Fringe Visibility Research Articles

Cone beam neutron interferometry: From modeling to applications

Phase-grating moiré interferometers (PGMIs) have emerged as promising candidates for the next generation of neutron interferometry, enabling the use of a polychromatic beam and manifesting interference patterns that can be directly imaged by existing neutron cameras. However, the modeling of the various PGMI configurations is limited to cumbersome numerical calculations and backward propagation models which often do not enable one to explore the setup parameters. Here we generalize the Fresnel scaling theorem to introduce a k-space model for PGMI setups illuminated by a cone beam, thus enabling an intuitive forward propagation model for a wide range of parameters and experimental setups. The interference manifested by a PGMI is shown to be a special case of the Talbot effect, and the optimal fringe visibility is shown to occur at the moiré location of the Talbot distances. We derive analytical expressions for the contrast and the propagating intensity profiles in various conditions and provide the first analysis of the PGMI dark-field imaging signal when considering sample characterization. The model's predictions are compared to experimental measurements and good agreement is found between them. Last, we propose and experimentally verify a method to recover contrast at typically inaccessible PGMI autocorrelation lengths. The presented work provides a toolbox for analyzing and understanding existing PGMI setups and their future applications, for example extensions to two-dimensional PGMIs and characterization of samples with nontrivial structures. Published by the American Physical Society 2024

Development and validation of a collaborative robotic platform based on monocular vision for oral surgery: an in vitro study.

Surgical robots effectively improve the accuracy and safety of surgical procedures. Current optical-navigated oral surgical robots are typically developed based on binocular vision positioning systems, which are susceptible to factors including obscured visibility, limited workplace, and ambient light interference. Hence, the purpose of this study was to develop a lightweight robotic platform based on monocular vision for oral surgery that enhances the precision and efficiency of surgical procedures. A monocular optical positioning system (MOPS) was applied to oral surgical robots, and a semi-autonomous robotic platform was developed utilizing monocular vision. A series of vitro experiments were designed to simulate dental implant procedures to evaluate the performance of optical positioning systems and assess the robotic system accuracy. The singular configuration detection and avoidance test, the collision detection and processing test, and the drilling test under slight movement were conducted to validate the safety of the robotic system. The position error and rotation error of MOPS were 0.0906 ± 0.0762mm and 0.0158 ± 0.0069degrees, respectively. The attitude angle of robotic arms calculated by the forward and inverse solutions was accurate. Additionally, the robot's surgical calibration point exhibited an average error of 0.42mm, with a maximum error of 0.57mm. Meanwhile, the robot system was capable of effectively avoiding singularities and demonstrating robust safety measures in the presence of minor patient movements and collisions during vitro experiment procedures. The results of this in vitro study demonstrate that the accuracy of MOPS meets clinical requirements, making it a promising alternative in the field of oral surgical robots. Further studies will be planned to make the monocular vision oral robot suitable for clinical application.

Inertia, Progress, or Regress? Observing and Explaining Heterogenous Tech Firm Demographic Diversity Trajectories

Tech firms are under strong pressure to increase their demographic diversity. While activists and scholars have tended to treat the sector as homogenously hostile to women and racialized minorities, recent theory on organizational inequalities stresses heterogeneity in firm-level inequality regimes. Beginning with an inductive exploration of variation in executive, managerial, and professional workforce trajectories, we find that between 2008 and 2016 most Tech firms show little change, but that there are also significant clusters of firms that were becoming either much more or much less diverse for all three occupational levels. We model these trajectories as a function of firm visibility, the regulation of federal contractors by the U.S. Department of Labor, and leadership composition. Multinomial logistic regression models show that firms with an increasing (decreasing) diversity pattern in managerial and executive positions are also more likely to become more (less) diverse in their much more numerous professional jobs. Managers are more influential than executive in this regard. Regulatory pressure is associated with increased executive diversity trajectories, but not with managerial or professional trajectories. We conclude that increased Tech diversity is possible but requires leadership, particularly at the middle manager level. In addition, regulatory and visibility pressures primarily produce symbolic shuffles in top jobs.

High-visibility energy-time entanglement system enabled by a low-loss silicon-integrated platform.

Energy-time (E-T) entanglement is widely employed in long-distance quantum entanglement distribution due to its strong robustness against transmission fluctuations. In this Letter, we report what we believe to be the first silicon monolithically integrated E-T entanglement system, which integrates the photon sources, wavelength demultiplexers, and Franson interferometers on a single chip. Also, by utilizing low-loss multimode waveguides in Franson interferometers, we measured an on-chip quantum interference visibility of 99.66% (±0.47%), to our knowledge one of the highest values for integrated E-T entanglement systems reported to date. The quantum interference after 1- and 5-km fiber propagation shows visibilities of 96.72% (±0.78%) and 97.46% (±1.23%), respectively. These results demonstrate the potential of using silicon monolithic integration for advance E-T entanglement-based quantum communication networks.

Bounded VNDF Sampling for the Smith-GGX BRDF

Sampling according to a visible normal distribution function (VNDF) is often used to sample rays scattered by glossy surfaces, such as the Smith-GGX microfacet model. However, for rough reflections, existing VNDF sampling methods can generate undesirable reflection vectors occluded by the surface. Since these occluded reflection vectors must be rejected, VNDF sampling is inefficient for rough reflections. This paper introduces an unbiased method to reduce the number of rejected samples for Smith-GGX VNDF sampling. Our method limits the sampling range for a state-of-the-art VNDF sampling method that uses a spherical cap-based sampling range. By using our method, we can reduce the variance for highly rough and low-anisotropy surfaces. Since our method only modifies the spherical cap range in the existing sampling routine, it is simple and easy to implement.

Requirements for probing chiral Casimir-Polder forces in a molecular Talbot-Lau interferometer

We theoretically investigate the influence of chiral Casimir-Polder (CP) forces in Talbot-Lau interferometry, based on three nanomechanical gratings. We study scenarios where the second grating is either directly written into a chiral material or where the nanomask is coated with chiral substances. We show requirements for probing enantiospecific effects in matter-wave interferometry in the transmission signal and the interference fringe visibility, which depend on the de Broglie wavelength and the molecular chirality. The proposed setup is particularly sensitive to CP forces in the nonretarded regime where chiral effects can be comparable in magnitude to their electric and magnetic counterparts. While the first and third gratings do not change the phase of the matter wave, applying a coating of chiral substances to them enhances the instrument's chiral selectivity. Published by the American Physical Society 2024

Advanced fabrication of polymer waveguide interferometric sensor utilizing interconnected holey fibers

A universally applicable approach is proposed for the fabrication of fiber-optic polymer sensors. The hollow-core fibers (HCFs) with inner diameters of 30 µm, 50 µm, and 75 µm are spliced coaxially with dual-hole fiber (DHF) or photonic crystal fiber (PCF). Owing to the sized-matched air holes within HCF and DHF/PCF, an interconnected in-fiber microchannel is constructed, which facilitates rapid and complete filling of the HCF’s central hole with liquid glue. After the ultraviolet-induced polymerization, a polymer Fabry-Perot interferometer is achieved by cutting the HCF end with a desired cavity length. Besides, the interference visibility is significantly enhanced by adding a refractive-index-modulated polymer cap onto the cutting surface. Experimental results demonstrate the optimized interference spectra and the interconnection of the matched air-hole fibers. The polymer sensor exhibits a signal-to-noise ratio of 56.8 dB for detecting pulsed ultrasonic waves, which is more than twice that of a partially polymer-filled sensor. Due to the hermetically-sealed structure, the sensor probe presents constrained performance with a temperature sensitivity of 230.2 pm/°C and a humidity sensitivity of 93.7 pm/%RH, which can be further improved by releasing the polymer waveguide from fiber cladding. Based on interconnected holey fibers, the proposed approach has a uniform size-controlled polymer waveguide dimension with increased spectrum visibility, rendering it suitable for a diverse range of microstructure-matched optical fibers.

Successive observation oriented scheduling and task planning of heterogeneous constellation

This paper put forward a method to address the problem, of how to select multiple satellites from a given heterogeneous constellation and plan their tasks to implement a temporary mission for ground or aerial targets successive observation, while hardly affecting the constellation’s original mission as much as possible. First, considering the observation geometric constraints of the satellite on the target, an observability analysis model for effective observation of the satellite on the target is established to characterize the observable spatio-temporal scope. Considering the time-length requirement of sustained observation on the target, a multi-satellite-to-target sustained observation model is constructed for the scheduling of satellites. Second, to address the problem of selecting task satellites in a given heterogeneous constellation, a mathematical model for task planning is established to maximize observation benefits and minimize task burdens. Third, a hybrid method of multi-satellite scheduling and task planning is designed with fault tolerance, based on dynamic programming and an improved contract network protocol algorithm. Next, a joint simulation software system is established through the secondary development of STK and Python, which includes satellite-target observability analysis, task satellite selection, task allocation and planning, and full process visible demonstration functions. Finally, simulation cases verified the effectiveness and superiority of the proposed technique.

Stellar interferometer experiment by measuring visibilities at different wavelengths

In this work we develop an experiment wherein the variation of the fringe visibilities with wavelength provides insights into the geometry of various stellar sources or components. The experiment is based on the Michelson stellar interferometer in which a filter wheel has been inserted between a detecting camera and a telescope obscured by a double-aperture lid. The spatial and temporal incoherent light emitting from stellar sources has been simulated using polymer optical fibres and a broadband light-emitting diode. By measuring the visibilities of the central fringe at different wavelengths we are able to determine the morphology of the analysed light sources, provided that the baseline used is sufficiently long. The experiment is suitable for postgraduate students seeking to delve deeper into light coherence theory and to gain practical experience in optical stellar interferometry.

A multi-mode free-space delay interferometer with no refractive compensation elements for phase-encoded QKD protocols

We demonstrate a compensation-free approach to the realization of multi-mode delay interferometers, mainly for use in phase-encoded quantum key distribution (QKD). High interference visibility of spatially multi-mode beams in unbalanced Michelson or Mach–Zehnder interferometers with a relatively wide range of delays is achieved by the appropriate choice of the transverse size of the beam. We provide a simple theoretical model that gives a direct connection between the visibility of interference, the delay and the beam parameters. The performed experimental study confirms our theoretical findings and demonstrates measured visibility of up to 0.95 for a delay of 2 ns. Our approach’s simplicity and robust performance make it a practical choice for the implementation of QKD systems, where a quantum signal is received over a multi-mode fiber. The important application of such a configuration is an intermodal QKD system, where the free-space atmospheric communication channel is coupled into a span of the multi-mode fiber, delivering the spatially distorted beam to the remote receiver with minimal coupling loss.

Analysis of the Sapphire Fiber Fabry-Perot Interferometer Fringe Visibility under Different Excitation Conditions

In this paper, a theoretical analysis of how the excitation conditions affect the sapphire fiber Fabry-Perot interferometer (SFPI) visibility was performed. The conditions were considered, in which an SFPI was excited by a single-mode fiber (SMF), a multimode fiber (MMF), and a fiber collimator. The finite difference method (FDM) was used to realize the numerical solution of the modal electric fields, and then, the modal excited distributions in the sapphire fiber and the SFPI visibility were calculated. The results showed that different numbers of modes were excited in sapphire fibers under different excitation conditions and finally affected the fringe visibility of the SFPI. The fiber collimator excited the fewest modes and the visibility remained at the highest level. Finally, an experiment was performed, and the experimental results agreed well with the theoretical results.

The Gender- and Sexuality-Based Harms of Refugee Externalization: A Role for Human Rights Due Diligence

Abstract Refugee externalization arrangements are increasingly common in refugee-receiving global North States. Such arrangements have broad-ranging and significant human rights implications, especially (but not only) for refugee women and LGBTQI refugees who may be at increased risk of gender- or sexuality-based harm. This is particularly the case where refugees are placed in situations of risk or harm as a result of a ‘sending’ State’s extraterritorial regime, or where domestic laws in receiving States outlaw certain practices such as pregnancy termination or same-sex sexual activity. There has been limited scholarly analysis of the gendered impacts of externalization policies, and States rarely take into account the gendered implications of externalization when implementing these policies. This article examines the possibilities and limits of international human rights law to protect refugees at risk of gender- and sexuality-based harms through a focus on States’ positive due diligence obligations. While there is limited jurisprudence on the scope of such obligations in the context of refugee externalization, the article emphasizes that due diligence human rights obligations require sending States to adopt effective measures to protect people from unlawful discrimination and from cruel, inhuman or degrading treatment. Due diligence obligations also offer a vital accountability mechanism for violations in extraterritorial settings through their potential preventative, remedial, and visibility functions. Using the case study of Australia’s extraterritorial asylum regime in the Pacific, the article argues that such obligations encompass identifying and addressing foreseeable risks of gender- and sexuality-based harm, both prior to forcibly transferring refugees abroad and on an ongoing basis. Further, it argues that the gender- and sexuality-based human rights impacts of Australia’s externalization regime have immediate and urgent relevance as other States consider or implement similar policies.

On-Chip Quantum Information Processing with Distinguishable Photons.

Multiphoton interference is at the heart of photonic quantum technologies. Arrays of integrated cavities can support bright sources of single photons with high purity and small footprint, but the inevitable spectral distinguishability between photons generated from nonidentical cavities is an obstacle to scaling. In principle, this problem can be alleviated by measuring photons with high timing resolution, which erases spectral information through the time-energy uncertainty relation. Here, we experimentally demonstrate that detection can be implemented with a temporal resolution sufficient to interfere photons detuned on the scales necessary for cavity-based integrated photon sources. By increasing the effective timing resolution of the system from 200 to 20ps, we observe a 20% increase in the visibility of quantum interference between independent photons from integrated microring resonator sources that are detuned by 6.8GHz. We go on to show how time-resolved detection of nonideal photons can be used to improve the fidelity of an entangling operation and to mitigate the reduction of computational complexity in boson sampling experiments. These results pave the way for photonic quantum information processing with many photon sources without the need for active alignment.

A four-grating interferometer for x-ray multi-contrast imaging.

X-ray multi-contrast imaging with gratings provides a practical method to detect differential phase and dark-field contrast images in addition to the x-ray absorption image traditionally obtained in laboratory or hospital environments. Systems have been developed for preclinical applications in areas including breast imaging, lung imaging, rheumatoid arthritis hand imaging and kidney stone imaging. Prevailing x-ray interferometers for multi-contrast imaging include Talbot-Lau interferometers and universal moiré effect-based phase-grating interferometers. Talbot-Lau interferometers suffer from conflict between high interferometer sensitivity and large field of view (FOV) of the object being imaged. A small period analyzer grating is necessary to simultaneously achieve high sensitivity and large FOV within a compact imaging system but is technically challenging to produce for high x-ray energies. Phase-grating interferometers suffer from an intrinsic fringe period ranging from a few micrometers to several hundred micrometers that can hardly be resolved by large area flat panel x-ray detectors. The purpose of this work is to introduce a four-grating x-ray interferometer that simultaneously allows high sensitivity and large FOV, without the need for a small period analyzer grating. The four-grating interferometer consists of a source grating placed downstream of and close to the x-ray source, a pair of phase gratings separated by a fixed distance placed downstream of the source grating, and an analyzer grating placed upstream of and close to the x-ray detector. The object to be imaged is placed upstream of and close to the phase-grating pair. The distance between the source grating and the phase-grating pair is designed to be far larger than that between the phase-grating pair and the analyzer grating to promote simultaneously high sensitivity and large FOV. The method was evaluated by constructing a four-grating interferometer with an 8µm period source grating, a pair of phase gratings of 2.4µm period, and an 8µm period analyzer grating. The fringe visibility of the four-grating interferometer was measured to be ≈24% at 40kV and ≈18% at 50kV x-ray tube operating voltage. A quartz bead of 6mm diameter was imaged to compare the theoretical and experimental phase contrast signal with good agreement. Kidney stone specimens were imaged to demonstrate the potential of such a system for classification of kidney stones. The proposed four-grating interferometer geometry enables a compact x-ray multi-contrast imaging system with simultaneously high sensitivity and large FOV. Relaxation of the requirement for a small period analyzer grating makes it particularly suitable for high x-ray energy applications such as abdomen and chest imaging.

The GRAVITY young stellar object survey

Context. Temporal variability in the photometric and spectroscopic properties of protoplanetary disks is common in young stellar objects. However, evidence pointing toward changes in their morphology over short timescales has only been found for a few sources, mainly due to a lack of high-cadence observations at high angular resolution. Understanding this type of variation could be important for our understanding of phenomena related to disk evolution. Aims. We study the morphological variability of the innermost circumstellar environment of HD 98922, focusing on its dust and gas content. Methods. Multi-epoch observations of HD 98922 at milliarcsecond resolution with VLTI/GRAVITY in the K-band at low (R = 20) and high (R = 4000) spectral resolution are combined with VLTI/PIONIER archival data covering a total time span of 11 yr. We interpret the interferometric visibilities and spectral energy distribution with geometrical models and through radiative transfer techniques using the code MCMax. We investigated high-spectral-resolution quantities (visibilities and differential phases) to obtain information on the properties of the HI Brackett-γ (Brγ)-line-emitting region. Results. Comparing observations taken with similar (u,v) plane coverage, we find that the squared visibilities do not vary significantly, whereas we find strong variability in the closure phases, suggesting temporal variations in the asymmetric brightness distribution associated to the disk. Our observations are best fitted by a model of a crescent-like asymmetric dust feature located at ~1 au and accounting for ~70 % of the near-infrared (NIR) emission. The feature has an almost constant magnitude and orbits the central star with a possible sub-Keplerian period of ~12 months, although a 9 month period is another, albeit less probable, solution. The radiative transfer models show that the emission originates from a small amount of carbon-rich (25%) silicates, or quantum-heated particles located in a low-density region. Among different possible scenarios, we favor hydrodynamical instabilities in the inner disk that can create a large vortex. The high spectral resolution differential phases in the Brγ line show that the hot-gas compact component is offset from the star and in some cases is located between the star and the crescent feature. The scale of the emission does not favor magnetospheric accretion as a driving mechanism. The scenario of an asymmetric disk wind or a massive accreting substellar or planetary companion is discussed. Conclusions. With this unique observational data set for HD 98922, we reveal morphological variability in the innermost 2 au of its disk region. This property is possibly common to many other protoplanetary disks, but is not commonly observed due to a lack of high-cadence observation. It is therefore important to pursue this approach with other sources for which an extended dataset with PIONIER, GRAVITY, and possibly MATISSE is available.

Quantum Light Generation Based on GaN Microring toward Fully On-Chip Source.

An integrated quantum light source is increasingly desirable in large-scale quantum information processing. Despite recent remarkable advances, a new material platform is constantly being explored for the fully on-chip integration of quantum light generation, active and passive manipulation, and detection. Here, for the first time, we demonstrate a gallium nitride (GaN) microring based quantum light generation in the telecom C-band, which has potential toward the monolithic integration of quantum light source. In our demonstration, the GaN microring has a free spectral range of 330GHz and a near-zero anomalous dispersion region of over 100nm. The generation of energy-time entangled photon pair is demonstrated with a typical raw two-photon interference visibility of 95.5±6.5%, which is further configured to generate a heralded single photon with a typical heralded second-order autocorrelation g_{H}^{(2)}(0) of 0.045±0.001. Our results pave the way for developing a chip-scale quantum photonic circuit.

Numerical investigation on the effect of extra-feedback target position on the fringe visibility in a dual optical feedback interferometry system.

Optical feedback interferometry (OFI) exhibits good potential in laboratory and engineering applications as an interferometric measurement technology with unique structure. One challenge of this technology is that the OFI signals may be feeble, and the OFI fringe visibility is low when the optical feedback strength is weak. It has been demonstrated that the OFI fringe amplitude can be enhanced by introducing an extra-feedback into an OFI system. At the same time, it has been confirmed that the position of the extra-feedback target must be strictly controlled as it will directly affect the fringe amplitude. However, the details of how the extra-feedback positions affect the OFI fringe amplitude, and its underpinning mechanism still needs to be unveiled. In this paper, we aim to theoretically investigate the influence of the extra-feedback target position on the OFI fringe amplitude and explore the underpinning mechanism. Firstly, a simplified analytical model for characterizing a dual-channel optical feedback interferometry (DOFI) system in steady state was derived from the Lang-Kobayashi equations. A method of solving the analytical model was developed to further explore the nature of a DOFI system. On top of that, the influence of the extra-feedback target position on the OFI fringe amplitude and its underpinning mechanism was explored, based on which the criteria for how to achieve large fringe amplitudes were summarized. The obtained results provide helpful guidance in constructing a DOFI system with enhanced fringe visibility, and further promote the practical applications of OFI technology.

Prescriptive method for fiber polarization compensation in two bases.

Single-mode optical fibers exhibit a small but non-negligible birefringence that induces random polarization rotations during light propagation. In classical interferometry these rotations give rise to polarization-induced fading of the interferometric visibility, and in fiber-based polarimetric sensors as well as quantum optics experiments, they scramble the information encoded in the polarization state. Correcting these undesired rotations is consequently an important part of many experiments and applications employing optical fibers. In this Lab Note we review an efficient method for fully compensating fiber polarization rotations for general input states. This method was not originally devised by us, but does, to the best of our knowledge, not appear in the literature, and our interactions with the community have indicated that it is not well known.

The Inner Disk Rim of HD 163296: Linking Radiative Hydrostatic Models with Infrared Interferometry

Previous studies of the protoplanetary disk HD 163296 revealed that the morphology of its sub-au infrared emission encompasses the terminal sublimation front of dust grains, referred to as the inner rim, but also extends into the (supposedly) dust-free region within it. Here, we present a set of radiative hydrostatic simulations of the inner rim in order to assess how much the rim alone can contribute to the observed interferometric visibilities V, half-light radii R hl, and fractional disk fluxes F in the wavelength range 1.5–13 μm. In our set of models, we regulate the cooling efficiency of the disk via the boundary condition for radiation diffusion and we also modify the shape of the sublimation front. We find that when the cooling efficiency is reduced, the infrared photosphere at the rim becomes hotter, leading to an increase in R hl sufficient to match the observations. However, the near-infrared disk flux is typically too low ( F≃0.25 at 1.5 μm), resulting in H-band visibility curves located above the observed data. We show that the match to the H-band observations up to moderate baselines can be improved when a wall-shaped rather than curved sublimation front is considered. Nevertheless, our model visibilities always exhibit a bounce at long baselines, which is not observed, confirming the need for additional emission interior to the rim. In summary, our study illustrates how the temperature structure and geometry of the inner rim need to change in order to boost the rim’s infrared emission.

Non-local temporal interference

Although position and time have different mathematical roles in quantum mechanics, with one being an operator and the other being a parameter, there is a space–time duality in quantum phenomena—a lot of quantum phenomena that were first observed in the spatial domain were later observed in the temporal domain as well. In this context, we propose a modified version of the double-double-slit experiment using entangled atom pairs to observe a non-local interference in the arrival time distribution, which is analogous to the non-local interference observed in the arrival position distribution. However, computing the arrival time distribution in quantum mechanics is a challenging open problem, and so to overcome this problem we employ a Bohmian treatment. Based on this approach, we numerically demonstrate that there is a complementary relationship between the one-particle and two-particle interference visibilities in the arrival time distribution, which is analogous to the complementary relationship observed in the position distribution. These results can be used to test the Bohmian arrival time distribution in a strict manner, i.e., where the semiclassical approximation breaks down. Moreover, our approach to investigating this experiment can be applied to a wide range of phenomena, and it seems that the predicted non-local temporal interference and associated complementary relationship are universal behaviors of entangled quantum systems that may manifest in various phenomena.