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The National Metrology Institute of Japan (NMIJ) developed an accurate two-point diameter measurement system for a sphere by using a micro-coordinate measuring machine (μ-CMM) with a gauge block for calibrating the radius of the μ-CMM probe. The surface roughness of end faces of the gauge block is a key uncertainty factor and, to reduce this in calibrating the μ-CMM probe, a newly fabricated silicon gauge block with a polished surface roughness of a few nanometers or less was used. To overcome poor repeatability caused by interaction forces acting on the probe, we developed a μ-CMM probe with T-shaped sharp styli and an 8-μm tip radius, which minimized the contact area between the stylus tip and gauge block. A calibrated μ-CMM probe (expanded uncertainty of 7.4 nm; k = 2) equipped with the newly developed T-shaped sharp styli was used to measure the mean two-point diameter of a sphere with an expanded uncertainty of 15 nm (k = 2). • High accuracy two-point diameter calibration system with μ-CMM was developed. • Silicon gauge block with a surface roughness of a few nanometers or less was proposed as a reference standard. • A μ-CMM probe with T-shaped sharp diamond styli for measuring silicon gauge blocks was developed. • Mean two-point diameter of reference sphere for μ-CMM calibrated with 15 nm uncertainty. [ABSTRACT FROM AUTHOR]

A new spectral super-resolution technique was proposed by combining the Fabry–Perot interferometer (FPI) with Temporally and Spatially Modulated Fourier Transform Imaging Spectrometer (TSMFTIS). This study uses the multi-beam interference of the FPI to modulate the target spectrum periodically, and it acquires the modulated interferogram through TSMFTIS. The combined interference of the two techniques overcomes the limitations of the maximum optical path difference (OPD) on spectral resolution. FPI is used to encode high-frequency interference information into low-frequency interference information, proposing an inversion algorithm to recover high-frequency information, studying the impact of FPI optical defects on the system, and proposing targeted improvement algorithms. The simulation results indicate that this method can achieve multi-component joint interference imaging, improving spectral resolution by twofold. This technology offers advantages such as high throughput, stability, simple and compact structure, straightforward principles, high robustness, and low cost. It provides new insights into TSMFTIS spectral super-resolution research. [ABSTRACT FROM AUTHOR]

A sensitivity-enhanced temperature sensor based on a Mach–Zehnder interferometer (MZI) coated by polydimethylsiloxane (PDMS) film is proposed and investigated. The MZI with a compact size of 2.28 mm is fabricated by embedding a tapered single-mode fiber (SMF) between two multimode fibers (MMFs). Since PDMS has a higher thermo-optical coefficient than silica, the proposed sensor has better temperature sensing performance than the case without PDMS coating, which is demonstrated by simulation and experiment. The experimental results show that the sensitivity of the proposed sensor is as high as −1.06 nm/°C in the range from −5 °C to 45 °C. [ABSTRACT FROM AUTHOR]

The radio source J0028+0035 is a recently discovered double–double radio galaxy at redshift z = 0.398 . Its relic outer lobes are separated by about 3 ′ in the sky, corresponding to ∼1 Mpc projected linear size. Inside this large-scale structure, the inner pair of collinear lobes span about 100 kpc. In the arcsec-resolution radio images of J0028+0035, there is a central radio feature that offers the intriguing possibility of being resolved into a pc-scale, third pair of innermost lobes. This would make this radio galaxy a rare triple–double source where traces of three distinct episodes of radio activity could be observed. To reveal the compact radio structure of the central component, we conducted observation with the European Very Long Baseline Interferometer Network and the enhanced Multi Element Remotely Linked Interferometer Network. Our 1.66 GHz image with high (∼5 milliarcsec) resolution shows a compact central radio core with no indication of a third, innermost double feature. The observation performed in multi-phase-centre mode also revealed that the physically unrelated but in projection closely separated background source 5BZU J0028+0035 has a single weak, somewhat resolved radio feature, at odds with its blazar classification. [ABSTRACT FROM AUTHOR]

The sensitivity of coherent anti-Stokes Raman spectroscopy (CARS) is limited by the shot-noise from the probe fields used for stimulation and the non-resonant background noise. We have investigated the performance of the squeezing-enhanced version of CARS under homodyne detection and sum-intensity detection schemes, compared with the shot-noise limit (SNL) and quantum Cramér-Rao bound (QCRB). Our analysis shows homodyne detection performs better than sum-intensity and known single-intensity detection scheme results. It also provides a broader working range and shows more robustness against internal photon losses and remarkably improved performance in the gain-imbalanced configuration of SU(1,1) interferometer. As a result, we expect that our findings will be useful in quantum sensing and imaging techniques. [ABSTRACT FROM AUTHOR]

On-chip Fourier transform spectrometer (FTS) is a promising technology due to the compact size, low cost, and relatively high throughput. In this work, we design, fabricate, and characterize a Mach-Zehnder interferometer (MZI) FTS based on SU-8 polymer waveguide. The optical path length difference of MZI is tuned by a heater with a maximum power consumption of 2.2 W. The interference signal is analyzed by Fourier transform algorithm, to retrieve the spectrum of light source. The footprint of the fabricated FTS device is only 2 × 12 mm2, with the spectral bandwidth of ~100 nm and resolution <20 nm. [ABSTRACT FROM AUTHOR]

The observation and evaluation of vibration signals is crucial for enhancing engineering quality and ensuring the safe operation of equipment. This paper proposes a fiber-optic vibration sensor based on the Sagnac interference principle. The polarization-maintaining fiber (PMF) is spliced between two single mode fibers (SMFs) to form the SMF-PMF-SMF (SPS) fiber structure. The Sagnac interferometer consists of an SPS fiber structure connected to a 3 dB coupler. Due to the principle of the elastic-optical effect, the interferometric spectrum of the PMF-based Sagnac interferometric structure changes when the PMF is subjected to stress, enabling vibration to be measured. The experimental results show that the relative measurement error of the fiber-optic vibration sensor for healthy and faulty bearings is less than 1.8%, which verifies the effectiveness and accuracy of the sensor. The sensor offers benefits of excellent anti-vibration fatigue characteristics, simple production, small size, light weight, and has a wide range of applications in mechanical engineering, fault detection, safety and security, and other fields. [ABSTRACT FROM AUTHOR]

The Einstein Telescope (ET) will be a third-generation Gravitational Wave (GW) detector that will tackle cutting-edge technological challenges. The ET will be constructed at a depth of 200–300 m to isolate it from vibrations caused by seismic waves and human activities, which are sources of noise for GW detection. To meet the ET's objectives, it will be necessary to improve low-frequency sensitivity by about two orders of magnitude compared to current interferometers (LIGO, Virgo). Magnetic noise is a limiting noise in the frequency range from a few Hz up to around 100 Hz in future GW detectors. This article will discuss the magnetic noise mitigation strategies under development, based on experiences from Virgo. [ABSTRACT FROM AUTHOR]

The Atacama Millimeter/Submillimeter Array (ALMA) remains unparalleled in sensitivity at radio frequencies above 35 GHz. In this paper, we explore ALMA's potential for narrow-band technosignature detection, considering factors such as the interferometer's undistorted field of view, signal dilution due to significant drift rates at high frequencies and the possibility of spectral confusion. We present the first technosignature survey using archival ALMA data in Band 3, focusing on two spectral windows centred on 90.642 and 93.151 GHz. Our survey places new limits at these frequencies on the prevalence of extraterrestrial transmitters for 28 galactic stars, selected from the Gaia DR3 catalogue. We employ a stellar 'bycatch' method to sample these objects within the undistorted field of view of four ALMA calibrators. For the closest star in our sample, we find no evidence of transmitters with |$\mathrm{ EIRP}_{\mathrm{ min}} \gt 7 \times 10^{17}$| W. To the best of our knowledge, this represents the first technosignature search conducted using ALMA data. [ABSTRACT FROM AUTHOR]

High-dimensional quantum key distribution (QKD) offers secure communication with key rates that surpass those of QKD protocols utilizing two-dimensional encoding. However, existing high-dimensional QKD protocols require additional experimental resources, such as multiport interferometers and multiple detectors, thereby increasing the cost of high-dimensional systems and limiting their use. We introduce and analyze a high-dimensional QKD protocol that requires only standard two-dimensional hardware. We provide security analysis against individual and coherent attacks, establishing upper and lower bounds on the secure key rates. We tested our protocol on a standard two-dimensional QKD system over a 40 km fiber link, achieving a twofold increase in secure key rate compared to the standard two-dimensional coherent one-way protocol, without any hardware modifications. This work offers a significant improvement in the performance of already deployed QKD systems through simple software updates and holds broad applicability across various QKD schemes, making high-dimensional QKD practical for widespread use. [ABSTRACT FROM AUTHOR]

The present electrostatic accelerometers (EA) drift at low frequencies. To address this problem, integrating a cold atom interferometry (CAI) accelerometer could be beneficial, as it offers the potential for superior long-term stability. The CAI-based accelerometers (CAI ACC) are accurate and stable, but they have some issues with long dead times and a relatively small dynamic range. A way to address these problems is to combine a CAI ACC with an EA in a hybrid configuration. Using CAI ACC in an upcoming satellite gradiometry mission can give stable and accurate measurements of the static Earth's gravity field. Three scenarios have been considered in this study: first, a realistic scenario involving current-generation and realistic hybrid accelerometers; second, a semi-realistic scenario with the same accelerometers and an accurate gyroscope; and third, using highly accurate hybrid/CAI accelerometers with an optimistic gyroscope. One significant aspect was on detecting temporal gravity changes, which cannot compare to the effectiveness of the low-low satellite-to-satellite tracking (LLSST) principle. But, quantum gradiometers can significantly enhance solutions for the static gravity field, provided one has accurate observations of the satellite orientation available. [ABSTRACT FROM AUTHOR]

Spatial heterodyne spectroscopy (SHS) based on prism dispersion is a novel technique designed to overcome the limitations of traditional grating-based SHS, which is affected by grating diffraction. However, there are still some challenges with this technique, one of which is that the fringe localization plane (FLP) moves with changes in wavelength. This paper proposes a prism-based tunable SHS where the FLP is fixed, utilizing prism–bimirror–mirror structures. The theoretical spectral resolving power, based on an example, is higher than 1300 in the spectral range from 10,000 cm−1 to 25,641 cm−1 and is approximately 27,595 at 25,641 cm−1. Furthermore, we propose solutions to simplify the motion control system and address the problem of spectral aliasing. [ABSTRACT FROM AUTHOR]

We consider an interferometer based on chiral Majorana and Dirac modes in a hybrid superconductor/ferromagnet/superconductor Josephson junction on top of a topological material. These one-dimensional bound chiral modes can carry Josephson current, which results in an unusual current–phase relation. Domain walls in the magnetic layer may influence the supercurrent. We demonstrate that the supercurrent depends on the distance between the domain walls, and on the other hand, it controls the interaction of the domain walls and thus the dynamics of the magnetic layer. [ABSTRACT FROM AUTHOR]

This paper explores the quantum and classical descriptions of gravitational wave detection in interferometers like LIGO. We demonstrate that a graviton scattering and quantum optics model succeeds in explaining the observed arm displacements, while the classical gravitational wave approach and a quantum graviton energy method also successfully predict the correct results. We provide a detailed analysis of why the quantum graviton energy approach succeeds, highlighting the importance of collective behavior and the quantum–classical correspondence in gravitational wave physics. Our findings contribute to the ongoing discussion about the quantum nature of gravity and its observable effects in macroscopic physics. [ABSTRACT FROM AUTHOR]

Atom interferometry shows high sensitivity for inertial measurements in the laboratory, but it faces difficulties in field applications because of a trade-off between sensitivity and size. Therefore, there is an urgent need to develop a small sensor with high resolution for measuring acceleration and rotation in inertial navigation applications. Presented here is a miniaturized inertial sensor capable of measuring acceleration and rotation simultaneously based on high-resolution dual atom interferometers. A sensor head is integrated within a volume of 100 l, in which the vacuum chambers are fabricated by bonding quartz-glass windows with epoxy resin. A photoelectric cabinet is composed of four 3U rack units by integrating optical modules and electronic units. Dual atom interference fringes with a contrast of 29% are observed, and the acceleration and rotation are measured simultaneously by extracting their phase shifts. By developing a temperature compensation method to eliminate phase drifts caused by the thermal deformation of the Raman mirrors and using wave vector reversal to eliminate the phase drifts independent of the direction of the wave vector, measurement resolutions of 40 ng at 518 s and 6.1 nrad/s at 10 880 s are achieved for acceleration and rotation, respectively, from Allan deviations. [ABSTRACT FROM AUTHOR]

In this paper, a scheme for realizing low-threshold dual-polarization electro-optic nonlinear activation functions is proposed, designed, and experimentally demonstrated. This scheme relies on a structure composed of an optical power splitter and a thermo-optic modulator based on Mach–Zehnder interferometer, which are optimized by using direct binary search and particle swarm optimization algorithms. When a fixed proportion of the input optical signal is transformed into the electrical signal and the remaining input optical signal is modulated by using the thermo-optic effect, the rectified linear unit activation function with a low-threshold power of 0.2 mW for transverse-electric polarization and the Gaussian activation function with a low-threshold power of 0.1 mW for transverse-magnetic polarization can be measured separately. If the above-mentioned two nonlinear activation functions are introduced into the convolutional neural network to perform the modified National Institute of Standards and Technology handwritten digit classification task, validation accuracies of 97.3% and 96.85% will be achieved. [ABSTRACT FROM AUTHOR]

In order to explore the interplay among heat, charge, and spin, we investigate the spin-related thermoelectricity of a hybrid double quantum dot Aharonov–Bohm interferometer with Rashba spin–orbit coupling (RSOC). Interestingly, the nonzero RSOC phase difference can induce significant spin-dependent thermoelectric transport. Not only can the strong violation of the Wiedemann-Franz law be obtained, but also a pure spin-Seebeck effect can be produced, which may serve as a pure spin-current generator. The influence of system parameters on thermoelectric coefficients (especially for spin counterparts) are analyzed in detail, and the underlying physics is further elucidated. Furthermore, the spin figure of merit can be much larger than the charge one, which, thus, provides a realistic possibility of engineering spin thermoelectric devices with high performance. These results obtained may be of interest for developing spin thermoelectric devices in the field of spin caloritronics. [ABSTRACT FROM AUTHOR]

To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/°C, which is 17.09 times that of a single FSI structure (−1.69 nm/°C) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/°C). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 °C variation based on 1 °C drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects. [ABSTRACT FROM AUTHOR]

It has been shown that measurements involving indefinite causal order can be superior to those in which a sequence of operations occurs in a specified order. In optics, such measurements are realized naturally in a Sagnac interferometer. We show that such an arrangement can measure the solid angle (on the Poincaré sphere) enclosed by a sequence of unitary transformations of the polarization. This is the Pancharatnam–Berry phase. Extension from the classical or single-photon treatment to a fully quantized treatment allows the analysis of the interferometer for arbitrary quantum states of light. This article is part of the theme issue 'The quantum theory of light'. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusions The complementary absorption contrast CT (ACT) and differential phase contrast CT (DPCT) can be generated simultaneously from an x‐ray computed tomography (CT) imaging system incorporated with grating interferometer. However, it has been reported that ACT images exhibit better spatial resolution than DPCT images. By far, the primary cause of such discrepancy remains unclear.The purpose of this study is to investigate the underlying cause of the resolution discrepancy between ACT and DPCT in a grating interferometer CT imaging system.In this study, theoretical derivations were performed with a π$\pi$‐phase Talbot–Lau grating interferometer system to model the signal formation mechanism of absorption imaging and phase imaging, respectively. In addition, physical, and numerical experiments were conducted to verify the theoretical findings and assess the resolution discrepancy between ACT and DPCT under various conditions. Herein, the ACT and DPCT images were reconstructed from the filtered‐back‐projection algorithm using a standard Ramp filter and a standard Hilbert filter, respectively.Experiments demonstrated that the spatial resolution of ACT and DPCT images are primarily impacted by the beam diffraction induced signal splitting. In particular, lower modulation transfer function (MTF) was observed for DPCT than ACT due to the opposite‐superposition of phase signals. In addition, factors such as focal spot size, beam spectra, object composition, sample size, and detector pixel size were found to have minor impacts on the MTFs of both ACT and DPCT.In conclusion, this study reveals that the opposite‐superposition of split phase signals causes the spatial resolution reduction in DPCT imaging. [ABSTRACT FROM AUTHOR]

This paper presents an extensive investigation of the signal fringe profile for the Fizeau interferometer used in the first spaceborne wind lidar Aeolus, and considers the fundamental implications for the wind measurement accuracy in Aeolus and future systems. The early Aeolus design phase considered that the basic fringe would be made up of a Fizeau instrumental component of ≈ 100 MHz (FWHM), folded with the laser pulse spectral width of ≈ 50 MHz (FWHM), both of Lorentzian form. Fringe anomalies observed before the mission and related to surface defects in the interferometer plates, triggered the development of wave-optic methods for analysis of the fringe formation. These methods, herein described in an instructional Appendix, were subsequently found to be essential for rigorous modelling of complex fringes for different physical and optical arrangements. Initial signal returns from Aeolus suggested that the Fizeau fringe profile was in fact broadened with a large Gaussian component. The laser pulse was subsequently shown to have a profile close to Gaussian of ≈ 45 MHz (FWHM) and thus provided a partial contribution. However, detailed examination of experimental Aeolus fringes constructed from ground return signals, showed a large Gaussian component up to ≈ 130 MHz (FWHM). Wave-optic modelling established that Fizeau 'aperture broadening', of this form and magnitude, would be generated for the input signal beam of 500 µ rad field of view set at large angles of incidence of 300 µ rad. These findings have strong implications for fringe shift and wind measurement accuracy, as given in the quantum limited Cramer-Rao expression and the paramount importance of minimising line width. Extensive modelling and simulation for the broadened profiles calculated above, shows good agreement with measured Aeolus global wind measurement accuracies, and indicates that loss of signal could be due to beam clipping at the field stop for such large AOI. It is established that optimisation of the present Aeolus Fizeau parameters could lead to a factor of 2.5 improvement in wind measurement precision. Future upgrades of the Fizeau interferometer and the laser within reasonable parameters, suggest the potential for an factor of 7.6 improvement on the present performance. [ABSTRACT FROM AUTHOR]

This paper presented an extended double-subsegment discrete Fourier transform (DS-DFT) algorithm as a tool for the fine spectral estimation of high-noise environments, which was previously effective in low-noise scenarios, and as such, its application to the analysis of noisy signals observed by a satellite-based interferometer was investigated. The observation of satellite-borne Doppler asymmetric spatial heterodyne spectroscopy (DASH) was first simulated to obtain the signals of low- and high-noise levels; then, a practical criterion to classify noise levels in the interferograms based on the DS-DFT results was introduced and validated by calculating the SNR. For high-noise signals, DS-DFT remains robust by employing phase differences and amplitude ratios for fine frequency estimation. [ABSTRACT FROM AUTHOR]

A wavelength-switchable ring-cavity ytterbium-doped fiber laser utilizing an all-fiber Lyot interferometer filter was proposed and experimentally demonstrated. Firstly, the Lyot filter was constructed using a polarization-maintaining fiber (PMF) to obtain a comb interferometer effect, and the free spectrum ranges corresponding to 2.5 and 1 m PMF were 2.2 and 6.4 nm, respectively. Then, wavelength-switchable ytterbium-doped fiber emission was realized in the experiment, and the tunable range for the single-wavelength laser was from 1073.76 to 1086.78 nm, with a power variation of less than 1.959 dB. During the experiment, four different sets of double-wavelength lasers were achieved by adjusting the polarization controller (PC) from 1071.64 to 1081.65 nm; in addition, three different sets of triple-wavelength lasers were realized, and the signal-to-noise ratio (SNR) was more than 33.031 dB. For stable single-, double-, and triple-wavelength lasers, the power shifts were less than 0.574, 0.631, and 1.195 dB, respectively. Through adjusting the PC, quadruple-wavelength-switchable lasers could be realized with an SNR exceeding 26.233 dB. [ABSTRACT FROM AUTHOR]

The past two decades have seen rapid development of optical atomic clocks with fractional performance at 10−18 level or even below. Dissemination of optical atomic clocks into microwave domain and their intercomparisons using optical frequency combs as clockwork requires precise measurements of their carrier-envelope offset frequencies (fceo). To this end, passive stabilization to zero offset frequency has been considered as a promising approach. However, previous studies often indicate imperfections in passive stabilization schemes. Therefore, in this Letter, aiming to unveil the in-depth noise performance and origin of fceo of passively stabilized frequency combs, a frequency-shifted f-2f interferometer is presented to characterize the fceo frequency stability, frequency shift, frequency uncertainty, linewidth, and phase noise. The stability observed amounts to 2.46 × 10−17 and 4.05 × 10−20 in 1 and 10 000 s, respectively. The linewidth of fceo is 3.7 mHz, with resulting phase noise of − 40 dBrad2/Hz and −64 dBrad2/Hz at 1 and 10 Hz offset frequency, respectively. The phase noise at > 1 kHz is confirmed to be of stochastic origin through correlation analysis. The measured fceo is conclusively determined as −75(14) μHz. [ABSTRACT FROM AUTHOR]

This article explores methods to enhance the sensitivity of holographic interferometers, particularly through digital techniques. Theoretical foundations are laid out, detailing the mathematical operations involved in recording and reconstructing holograms, emphasizing the role of digital processing in improving sensitivity. Experimental results illustrate the practical application of these methods, demonstrating significant enhancements in sensitivity through digital holography. [ABSTRACT FROM AUTHOR]

To overcome the limitations of phase sampling points in testing aspherical surface wavefronts using traditional interferometers, we propose a high-spatial-resolution method based on multi-directional orthogonal lateral shearing interferometry. In this study, we provide a detailed description of the methodology, which includes the theoretical foundations and experimental setup, along with the results from simulations and experiments. By establishing a relational model between the multi-directional differential wavefront and differential Zernike polynomials, we demonstrate high-spatial-resolution wavefront reconstruction using multi-directional orthogonal lateral shearing interferometry. Theoretical calculations and simulations of aspherical surface wavefront testing are followed by experimental verification on an aspherical surface with a known asphericity. Comparing the measurement results with those from the LuphoScan profilometer, we achieve a relative measurement error with an RMS precision better than λ/100. [ABSTRACT FROM AUTHOR]

The Michelson-Morley optical interferometric experiment is historically very important and stands at the basis of the developments that contributed to the acceptance of the special theory of relativity. The Sagnac experiment is much less known and considered from the theoretical point of view, even if it presently has a large field of very useful technological applications, namely in the field of compass gyroscopes. Here, we present a discussion on the temporal precision of these devices that undoubtedly shows the great advantage of the Sagnac device design. [ABSTRACT FROM AUTHOR]

Photonic materials, which react to light, have garnered interest due to their capability to exhibit adjustable structural colors. Typically, light targets the UV, visible, or near-IR spectrums. In this study, microgel-based photonic materials that are capable of reversibly responding to X-rays have been engineered. To accomplish this, azobenzene (Azo)-containing poly(N-isopropylacrylamide) (pNIPAm)-based microgels are synthesized. Subsequently, ZnS scintillator and Cr/Au are applied on each side of the poly(methyl methacrylate (PMMA) substrate. Subsequently, the Azo MG monolayer is deposited onto the Au surface, followed by the deposition of an additional layer of Cr/Au. This process generates ZnS/PMMA/Cr/Au/Azo MG/Cr/Au or ZnS/Au-Azo MG-Au structure. Functioning as a typical interferometer, ZnS/Au-Azo MG-Au demonstrates tunable colors based on the separation distance between the two Au layers. The ZnS scintillator can absorb and convert X-rays into UV light, initiating the transition of the Azo groups from a trans to a cis state. Consequently, this transition causes the Azo MG to swell. As Azo MG swells, the distance between the two Au layers increases, resulting in a red-shift of approximately 350 nm in the optical signal of the ZnS/Au-Azo MG-Au interferometer. Remarkably, this X-ray responsivity of the interferometer is reversible, as it returns to its initial state after being stored in the dark for 24 h. To demonstrate its capabilities, the ZnS/Au-Azo MG-Au interferometer successfully releases a drug when triggered by X-ray stimulation, thus validating its potential. The microgel-based interferometers hold significant promise for applications in chemoradiotherapy, radiobiology, and actuators in space. [ABSTRACT FROM AUTHOR]

Fiber-optic Mach–Zehnder interferometers are widely used in research areas such as telecommunications, spectroscopy, and quantum information. These optical structures are known to be affected by phase fluctuations that are usually modeled as multiparametric noise. This multidimensional noise must be stabilized or compensated for to enable fiber-optic Mach–Zehnder architectures for practical applications. In this work, we study the effectiveness of a modified Perturb-and-Observe (P&O) algorithm to control multidimensional phase noise in fiber-based multi-arm Mach–Zehnder interferometers. We demonstrate the feasibility of stabilizing multidimensional phase noise by numerical simulations using a simple feedback control scheme and analyze the algorithm's performance for systems up to dimension 8 × 8 . We achieved minimal steady-state errors that guarantee high optical visibility in complex optical systems with N × N matrices (with N = [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ] ). [ABSTRACT FROM AUTHOR]

The superconducting sigma neuron is a single-junction interferometer, with a part of the circuit shunted by an additional inductance, which is also used to generate the output signal. It was previously predicted that the transfer function of this device would be close to the sigmoidal one at a certain relation between the values of inductance of its parts. This interferometer can be fabricated as a multilayer thin-film structure over a superconducting screen, which allows measuring the output magnetic flux in a single element. An analysis of the experimental data showed that the use of a superconducting screen did not ensure complete independence of the sigma neuron elements, as was assumed in the theoretical model. This paper presents a generalized model of the stationary state of a sigma neuron that takes into account the interaction between all its parts, including the input and readout elements. [ABSTRACT FROM AUTHOR]

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Vector bending sensors can be utilized to detect the bending curvature and direction, which is essential for various applications such as structural health monitoring, mechanical deformation measurement, and shape sensing. In this work, we demonstrate a temperature-insensitive vector bending sensor via parallel Farby–Perot interferometers (FPIs) fabricated by etching and splicing a multicore fiber (MCF). The parallel FPIs made in this simple and effective way exhibit significant interferometric visibility with a fringe contrast over 20 dB in the reflection spectra, which is 6 dB larger than the previous MCF-based FPIs. And such a device exhibits a curvature sensitivity of 0.207 nm/m−1 with strong bending-direction discrimination. The curvature magnitude and orientation angle can be reconstructed through the dip wavelength shifts in two off-diagonal outer-core FPIs. The reconstruction results of nine randomly selected pairs of bending magnitudes and directions show that the average relative error of magnitude is ~4.5%, and the average absolute error of orientation angle is less than 2.0°. Furthermore, the proposed bending sensor is temperature-insensitive, with temperature at a lower sensitivity than 10 pm/°C. The fabrication simplicity, high interferometric visibility, compactness, and temperature insensitivity of the device may accelerate MCF-based FPI applications. [ABSTRACT FROM AUTHOR]

We propose a terrestrial detector for gravitational waves with frequencies between 0.3 and 5 Hz based on atom interferometry. As key elements, we discuss two symmetric matter-wave interferometers, the first one with a single loop and the second one featuring a folded triple-loop geometry. The latter eliminates the need for atomic ensembles at femtokelvin energies imposed by the Sagnac effect in other atom interferometric detectors. The folded triple-loop geometry also combines several advantages of current vertical and horizontal matter wave antennas and enhances the scalability in order to achieve a peak strain sensitivity of 2 × 10 − 21 / Hz . [ABSTRACT FROM AUTHOR]

An adaptive differential-phase-shifting (DPS) quantum key distribution (QKD) protocol improved by encoding asynchronous-bit-rate with harmonic clock tunability, decoded by shortened delay-line interferometer (DLI) with enhancing stability, and received by single-photon detection with long hold-off is demonstrated to realize low-erroneous transmission. To achieve long-term stabilized visibility with a maintained quantum bit-error-ratio (QBER) and secure key rate, the shortened and polarized DLI enlarges its free-spectral range (FSR) and reduces its power-to-wavelength slope (δP/δλ) to suppress its sensitivity to thermal gradient, channel leakage, and wavelength disturbance. Extremely low power and wavelength drifts of ΔP/P < ±0.02% and Δλ/λ = ±6.45 × 10−8 can be achieved, even when using a single-mode QKD carrier with a relatively broadened 300-kHz linewidth. Flexibly expanding the 1-bit-delay FSR of the polarized DLI from 0.04 to 1.00 GHz improves its immunity to environmental disturbances, enabling the DPS-QKD decoding with 210–213 patterns, 3.2% QBER, and 17.46-kbit/s under 0.22 photon/pulse in average. The asynchronous-bit-rate DPS-QKD protocol enables harmonic expansion of DLI's FSR at limited single-photon avalanche detector's bit rate, which lengthens the duration of stable visibility to support long-pattern DPS-QKD. [ABSTRACT FROM AUTHOR]

Cloud droplet number concentration (Nd) can be retrieved through passive satellite observation. These retrievals are useful due to their wide spatial and temporal coverage. However, the accuracy of the retrieved values is not well understood. In this paper, we compare satellite Nd derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument with in situ aircraft measurements using a phase Doppler interferometer onboard three flight campaigns sampling marine stratocumulus clouds. Intercomparison of Nd values shows that the discrepancy between retrieved and in situ Nd can be ±50 % or more. In the mean, there is evidence of an overestimation bias by MODIS retrievals, although the sample size is insufficient for statistical certainty. We find that MODIS Nd is best interpreted as representative of the mid-cloud region, as there is almost always a greater discrepancy from in situ values near cloud top and cloud base. We also find evidence of cases where Nd is accurately retrieved, but effective radius is not, presumably due to offsetting errors in other retrieval parameters. Vertical profiles of extinction coefficient β , liquid water content L , and effective radius re measured during sawtooth-pattern flight legs through cloud top are also compared to implicit MODIS retrieval profiles. For the one case with Nd agreement, all profiles match well. For seven cases with significant disagreement, there is no consistent underlying cause. The discrepancy originates from either: (a) discrepancy in the re profile, (b) discrepancy in the β and L profiles, or (c) discrepancy in both. [ABSTRACT FROM AUTHOR]

Silicon photonics enables the construction of chip-scale spectrometers, in which those using a single tunable interferometer provide a simple and cost-effective solution. Among various tuning mechanisms, electrostatic MEMS reconfiguration stands out as an ideal candidate, given its high tuning efficiency and ultra-low power consumption. Nonetheless, MEMS devices face significant noise challenges arising from their susceptible minuscule components, adversely impacting spectral resolution. Here, we propose a distinct paradigm of spectrometers through synergizing an easily-fabricated MEMS-reconfigurable low-loss waveguide coupler on a silicon photonic chip and a convolutional autoencoder denoising (CAED) mechanism. The spectrometer offers a 300 nm bandwidth and a reconstruction resolution of 0.3 nm in a noise-free condition. In a noisy environment with a signal-to-noise ratio as low as 30 dB, the reconstruction resolution of the interferograms processed by the CAED exhibits an enhancement from 1.2 to 0.4 nm, approaching the noise-free value. Our technology is envisaged to provide a powerful and cost-effective solution for applications requiring accurate, broadband, and energy-efficient spectral analysis. The Internet-of-Things era desiderates miniature spectrometers. Here, the authors present a chip-scale spectrometer through synergizing MEMS modulation and autoencoder denoising, achieving accurate, broadband, and energy-efficient spectral analysis. [ABSTRACT FROM AUTHOR]

Ellipse fitting is a technique which is used to extract differential phase in cold-atom interferometers, particularly in situations where common-mode noise needs to be suppressed. We use numerical simulation to investigate errors in the ellipse fitting process; specifically, errors due to the presence of additive noise, linear drift in ellipse offset and amplitude, as well as an error that can arise from fringe normalisation. Errors are found to manifest in two ways: bias in the ellipse phase measurement and incomplete suppression of common mode phase noise. We quantify these errors for three different ellipse fitting algorithms and discuss the applicability of these results to future cold atom sensors. [ABSTRACT FROM AUTHOR]

This article investigates the atomization characteristics of a streamlined direct‐injection atomizer, which finishes the atomization process by coupling the air swirl with the conventional direct injector. First, we used experimental methods to focus on controlling its structural parameters and the liquid‐to‐gas flow ratio. We used a phase Doppler interferometer to measure the Sauter mean diameter (SMD) of the droplets and used a high‐speed camera to capture the atomization field images. The experimental results showed that, under all test conditions, the overall range of the SMD was from 84 to 100 μm. It was found that a higher liquid‐to‐gas flow ratio resulted in a smaller SMD, a larger distance between the liquid and air outlets led to a larger SMD, and an increase in the axial angle of the liquid jet led to a smaller SMD. We found the influence parameters of the atomization characteristics of the streamlined direct‐injection atomizer based on the dimensional analysis, namely, π theorem. In addition, a calculation formula for the SMD was proposed, with multiple linear regression conducted on the sample data from experiment. Based on the findings of this study, the streamlined direct‐injection atomizer can be used to dynamically control its spray characteristics according to the requirements of aviation engine combustion chambers. [ABSTRACT FROM AUTHOR]

The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionization (EoR). This has led to the construction of low-frequency radio interferometric arrays, such as the Hydrogen Epoch of Reionization Array (HERA), aimed at systematically mapping this emission for the first time. Precision calibration, however, is a requirement in 21 cm radio observations. Due to the spatial compactness of HERA, the array is prone to the effects of mutual coupling, which inevitably lead to non-smooth calibration errors that contaminate the data. When unsmooth gains are used in calibration, intrinsically spectrally smooth foreground emission begins to contaminate the data in a way that can prohibit a clean detection of the cosmological EoR signal. In this paper, we show that the effects of mutual coupling on calibration quality can be reduced by applying custom time-domain filters to the data prior to calibration. We find that more robust calibration solutions are derived when filtering in this way, which reduces the observed foreground power leakage. Specifically, we find a reduction of foreground power leakage by 2 orders of magnitude at |$k_\parallel \approx 0.5$| h Mpc |$^{-1}$|⁠. [ABSTRACT FROM AUTHOR]

Accurate and stable measurement of inertial quantities is essential in geophysics, geodesy, fundamental physics, and inertial navigation. Here, we present an architecture for a compact cold-atom accelerometer-gyroscope based on a magnetically launched atom interferometer. Characterizing the launching technique, we demonstrate 700-parts per million gyroscope scale factor stability over 1 day, while acceleration and rotation rate bias stabilities of 7 × 10-7 meters per second squared and 4 × 10-7 radians per second are reached after 2 days of integration of the cold-atom sensor. Hybridizing it with a classical accelerometer and gyroscope, we correct their drift and bias to achieve respective 100-fold and 3-fold increase on the stability of the hybridized sensor compared to the classical ones. Compared to a state-of-the-art atomic gyroscope, the simplicity and scalability of our launching technique make this architecture easily extendable to a compact full six-axis inertial measurement unit, providing a pathway toward autonomous positioning and orientation using cold-atom sensors. [ABSTRACT FROM AUTHOR]

We present the analysis of observations of three pulsars at a frequency of 327 MHz with the ground-space interferometer RadioAstron. The main scintillation parameters were measured: the decorrelation bandwidth and the scintillation time . We have found that these parameters vary significantly over time. For PSR B1133+16, the decorrelation bandwidth varied from 100 to 350 kHz for the period of 2014 to 2018. For PSR B0919+06 varied from 36 to 195 kHz over approximately the same time period. In the direction of the observed pulsars, the power-law indices for the spatial inhomogeneity spectrum of the scattering plasma were estimated. The characteristic frequency and time scales of the diffractive scintillations for PSR B0809+74 are comparable to the receiver bandwidth and observation time, respectively. Therefore, only a lower limit for can be obtained for this pulsar. The mean value is for PSR B1133+16 and for PSR B0919+06. We have also measured the angular diameter of the average scattering disks, , for these two pulsars. For PSR B0919+06, mas, and for B1133+16, 1.6 mas. We provide the estimates of the distance to the scattering screens. All measured parameters have been compared with previously published data. [ABSTRACT FROM AUTHOR]

This study introduces a Sagnac Interferometer (SI) fiber sensor that integrates Polarization-Maintaining Fibers (PMFs) with a Tilted Fiber Bragg Grating (TFBG) for the dual-parameter measurement of strain and lateral pressure. By incorporating a 6° TFBG with PMFs into the SI sensor, its sensitivity is significantly enhanced, enabling advanced multi-parameter sensing capabilities. The sensor demonstrates a temperature sensitivity of −1.413 nm/°C and a lateral pressure sensitivity of −4.264 dB/kPa, as validated by repeated experiments. The results exhibit excellent repeatability and high precision, underscoring the sensor's potential for robust and accurate multi-parameter sensing applications. [ABSTRACT FROM AUTHOR]

A four-quadrant wind imaging interferometer is a new generation of wind imaging interferometer with the valuable features of being monolithic, compact, light, and insensitive to temporal variations in the source. Its applications include remote sensing of the wind field of the upper atmosphere and observing important dynamical processes in the mesosphere and lower thermosphere. In this paper, we describe a new phase step determination approach based on the Lissajous figure, which provides an efficient, accurate, and visual method for the characterization and calibration of this type of instrument. Using the data from wavelength or thermal fringe scanning, the phase steps, relative intensities, and instrument visibilities of four quadrants can be retrieved simultaneously. A general model for the four-quadrant wind imaging interferometer is described and the noise sensitivity of this method is analyzed. This approach was successfully implemented with four-quadrant wind imaging interferometer prototypes, and its feasibility was experimentally verified. [ABSTRACT FROM AUTHOR]

This paper presents a tunable, switchable multi-wavelength emission from an erbium-doped fiber ring laser, enabled by adjusting the spectral fringe visibility of a fiber interferometer filter. The filter is formed with specially designed concatenated tapered fibers to configure a Mach-Zehnder fiber interferometer (MZFI). The laser emission is highly flexible and reconfigurable, allowing for tuning between single- and dual-wavelength operation. The laser can switch sequentially from one up to six wavelengths by fixing the curvature and adjusting the polarization state. The lasing emission is generated over a stable wavelength range between 1559.59 nm and 1563.54 nm, exhibiting an optical signal-to-noise ratio (OSNR) exceeding ~35 dB. The performance of amplitude and wavelength fluctuations were evaluated, indicating an appropriate stability of ~3 dB and a shift less than 0.1 nm within a 45 min period at room temperature. A detailed comparison with the literature is given. [ABSTRACT FROM AUTHOR]

A wavelength-switchable ytterbium-doped mode-locked fiber laser is reported in this article. Two Mach–Zehnder interferometers (MZIs, denoted as MZI1, MZI2) with close free spectral ranges (FSRs) are connected in series to form a Vernier effect sensor. By utilizing the filtering effect of the Vernier effect sensor, the wavelength-switchable output of an ytterbium-doped mode-locked fiber laser is realized. When the 3 dB bandwidth of the Vernier effect filter is set to be 5.31 nm around 1073.42 nm, stable dissipative solitons are obtained. Stretching MZI1 horizontally, the central wavelengths of the pulses can be switched among 1073.42 nm, 1055.38 nm, and 1036.22 nm, with a total tunable central wavelength range of 37.2 nm. When the 3 dB bandwidth of the Vernier effect filter is set to be 4.07 nm, stable amplifier similaritons are obtained. Stretching MZI1 horizontally, the central wavelengths of the pulses are switchable among 1072.71 nm, 1060.15 nm, 1048.92 nm, and 1037.26 nm, with a total tunable central wavelength range of 35.15 nm. Compared with traditional fiber interference filters, the Vernier effect filter has a higher sensitivity, making wavelength switching more convenient and providing a wider tuning range for the ytterbium-doped mode-locked fiber laser. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate high-extinction stop-band photonic filters based on Mach–Zehnder interferometer (MZI)-coupled silicon nitride (Si3N4) resonators fabricated using I-line lithography technology. Leveraging the low-loss silicon nitride waveguide, our approach enables the creation of stable, high-performance filters suitable for applications in quantum and nonlinear photonics. With destructive interference at the feedback loop, photonic filters with an extinction ratio of 35 dB are demonstrated with four cascaded MZI-coupled resonators. This cascading design not only enhances the filter's extinction but also improves its spectral sharpness, providing a more selective stop-band profile. Experimental results agree well with the theoretical results, showing linear scaling of extinction ratios with the number of cascaded MZI-coupled resonators. The scalability of this architecture opens the possibility for further integration and optimization in complex photonic circuits, where high extinction ratios and precise wavelength selectivity are critical for advanced signal processing and quantum information applications. [ABSTRACT FROM AUTHOR]

Using a 30–250 MHz VHF interferometer, we observed a previously unreported mode of initial lightning development inside thunderclouds. This mode is defined by continuous VHF radiation spanning several km within the first few milliseconds of lightning initiation. Following flash initiation through fast positive breakdown at high altitudes above 9 km, the VHF radiation front of upward negative streamers ascended continuously at a speed of ∼1.0 × 106 m/s, forming a continuous initial breakdown burst (CIBB) about 2 km in length. For the two CIBBs analyzed, the long and narrow CIBB channel was traversed by dart leaders that occurred later in the flash, indicating that the CIBB channel belongs to what becomes the main conducting leader channel. In contrast to classic initial breakdown pulses (IBPs) with sub‐pulses superimposed on the rising edge, CIBBs produced a series of discrete, narrow LF pulses (<10 μs) with an average time interval of 0.20 and 0.14 ms, respectively. We speculate that a CIBB is a continuously developing negative streamer system in the high electric field region at high altitudes, with connections of internal plasma channels producing LF pulses. These results have implications for physical conditions conducive to the formation of a long and continuous negative streamer system. Plain Language Summary: How lightning develops inside thunderclouds in the first few milliseconds is still not fully understood. Previous research showed that lightning initially propagates with intermittent bursts of strong radio emissions and electromagnetic pulses called initial breakdown pulses (IBPs), forming distinct steps. In contrast, this study discovered a new mode of initial lightning development in the form of continuous initial breakdown burst (CIBB) of several km in length. The observation was made in two in‐cloud lightning flashes that initiated at high altitudes above 9 km. This finding shed light on the physical conditions conducive for the development of a long and continuous negative streamer system inside thunderclouds. Key Points: We observed a new mode of initial lightning development in the form of continuous initial breakdown burst (CIBB) of several km in lengthTwo CIBBs started immediately after lightning initiation at high altitudes above 9 km, emitting VHF radiation continuouslyThe VHF radiation front ascends continuously at ∼1 × 106 m/s for 2 km, accompanied by several narrow pulses differing from classic IBPs [ABSTRACT FROM AUTHOR]

Optical wireless technology has a great potential in realizing high speed secure communication. In this paper, Gold sequence generator is proposed and investigated. The sequence is generated by modulo-2 addition of maximum length sequences. Furthermore, cross talk and extinction ratio at varying switching voltage is analyzed. The outcome successfully demonstrates the feasibility of optical Gold sequence using Mach–Zehnder interferometer as a compact solution. [ABSTRACT FROM AUTHOR]

A robust strain sensor is demonstrated based on a microfiber Mach–Zehnder interferometer (MMZI) encapsulated by the polymer polydimethylsiloxane (PDMS). Benefiting from the low Young's modulus of PDMS, both a robust structure and high sensitivity can be realized based on three different encapsulations. In the experiment, the proposed sensors are fabricated and tested with strain sensitivities ranging from −20.95 pm/με to 127.00 pm/με within the wavelength range of 1200–1650 nm. Compared with the bare MMZI sensor, at least one order of magnitude higher sensitivity is reached. To further evaluate the performance of the sensor, the dependences of sensitivity on probing wavelength and the different types and quantities of polymers used in encapsulation are discussed. Results show that the sensitivity of the sensor will increase with the probing wavelength. The type and quantity of polymer used are also very critical to sensitivity. Additionally, a response time of 24.72 ms can be reached. Good recoverability and repeatability of the sensor are also demonstrated by repeated experiments. The strain sensor demonstrated here shows the advantages of simple fabrication, robust structure, high and tunable sensitivity, fast response, good recoverability and repeatability. [ABSTRACT FROM AUTHOR]

Non‐volatile charge‐trap flash memory (CTM) co‐located with heterogeneous III‐V/Si photonics is demonstrated. The wafer‐bonded III‐V/Si CTM cell facilitates non‐volatile optical functionality for a variety of devices such as Mach–Zehnder Interferometers (MZIs), asymmetric MZI lattice filters, and ring resonator filters. The MZI CTM exhibits full write/erase operation (100 cycles with 500 states) with wavelength shifts of Δλnon‐volatile = 1.16 nm (Δneff,non‐volatile ≈ 2.5 × 10−4) and a dynamic power consumption <20 pW (limited by measurement). Multi‐bit write operation (2 bits) is also demonstrated and verified over a time duration of 24 h and most likely beyond. The cascaded second order ring resonator CTM filter exhibited an improved ER of ≈7.11 dB compared to the MZI and wavelength shifts of Δλnon‐volatile = 0.041 nm (Δneff, non‐volatile = 1.5 × 10−4) with similar pW‐level dynamic power consumption as the MZI CTM. The ability to co‐locate photonic computing elements and non‐volatile memory provides an attractive path toward eliminating the von‐Neumann bottleneck. [ABSTRACT FROM AUTHOR]