Design Of Interferometer Research Articles

One-grating common-path phase-shifting interferometer for quantitative phase imaging

A one-grating common-path phase-shifting interferometer for quantitative phase imaging is proposed as an improvement over the original interferometer design. In the original version, the setup is long, involving a grating pair, and requires precise mechanical translation of the grating, which poses difficulties for practical applications. The proposed interferometer utilizes grating multiplexing to reduce the length of the optical setup and uses a phase-only spatial light modulator to implement pinhole filtering and phase shifting simultaneously without any moving parts, making it more conducive for the realization of a practical version.

High-resolution optical fiber underwater acoustic sensor enhanced by PDMS coating

This study introduces a high-resolution optical fiber underwater acoustic sensor utilizing a Fabry-Perot (FP) interferometer design. The sensor consists of a single-mode fiber (SMF) integrated with polydimethylsiloxane (PDMS), forming an FP cavity at the coated SMF terminus. The exceptional elasticity of PDMS amplifies vibrations from acoustic stimuli, modulating the FP cavity for effective acoustic wave detection. This integration of the probe within a single fiber, along with the PDMS coating technique, enhances the sensor’s SNR, resolution, and frequency response. The sensor’s simplicity, cost-effectiveness, superior signal-to-noise ratio, and low power consumption make it a promising tool for underwater acoustic applications.

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Designing precision measurement of the gravitational Aharonov-Bohm effect in microgravity

The gravitational Aharonov-Bohm (GAB) effect serves as the gravitational counterpart to the electromagnetic Aharonov-Bohm effect. Despite the concept’s inception in 1967, a rigorous experimental test of the GAB effect remains elusive. While recent endeavors with ground-based apparatus show promise in uncovering hints of the GAB effect, we propose a precise yet practical experiment to deterministically measure the GAB phase shift using cold atom interferometry in a microgravity environment, such as an orbital space station or drop tower. We conduct a thorough analysis of the experiment’s principles and derive key parameters. Our calculations suggest that it is feasible to precisely measure a significant GAB phase shift within known engineering constraints. Additionally, our design of the cold atom interferometer possesses a unique sensitivity to potential but insensitivity to force, which can be further refined to effectively mitigate adverse effects associated with nonzero inertial forces acting on the cold atoms. These endeavors will ultimately pave the way for experimental exploration into the quantum nature of gravity.

High-performance silicon nitride (de)multiplexer based on ring-assisted MZIs.

We present the design and experimental characterization of the first multistage ring-assisted Mach-Zehnder interferometer (RAMZI) lattice (de)multiplexer implemented with silicon nitride optimized for four channels with a spacing of 100 GHz in the L-band. The device comprises two RAMZI stages to provide a sharp box-like response characterized by a shape factor of 0.9, a flat passband over the entire channel, and a crosstalk level better than -14 dB. The maximally flat passband of the demultiplexer enables a passband width twice that of the maximum spectral excursion defined in the NG-PON2 standard.

Design and fabrication of asymmetric Mach-Zehnder interferometers based on EpoClad and EpoCore strip waveguides

Integrated polymeric optical interferometers offer the possibility of developing sensors with low cost, scalability, and easy integration. Although they are not yet competitive with inorganic materials in terms of sensitivity, they have good biocompatibility in general, and suitable designs may provide sufficient sensitivity for biosensing. A new design for integrated Mach-Zehnder interferometers based on asymmetric arms with different widths has been proposed and experimentally demonstrated, avoiding the need for additional fabrication steps for an interaction window where biosamples are placed. The basic sensory principle is built upon the non-zero variation in the difference of the effective refractive index between the two arms due to their different dimensions, causing a phase variation in the output signal. In this work, we present a design optimization method and fabrication results by e-beam lithography for integrated asymmetric Mach-Zehnder interferometers based on strip waveguides made from EpoClad and EpoCore polymers. The operation wavelength was set to 650 nm. The optimization algorithm is based on open-source mode-solver simulations that return the optimal fabrication dimensions of the interferometer, avoiding high-order modes and enhancing single-mode confinement.

Optical Interferometric MEMS Accelerometers

AbstractLaser interferometry is one of the most accurate measurement technologies whose displacement resolution can reach the femtometer (fm) level. With the development of Micro‐Electro‐Mechanical Systems(MEMS) technology, many excellent optical interferometric MEMS sensors have emerged, which play an essential role in intelligent manufacturing, aerospace, and many other fields. Among them, optical interferometric MEMS accelerometers develop rapidly due to their high sensitivity, low noise, and anti‐electromagnetic interference advantages. Lots of research in optical interferometric chip design, micro‐nano fabrication process, signal demodulation algorithm, and range extension technology are performed, and different types of MEMS accelerometers based on the optical interferometric principles are developed, which have been demonstrated and applied in the fields of disaster monitoring, equipment operation and maintenance, and resource exploration. This paper reviews the development status of optical interferometric MEMS accelerometers, mainly focusing on the critical problems and solutions that need to be solved in the development process of optical interferometric accelerometers, and finally introduces the typical application scenarios.

Design and Construction of the Optical Bench Interferometer for the Taiji Program.

A kind of full-function two-sided optical bench interferometer (OBI) is designed to meet the practical requirements of the Taiji Program for space gravitational wave detection. The main optical paths are arranged on the A-side for transmission and interference, and other optical paths and electronic devices are placed on the B-side. According to the design scheme, we successfully constructed two OBIs by using hydrogen-oxygen catalytic stress-free bonding technology. When the OBI is installed and adjusted, the position and Angle error of the interference beam are controlled within 30 μm and 50 μrad through the self-designed precision mechanical clamping mechanism and beam position measuring device. The built OBI was placed on the vibration isolation platform in the vacuum tank for the stability test. The test results show that the noise of the OBI is less than 10 pm/√Hz in the frequency band of 0.1 Hz to 1 Hz, which meets the noise budget requirements of the Taiji Pathfinder in the middle- and high-frequency band.

Design, Operation, and Characterization of a Laboratory Spatial-Spectral Fourier Transform Interferometer

Design, Operation, and Characterization of a Laboratory Spatial-Spectral Fourier Transform Interferometer

Development of sweep frequency ultrasonic interferometer for high precision velocity measurement in liquids.

An ultrasonic interferometer with variable separation between the transducer and reflector is widely used for the measurement of ultrasonic propagation velocity in liquids. The inherent limitation of such an interferometer is due to the mechanical movement of its reflector for ultrasonic wavelength measurement in a liquid medium. It is observed that the ultrasonic velocity measurement precision is adversely affected at higher frequencies compared to lower ones. For instance, in our experimentation, a standard deviation of ±21.5m/s (±1.43%) was obtained for velocity measurement at 1.84MHz with the consideration of two consecutive maxima, which increases drastically to ±76.8m/s (±5.12%) at 9.4MHz. These measurements can significantly be improved by considering many maxima and averaging for wavelength estimation. However, it still requires design attention and improvement, particularly for higher frequencies. In this article, a sweep-frequency based ultrasonic interferometer design with a fixed separation for liquid characterization is proposed and described. This technique overcomes the limitations of mechanical movement systems and also provides a better and uniform precision for lower as well as higher frequencies. The functionality of the developed sweep frequency method was tested in water, carbon tetrachloride, ethylene glycol, and glycerol, which shows good agreement with literature values. The velocity measurement in double distilled water by the developed technique at 1Hz sweep resolution has shown an improved standard deviation of ±0.74m/s (±0.05%) at 9.4MHz.

Sensing and control scheme for the inteferometer configuration with an L-shaped resonator

The detection of high-frequency gravitational waves (GWs) around kHz is critical to understand the physics of binary neutron star mergers. A new interferometer design has been proposed in (Zhang et al 2023 Phys. Rev. X 13 021019), featuring an L-shaped optical resonator as the arm cavity, which resonantly enhances kHz GW signals. This new configuration has the potential to achieve better high-frequency sensitivity than the dual-recycled Fabry–Perot Michelson. In this paper, we propose a sensing and control scheme for this configuration. Despite having the same number of length degrees of freedom as the dual-recycled Fabry–Perot Michelson, the new configuration requires one less degree of freedom to be controlled owing to the system’s insensitive to the fluctuation of . We have also shown that introducing the Schnupp asymmetry is ineffective for controlling the signal-recycling cavity length. Therefore, we propose adding control fields from the dark port to control this auxiliary degree of freedom.

First on-sky results of a Fabry–Perot Instrument for Oxygen Searches (FIOS) prototype

Context. The upcoming Extremely Large Telescopes (ELTs) are expected to have a sufficient collecting area required to detect potential biosignature gases such as molecular oxygen, O2, in the atmosphere of terrestrial planets around nearby stars. Aims. One of the most promising detection methods is transmission spectroscopy. To maximize our capability to detect O2 using this method, spectral resolutions R ≥ 300 000 are required to fully resolve the absorption lines in an Earth-like exoplanet atmosphere and disentangle the signal from telluric lines. Methods. Current high-resolution spectrographs typically achieve a spectral resolution of R ~ 100 000. Increasing the resolution in seeing limited observations and/or instruments requires drastically larger optical components, making these instruments even more expensive and hard to fabricate and assemble. Instead, we demonstrate a new approach to high-resolution spectroscopy. We implemented an ultra-high spectral resolution booster to be coupled to a high-resolution spectrograph. The instrument is based on a chained Fabry-Perot array which generates a hyperfine spectral profile. Results. We present on-sky telluric observations with a lab demonstrator. Depending on the configuration, this two-arm prototype reaches a resolution of R = 250 000–350 000. After carefully modeling the prototype’s behavior, we propose a Fabry-Perot Interferometer (FPI) design for an eight-arm array configuration aimed at ELTs capable of exceeding R = 300 000. Conclusions. The novel FPI resolution booster can be plugged in at the front end of an existing R = 100 000 spectrograph to overwrite the spectral profile with a higher resolution for exoplanet atmosphere studies.

Computational analysis of a scalable optically homogeneous free-space interferometer.

This study describes a scalable optically homogeneous free-space interferometer. Computationally modeled as an unbroken block of fused silica, the interferometer's six-sided design is simple and intuitive, exploiting total internal reflection and refraction to split and recombine a collimated input beam. During propagation, one portion of the split beam remains within the substrate to act as a reference beam. The second portion of the split beam is exposed to the surrounding environment, enabling real-world environment characterization in real time. Validation of the interferometer concept is performed using numerical and analytical techniques. Based on its scalability and robustness, the proposed interferometer design is primed for applications in atmospheric sensing, passive chemical detection, and spaceborne technologies.

Conceptual design of a sorption-based cryochain for the ETpathfinder

Next-generation gravitational wave detectors, including the Einstein Telescope [1][2], aim to achieve amplitude-spectral-density strain sensitivities on the order 10−24m/Hz[3]. In the low-frequency band such sensitivities can only be obtained when thermal noise, mainly stemming from the mirror coating, is reduced by employing cryogenic cooling techniques for the mirrors. The optical surface of the mirror should not vibrate with strain noise amplitude spectral densities above 10−20m/Hz for the cryogenic mirrors in the Einstein Telescope [3]. The ETpathfinder research facility [4][5], aims to facilitate the development and testing of critical new technologies required for the design and operation of future gravitational wave detectors. A key enabling technology for the design and operation of such advanced interferometers is the cryogenic system that cools the main optics to a temperature of approximately 10 K. Given the stringent requirements on vibrational noise for these optics, the cryogenic cooling under continuous operation should be essentially vibration free. Joule-Thomson cryocoolers using sorption compressors are known to generate an absolute minimum of vibrational noise during operation. We propose a modular cryochain design comprised of a system of sorption compressors and Joule-Thomson cold stages fitting the ETpathfinder project requirements. In this paper, we present the conceptual design of the cooler chain that is based on a parallel cascade arrangement of a 40 K neon stage, a 15 K hydrogen stage and a 8 K helium stage. The operating parameters of the sorption-based cooler chain are selected via a hybrid modeling workflow, aiming to optimize performance and other design considerations within an envelope of acceptable design parameters.

First Observations With a GNSS Antenna to Radio Telescope Interferometer

AbstractWe describe the design of a radio interferometer composed of a Global Navigation Satellite Systems (GNSS) antenna and a Very Long Baseline Interferometry radio telescope. Our eventual goal is to use this interferometer for geodetic applications including local tie measurements. The GNSS element of the interferometer uses a unique software‐defined receiving system and modified commercial geodetic‐quality GNSS antenna. We ran three observing sessions in 2022 between a 25 m radio telescope in Fort Davis, Texas (FD‐VLBA), a transportable GNSS antenna placed within 100 m, and a GNSS antenna placed at a distance of about 9 km. We have detected a strong interferometric response with a Signal‐to‐Noise Ratio (SNR) of over 1,000 from Global Positioning System and Galileo satellites. We also observed natural radio sources including Galactic supernova remnants and Active Galactic Nuclei located as far as one gigaparsec, thus extending the range of sources that can be referenced to a GNSS antenna by 18 orders of magnitude. These detections represent the first observations made with a GNSS antenna to radio telescope interferometer. We have developed a novel technique based on a Precise Point Positioning solution of the recorded GNSS signal that allows us to extend integration time at 1.5 GHz to at least 20 min without any noticeable SNR degradation when a rubidium frequency standard is used.

Acoustic Michelson interferometer based on a phononic crystal

A practical and highly sensitive acoustic Michelson interferometer with a small form factor is introduced. It involves two different types of phononic crystals composed of steel rods in water acting as a medium for self-collimated waves and mirrors for the reference and sample beams, as well as a beam splitter formed by modified scatterers arranged diagonally. Finite-element method simulations are employed to demonstrate its operation around 200 kHz. Equifrequency contour analysis reveals self-collimation of ultrasonic waves between 190 and 210 kHz. Introduction of the beam splitter and mirror phononic crystals is not detrimental to self-collimation where outgoing waves from the two interferometer arms interfere such that the output intensity varies in a cosine squared manner. Consequently, maximum sensitivity is achieved when the movable mirror displacement is either zero or half of the interferometer phononic crystal period. On small intervals in these ranges, micrometer-scale displacement resolution is achievable, as the output intensity drops by 0.2% per micrometer. Thus, displacements smaller than a percent of the wavelength are easily resolvable. Nanoscale resolution can be obtained with a scaled down interferometer design. Moreover, application to liquid concentration sensing by considering ethanol–water binary mixture is demonstrated. A percent increase in weight fraction of ethanol up to 10% in the mixture leads to an intensity drop as high as 2%. Thus, significantly higher sensitivities compared to sensing schemes based on resonance frequency shift are attainable. The proposed approach can be adapted for surface acoustic waves in strain measurement or biosensing.

Suppression of laser phase noise by using updated common arm locking

The space-borne gravitational wave (GW) detectors, e.g., LISA, TianQin, TaiJi, are designed to measure the GW in the low-frequency regime (0.1 mHz to 1 Hz). The arm length mismatches in the flying constellation prevent exact laser phase noise cancellation. For a typical Michelson interferometric design such as LISA, the two arms will differ by a few percent and the uncanceled fluctuation from the ultra-stable laser is about 5 orders larger than the sensitivity goal in the science band (0.1 mHz to 1 Hz). In this work, we try to resolve this discrepancy in real time by using an arm locking technique. Unlike the analysis in previous literatures, we use the subtraction of one closed loop phase meter output from another one at the main spacecraft to cancel the laser phase noise further. We find that, with a careful design of the arm locking controller, the laser phase noise can be suppressed below the level of secondary noises in most parts of the science band. We point out that since the nulls always exist in the presence the GW transfer function of Michelson interferometer, there is no need to move the nulls to outside the science band by using a complicated arm locking sensor. Then, a study on the Doppler frequency pulling for the system has been carried out, and the result suggests that the pulling rate can meet the requirement. Finally, a good agreement between the time-series simulation in Simulink and theoretical result indicates the feasibility of this scheme. Therefore, the suppression of laser phase noise can possibly be realized in real time with prestabilization and updated common arm locking techniques. Our work can provide a back-up strategy for the implementation of arm locking in future space-borne GW detectors.

Free-space interferometer design for optical frequency dissemination and out-of-loop characterization below the 10−21-level

For improving the performance of optical frequency dissemination and the resolution of its out-of-loop (OOL) characterization, we investigate a compact free-space interferometer design in which a monolithic assembly forms the reference arm. Two interferometer designs are realized, and their environmental sensitivity is analyzed based on the properties of the materials involved. We elucidate that in these designs the temperature sensitivities of the out-of-loop signal paths are greater than for the reference arm. As the estimated temperature-variation-induced frequency transfer errors are observed to be the relevant limitation, the out-of-loop characterization signal can be regarded as a trustworthy upper limit of the frequency transfer error to a remote place. We demonstrate a fractional frequency transfer uncertainty and OOL characterization resolution of ≤2.7×10−21 over many measurement runs. With a value of (0.23±1.07)×10−22 the weighted mean offset is significantly below the best reported results so far.

Implementation of coherence imaging spectroscopy for ion flow measurements in the Compact Toroidal Hybrid experiment

A new coherence imaging spectroscopy (CIS) system has been characterized and validated for measurements of impurity ion velocity in the Compact Toroidal Hybrid (CTH) experiment. CIS is an interferometric technique providing very high spatial resolution of line-integrated ion flows; however, these measurements are highly sensitive to environmental factors such as temperature fluctuations. A compact interferometer design housed in a thermally regulated environment yields CIS measurement variations due to thermal fluctuations of 0.25 km/s. CIS measurements of He+ flows in the outer regions of CTH are benchmarked using two optical grating spectrometers. The deviation between the measurements is typically less than 2 km/s for multiple lines of sight which is well within the uncertainties of the diagnostics. Additional experiments demonstrate a moderate robustness of ion flows in the outer region of CTH to changing the vacuum transform, direction of the magnetic field, and plasma current. In contrast, regions of complete flow reversal are observed when a bias probe is inserted into the plasma edge.

Fast reconstruction of programmable integrated interferometers.

Programmable linear optical interferometers are important for classical and quantum information technologies, as well as for building hardware-accelerated artificial neural networks. Recent results showed the possibility of constructing optical interferometers that could implement arbitrary transformations of input fields even in the case of high manufacturing errors. The building of detailed models of such devices drastically increases the efficiency of their practical use. The integral design of interferometers complicates its reconstruction since the internal elements are hard to address. This problem can be approached by using optimization algorithms [Opt. Express29, 38429 (2021)10.1364/OE.432481]. In this paper, we present what we believe to be a novel efficient algorithm based on linear algebra only, which does not use computationally expensive optimization procedures. We show that this approach makes it possible to perform fast and accurate characterization of high-dimensional programmable integrated interferometers. Moreover, the method provides access to the physical characteristics of individual interferometer layers.