued double-sideband (CV-DSB) direct detection (DD) system can minimize the cost of the photonic circuit, since it replaces two stable narrow-linewidth lasers with only a low-cost un-cooled laser in the transmitter while maintaining a similar spectral efficiency. In the carrier-assisted DD system, the carrier power accounts for a large proportion of the total optical signal power. Reducing the carrier to signal power ratio (CSPR) can improve the information-bearing signal power and thus the achievable system performance. To date, the minimum required CSPR is ∼7 dB for all the reported CV-DSB DD systems having electrical bandwidths of approximately half of baud rates. In this paper, we propose a deep-learning-enabled DD (DLEDD) scheme to recover the full optical field of the transmitted signal at a low CSPR of 2 dB in experiment. Our proposal is based on a dispersion-diversity receiver with an electrical bandwidth of ∼61.0% baud rate and a high tolerance to laser wavelength drift. A deep convolutional neural network enables accurate signal recovery in the presence of a strong signal-signal beat interference. Compared with the conventional method, the proposed DLEDD scheme can reduce the optimum CSPR by ∼8 dB, leading to a significant signal-to-noise ratio improvement of ∼5.8 dB according to simulation results. We experimentally demonstrate the optical field reconstruction for a 28-GBaud 16-ary quadrature amplitude modulation signal after 80-km single-mode fiber transmission based on the proposed DLEDD scheme with a 2-dB optimum CSPR. The results show that the proposed DLEDD scheme could offer a high-performance solution for cost-sensitive applications such as data center interconnects, metro networks, and mobile fronthaul systems.

A 1.3-mW 73.3-dB DR 10-MHz Bandwidth CT Delta-Sigma Modulator with a Charge-Recycled SC DAC and 52.7-dB Alias Rejection

A multi-level DAC with high intrinsic linearity and low power consumption enables a greater design space for wide-band continuous-time (CT) Delta-Sigma modulators (DSMs). This manuscript introduces an intrinsically highly linear 5-level switched-capacitor (SC) DAC with a power-saving charge recycling technique for wideband CT DSMs. We also adopt a distinct modulator architecture that places a large low-pass filter (LPF) capacitor at the input of the first amplifier. This architecture substantially enhances the modulator’s power efficiency and restores the modulator’s alias rejection ratio (AR) in the presence of an SC type of DAC. To validate the proposed techniques, a DSM prototype with a 10-MHz bandwidth and 800 MHz sampling rate (fs) is fabricated in a 65-nm CMOS technology. Consuming 1.3 mW from a 1.2-V supply, the prototype achieves a peak signal-to-noise-plus-distortion ratio of 72.3 dB and a dynamic range of 73.3 dB in experiments. The corresponding Warden’s and Schreier’s figures of merits are 19.3 fJ/conv-step and 171.2 dB, respectively. The measured ARs are 52.7 dB and 54.3 dB at fs and 2fs, respectively. The DSM further tolerates an rms clock jitter of 11 ps.

Performance improvement for compressive light field display based on the depth distribution feature.

Compressive light field (CLF) display using multi-layer spatial light modulators (SLMs) is a promising technique for three-dimensional (3D) display. However, conventional CLF display usually uses the reference plane with fixed depth, which does not consider the relationship between the depth distribution of the object and the image quality. To improve the quality of the reconstructed image, we further analyze the relationship between them in the paper. The theoretical analysis reveals that the object with a closer distance to the physical layer has a better reconstruction quality when the SLM layers have the same pixel density. To minimize the deviation between the reconstructed light field and the original light field, we propose a method based on the depth distribution feature to automatically guide the light field optimization without increasing the layered number or the refresh rate. When applied to a different scene, it could detect the dense region of depth information and map them as close to the physical layers as possible by offsetting the depth of the reference plane. Simulation and optical experiments with the CLF display are demonstrated to verify the proposed method. We implement a CLF display that consists of four-layer stacked display panels and the distance between two adjacent layers is 5cm. When the proposed method is applied, the peak signal-to-noise ratio (PSNR) is improved by 2.4dB in simulations and 1.8dB in experiments.

Enhanced Modal Coupling Loss in a Two-Mode SOI Waveguide of Broken Parity-Time Symmetry

Effect of optical loss, presented in a superstructure grating with a complex refractive index profile, on the mode coupling is studied in a two-mode silicon-on-insulator waveguide. In this scheme, both our theory and experimental results indicate that the optical loss not only provides optical absorption of a targeted output mode and thus the corresponding modal coupling loss, but also induces a broken parity-time symmetry phase that strongly prohibits power coupling from the incident mode to the output mode. As a result, the latter can give rise to a much-enhanced modal coupling loss of the targeted output mode. Under a reasonable device length about 37 μ m, the enhancement factor can be as high as ∼20 dB in simulation and ∼17 dB in experiment. This paper may offer a different way to exploit the role of optical loss in boosting modal coupling loss that can directly translate to power extinction ratio. It thus may find potential applications in novel intensity modulator designs.

Directional side scattering of light by a single plasmonic trimer

AbstractDirectional side scattering of light by individual gold nanoparticles (AuNPs) trimers assembled by the atomic force microscope (AFM) nanomanipulation method is investigated in experiment and theory. The AFM nanomanipulation approach brings an active way to construct ultracompact and effective optical nanoantennas. Different configurations of the trimers are constructed in situ via AFM nanomanipulation. Unidirectional side scattering of light by a single trimer is demonstrated with a broad response bandwidth over 400 nm and directivity up to ∼7.8 dB in experiments. The near‐field plasmon coupling of the AuNPs is simulated with the 3D finite‐difference time‐domain method and the far‐field radiation patterns are calculated by employing near‐field‐to‐far‐field transformation methods. The calculated results are in agreement with the experiments qualitatively. The physical origin is revealed intuitively by employing a simple phenomenological “two‐dipole” model. The unidirectional light scattering is due to the interference between multiple plasmonic resonance modes of the trimers. The study contributes to the understanding of the optical response of complex nanostructures and optimizing nanoantenna performances for practical applications, e.g. increasing the detection efficiency of surface‐enhanced spectroscopy. image

Corrigendum: Independent impacts of age and hearing loss on spatial release in a complex auditory environment

In Gallun et al. (2013), the sensation levels of the stimuli were incorrectly calculated. The calculation described on page 6 was implemented correctly, but the conversion from HL (hearing level) to SPL (sound pressure level in standardized units) was not correct for the headphones used in the experiment. Rather than adding 22 dB to the HL value, it would have been correct to add 12.5 dB to the HL value (ANSI, 2004). Consequently, the value reported in sensation level (SL), which is the level in dB relative to the speech reception level, was reported as 9.5 dB lower than is correct. The following changes should be made to clarify this issue. Bold text indicates where changes have occurred. The sentence that begins on the end of page 5 and continues onto page 6 should read: This was achieved by first measuring the level at which each listener could just identify speech presented by the audiologist over the audiometer, transforming that value from hearing level (HL) to dB SPL by adding 12.5 dB, and then adding 39.5 dB to that level to obtain the level of the target sentence, which was always fixed during the adaptive tracking procedure. The final sentence in the first paragraph of page 6 should read: No listeners were tested for whom the 39.5 dB SL level would have resulted in maskers that exceeded 85 dB SPL. The second sentence in the Results section on the top of page 6 should read: Target levels, which were set 39.5 dB above the SRT, varied from 47 dB SPL to 72 dB SPL, reflecting the 25 dB range of SRT values in the sample. The third sentence in the second column of page 7 should read: This is likely due to two factors: the better overall hear- ing of the participants (PTAs for the frequencies 0.5, 1, and 2 kHz were 15.1 dB in Experiment One and 9.4 dB in Experiment Two) and the use of an equal SL target set at 39.5 dB above individual SRTs for each ear.

Experimental identification of smart material coupling effects in composite structures

Smart composite structures have an enormous potential for industrial applications, in terms of mass reduction, high material resistance and flexibility. The correct characterization of these complex structures is essential for active vibration control or structural health monitoring applications. The identification process generally calls for the determination of a generalized electromechanical coupling coefficient. As this process can in practice be difficult to implement, an original approach, presented in this paper, has been developed for the identification of the coupling effects of a smart material used in a composite curved beam. The accuracy of the proposed identification technique is tested by applying active modal control to the beam, using a reduced model based on this identification. The studied structure was as close to reality as possible, and made use of integrated transducers, low-cost sensors, clamped boundary conditions and substantial, complex excitation sources. PVDF (polyvinylidene fluoride) and MFC (macrofiber composite) transducers were integrated into the composite structure, to ensure their protection from environmental damage. The experimental identification described here was based on a curve fitting approach combined with the reduced model. It allowed a reliable, powerful modal control system to be built, controlling two modes of the structure. A linear quadratic Gaussian algorithm was used to determine the modal controller–observer gains. The selected modes were found to have an attenuation as strong as −13 dB in experiments, revealing the effectiveness of this method. In this study a generalized approach is proposed, which can be extended to most complex or composite industrial structures when they are subjected to vibration.

Numerical model of dual-wavelength erbium-doped fiber ring laser based on gain-equilibrium method

A novel numerical model of the dual-wavelength fiber ring lasers utilizing gain-equilibrium method is presented by developing the two level, homogeneous Giles model. To obtain the simulation method, the gain equilibrium condition is derived and modified to adapt to the iterative procedure in simulations. This condition is confirmed by both the numerical and experimental results, which indicate that the cavity losses of both wavelength channels play important roles in maintaining stable dual-wavelength emitting. The tolerant loss-bias is 0.05 dB in simulations and 0.4 dB in experiments, respectively. The difference between numerical and experimental results reveals that the inhomogeneous linewidth broadening of EDF contributes mostly to the improved power stability, but the loss vibrations play an important role in this effect.

Low loss fusion splicing polarization-maintaining photonic crystal fiber and conventional polarization-maintaining fiber

An efficient and simple method of fusion splicing of a Polarization-Maintaining Photonic Crystal Fiber (PM-PCF) and a conventional Polarization-Maintaining Fiber (PMF) with a low loss of 0.65dB in experiment is reported. The minimum bending diameter of the joint can reach 2cm. Theoretical calculation of the splicing loss based on mode field diameters (MFDs) mismatch of the two kinds of fibers is given. All parameters affected the splicing loss were studied.

Performance Evaluation of Ultrasonic Nakagami Image in Tissue Characterization

Conventional ultrasonic B-mode images qualitatively describe tissue structures but are unsuitable for quantitative analyses of scatterer properties. We have recently developed an ultrasonic parametric imaging technique based on the Nakagami statistical distribution that is able to quantify scatterer concentrations. The aim of the present study is to further explore both the behavior of a Nakagami image in characterizing different scatterer structures at different signal-to-noise ratios (SNRs) and the feasibility of Nakagami imaging using a general commercial ultrasound scanner for tissue examinations. Simulations, experiments on a tissue-mimicking phantom and in vitro measurements on a muscle tissue before and after microwave treatment were carried out. The SNR and contrast-to-noise ratio (CNR) were estimated to quantify image performance. The results demonstrate that a Nakagami image can differentiate different scatterer concentrations for single, hypoechoic and hyperechoic targets. Also, a Nakagami image, when combined with an ultrasound scanner, can complement the B-scan to characterize tissue and to identify the region of interest with a larger CNR. However, the noise effect can degrade the performance of a Nakagami image. When the signal SNR decreased to 15 dB in simulations and to 8 dB in experiments, the CNR of the hyperechoic Nakagami image decreased by 4% and 27%, respectively, and that of the hypoechoic one decreased by 42% and 80%, respectively. These results indicate that a Nakagami image behaves well in identifying regions with high scatterer concentrations but does not perform well when both the scatterer concentration and SNR are low.

弾性同期支持による防振ハンマ (第4報)

This paper deals analytically with improvement of the reduction effect of the transmissive force level on the hammering machine with the impact isolation anvil. In the case of light damping, drive frequency above a primary resonance of the hammer system and a long distant setting gap of the anvil head, the force from the hammer system gains in power more than that from the anvil system by increase of amplitude of the hammer's motion. Vibration interference is applied to improve of the reduction effect of the force level in addition to vibration isolation by means of the anvil mounted on an isolation spring. The two hammers are drived out of phase by the only one spindle. The twin type machine shows the efficient reduction effect in the above conditions in which the single type machine with the anvil is ineffective. Decrease of the reduction effect by disagreement of coefficient of restitution and mass of the work is small, but disagreement of the setting gap is influenced to some extent. The reduction effect was improved about 12 dB in experiment.