Sagnac Research Articles

The characteristic analysis of temperature sensor based on a fabricated microstructure fiber by digital image processing technique and finite element method

A temperature sensor based on a Sagnac interferometer by the actual microstructure fiber (MSF) selectively filled with ethanol has been designed in this paper. We obtained the vectorized cross-section of MSF using the method of the digital image processing technique and the finite element method. This method can model the actual cross section structure of MSF rapidly by gray scale processing, filtering, threshold, and edge detection and be applied to the calculation and simulation of the actual MSF perfectly. The air holes on both sides of the core were filled with ethanol to improve the birefringence of the MSF. The simulation result showed that the dip wavelength in transmission spectrum has a blue-shift when the temperature increasing. The average sensitivity can be up to 1 nm °C−1 as the temperature rises from 25 °C to 75 °C. It can be tested in a wide temperature range, which plays a profound role in practical application.

Highly sensitive photonic crystal fiber salinity sensor based on Sagnac interferometer

For a sensor, high sensitivity, structural simplicity, and longevity are highly desired for measurement of salinity in seawater. This work proposed an ultrahigh sensitive photonic crystal fiber (PCF) salinity sensor based on the sagnac interferometer (SI). The propagation characteristics of the proposed PCF are analyzed by the finite element method (FEM). The achieved sensitivity reaches up to 37,500 nm/RIU and 7.5 nm/% in the salinity range from 0% to 100%. The maximum resolutions of 2.66 × 10−06 RIU and 1.33 × 10−02% are achieved with high linearity of 0.9924 for 2.20 cm length of the proposed PCF. Owing to such excellent results, this proposed sensor offers the potential to measure the salinity of seawater.

Spin-rotation coupling observed in neutron interferometry

Einstein’s theory of general relativity and quantum theory form the two major pillars of modern physics. However, certain inertial properties of a particle’s intrinsic spin are inconspicuous while the inertial properties of mass are well known. Here, by performing a neutron interferometric experiment, we observe phase shifts arising as a consequence of the spin’s coupling with the angular velocity of a rotating magnetic field. This coupling is a purely quantum mechanical extension of the Sagnac effect. The resulting phase shifts linearly depend on the frequency of the rotation of the magnetic field. Our results agree with the predictions derived from the Pauli–Schrödinger equation.

Distributed vibration sensing with high frequency response by using WDM based integrated scheme

Distributed vibration sensing measurement with high frequency response is still a challenging task in distributed optical fiber vibration sensing systems. In this paper, a WDM based integrated scheme is proposed to directly demodulate the high frequency vibration signal with high spatial resolution by merging the phase sensitive optical time-domain reflectometry and the Sagnac interferometer. A maximum frequency response of ~2.5 MHz and a spatial resolution of 20 m have been achieved in a 4 km sensing fiber link. Comparison to conventional sensing structure, the proposed scheme shows great application potential in the field of distributed vibration sensing system.

Gravitational waves and the Sagnac effect**This paper is dedicated to the memory of my late father Werner Frauendiener.

Light propagating in opposite directions around the same loop in general shows a relative phase shift when recombined. This phenomenon is known as the Sagnac effect after Georges Sagnac who, in 1913, demonstrated with an interferometer on a rotating table that the phase shift depended on the angular velocity of the table. In previous work we have given a very general formula for the Sagnac effect, valid in full general relativity. The relativistic effect not only contains the ‘classical’ contribution from the rotation of the laboratory but also contributions due its acceleration and due to incoming gravitational waves. Here, we point out a major consequence of this gravitational effect which may have implications for third generation gravitational wave detectors. We describe ‘antenna’ designs which pick out specific components of the Weyl tensor describing the incident gravitational waves.

Aharonov—Bohm oscillations and distributions of equilibrium current in open quantum dot and ring interferometer

Magnetotransport in submicron devices formed on the basis of GaAs/AlGaAs structures is simulated by the method of nonequilibrium Green functions. In the one-particle approximation, the influence of a perpendicular magnetic field on electron transmission through a quasi-one-dimensional quantum dot and the Aharonov—Bohm interferometer is considered. Two-terminal conductance and magnetic moment of the devices are calculated. Two-dimensional patterns of equilibrium (persistent) currents are obtained. The correlations between energy dependences of magnetic moment and conductance are considered. For the quasi-one-dimensional quantum dot, regular conductance oscillations similar to the ABOs were found at low magnetic fields (0.05—0.4 T). In the case of a ring interferometer, the contribution to the total equilibrium current and magnetic moment at a given energy can change sharply both in magnitude and in sign when the magnetic field changes within the same Aharonov—Bohm oscillation. The conductance through the interferometer is determined not by the number of propagating modes, but rather by the influence of triangular quantum dots at the entrances to the ring, causing back scattering. Period of calculated ABOs corresponds to that measured for these devices.

Thermal Relaxation Spectra for Evaluating Luminescence Quantum Efficiency of CASN:Eu2+ Measured by Balanced-Detection Sagnac-Interferometer Photothermal Deflection Spectroscopy

Highly sensitive broadband photothermal spectroscopy with a white-light lamp as the excitation source was developed by combining a Sagnac interferometer and balanced detection with a photothermal deflection method. A probe beam was split by a birefringent crystal CaCO3 into signal and reference beams with a balanced intensity. This balanced detection enabled the measurement of photoexcited thermal relaxation spectra of materials in the air over the whole visible range in the weak excitation limit 50 µW/cm2. The photothermal excitation spectrum of Eu2+-doped CaAlSiN3 phosphors (CASN:Eu2+) with a high luminescent quantum efficiency was measured to be distinctly different from the photoluminescence excitation spectrum which reflects the absorption spectrum, revealing the thermal relaxation mechanism of the phosphor. Assuming a typical non-radiative relaxation from the higher excited states to the lowest excited state and successively to the ground state, it is demonstrated that the photoluminescence efficiency of the phosphors is readily evaluated simply by comparing the photothermal and photoluminescence excitation spectra.

Widely-tunable mid-infrared ring cavity pump-enhanced OPO and application in photo-thermal interferometric trace ethane detection.

The development of a broadly and accurately tunable single-frequency mid-infrared laser source and its application to a sensitive laser absorption detection method are described. Photo-thermal interferometric spectroscopy is employed as a phase-sensitive method to detect the minute refractive index change caused by the heating of a gas under laser radiation. A separate probe beam allows for the spectrally-interesting mid-infrared region to be examined whilst utilizing low cost, high detectivity photodetectors in the visible/near-infrared region. We also describe the implementation of a Sagnac interferometer to minimize the effects of environmental perturbation and provide inherent passive stability. A continuous-wave ring-cavity pump-enhanced OPO has been developed to provide excitation light from 3-4 µm at 140 mW with the ability to mode-hop tune continuously over 90 cm-1 in 0.07 cm-1 steps. Complementary use of both detection apparatus and excitation source has allowed for presence of ethane to be detected down to 200 parts per billion.

A Sensing Interrogation System for Sagnac Interferometer With Polarization Maintaining Fiber Utilizing Microwave Photonic Filtering Technique

In this paper, a sensing interrogation scheme for Sagnac interferometer (SI) with polarization maintaining fiber (PMF) by using microwave photonic filtering technique has been theoretically analyzed and experimentally demonstrated. In our experiment, the SI acts as the sensing element as well as a spectrum slicer in the single-passband microwave photonic filter (MPF). The central frequency of the MPF’s passband moves to lower frequency when the temperature is increased. Hence, the measurands can be demodulated by monitoring the central frequency of the MPF’s passband in Radio Frequency (RF) domain. Comparing with the interrogation by tracking dip wavelength of the interference patterns in the optical domain and using the product of birefringence and the length of PMF in the SI structure for interrogation, the proposed interrogation system converts the wavelength variations of the interferometer patterns in optical domain to the frequency changes in electronic domain directly by utilizing opto-electronic devices, and thus has an unlimited measurement range, less limitations by resolution limitation of measuring instruments and less cross-sensitivity problems.

Geometric phase shift sensitivity in an area chirped array of atom interferometers

Measuring geometric phase shifts has various applications in both quantum and classical interferometry such as measuring acceleration, distances, rotation and magnetic flux. Theoretical analysis of coupled ring arrays has been shown to be a promising design for creating small inertial rotation sensors on atom chips. In this paper we build on the theoretical models of transmission of matter waves through an area chirped array of ring interferometers to determine phase regions of the transmission that exhibit high sensitivity to geometric phase shifts,these regions are indicated by sharp transmission resonances. We calculate the slopes of transmission resonances for a range of values for two parameters, the chirp factor γ and the product of the wave number and ring circumference kL, we look at the behavior of the slopes of these transmission resonances for defined ranges of kL and γ to see in search of transmission resonances with extreme slopes. We find transmission resonances with sensitivities to geometric phase shifts that exceed those found in previous models of area chirped arrays by several orders of magnitude. The area chirp is applied such that the geometric phase shifts (θGP) in each ring of the array can be expressed in terms of the geometric phase shift in the reference ring of the array, this enables the transmission function T(θGP) to be calculated in terms of the phase shift of a single ring. We investigate T(θGP) for various ring sizes, wave numbers, and chirp factor and look for values of these parameters that lead to sharp transmission resonances in T(θGP). We calculate the sensitivities of rotation via the Sagnac effect and magnetic flux via Aharonov Bohm effect based on the sensitivity of the transmission resonances found in our transmission functions.

Comment on “On the general relativistic framework of the Sagnac effect” EPJC 79:187

In a recent paper EPJC 79:187 the general relativistic framework of the Sagnac effect was investigated. We have some comments on this paper. We show that their conclusion about the apparent variation of the speed of light does not hold in stationary spacetimes. Also, We show that their definition of gravitational Coriolis potential and gravitational Coriolis time dilation are inconsistent with what is stated in standard references.

Super-resolved angular displacement estimation based upon a Sagnac interferometer and parity measurement.

Super-resolved angular displacement estimation is of crucial significance to the field of quantum information processing. Here we report an estimation protocol based on a Sagnac interferometer fed by a coherent state carrying orbital angular momentum. In a lossless scenario, through the use of parity measurement, our protocol can achieve a 4ℓ-fold super-resolved output with quantum number ℓ; meanwhile, a shot-noise-limited sensitivity saturating the quantum Cramér-Rao bound is reachable. We also consider the effects of several realistic factors, including nonideal state preparation, photon loss, and inefficient measurement. Finally, with mean photon number N¯=2.297 and ℓ = 1 taken, we experimentally demonstrate a super-resolved effect of angular displacement with a factor of 7.88.

Controlling the dynamical scale factor in a trapped atom Sagnac interferometer

Sagnac interferometers with massive particles promise unique advantages in achieving high precision measurements of rotation rates over their optical counterparts. Recent proposals and experiments are exploring non-ballistic Sagnac interferometers where trapped atoms are transported along a closed path. This is achieved by using superpositions of internal quantum states and their control with state-dependent potentials. We address emergent questions regarding the dynamical behavior of Bose-Einstein condensates in such an interferometer and its impact on rotation sensitivity. We investigate complex dependencies on atomic interactions as well as trap geometries, rotation rates, and speed of operation. We find that temporal transport profiles obtained from a simple optimization strategy for non-interacting particles remain surprisingly robust also in the presence of interactions over a large range of realistic parameters. High sensitivities can be achieved for short interrogation times far from the adiabatic regime. This highlights a route to building fast and robust guided ring Sagnac interferometers with fully trapped atoms.

Strain and temperature discrimination based on a Sagnac interferometer with three sections of high birefringence fibers

We present an all-fiber sensor for strain and temperature discrimination by inserting three sections of high birefringence fibers into a Sagnac loop. The principle for strain and temperature discrimination is based on monitoring the wavelength shifts of two different resonant dips that show different sensitivities to temperature and strain. The sensitivities for strain and temperature are measured to be − 0.93 n m / ∘ C and 21 pm/µɛ with discriminative errors of ± 0.3 ∘ C and ± 12 µ ε . The proposed sensor with high sensitivity, simple configuration, and low cost may be a promising candidate for various strain and temperature-sensing applications.

Measuring weak magnetic field via dissipatively coupled opto-mechanical system

In this paper, we propose a scheme for the detection of weak magnetic field based on dissipatively coupled optomechanical system. The system considered here is composed of a perfect mirror and a compound mirror formed by a Michelson–Sagnac interferometer (MSI) with a movable membrane. When the transmissivity of MSI is close to zero, it sensitively depends upon the position of membrane. Under this condition, the two mirrors results in an effective Fabry–Perot interferometer (FPI) whose linewidth depends upon the position of the membrane. We show that by applying current to the membrane in the presence of magnetic field, the position of the membrane changes which in turn changes the linewidth of the effective FPI. This change can be observed in the spectrum of the output field and consequently enables us to measure weak magnetic field. Thus an optical detection technique is proposed for the detection of weak magnetic field.

Coherence-based measurement of non-Markovian dynamics in an open quantum system

We present a theoretical scheme and its experimental proof of principle for an open quantum system undergoing Markovian and non-Markovian evolutions. We exhibit these two regimes by diagnosing them with the relative entropy of coherence of two polarization qubits playing the roles of system and ancilla. These are initially prepared in a polarization maximally entangled state of a photon pair produced by spontaneous parametric down-conversion. We induce Markovian and non-Markovian regimes in the system's dynamics with the help of two auxiliary qubits, experimentally implemented by optical paths in a layout of Sagnac and Mach-Zehnder interferometers. We replicate system-environment interactions by means of an amplitude damping channel and a suitably designed inversion of it. In our scheme, one needs only two experimentally accessible parameters to achieve Markovian and non-Markovian regimes.

Q-switched laser with self-mode-filtering interferometric vortex output coupler

Vortex lasers are an attractive prospect for efficient generation of high-quality beams in compact, environmentally robust, and turnkey systems. We demonstrate conversion of a Q-switched, diode-pumped Nd:YVO4, TEM00 Gaussian laser into a vortex laser source by replacing the output coupling mirror by a vortex output coupler (VOC) based on an imbalanced Sagnac interferometer. The Q-switched VOC laser generated a vortex output with 5.1 W average power, slope efficiency of 46% at 150 kHz pulse repetition rate, only marginally lower than the 5.4W and 49% slope efficiency of the plane mirror laser. Vortex handedness was switchable with a single VOC control without loss of vortex power. In both handedness cases, the vortex mode quality was assessed to be excellent by detailed analysis of the vortex phase profile and propagation characteristics and comparison to an ideal vortex. Further investigation verified the ability for the VOC laser to self-mode-filter the intracavity mode, showing maintenance of high TEM00 quality even after introducing deliberate mode to pump size mismatch, when the equivalent plane mirror laser becomes multimode. This work highlights the potential of the VOC as a simple route to high powered structured light sources using just standard high-power handling mirror components and its self-mode-filtering property to compensate intra-cavity spatial mode degradation when power-scaling.

Classical tests on a charged Weyl black hole: bending of light, Shapiro delay and Sagnac effect

In this paper, we apply the classical test of general relativity on a charged Weyl black hole, the exterior geometry of which is defined by altering the spherically symmetric solutions of the Weyl conformal theory of gravity. The tests are basically founded on scrutinizing the angular geodesics of light rays propagating in the gravitating system caused by the black hole. In this investigation, we bring detailed discussions about the bending of light, together with two other relativistic effects, known as the Shapiro and the Sagnac effects. We show that the results are in good conformity with the general relativistic effects, in addition to giving long-distance corrections caused by the cosmological nature of the background geometry under study.

Real-time observation of the optical Sagnac effect in ultrafast bidirectional fibre lasers

Active ring laser gyroscopes (RLG) operating on the principle of the optical Sagnac effect are preferred instruments for a range of applications, such as inertial guidance systems, seismology, and geodesy, that require both high bias stability and high angular velocity resolutions. Operating at such accuracy levels demands special precautions like dithering or multi-mode operation to eliminate frequency lock-in or similar effects introduced due to synchronisation of counter-propagating channels. Recently proposed bidirectional ultrafast fibre lasers can circumvent the limitations of continuous wave RLGs. However, their performance is limited due to the nature of the highly-averaged interrogation of the Sagnac effect. In general, the performance of current optical gyroscopes relies on the available measurement methods used for extracting the signal. Here, by changing the paradigm of traditional measurement and applying spatio-temporal intensity processing, we demonstrate that the bidirectional ultrafast laser can be transformed to an ultrafast gyroscope with acquisition rates of the order of the laser repetition rate, making them at least two orders of magnitude faster than commercially deployed versions. We also show the proof-of-principle for dead-band-free round trip time-resolved spectral domain measurements using the Dispersive Fourier Transform, further enhancing the gyroscopic sensitivity. Our results reveal the high potential of application of novel methods of signal measurements in mid-sized ultrafast fibre laser gyroscopes to achieve performances that are currently available only with large-scale RLGs.

Геометрическая оптика во вращающемся диэлектрике

Rotating solid-state homogeneous isotropic dielectric without dispersion in the accompanying rotation of the reference frame turns out to be an inhomogeneous anisotropic medium due to the influence of two competing physical mechanisms: the inhomogeneity of free space caused by rotation and entrainment of light by the moving medium. In a rotating dielectric in the geometric optics approximation the eikonal equation and the corresponding system of ordinary differential equations in characteristic form are obtained. The solutions of the equations with the calculated parameters determined using of the first integrals of the system are pairs "opposite “R-ray trajectories and f - phase trajectories fronts. A formula for the intensity of a light pulse propagating along an arbitrary R-trajectories was obtained. "Oncoming “trajectories of both types do not have common points and are shifted to opposite sides of a straight line between end points. Their structural parameters (minimum distance to the axis of rotation, the length of the arc, the region of determination by the azimuthal coordinate, the optical length, etc.) change under the influence of both physical mechanisms, depending on the speed of rotation. Closed optical paths in the RRF for the relay network and for the two-mirror Fabry-Perot resonator in generating laser can be created using two types of mirrors that are adaptable to the frequency of rotation which normals to the reflecting surfaces must have certain different angles with the ray vectors and wavefronts of radiation arriving at the reflector. The Sagnac effect is a consequence inhomogeneity (deformation) of free space along the azimuthal coordinate, and its value is the result of the competing influence of both physical mechanisms.