Showing papers on "Astronomical interferometer published in 2021"

Ultrasensitive temperature sensor with Vernier-effect improved fiber Michelson interferometer

Abstract: A novel fiber Michelson interferometer (FMI) based on parallel dual polarization maintaining fiber Sagnac interferometers (PMF-SIs) is proposed and experimentally demonstrated for temperature sensing. The free spectral range (FSR) difference of dual PMF-SIs determines the FSR of envelope and sensitivity of the sensor. The temperature sensitivity of parallel dual PMF-SIs is greatly enhanced by the Vernier effect. Experimental results show that the temperature sensitivity of the proposed sensor is improved from -1.646 nm/°C (single PMF-SI) to 78.984 nm/°C (parallel dual PMF-SIs), with a magnification factor of 47.99, and the temperature resolution is improved from ±0.03037°C to ±0.00063°C by optimizing the FSR difference between the two PMF-SIs. Our proposed ultrasensitive temperature sensor is with easy fabrication, low cost and simple configuration which can be implemented for various real applications that need high precision temperature measurement.

A tunable Fabry-Pérot quantum Hall interferometer in graphene

Abstract: Electron interferometry with quantum Hall (QH) edge channels in semiconductor heterostructures can probe and harness the exchange statistics of anyonic excitations. However, the charging effects present in semiconductors often obscure the Aharonov–Bohm interference in QH interferometers and make advanced charge-screening strategies necessary. Here we show that high-mobility monolayer graphene constitutes an alternative material system, not affected by charging effects, for performing Fabry–Perot QH interferometry in the integer QH regime. In devices equipped with gate-tunable quantum point contacts acting on the edge channels of the zeroth Landau level, we observe—in agreement with theory—high-visibility Aharonov–Bohm interference widely tunable through electrostatic gating or magnetic fields. A coherence length of 10 μm at a temperature of 0.02 K allows us to further achieve coherently coupled double Fabry–Perot interferometry. In future, QH interferometry with graphene devices may enable investigations of anyonic excitations in fractional QH states. Similar to optical waves, electrons can also interfere, but they require high-quality devices with minimal scattering for an experimental observation of this effect. An interferometer based on a single sheet of graphene provides an alternative to the more standard semiconductor devices and may in future enable access to exotic quantum effects, such as anyon braiding.

Slow light bimodal interferometry in one-dimensional photonic crystal waveguides

Abstract: Strongly influenced by the advances in the semiconductor industry, the miniaturization and integration of optical circuits into smaller devices has stimulated considerable research efforts in recent decades. Among other structures, integrated interferometers play a prominent role in the development of photonic devices for on-chip applications ranging from optical communication networks to point-of-care analysis instruments. However, it has been a long-standing challenge to design extremely short interferometer schemes, as long interaction lengths are typically required for a complete modulation transition. Several approaches, including novel materials or sophisticated configurations, have been proposed to overcome some of these size limitations but at the expense of increasing fabrication complexity and cost. Here, we demonstrate for the first time slow light bimodal interferometric behaviour in an integrated single-channel one-dimensional photonic crystal. The proposed structure supports two electromagnetic modes of the same polarization that exhibit a large group velocity difference. Specifically, an over 20-fold reduction in the higher-order-mode group velocity is experimentally shown on a straightforward all-dielectric bimodal structure, leading to a remarkable optical path reduction compared to other conventional interferometers. Moreover, we experimentally demonstrate the significant performance improvement provided by the proposed bimodal photonic crystal interferometer in the creation of an ultra-compact optical modulator and a highly sensitive photonic sensor.

Sensitivity-enhanced microwave-photonic optical fiber interferometry based on the Vernier effect.

Abstract: This paper proposes optical carrier microwave interferometry (OCMI)-based optical fiber interferometers for sensing applications with improved measurement sensitivity with the assistance of the Vernier effect. Fabry-Perot interferometers (FPIs) are employed in the proof of concept. A single-FPI-OCMI system is first demonstrated for measurements of variations of temperatures by tracking the spectral shift of the interferogram in microwave domain. By cascading two FPIs with slightly different optical lengths, the Vernier effect is generated in the magnitude spectrum of the system with a typical amplitude-modulated signal. By tracking the shift of the envelope signal, temperature measurements are experimentally demonstrated with greatly enhanced sensitivity. The amplification factor for the measurement sensitivity can be easily adjusted by varying the length ratio of the two cascaded FPIs. In addition to the experimental demonstration, a complete mathematical model of the FPI-OCMI system and the mechanism for the amplified sensitivity due to Vernier effect is presented. Numerical calculations are also performed to verify the analytical derivations.

Quantum Hall Valley Splitters and a Tunable Mach-Zehnder Interferometer in Graphene.

Abstract: Graphene is a very promising test bed for the field of electron quantum optics. However, a fully tunable and coherent electronic beam splitter is still missing. We report the demonstration of electronic beam splitters in graphene that couple quantum Hall edge channels having opposite valley polarizations. The electronic transmission of our beam splitters can be tuned from zero to near unity. By independently setting the beam splitters at the two corners of a graphene p-n junction to intermediate transmissions, we realize a fully tunable electronic Mach-Zehnder interferometer. This tunability allows us to unambiguously identify the quantum interferences due to the Mach-Zehnder interferometer, and to study their dependence with the beam-splitter transmission and the interferometer bias voltage. The comparison with conventional semiconductor interferometers points toward universal processes driving the quantum decoherence in those two different 2D systems, with graphene being much more robust to their effect.

Point absorbers in Advanced LIGO

Abstract: Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.

Twin-lattice atom interferometry

Abstract: Inertial sensors based on cold atoms have great potential for navigation, geodesy, or fundamental physics. Similar to the Sagnac effect, their sensitivity increases with the space-time area enclosed by the interferometer. Here, we introduce twin-lattice atom interferometry exploiting Bose-Einstein condensates of rubidium-87. Our method provides symmetric momentum transfer and large areas offering a perspective for future palm-sized sensor heads with sensitivities on par with present meter-scale Sagnac devices. Our theoretical model of the impact of beam splitters on the spatial coherence is highly instrumental for designing future sensors. Atom interferometers can be useful for precision measurement of fundamental constants and sensors of different type. Here the authors demonstrate a compact twin-lattice atom interferometry exploiting Bose-Einstein condensates (BECs) of 87 Rb atoms.

Spectrally multimode integrated SU(1,1) interferometer

Abstract: Nonlinear SU(1,1) interferometers are fruitful and promising tools for spectral engineering and precise measurements with phase sensitivity below the classical bound. Such interferometers have been successfully realized in bulk and fiber-based configurations. However, rapidly developing integrated technologies provide higher efficiencies, smaller footprints, and pave the way to quantum enhanced on-chip interferometry. In this work, we theoretically demonstrate an integrated architecture of the multimode SU(1,1) interferometer. The presented interferometer includes a polarization converter between two photon sources and utilizes a continuous-wave (CW) pump. We show that this configuration results in almost perfect destructive interference at the output and supersensitivity regions below the classical limit. In addition, we discuss the fundamental difference between single-mode and highly multimode SU(1,1) interferometers in the properties of phase sensitivity and its limits. Finally, we explore how to improve the phase sensitivity by filtering the output radiation and using different seeding states in different modes with various detection strategies.

Point absorbers in Advanced LIGO

Abstract: Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nano-meter scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduces the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power build-up in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and hence, limit GW sensitivity, but suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.

Microwave-photonic optical fiber interferometers for refractive index sensing with high sensitivity and a tunable dynamic range.

Abstract: We propose and demonstrate an extremely simple yet novel sensing strategy for measurements of a refractive index (RI) based on microwave-photonic optical fiber interferometry. A hybrid interferometric system based on an incoherent optical interferometer (i.e., a Michelson interferometer [MI]) and a coherent optical interferometer (i.e., a Fabry–Perot interferometer [FPI]) is constructed simply by using a low-cost off-the-shelf fiber coupler. The sensing arm of the MI is highly sensitive to a surrounding RI based on Fresnel reflection, where variations of the ambient RI cause changes in both the reflection magnitudes of the resonance frequencies and fringe visibility of the reflection spectra in the microwave domain. The coherent FPI is employed to tune the dynamic range of the MI by adjusting the effective reflectance of the reference arm of the MI. Essentially, other approaches that can vary the reflectance of the reference arm of the MI can also be used to tune the dynamic range of the system based on the proposed strategy. The experimental results are in good agreement with theoretical predictions. The prominent advantages of the sensor, including low cost, ease of fabrication, robustness, compactness, high sensitivity, and tunable dynamic range, make it a strong candidate in various chemical, biological, and environmental applications.

Statistical inference approach to time-delay interferometry for gravitational-wave detection

Abstract: The future space-based gravitational wave observatory laser interferometer space antenna (LISA) will consist of a constellation of three spacecraft in a triangular constellation, connected by laser interferometers with 2.5 million-kilometer arms. Among other challenges, the success of the mission strongly depends on the quality of the cancellation of laser frequency noise, whose power lies 8 orders of magnitude above the gravitational signal. The standard technique to perform noise removal is time-delay interferometry (TDI). TDI constructs linear combinations of delayed phasemeter measurements tailored to cancel laser noise terms. Previous work has demonstrated the relationship between TDI and principal component analysis (PCA). We build on this idea to develop an extension of TDI based on a model likelihood that directly depends on the phasemeter measurements. Assuming stationary Gaussian noise, we decompose the measurement covariance using PCA in the frequency domain. We obtain a comprehensive and compact framework that we call PCI for ``principal component interferometry'' and show that it provides an optimal description of the LISA data analysis problem.

Phase sensitivity approaching the quantum Cramér-Rao bound in a modified SU(1,1) interferometer

Abstract: SU(1,1) interferometers, based on the usage of nonlinear elements, are superior to passive interferometers in phase sensitivity. However, the SU(1,1) interferometer cannot make full use of photons carrying phase information as the second nonlinear element annihilates some of the photons inside. Here we focus on improving phase sensitivity and propose a different protocol based on a modified SU(1,1) interferometer, where the second nonlinear element is replaced by a beam splitter. We utilize two coherent states as inputs and implement balanced homodyne measurement at the output. Our analysis suggests that the protocol we propose can achieve the sub-shot-noise-limited phase sensitivity and is robust against photon loss as well as background noise. Our work is important for practical quantum metrology using SU(1,1) interferometers.

Investigation and Mitigation of Noise Contributions in a Compact Heterodyne Interferometer.

Abstract: We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A noise floor of 3.31×10−11m/Hz at 100 mHz is achieved after applying our noise subtraction algorithm to a benchtop prototype interferometer that showed a noise level of 2.76×10−10m/Hz at 100 mHz when tested in vacuum at levels of 3×10−5 Torr. Based on the previous results, we investigated noise estimation and subtraction techniques of non-linear optical pathlength noise, laser frequency noise, and temperature fluctuations in heterodyne laser interferometers. For each noise source, we identified its contribution and removed it from the measurement by linear fitting or a spectral analysis algorithm. The noise correction algorithm we present in this article can be generally applied to heterodyne laser interferometers.

Accurate Self-Configuration of Rectangular Multiport Interferometers.

Abstract: Multiport interferometers based on integrated beamsplitter meshes are widely used in photonic technologies. While the rectangular mesh is favored for its compactness and uniformity, its geometry resists conventional self-configuration approaches, which are essential to programming large meshes in the presence of fabrication error. Here, we present a new configuration algorithm, related to the $2\times 2$ block decomposition of a unitary matrix, that overcomes this limitation. Our proposed algorithm is robust to errors, requires no prior knowledge of the process variations, and relies only on external sources and detectors. We show that self-configuration using this technique reduces the effect of fabrication errors by the same quadratic factor observed in triangular meshes. This relaxes a significant limit to the size of multiport interferometers, removing a major roadblock to the scaling of optical quantum and machine-learning hardware.

Multi-loop atomic Sagnac interferometry

Abstract: The sensitivity of light and matter-wave interferometers to rotations is based on the Sagnac effect and increases with the area enclosed by the interferometer. In the case of light, the latter can be enlarged by forming multiple fibre loops, whereas the equivalent for matter-wave interferometers remains an experimental challenge. We present a concept for a multi-loop atom interferometer with a scalable area formed by light pulses. Our method will offer sensitivities as high as $2\cdot10^{-11}$ rad/s at 1 s in combination with the respective long-term stability as required for Earth rotation monitoring.

Design, alignment, and calibration of a focused laser differential interferometer.

Abstract: Methods are presented for systematic selection of optical components and dimensions for the design of both single- and double-focused laser differential interferometers (FLDIs). Step-by-step instructions for the assembly and alignment of each FLDI component are given, including detailed figures of the interferometer fringe behavior, as the required infinite-fringe configuration is approached. Calibration and data post-processing techniques are provided in order to obtain quantitative signals from the FLDI.

Giant Displacement Sensitivity Using Push-Pull Method in Interferometry

Abstract: We present a giant sensitivity displacement sensor combining the push-pull method and enhanced Vernier effect. The displacement sensor consists in two interferometers that are composed by two cleaved standard optical fibers coupled by a 3 dB coupler and combined with a double-sided mirror. The push pull-method is applied to the mirror creating a symmetrical change to the length of each interferometer. Furthermore, we demonstrate that the Vernier effect has a maximum sensitivity of two-fold that obtained with a single interferometer. The combination of the push-pull method and the Vernier effect in the displacement sensors allows a sensitivity of 60 ± 1 nm/μm when compared with a single interferometer working in the same free spectral range. In addition, exploring the maximum performance of the displacement sensors, a sensitivity of 254 ± 6 nm/μm is achieved, presenting a M-factor of 1071 and MVernier of 1.9 corresponding to a resolution of 79 pm. This new solution allows the implementation of giant-sensitive displacement measurement for a wide range of applications.

Super-resolution imaging by optical incoherent synthetic aperture with one channel at a time

Abstract: Imaging with an optical incoherent synthetic aperture (SA) means that the incoherent light from observed objects is processed over time from various points of view to obtain a resolution equivalent to single-shot imaging by the SA larger than the actual physical aperture The operation of such systems has always been based on two-wave interference where the beams propagate through two separate channels This limitation of two channels at a time is removed in the present study with the proposed SA where the two beams pass through the same single channel at any given time The system is based on a newly developed self-interference technique named coded aperture correlation holography At any given time, the recorded intensity is obtained from interference between two waves co-propagating through the same physical channel One wave oriented in a particular polarization is modulated by a pseudorandom coded phase mask and the other one oriented orthogonally passes through an open subaperture Both subapertures are multiplexed at the same physical window The system is calibrated by a point spread hologram synthesized from the responses of a guide star All the measurements are digitally processed to achieve a final image with a resolution higher than that obtained by the limited physical aperture This unique configuration can offer alternatives for the current cumbersome systems composed of far apart optical channels in the large optical astronomical interferometers Furthermore, the proposed concept paves the way to an SA system with a single less-expensive compact light collector in an incoherent optical regime that may be utilized for future ground-based or space telescopes

Colossal Enhancement of Strain Sensitivity Using the Push-Pull Deformation Method

Abstract: In this work, a colossal enhancement of strain sensitivities through the push-pull deformation method in interferometry is reported for the first time. For the demonstration of the new method, two cascaded interferometers in a fiber loop mirror are used. Usually, strain is applied at the fiber end of the interferometers. In this work, we propose applying strain at the middle of the two cascaded interferometers whereas the fiber ends of the sensor are fixed. Strain is then applied in the fusion region between the two-cascaded interferometers in a push-pull configuration, thus ensuring simultaneously the extension of one interferometer and the compression of the other. Although the carrier signal is maintained constant, the proposed technique induces a colossal enhancement of sensitivity in the envelope signal. Strain sensitivities up to 10000 pm/ $\mu \varepsilon $ are achieved.

Stability of Self-Configuring Large Multiport Interferometers.

Abstract: Realistic multiport interferometers (beamsplitter meshes) are sensitive to component imperfections, and this sensitivity increases with size. Self-configuration techniques can be employed to correct these imperfections, but not all techniques are equal. This paper highlights the importance of algorithmic stability in self-configuration. Naive approaches based on sequentially setting matrix elements are unstable and perform poorly for large meshes, while techniques based on power ratios perform well in all cases, even in the presence of large errors. Based on this insight, we propose a self-configuration scheme for triangular meshes that requires only external detectors and works without prior knowledge of the component imperfections. This scheme extends to the rectangular mesh by adding a single array of detectors along the diagonal.

Silicon photonic on-chip spatial heterodyne Fourier transform spectrometer exploiting the Jacquinot’s advantage

Abstract: Silicon photonics on-chip spectrometers are finding important applications in medical diagnostics, pollution monitoring, and astrophysics. Spatial heterodyne Fourier transform spectrometers (SHFTSs) provide a particularly interesting architecture with a powerful passive error correction capability and high spectral resolution. Despite having an intrinsically large optical throughput (etendue, also referred to as Jacquinot’s advantage), state-of-the-art silicon SHFTSs have not exploited this advantage yet. Here, we propose and experimentally demonstrate for the first time, to the best of our knowledge, an SHFTS implementing a wide-area light collection system simultaneously feeding an array of 16 interferometers, with an input aperture as large as 90µm×60µm formed by a two-way-fed grating coupler. We experimentally demonstrate 85 pm spectral resolution, 600 pm bandwidth, and 13 dB etendue increase, compared with a device with a conventional grating coupler input. The SHFTS was fabricated using 193 nm deep-UV optical lithography and integrates a large-size input aperture with an interferometer array and monolithic Ge photodetectors, in a 4.5mm2 footprint.

Physically significant phase shifts in matter-wave interferometry

Abstract: Many different formalisms exist for computing the phase of a matter-wave interferometer. However, it can be challenging to develop physical intuition about what a particular interferometer is actually measuring or about whether a given classical measurement provides equivalent information. Here, we investigate the physical content of the interferometer phase through a series of thought experiments. In low-order potentials, a matter-wave interferometer with a single internal state provides the same information as a sum of position measurements of a classical test object. In high-order potentials, the interferometer phase becomes decoupled from the motion of the interferometer arms, and the phase contains information that cannot be obtained by any set of position measurements on the interferometer trajectory. This phase shift in a high-order potential fundamentally distinguishes matter-wave interferometers from classical measuring devices.

Quantum optical coherence: From linear to nonlinear interferometers

Abstract: Interferometers provide a highly sensitive means to investigate and exploit the coherence properties of light in metrology applications. However, interferometers come in various forms and exploit different properties of the optical states within. In this paper, we introduce a classification scheme that characterizes any interferometer based on the number of involved nonlinear elements by studying their influence on single-photon and photon-pair states. Several examples of specific interferometers from these more general classes are discussed, and the theory describing the expected first-order and second-order coherence measurements for single-photon and single-photon-pair input states is summarized and compared. These theoretical predictions are then tested in an innovative experimental setup that is easily able to switch between implementing an interferometer consisting of only one or two nonlinear elements. The resulting singles and coincidence rates are measured in both configurations and the results are seen to fit well with the presented theory. The measured results of coherence are tied back to the presented classification scheme, revealing that our experimental design can be useful in gaining insight into the properties of the various interferometeric setups containing different degrees of nonlinearity.

Faraday Michelson Interferometers for Signal Demodulation of Fiber-Optic Sensors

Abstract: We developed an all-fiber-based optical demodulator for the signal interrogation of low-coherence fiber-optic Fabry–Perot interferometric sensors. The optical demodulator consists of a Michelson interferometer implemented by using a 3 × 3 fiber coupler and two fiber-coupled Faraday reflectors with tunable fiber delay lines. The demodulator's output contains two optical interference signals with a constant phase shift and the output shows no sensitivity to the polarization variation in the light source or fibers. A digital phase recovery algorithm is used to extract the measurand information from the phase-shifted signals at high accuracy, high dynamic range, and high stability. The optical demodulator has been applied to the measurement of high-frequency vibrations and strains using fiber-optic sensors.

Negative curvature hollow core fiber sensor for the measurement of strain and temperature

Abstract: Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.

A Heterodyne Interferometer with Separated Beam Paths for High-Precision Displacement and Angular Measurements

Abstract: As standard concepts for precision positioning within a machine reach their limits with increasing measurement volumes, inverse concepts are a promising approach for addressing this problem. The inverse principle entails other limitations, as for high-precision positioning of a sensor head within a large measurement volume, three four-beam interferometers are required in order to measure all necessary translations and rotations of the sensor head and reconstruct the topography of the reference system consisting of fixed mirrors in the x-, y-, and z-directions. We present the principle of a passive heterodyne laser interferometer with consequently separated beam paths for the individual heterodyne frequencies. The beam path design is illustrated and described, as well as the design of the signal-processing and evaluation algorithm, which is implemented using a System-On-a-Chip with an integrated FPGA, CPU, and A/D converters. A streamlined bench-top optical assembly was set up and measurements were carried out to investigate the remaining non-linearities. Additionally, reference measurements with a commercial homodyne interferometer were executed.

Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit

Abstract: Interferometers are essential elements in classical and quantum optical systems. The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance. Here, we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors. Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference. Average interference visibility over 12 h is above 99%, and the variations are less than 0.5%, even with active random polarization disturbance. The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.

Architecture agnostic algorithm for reconfigurable optical interferometer programming.

Abstract: We develop the learning algorithm to build an architecture agnostic model of a reconfigurable optical interferometer. A procedure of programming a unitary transformation of optical modes of an interferometer either follows an analytical expression yielding a unitary matrix given a set of phase shifts or requires an optimization routine if an analytic decomposition does not exist. Our algorithm adopts a supervised learning strategy which matches a model of an interferometer to a training set populated by samples produced by a device under study. A simple optimization routine uses the trained model to output phase shifts corresponding to a desired unitary transformation of the interferometer with a given architecture. Our result provides the recipe for efficient tuning of interferometers even without rigorous analytical description which opens opportunity to explore new architectures of the interferometric circuits.