Visibility Of Interference Fringes Research Articles

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

Modeling and design of high-sensitivity dual optical feedback interferometry measurement system enhanced by period-one dynamics

Laser optical feedback interferometry (OFI) is a unique one-channel interferometric measurement technology with the advantages of compact structure, low implementation cost and easy alignment. However, it has a critical challenge that the visibility of interference fringe is often low and further induces low measurement sensitivity, especially in occasions when the optical feedback strength is feeble, e.g., biomedical and fluid detection. Recently, it has been demonstrated that period-one (P1) dynamics can enhance the measurement sensitivity by introducing extra optical feedback to form a dual optical feedback interferometry (DOFI) system. However, the details of the enhancement mechanism and how to design such a system are still required to unveil. In this paper, comprehensive discussions of designing a DOFI system with high measurement sensitivity enhanced by P1 dynamics are presented. First, based on the modified Lang-Kobayashi equations, a mathematical sensing model of a DOFI system working in P1 state was established. Then, simulations were carried out to verify the validity of the proposed model. After that, factors that determine the sensitivity enhancement were analyzed, based on which, theoretical analysis of achieving optimal sensitivity enhancement was performed. Next, we discussed the operation region of a DOFI system in P1 state and investigated the influence of the system parameters on the operation region. At last, experiments were conducted to verify the theoretical analyses. The results of this work provide helpful guidance for the construction of high-sensitivity DOFI sensing and measurement systems.

Influence of polarization and the environment on wave–particle duality

Wave-particle duality is certainly one of the most curious concepts of contemporary physics, which ascribes mutually exclusive behaviors to quantum systems that cannot be observed simultaneously. In the context of two-path interferometers, these two behaviors are usually described in terms of the visibility of interference fringes and the path distinguishability. Here, we use quantum information-theoretic tools to derive quantifiers of these two properties, which account for the combined influence of path probability and polarization, and demonstrate that they satisfy a complementarity relation. We further show that the derived quantities can work as probes in the study of open quantum dynamics by revealing interesting facets of environment actions, such as: decoherence, depolarization and scattering.

Optical fiber polarization-entangled photon pair source using intermodal spontaneous four-wave mixing in the visible spectral band

The theoretical and experimental investigation results of the generation of the polarization-entangled photon pairs operating at visible wavelengths are reported. The generation of polarization-entangled photon pairs was based on intermodal spontaneous four-wave mixing (IM-SFWM) using standard step-index few-mode fiber. It was shown theoretically that several combinations of IM-SFWM processes could occur depending on spatial modes of a pump beam. A polarization-entangled photon pair source based on Sagnac loop incorporating a segment of few-mode fiber were then experimentally created. A two-photon interference fringe visibility of our implemented photon pair source were 91.7% and 88.8% in H/V bases and D/A bases, respectively. A quantum state tomography was also conducted to reconstruct the density matrix of the generated state with a fidelity to a maximum entangled state of 93.1%.

非平衡光纤干涉仪的相位稳定方法研究

By using photons to carry quantum information, optical quantum information technology plays an essential role in quantum communication, quantum metrology, and linear optical quantum computing. In recent years, the unbalanced fiber interferometer has been widely applied in preparing, manipulating, and measuring photon qubits. However, the unbalanced fiber interferometer based on fiber devices is sensitive to the environment's thermal, mechanical, and acoustic noise. Thus, phase stabilization based on feedback control is essential in utilizing an unbalanced fiber interferometer. The existing phase stabilization methods typically employ a reference laser combined with optoelectronic detection, thus introducing additional noise to photon qubits. In this paper, we propose and demonstrate a feedback control method to stabilize a phase in an unbalanced fiber interferometer by combining weak coherent reference light and single photon counting. Using theoretical analysis, we realized the phase stabilization of an unbalanced fiber Michelson interferometer with an arm-length difference of about 1 m. The results showed that the jitter of the stabilized phase is less than 0.042 rad, while the visibility of single-photon interference fringes is higher than 99%.

NOA61-Polymer Fiber Fizeau Interferometer with a Flexible NOA65-Polymer Taper for Simultaneous Measurement of Tilt Angle and Temperature.

This study proposes and experimentally demonstrates a NOA61-polymer fiber Fizeau interferometer (PFFI) connected to a flexible NOA65-polymer taper (PT) for simultaneous measurement of tilt angle and temperature (T). The PT/PFFI fiber sensor consists of a taper-shaped flexible NOA65 polymer and single-mode fiber with an endface that is attached to a NOA61-polymer. The NOA61-polymer of PFFI is highly sensitive to variations of T with high repeatability and enables the simultaneous measurement of tilt angle by connecting with the highly flexible NOA65-PT. the interference fringe visibility of optical spectra in the PFFI can be highly controlled by the tilt angle of the PT and is thus capable of measuring tilt angles with high sensitivity. On the other hand, wavelength shifts of the spectra in the PFFI only occur when T varies. The proposed PT/PFFI can simultaneously detect the tilt state and the variation of surrounding T by measuring the optical spectral responses and eliminating cross sensitivity. Experimental results demonstrate the PT/PFFI can simultaneously measure tilt angles and T with good sensitivities and obtain averages of 0.4 dB/° and 0.17 nm/°C, respectively.

A Demodulation Scheme Based on Measuring Interference Fringe Visibility With a Highly Birefringent Fiber Based Michelson Interferometer

We propose a novel demodulation scheme based on measuring interference fringe visibility and demonstrate it using a typical Michelson interferometer (MI) configuration. The key component to achieve the scheme is a section of highly birefringent fiber (HBF) spliced into the sensing arm to function as the sensing element. The optical path difference (OPD) leads to interference fringes, while the birefringence of the HBF results in a visibility envelop. It is possible to detect measurands associated with birefringence through measuring the visibility, which is attributed to a flexible use of the fundamental principle of interferometry. As one of the potential applications, temperature sensing employing the MI configuration is performed. Moreover, the technique has the advantage of being immune to element instabilities, such as power fluctuation of the light source, phase shift of the reference arm, noise of the photo detector, and wavelength shift of the optical spectrum analyzer (OSA). This work may provide an alternative method to achieve high precision interferometry with low cost.

Optimal optical path difference of an asymmetric common-path coherent-dispersion spectrometer.

Optical path difference (OPD) is a very significant parameter in the asymmetric common-path coherent-dispersion spectrometer (CODES), which directly determines the performance of the CODES. In order to improve the performance of the instrument as much as possible, a temperature-compensated optimal optical path difference (TOOPD) method is proposed. The method does not only consider the influence of temperature change on the OPD but also effectively solves the problem that the optimal OPD cannot be obtained simultaneously at different wavelengths. Taking the spectral line with a Gaussian-type power spectral density distribution as a representative, the relational expression between the OPD and the visibility of interference fringes formed by the CODES is derived for the stellar absorption/emission line. Further, the optimal OPD is deduced according to the efficiency function, and the relationship between the optimal OPD and wavelength is analyzed. Then, based on the materials' dispersion characteristics, different optical materials are combined and added to the interferometer's reflected and transmitted optical path to implement the optimal OPD at different wavelengths, thereby improving the detection precision. Meanwhile, the materials whose refractive index negatively changes with temperature are selected to reduce or even offset the temperature impact on OPD, and hence the system's stability is improved and further improves the detection precision. Under certain input conditions, the material combination that approximates the optimal OPD is performed within the range of 0.66-0.9 µm. The simulation results show that the maximal difference between the optimal OPD obtained by the efficiency function and the OPD produced by the material combination is 0.733 mm for the absorption line and 1.122 mm for the emission line, which is reduced by 1 time compared with only one material. The influence of temperature on the OPD can be reduced by 2-3 orders of magnitude by material combination, which greatly ameliorates the stability of the whole spectrometer. Hence, the TOOPD method provides a new idea for further improving the high-precision radial velocity detection of the asymmetric common-path CODES.

Chaos-induced loss of coherence of a Bose-Einstein condensate

The mean-field limit of a bosonic quantum many-body system is described by (mostly) non-linear equations of motion which may exhibit chaos very much in the spirit of classical particle chaos, i.e. by an exponential separation of trajectories in Hilbert space with a rate given by a positive Lyapunov exponent $\lambda$. The question now is whether $\lambda$ imprints itself onto measurable observables of the underlying quantum many-body system even at finite particle numbers. Using a Bose-Einstein condensate expanding in a shallow potential landscape as a paradigmatic example for a bosonic quantum many-body system, we show, that the number of non-condensed particles is subject to an exponentially fast increase, i.e. depletion. Furthermore, we show that the rate of exponential depletion is given by the Lyapunov exponent associated with the chaotic mean-field dynamics. Finally, we demonstrate that this chaos-induced depletion is accessible experimentally through the visibility of interference fringes in the total density after time of flight, thus opening the possibility to measure $\lambda$, and with it, the interplay between chaos and non-equilibrium quantum matter, in a real experiment.

Interference at the single-photon level based on silica photonics robust against channel disturbance

Quantum key distribution (QKD) provides a solution for communication of unconditional security. However, the quantum channel disturbance in the field severely increases the quantum bit-error rate, degrading the performance of a QKD system. Here we present a setup comprising silica planar light wave circuits (PLCs), which is robust against the channel polarization disturbance. Our PLCs are based on the asymmetric Mach–Zehnder interferometer (AMZI), integrated with a tunable power splitter and thermo-optic phase modulators. The polarization characteristics of the AMZI PLC are investigated by a novel pulse self-interfering method to determine the operation temperature of implementing polarization insensitivity. Over a 20 km fiber channel with 30 Hz polarization scrambling, our time-bin phase-encoding QKD setup is characterized with an interference fringe visibility of 98.72%. The extinction ratio for the phase states is kept between 18 and 21 dB for 6 h without active phase correction.

Homogeneous broadening in the spectrum of a broadband erbium-doped fibre light source

Interference of wave trains separated out in an inhomogeneous emission spectrum of a superluminescent erbium-doped fibre source has been studied by scanning the wavelength of a spectrum analyser. The results demonstrate that, as the spectral resolution of the spectrum analyser decreases to a level corresponding to a sharp drop in interference fringe visibility relative to its original level, near 100 %, fringe visibility becomes dependent on the wavelength in the inhomogeneous spectrum of the source. The reason for this is that, at some characteristic resolution δλ (δλ > 0.5 nm in our case), the coherence time of wave trains is not limited by the spectral resolution of the spectrum analyser and is related to the inhomogeneous spectrum of the source, whose limiting width can be thought of as the homogeneous linewidth in the spectrum of the source. This feature can be used for evaluating homogeneous line broadening.

Dispersion-compensated polarization Sagnac interferometer with high imaging quality

Multistage diffraction of a dispersion-compensated polarization Sagnac interferometer (DCPSI) reduces the fringe visibility of interference fringes generated in a focal plane array, thereby leading to the poor quality of the reconstructed polarization images. In this paper, a double total reflection prism between the DCPSI and imaging lens is added to limit the effect of multistage diffraction and improve the imaging quality. First, the influence of multistage diffraction on the interference fringes and the ratio of fringe amplitude to the background was analyzed. Second, the range of angles of the two right angle prisms was calculated. Simulation and experiment were carried out to prove the superiority of the proposed method. Result shows that the ratio of fringe amplitude to the background increases from 1/5 to 1/3 and from 1/10 to 1/6 in simulation and experiment when a double total reflection prism structure is added respectively. This method can reduce the influence of multistage diffraction on interference fringes and improve the image quality of DCPSI effectively.

Spatial coherence properties of down converted biphoton field generated using partially coherent pump beam

We report a theoretical study of spatial coherence properties of down converted photons generated using partially spatially coherent pump beam. We investigate coincidence rate and biphoton visibility in two geometries, in which a double-slit is either placed in the path of pump beam or in the path of the signal and idler field. The study infers that the visibility of the interference fringes is strongly influenced by the pump parameters; pump size and pump spatial coherence length. Specifically, the visibility of interference fringes increases as the pump spatial coherence or the transverse size of the pump increases at the crystal plane. The increase in biphoton visibility with the propagation distance verifies the van Cittert-Zernike theorem for the two cases. Downconverted photons with controllable pump spatial coherence, which in turn controls the spatial coherence and entanglement of the downconverted photons, could find potential applications in quantum imaging, quantum communication and non-linear interferometry.

Evaluation of the radial inhomogeneity of a magnetic field by magnetic-sensitive Ramsey interference fringes at 87Rb atomic fountain clock

This paper demonstrates the evaluation of the radial inhomogeneity of the magnetic field of an atomic fountain clock, which affects the Ramsey interference fringe visibility. Based on the simplified inhomogeneous magnetic field model, the relationship between the fringe visibility and the inhomogeneity of the magnetic field is obtained; a magnetic field broadening limit of 70 pT for the fountain clock is observed when the interference fringes disappear. Magnetic field broadening of 100 pT in the local interaction region of the atomic fountain clock is measured by a special magnetic-sensitive Ramsey interference method. It is verified that the non-uniform widening of the magnetic field is the cause of the absence of interference fringes of adjacent lines.

Angled fiber-based Fabry–Perot interferometer

Herein, we propose and experimentally demonstrate a novel, to the best of our knowledge, all-fiber Fabry–Perot (FP) interferometer that is formed by a simple angled fiber that can function as a beam splitter. According to the principle of the angled fiber, we verify the influence of an oblique angle on the light propagation path and light intensity ratio. Subsequently, angled fiber-based FP interferometers are experimentally demonstrated, and the influence of the oblique angle on the visibility of interference fringes and temperature characteristics is investigated. Finally, the temperature characteristics of this proposed FP interferometer are investigated experimentally, and the temperature sensitivity is 12.62 and 10.89 pm/°C for 42° and 40° angled fiber-based fiber FP interferometers, respectively. This proposed FP interferometer is fabricated by using a simple angled fiber, which has the advantages of ease of fabrication and all-fiber characteristics and hence can meet the requirements of mass production and high stability in various practical application areas.

Coherent perfect absorption of single photons in a fiber network

Large distance implementation of quantum communication technologies requires coherent control of single photons in optical fiber networks. Here we demonstrate the phenomenon of coherent perfect absorption of single photons in a fully fiberized ultrathin plasmonic metamaterial fabricated at the end facet of an optical fiber. Continuous control of single-photon absorption probability is achieved by driving the network between the regimes of coherent total absorption and coherent total transmission. To circumvent phase fluctuations inherent to optical fiber networks, we implemented a reference-based postselection technique which yielded interference fringe visibility comparable to that of free space experiments. Coherent absorption of quantum light in fiber environment provides new opportunities for dissipative single-photon switching, filtering, and measurement, as well as for manipulation of entangled, weak coherent, and NOON states in optical fiber networks.

Highly sensitive gas refractive index sensor based on hollow-core photonic bandgap fiber.

A highly sensitive gas refractive index (RI) sensor based on hollow-core photonic bandgap fiber (HC-PBF) and Fourier transform white-light interferometry was experimentally demonstrated. HC-PBFs with lower loss than hollow silica tubes render a longer air cavity for the Fabry-Perot interferometers (FPIs) without a great deal of compromise to the fringe visibility of interference. Fourier transform phase demodulation method was employed in the experiment and a directly proportional relationship between the phase sensitivity and cavity length was demonstrated. For a cavity length of ∼24.9 mm, the sensor's gas RI sensitivity reaches up to 50775.54 µm/RIU in an air RI range from 1.000 to 1.030. Considering the cavity length demodulation resolution of 0.06 µm achieved by this method, the sensor can detect gas RI change with a resolution of 10-6 RIU, which can meet the sensing demand for almost all the gases. Moreover, the gas RI sensitivity and measurement range can be improved further by lengthening the HC-PBF. The high sensitivity, large dynamic range and good linearity of the proposed sensor make it a good candidate for biosensing, monitoring of modern chemical industry or gas laser systems.

Superbunching effect of classical light with a digitally designed spatially phase-correlated wave front

Superposition of multiple indistinguishable two-photon paths is introduced by means of a digital wave front encoding technique to design a spatially phase-correlated wave front of a light field, which could result in a superbunching effect with a bunching peak much larger than 2, the theoretical bunching peak of thermal light. Experimentally, we demonstrated a bunching peak of $11.72\ifmmode\pm\else\textpm\fi{}0.05$ with the digitally designed phase-correlated wave front of classical light, which can be improved further on. A significant improvement of the visibility of the second-order interference fringes and ghost imaging was also experimentally demonstrated. Our method provides a convenient digitally controllable way to implement superposition of multiple different but indistinguishable two-photon paths, and therefore to modify the optical coherence properties of photons. Such a superbunching effect may have potential applications in improving the visibility of correlation interference and imaging, and enhancing the efficiency of two-photon nonlinear effects such as two-photon absorption effect.

Observing momentum disturbance in double-slit "which-way" measurements.

Making a "which-way" measurement (WWM) to identify which slit a particle goes through in a double-slit apparatus will reduce the visibility of interference fringes. There has been a long-standing controversy over whether this can be attributed to an uncontrollable momentum transfer. Here, by reconstructing the Bohmian trajectories of single photons, we experimentally obtain the distribution of momentum change. For our WWM, the change we see is not a momentum kick that occurs at the point of the WWM, but rather one that nonclassically accumulates during the propagation of the photons. We further confirm a quantitative relation between the loss of visibility consequent on a WWM and the total (late-time) momentum disturbance. Our results emphasize the role of the Bohmian momentum in giving an intuitive picture of wave-particle duality and complementarity.

Interferometric quantum spectroscopy with undetected photons via distinguishability modulation.

Quantum spectroscopy with undetected photons (QSUP) utilizing the quantum entanglement of parametrically down-converted photons has emerged as a new spectroscopic platform. Here, we demonstrate a high-resolution and remote-measurement QSUP, where light-matter interactions and photon detections are performed in spectrally and spatially different regions. A dual-stimulated parametric down-conversion scheme with an optical frequency-comb pump and ultra-narrow coherent seed beam in an idler mode is used to generate path-entangled pairs of the undetected idler and measured frequency-comb signal photons. To demonstrate the frequency resolution of this scheme, a Fabry-Pérot cavity with a narrow bandwidth is used as a sample that modulates the distinguishability of one-photon-added coherent idler beams, which directly affects the interference fringe visibility of the entangled signal photons. We thus anticipate that the remote QSUP whose frequency resolution is determined by the linewidth of the coherent seed laser will enable the development of quantum spectroscopy featuring high resolution.