Utilization of Extrinsic Fabry-Perot Interferometers with Spectral Interferometric Interrogation for Microdisplacement Measurement

The paper presents a number of signal processing approaches for the spectral interferometric interrogation of extrinsic Fabry-Perot interferometers(EFPIs). The analysis of attainable microdisplacement resolution is performed and the analytical equations describing the dependence of resolution on parameters of the interrogation setup are derived. The efficiency of the proposed signal processing approaches and the validity of analytical derivations are supported by experiments. The proposed approaches allow the interrogation of up to four multiplexed sensors with attained resolution between 30 pm and 80 pm, up to three times improvement of microdisplacement resolution of a single sensor by means of using the reference interferometer and noisecompensating approach, and ability to register signals with frequencies up to 1 kHz in the case of 1 Hz spectrum acquisition rate. The proposed approaches can be used for various applications, including biomedical, industrial inspection, and others, amongst the microdisplacement measurement.

Study of the Sensing Characteristics of Irradiated Fiber Bragg Gratings and Fabry-Perot Interferometers Under Gamma Radiation

The sensing characteristics of irradiated fiber Bragg gratings(FBGs)and Fabry-Perot interferometers(FPIs)were investigated under a 2MGy dose of gamma radiation.The study found that the pressure sensitivity of FP sensors after irradiation was stable,while the temperature sensitivity of FBG sensors was unstable,and both wavelengths displayed a shift.These findings offer the possibility for the application of FP pressure sensors in the gamma radiation environments,and FBG sensors require further research to be suitable for application in the nuclear radiation environments.

Recent Progress in Multiparameter Measurement Based on Extrinsic Fiber-Optic Fabry-Perot Interferometers and Fiber Gratings

This paper presents a review of recent progress in simultaneous measurement of multiparameters including strain, temperature, vibration, transverse load, based on the combinations of extrinsic fiber-optic Fabry-Perot interferometers and fiber gratings.

Photonic Crystal Fiber Fabry-Perot Interferometers With High-Reflectance Internal Mirrors

We demonstrated an in-line micro fiber-optic Fabry-Perot interferometer with an air cavity which was created by multi-step fusion splicing a muti-mode photonic crystal fiber （MPCF） to a standard single mode fiber （SMF）. The fringe visibility of the interference pattern was up to 20 dB by reshaping the air cavity. Experimental results showed that such a device could be used as a highly sensitive strain sensor with the sensitivity of 4.5 pm/με. Moreover, it offered some other outstanding advantages, such as the extremely compact structure, easy fabrication, low cost, and high accuracy.

Coulomb-Dominated Oscillations in Fabry-Perot Quantum Hall Interferometers

Periodic resistance oscillations in Fabry-Perot quantum Hall interferometers are observed at integer filling factors of the constrictions, fc=1, 2, 3, 4, 5 and 6. Rather than the Aharonov-Bohm interference, these oscillations are attributed to the Coulomb interactions between interfering edge states and localized states in the central island of an interferometer, as confirmed by the observation of a positive slope for the lines of constant oscillation phase in the image plot of resistance in the 13 Vs plane. Similar resistance oscillations are also observed when the area A of the center regime and the backseattering probability of interfering edge states are varied, by changing the side-gate voltages and the configuration of the quantum point contacts, respectively. The oscillation amplitudes decay exponentially with temperature in the ramge of 40mK〈 T ≤ 130 mK, with a characteristic temperature T0 -25 mK, consistent with recent theoretical and experimental works.

Ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer using a beam collimator and its application for ultrasonic imaging of seismic physical models

An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer （FPI） is proposed and employed for ultra- sonic imaging of seismic physical models （SPMs）. The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber （MMF）, both of which are enclosed in a ceramic tube. The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity, leading to an increased spectral fringe visibility and thus a steeper spectral slope. By using the spectral sideband filtering technique, the collimated FP1 shows an improved ultrasonic response. Moreover, two-dimensional images of two SPMs are achieved in air by recon- structing the pulse-echo signals through using the time-of-flight approach. The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.

Elementary analysis of interferometers for wave particle duality test and the prospect of going beyond the complementarity principle

A distinct method to show a quantum object behaving both as wave and as particle is proposed and described in some detail. We make a systematic analysis using the elementary methodology of quantum mechanics upon Young＇s two-slit interferometer and the Mach-Zehnder two-arm interferometer with the focus placed on how to measure the interference pattern （wave nature） and the which-way information （particle nature） of quantum objects. We design several schemes to simultaneously acquire the which-way information for an individual quantum object and the high-contrast interference pattern for an ensemble of these quantum objects by placing two sets of measurement instruments that are well separated in space and whose perturbation of each other is negligibly small within the interferometer at the same time. Yet, improper arrangement and cooperation of these two sets of measurement instruments in the interferometer would lead to failure of simultaneous observation of wave and particle behaviors. The internal freedoms of quantum objects could be harnessed to probe both the which-way information and the interference pattern for the center-of-mass motion. That quantum objects can behave beyond the wave-particle duality and the complementarity principle would stimulate new conceptual examination and exploration of quantum theory at a deeper level.

Comparison of the sensitivities for atom interferometers in two different operation methods

We investigated the sensitivities of atom interferometers in the usual fringe-scanning method （FSM） versus the fringe- locking method （FLM）. The theoretical analysis shows that for typical noises in atom interferometers, the FSM will degrade the sensitivity while the FLM does not. The sensitivity-improvement factor of the FLM over the FSM depends on the type of noises, which is validated by numerical simulations. The detailed quantitative analysis on this fundamental issue is presented, and our analysis is readily extendable to other kinds of noises as well as other fringe shapes in addition to a cosine one.

Atom interferometers with weak-measurement path detectors and their quantum mechanical analysis

According to the orthodox interpretation of quantum physics, wave-particle duality(WPD) is the intrinsic property of all massive microscopic particles. All gedanken or realistic experiments based on atom interferometers(AI) have so far upheld the principle of WPD, either by the mechanism of the Heisenberg’s position-momentum uncertainty relation or by quantum entanglement. In this paper, we propose and make a systematic quantum mechanical analysis of several schemes of weak-measurement atom interferometer(WM-AI) and compare them with the historical schemes of strongmeasurement atom interferometer(SM-AI), such as Einstein’s recoiling slit and Feynman’s light microscope. As the critical part of these WM-AI setups, a weak-measurement path detector(WM-PD) deliberately interacting with the atomic internal electronic quantum states is designed and used to probe the which-path information of the atom, while only inducing negligible perturbation of the atomic center-of-mass motion. Another instrument that is used to directly interact with the atomic center-of-mass while being insensitive to the internal electronic quantum states is used to monitor the atomic centerof-mass interference pattern. Two typical schemes of WM-PD are considered. The first is the micromaser-cavity path detector, which allows us to probe the spontaneously emitted microwave photon from the incoming Rydberg atom in its excited electronic state and record unanimously the which-path information of the atom. The second is the optical-lattice Bragg-grating path detector, which can split the incoming atom beam into two different directions as determined by the internal electronic state and thus encode the which-path information of the atom into the internal states of the atom. We have used standard quantum mechanics to analyze the evolution of the atomic center-of-mass and internal electronic state wave function by directly solving Schr¨odinger’s equation for the composite atom-electron-photon system in these WM-AIs. We have also compared our analysis with the theoretical and experimental studies that have been presented in the previous literature. The results show that the two sets of instruments can work separately, collectively, and without mutual exclusion to enable simultaneous observation of both wave and particle nature of the atoms to a much higher level than the historical SM-AIs, while avoiding degradation from Heisenberg’s uncertainty relation and quantum entanglement. We have further investigated the space–time evolution of the internal electronic quantum state, as well as the combined atom–detector system and identified the microscopic origin and role of quantum entanglement, as emphasized in numerous previous studies. Based on these physics insights and theoretical analyses, we have proposed several new WM-AI schemes that can help to elucidate the puzzling physics of the WPD of the atoms. The principle of WM-AI scheme and quantum mechanical analyses made in this work can be directly extended to examine the principle of WPD for other massive particles.

Time-Modulated Hamiltonian for Interpreting Delayed-Choice Experiments via Mach-Zehnder Interferometers

Many delayed-choice experiments based on Mach-Zehnder interferometers （MZI） have been considered and made to address the fundamental problem of wave-particle duality. Conventional wisdom long holds that by inserting or removing the second beam splitter （BS2） in a controllable way, microscopic particles （photons, electrons, etc.） transporting within the MZI can lie in the quantum superposition of the wave and particle state as ψ= aw ψ wave ＋ ap ψ particle. Here we present an alternative interpretation to these delayed-choice experiments. We notice that as the BS2 is purely classical, the inserting and removing operation of the BS2 imposes a time- modulated Hamiltonian H mod （t） = a（t）Hin ＋ b（t）Hout, instead of a quantum superposition of H in and Hour as H = awHin ＋ apHout, to act upon the incident wave function. Solution of this quantum scattering problem, rather than the long held quantum eigen-problem yields a synchronically time-modulated output wave function as ψ mod （t） = a（t） ψ wave ＋b（t） ψ particle, instead of the stationary quantum superposition state ψ = aw ψ wave ＋ ap ψ particle. As a result, the probability of particle output from the MZI behaves as if they are in the superposition of the wave and particle state when many events over time accumulation are counted and averaged. We expect that these elementary but insightful analyses will shed a new light on exploring basic physics beyond the long-held wisdom of wave-particle duality and the principle of complementarity.

On Gravitational Waves: Did We Simply Detect the Gravitational Effect of the Sun on the Photons Moving in the Cavity of Interferometers LIGO and VIRGO?

On September 14, 2015 09:50:45 UTC, the two laser interferometers of the LIGO program simultaneously observed a first gravitational wave signal called GW150914. With the commissioning of the VIRGO interferometer in 2017, two other detections, GW170814 and GW170817, were observed and their positions given accurately by LIGO and VIRGO. In this article, I argue that the photons circulating in the cavities of the three interferometers of LIGO and VIRGO were sensitive to the field of attraction of the planets of our Solar System and more particularly to that of the Sun, and would not be due to a coalescence of black hole or neutron stars. The shape of the signals obtained by my interaction model (called GEAR) between the photons in the interferometer cavity and the gravitational field of the Sun is very similar to that of a compact binary coalescence, identical to those obtained by general relativity. Solving the equations of GEAR also gives the exact positions and pseudo-date of the coalescences of all the LIGO and VIRGO detections detected so far, and probably those that will come at the end of 2018 and beyond.

LIGO Experiments Cannot Detect Gravitational Waves by Using Laser Michelson Interferometers—Light’s Wavelength and Speed Change Simultaneously When Gravitational Waves Exist Which Make the Detections of Gravitational Waves Impossible for LIGO Experiments

It is proved strictly based on general relativity that two important factors are neglected in LIGO experiments by using Michelson interferometers so that fatal mistakes were caused. One is that the gravitational wave changes the wavelength of light. Another is that light’s speed is not a constant when gravitational waves exist. According to general relativity, gravitational wave affects spatial distance, so it also affects the wavelength of light synchronously. By considering this fact, the phase differences of lasers were invariable when gravitational waves passed through Michelson interferometers. In addition, when gravitational waves exist, the spatial part of metric changes but the time part of metric is unchanged. In this way, light’s speed is not a constant. When the calculation method of time difference is used in LIGO experiments, the phase shift of interference fringes is still zero. So the design principle of LIGO experiment is wrong. It was impossible for LIGO to detect gravitational wave by using Michelson interferometers. Because light’s speed is not a constant, the signals of LIGO experiments become mismatching. It means that these signals are noises actually, caused by occasional reasons, no gravitational waves are detected really. In fact, in the history of physics, Michelson and Morley tried to find the absolute motion of the earth by using Michelson interferometers but failed at last. The basic principle of LIGO experiment is the same as that of Michelson-Morley experiment in which the phases of lights were invariable. Only zero result can be obtained, so LIGO experiments are destined failed to find gravitational waves.

Systematic error suppression scheme of the weak equivalence principle test by dual atom interferometers in space based on spectral correlation

Systematic error suppression and test data processing are very important in improving the accuracy and sensitivity of the atom interferometer(AI)-based weak-equivalence-principle(WEP) test in space. Here we present a spectrum correlation method to investigate the test data of the AI-based WEP test in space by analyzing the characteristics of systematic errors and noises. The power spectrum of the Eotvos coefficient η, systematic errors, and noises in AI-based WEP test in space are analyzed and calculated in detail. By using the method, the WEP violation signal is modulated from direct current(DC) frequency band to alternating current(AC) frequency band. We find that the signal can be effectively extracted and the influence of systematic errors can be greatly suppressed by analyzing the power spectrum of the test data when the spacecraft is in an inertial pointing mode. Furthermore, the relation between the Eotvos coefficient η and the number of measurements is obtained under certain simulated parameters. This method will be useful for both isotopic and nonisotopic AI-based WEP tests in space.

Quantum transport through two series Aharonov-Bohm interferometers with zero total magnetic flux

With the help of nonequilibrium Green＇s function technique, the electronic transport through series Aharonov-Bohm （AB） interferometers is investigated. We obtain the AB interference pattern of the transition probability characterized by the Mgebraic sum φ and the difference θ of two magnetic fluxes, and particularly a general rule of AB oscillation period depending on the ratio of integer quantum numbers of the fluxes. A parity effect is observed, showing the asymmetric AB oscillations with respect to the even and odd quantum numbers of the total flux in antiparallel AB interferometers. It is also shown that the AB flux can shift the Fano resonance peaks of the transmission spectrum.

Common-mode noise rejection using fringe-locking method in WEP test by simultaneous dual-species atom interferometers

We theoretically investigate the application of the fringe-locking method（FLM） in the dual-species quantum test of the weak equivalence principle（WEP）.With the FLM,the measurement is performed invariably at the midfringe,and the extraction of the phase shift for atom interferometers is linearized.For the simultaneous interferometers,this linearization enables a good common-mode rejection of vibration noise,which is usually the main limit for high precision WEP tests of the dual-species kind.We note that this method also allows for an unbiased determination of the gravity accelerations difference,which meanwhile is ready to be implemented.

HYBRID OPTICAL BISTABILITY IN FABRY-PEROT INTERFEROMETER CONTAINING PLASMA

A hybrid optical bistable system of a plasma in a Fabry-Perot interferometer driven by a single-mode cw laser is proposed.The general expressions of the mirvimum change of the electron density for optical bistabili.ty and the changes of electron density at the"on"and"off"points of the optical bistabiIity are obtained theoretically,The necessary data for the design of the optical bistability in infrared to mm-Dave region are given.

A Terahertz Wavemeter Based on a Fabry-Perot Interferometer Composed of Two Identical Ge Etalons

A simple and convenient terahertz wavemeter based on a Fabry-Perot interferometer (FPI) is presented.The interferometer is composed of two identical Ge etalons,which act as high-reflectance mirrors for terahertz waves.The transmission characteristics of the Ge FPI are analyzed using multiple-beam interference theory.The theoretical finesse of the FPI,defined as a ratio of 2π to the phase halfwidth of the transmission fringes,is larger than 12.5.Here,the wavemeter is used to measure the wavelengths of an optically pumped NH3 terahertz laser.The experimental results indicate that the measuring uncertainties are within ±1%.Higher accuracy can be expected if the power or pulse energy of the terahertz source is more stable.

Tolerance-enhanced SU(1,1) interferometers using asymmetric gain

SU(1,1) interferometers play an important role in quantum metrology. Previous studies focus on various inputs and detection strategies with symmetric gain. In this paper, we analyze a modified SU(1,1) interferometer using asymmetric gain. Two vacuum states are used as the input and on–off detection is performed at the output. In a lossless scenario,symmetric gain is the optimal selection and the corresponding phase sensitivity can achieve the Heisenberg limit as well as the quantum Cramer–Rao bound. In addition, we analyze the phase sensitivity with symmetric gain in the lossy scenario.The phase sensitivity is sensitive to internal losses but extremely robust against external losses. We address the optimal asymmetric gain and the results suggest that this method can improve the tolerance to internal losses. Our work may contribute to the practical development of quantum metrology.

Experimental research on modulation degree of refractive index in the SCLP/E_7/C_(60) polymer using a fiber Fabry-Perot Interferometer

Modulation degree of refractive index is an important parameter for information storage in photorefractive materials. Using the relationship between the refractive index and the wavelengths of laser and the order of interference, we introduce a new method to measure the modulation degree of refractive index in photorefractive materials through detecting the shift of the interference fringe in a fiber Fabry-Perot interferometer with a CCD. The measurement precision is also analyzed. With this method, the modulation degree of refractive index in our prepared SCLP/E7/C 60 photorefractive polymer is measured for different external voltages and the external voltage corresponding to the maximal modulation degree of refractive index is reported. The dynamic change of refractive index in the SCLP/E7/C 60 is also studied, which will be helpful to understand the reaction mechanism of photochemistry in the material.

Real-time data processing method for CO_(2) dispersion interferometer on EAST

A real-time data processing system is designed for the carbon dioxide dispersion interferometer(CO_(2)-DI)on EAST.The system utilizes the parallel and pipelining capabilities of an fieldprogrammable gate array(FPGA)to digitize and process the intensity of signals from the detector.Finally,the real-time electron density signals are exported through a digital-to-analog converter(DAC)module in the form of analog signals.The system has been successfully applied in the CO_(2)-DI system to provide low-latency electron density input to the plasma control system on EAST.Experimental results of the latest campaign with long-pulse discharges on EAST(2022–2023)demonstrate that the system can respond effectively in the case of rapid density changes,proving its reliability and accuracy for future electron density calculation.