Modal Interferometer Research Articles

Label-free and highly-sensitive protamine detection by layer-by-layer assembled chitosan/heparin functionalized optical fiber mode interferometer

There is a strong requirement for label-free, selective and rapidly detection of Protamine (PRTM) due to that the PRTM and Heparin (Hep) have been widely used in clinical treatment. Here, an optical fiber interferometer biosensor that functionalized by layer-by-layer electrostatic assembled chitosan/heparin (CS/Hep) is proposed for PRTM detection. Experimental results proved that the refractive index (RI) sensitivity is related to thickness of CS/Hep overlayer, which is a key factor of sensor’s performance. The CS/Hep polyelectrolyte film coating extend its evanescent filed and can also be used as the signal amplification medium for PRTM detection due to the electrostatic interactions between PRTM and Hep. The optimal sensor that coated with 10 bilayers of CS/Hep, demonstrates RI sensitivity of 435.6 nm/RIU as well as ideal stability, and was chosen for PRTM detection. The CS/Hep based biosensor demonstrates a detection limit of 0.48 μg/mL and sensitivity of 0.1238 nm/(μg/mL) in the linear fitting range. Furthermore, the sensor illustrated ideal selectivity in serum samples and well reusability. Overall, the sensor features with high mechanical strength, ease of fabrication, real-time and label-free. This proposed sensor has potential applications for detecting PRTM in clinical applications.

Temperature-robust optical microphone with a compact grating interferometric module.

The high demand for advanced acoustic sensors has prompted optical microphones to become a current research hotspot; this is especially the case in light of the performance of existing electroacoustic microphones having reached the ceiling. In this work, a thermally stable optical microphone has been developed for sensitive detection of low-frequency acoustic signals. The microphone was prepared using a prestressed nickel diaphragm and a compact grating interferometric module. The adjacent surfaces of the diaphragm and grating form a short Fabry-Perot cavity, which makes the microphone robust to ambient temperature fluctuation due to the reduced thermal drift of its operating point relative to the quadrature point of the interferometer. The cavity length-operating wavelength relationship of the microphone operating at the quadrature point was obtained. The performance of the prepared microphone was tested using various methods. Experimental results show that the microphone enables stable operation at the quadrature point over a wide range of temperatures from 0°C to 60°C with low signal distortion and high sensitivity. The response of the prepared optical microphone to low-frequency drone noise was measured and compared with that obtained with a commercial electret condenser microphone.

H i intensity mapping with MeerKAT: forecast for delay power spectrum measurement using interferometer mode

ABSTRACT Neutral hydrogen (H i) intensity-mapping (IM) surveys are considered a promising tool for investigating the expansion history of the Universe. In this work, we explore the potential of MeerKAT H i IM observations in interferometer mode to estimate the power spectrum and constrain cosmological parameters within typical dark-energy models. We employ an approach called the ‘delay spectrum’, which allows us to separate the weak H i signal from foreground contamination in the frequency domain. Our findings indicate that the choice of survey fields significantly impacts the fractional errors on the power spectrum (ΔP/P) within a limited observational time of 10 h. As the integration time increases from 10–10 000 h, ΔP/P progressively decreases until cosmic variance begins to dominate. For a total observation time of 10 000 h, the lowest ΔP/P at low k can be achieved by tracking 100 points for the MeerKAT L band (900–1200 MHz) and 10 points for the MeerKAT UHF band (580–1000 MHz). Next, we assess the performance of H i IM in constraining typical dark-energy models. We find that the MeerKAT H i IM survey in interferometer mode demonstrates limited capability in constraining the dark-energy equation of state, even when combined with Planck data. Our analysis serves as a valuable guide for future MeerKAT observations in H i IM surveys.

EVALUATION OF THE EFFECTS OF ZDDP AND GRAPHENEADDITIVES IN PAO 8 OIL ON THE TRIBOLOGICAL PROPERTIESOF TIALN COATING

This paper investigates the tribological effects of graphene and anti-wear zinc dialkyl dithiophosphates(ZDDP). Friction tests have been carried out on a tribological tester which operates as a ball and disc assemblyin a frictional, sliding motion. Tests were carried out with a load of 10 N over a sliding distance of 1000 m.TiAlN coated HS6-5-2C steel discs, and 100Cr6 steel balls were used in the tests. Tests were conducted underlubrication conditions with poly()olefin oil PAO 8 with graphene and/or ZDDP. The chemical compositionof the TiAlN coating was studied using a scanning electron microscope, and the wear marks on the discs andballs were observed. The geometric structure of the samples was analysed before and after the friction testsusing a confocal microscope with interferometric mode. The results indicated that the addition of ZDDP andgraphene to the poly()olefin oil had an effect on reducing the friction coefficient.

Refractive index sensor based on multiple Fano resonances excited by MIM waveguide couplessd hexagonal nut and square ring resonators

This study proposed a micro-nano structure capable of generating multiple Fano resonances for refractive index sensing of gases and liquids. The structure consists of a metal-insulator-metal waveguide with a baffle and two resonators, one of hexagonal nut and one of square ring. The transmission spectrum shows that the designed structure can generate up to five Fano resonances tuned by different resonators. The data obtained are fitted by multi-mode interferometric coupling mode theory, and the results are in good agreement. The sensing performance of the structure is investigated in the refractive index ranges of 1.00–1.10 and 1.30–1.40. The corresponding maximum sensitivity and maximum figure of merit are up to 998 nm/RIU and 49016, 1026 nm/RIU and 14890, respectively. The designed structure can be used as gas and liquid sensors and have great potential for micro-nasno sensing and biochemical medicine applications.

Highly sensitive temperature and strain sensor based on polarization mode interferometer with Vernier effect

A new cascaded optical fiber temperature and strain sensor based on polarization mode interferometer (PMI) and Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally. The PMI made by fusion splicing a segment of polarization maintaining fiber (PMF) after a polarizer is used as a sensing interferometer. Integrating a FPI as a reference interferometer cascaded after the PMI to generate the Vernier effect and improve sensitivity. The FPI is made from a small segment of hollow core photonic crystal fiber (HCPCF), which is fusion spliced to PMF and multi-mode fiber (MMF) at each end to form two reflective surfaces of FPI. Based on numerical simulations, a suitable free spectral range (FSR) of the sensor is produced. Experimental results show that the temperature sensitivity can be improved from −1.095 nm/℃ to −22.753 nm/℃ and the strain sensitivity can be improved from 2.17 pm/με to 38.89 pm/με by using the Vernier effect. The measured amplification factors are about 21 and 18,respectively. The high sensitivity of PMI and FPI cascaded sensors with the Vernier effect offers a new option for simultaneous measurements in the field of temperature and strain.

Synthesis and Characterization of Electro-Optic Polyurethaneimide-Polyimide Copolymers

Polyurethaneimide prepolymer was synthesized using the synthesized chromophore C containing tricyanofuran, hexafluorodianhydride and phenyl diisocyanate as monomers. Polyimide prepolymers were synthesized using fluorinated aromatic diether dianhydride and fluorinated aromatic diamine as monomers. Polyurethaneimide-polyimide (PUI-FPI) copolymers were then synthesized by a polycondensation reaction of the polyimide and polyurethaneimide prepolymers. The electro-optic (EO) PUI-FPI copolymers had a special segment structure and concentrate the advantages of polyurethaneimide and polyimide. The copolymers exhibited good film-forming properties, high glass transition temperature (Tg =196 °C), and high thermal stability (Td up to 358 °C). The copolymers possessed a high EO coefficient (γ33 =72 pm/V) at the 1550 nm wavelength, good long-term electro-poled orientation stability, and low optical propagation loss (1.2–1.4 dB/cm) at 1550 nm. Mach-Zehnder interferometric electro-optic modulators were designed and fabricated using the synthesized copolymer as the waveguide material. The prepared polymer optical waveguide EO modulators showed a good low-frequency electro-optic modulation response. The results showed that the synthesized polyurethaneimide-polyimide copolymers meeted the performance requirements for the preparation of polymeric optical waveguide devices and were suitable as polymeric electro-optic waveguide materials.

Simultaneous measurement three parameters of temperature, strain, and curvature by thin-core fiber based-Mach-Zehnder interferometer

A Mach-Zehnder interferometer (MZI) sensor for simultaneous measurement of three parameters is developed. The sensor structure is spliced by single-mode fiber, no-core fiber, thin-core fiber (TCF) and single-mode fiber in turn, where the sensing element is TCF. Due to the different core diameters of three types of optical fibers, the light in the transmission process excites a number of higher-order modes and interacts to form a mode interferometer. The interference spectrum produces many resonance peaks that are sensitive to different parameters. We select three resonant peaks sensitive to temperature, strain and bending for measuring temperature, strain and curvature. The experimental results display that the resonant wavelength of the sensor transmission spectrum drifts linearly as a function of the environmental parameters, with a maximum sensitivity of 248.7 pm/℃ for temperature, −2 pm/με for strain and −24.784 nm/m−1 for curvature. Selecting three resonance peaks to construct a measurement matrix realizes three-parameters simultaneous measurement and eliminates the cross-sensitivity among the three physical quantities. In addition, the proposed sensor possesses appealing characteristics of facile manufacturing process, compact size, high sensitivity, good linear fitting, robustness and low cost, and the sensor has a broad application prospect in the field of multi-parameter simultaneous measurement. In short, only one MZI in the optical fiber can realize the simultaneous monitoring of temperature, strain and bending, which provides a new solution for creating a compact multi-parameter sensor for structural health monitoring.

Multi-image x-ray interferometer module: I. Design concept and proof-of-concept experiments with fine-pitch slits

We propose an x-ray imaging system, multi-image x-ray interferometer module (MIXIM), with which a very high angular resolution can be achieved even with a small system size. MIXIM is composed of equally spaced multiple slits and an x-ray detector, and its angular resolution is inversely proportional to the distance between them. Here, we report our evaluation experiments of MIXIM with a newly adopted CMOS sensor with a high spatial resolution of 2.5 μm. Our previous experiments with a prototype MIXIM were limited to one-dimensional imaging, and more importantly, the achieved angular resolution was only ∼1 ″ , severely constrained due to the spatial resolution of the adopted sensor with a pixel size of 4.25 μm. By contrast, one-dimensional images obtained in this experiment had a higher angular resolution of 0.5″ when a configured system size was only ∼1 m, which demonstrates that MIXIM can simultaneously realize a high angular resolution and compact size. We also successfully obtained a two-dimensional profile of an x-ray beam for the first time for MIXIM by introducing a periodic pinhole mask. The highest angular resolution achieved in our experiments is smaller than 0.1″ with a mask-sensor distance of 866.5 cm, which shows the high scalability of MIXIM.

Temperature-insensitive refractive index sensor based on a spindle-shaped few-mode fiber modal interferometer.

A designed temperature-insensitive modal interferometer for refractive index measurement based on spindle-shaped few-mode fiber (FMF) is proposed and demonstrated. The interferometer consisting of a specific length of FMF fused between two specific lengths of single-mode fibers is bent into a balloon shape and then burned by a flame into a spindle shape to sensitize. Due to the bending of the fiber, part of the light leaks from the core to the cladding and excites the higher-order modes, and the four modes in the core of FMF interfere with the higher-order modes in the cladding. Therefore, the sensor is more sensitive to the surrounding refractive index. The experimental results show that the highest sensitivity is 237.3nm/RIU from 1.333 to 1.365. The sensor is insensitive to temperature, which solves the problem of temperature cross talk. In addition, with its advantages of a small mechanism, simple fabrication, low loss, and good mechanical strength, the proposed sensor has broad application prospects in chemical production, fuel storage, environmental monitoring, and other fields.

Quantum-enhanced differential atom interferometers and clocks with spin-squeezing swapping

Thanks to common-mode noise rejection, differential configurations are crucial for realistic applications of phase and frequency estimation with atom interferometers. Currently, differential protocols with uncorrelated particles and mode-separable settings reach a sensitivity bounded by the standard quantum limit (SQL). Here we show that differential interferometry can be understood as a distributed multiparameter estimation problem and can benefit from both mode and particle entanglement. Our protocol uses a single spin-squeezed state that is mode-swapped among common interferometric modes. The mode swapping is optimized to estimate the differential phase shift with sub-SQL sensitivity. Numerical calculations are supported by analytical approximations that guide the optimization of the protocol. The scheme is also tested with simulation of noise in atomic clocks and interferometers.

High-efficiency thin-film lithium niobate modulator with highly confined optical modes.

We demonstrate a low-loss, high-efficiency lithium niobate electro-optic (EO) modulator with optical isolation trenches to achieve stronger field confinement and reduced light absorption loss. The proposed modulator realized considerable improvements, including a low half-wave voltage-length product of 1.2 V·cm, an excess loss of ∼2.4 dB, and a broad 3-dB EO bandwidth of over 40 GHz. We developed a lithium niobate modulator with, to the best of our knowledge, the highest reported modulation efficiency of any Mach-Zehnder interferometer (MZI) modulator.

Dispersion turning point-enhanced photothermal interferometry gas sensor with an optical microfiber interferometer

Photothermal interferometry (PTI) spectroscopy is a background-free and ultrasensitive gas or chemical sensing method. To date, most works have focused on applying different techniques to improve the sensitivity of PTI gas sensors via enhancing the photothermal (PT) phase modulation. Herein, we develop an all-fiber dispersion turning point (DTP)-enhanced PTI gas sensor with a taper-based mode interferometer in which the PT phase detection sensitivity of the interferometer is enhanced in a millimeter-long single fiber PTI configuration, which has not been studied yet. The design is demonstrated by conducting the measurement of acetylene with a 3-mm-long, 2.29-μm-diamter microfiber interferometer. A lower detection limit of 965 parts per billion (ppb) acetylene is achieved when the probe wavelength is operating near DTP, showing 16 times enhancement. Besides, theoretical analysis shows that the sensitivity of phase detection would be enormously enhanced when the dispersion factor approaching zero. By optimal design of the taper-based mode interferometer, together with thinner fiber diameter and longer fiber length, gas detection may be further improved by double enhancement of both PT phase generation and phase detection. With advantages of high sensitivity, compact size and low cost, the proposed all-fiber DTP-enhanced PTI gas sensor is potentially promising for ultra-sensitive trace chemical or biochemical sensing.

Superresolution imaging with multiparameter quantum metrology in passive remote sensing

We study super-resolution imaging theoretically using a distant $n$-mode interferometer in the microwave regime for passive remote sensing, used, e.g., for satellites like the ``Soil Moisture and Ocean Salinity'' (SMOS) mission to observe the surface of the Earth. We give a complete quantum-mechanical analysis of multiparameter estimation of the temperatures on the source plane. We find the optimal detection modes by combining incoming modes with an optimized unitary that enables the most informative measurement based on photon counting in the detection modes and saturates the quantum Cram\'er-Rao bound from the symmetric logarithmic derivative for the parameter set of temperatures. In our numerical analysis, we achieved a quantum-enhanced super-resolution by reconstructing an image using the maximum likelihood estimator with a pixel size of 3 km, which is ten times smaller than the spatial resolution of SMOS with comparable parameters. Further, we find the optimized unitary for uniform temperature distribution on the source plane, with the temperatures corresponding to the average temperatures of the image. Even though the corresponding unitary was not optimized for the specific image, it still gives a super-resolution compared to local measurement scenarios for the theoretically possible maximum number of measurements.

Quasi-common-path off-axis interferometric quantitative phase microscopy based on amplitude-division

A quasi-common-path off-axis interferometric quantitative phase microscopy (iQPM) is proposed using amplitude-division in this paper. Utilizing a quasi-common-path interferometric module, our method divides the object beam into two copies using a beam-splitter and two mirrors after the output of the microscope, while spatially filters one of the copies to act as the reference beam, and thus yields off-axis interference at the camera plane. The compact module is built using simple optical elements without the requirements of special optical skills and/or complex alignment. In contrast to the previous common-path off-axis iQPMs, the proposed method can flexibly adjust each channel to improve the visibility and/or frequency of the interferogram. Several experimental results are presented to demonstrate the validity and stability of the proposed iQPM.

Full Stokes polarimetry using a monolithic off-axis polarizing interferometer and a 2D array sensor.

This paper describes a full Stokes polarimeter employing a monolithic off-axis polarizing interferometric module and a 2D array sensor. The proposed passive polarimeter provides a dynamic full Stokes vector measurement capability of around 30Hz. As the proposed polarimeter employs no active devices and is operated by employing an imaging sensor, it has significant potential to become a highly compact polarization sensor for smartphone applications. To show the feasibility of the proposed passive dynamic polarimeter scheme, the full Stokes parameters of a quarter-wave plate are extracted and displayed on a Poincare sphere by varying the polarization state of the measured beam.

Mapping lava flow from the Kilauea eruption of 2018 in the east rift zone using space-based synthetic aperture radar

ABSTRACT Lava flows from volcanoes can significantly destroy infrastructure, although they rarely threaten human life. Mapping lava flows is essential to managing the volcanic hazard during eruptions and understanding significant changes in geomorphology after eruptions. In 2018, the eruption of Kilauea, Hawaii’s youngest and most active volcano, destroyed more than 700 homes, farmlands, and roads. Active lava flow tracking is crucial for providing timely warnings to evacuate residents and protect infrastructure. We constructed a map of the lava flow in the East Rift Zone (ERZ) during the Kilauea volcanic eruption in 2018 using remotely sensed satellite synthetic aperture radar observations. We processed 23 C-band Sentinel-1 A/B interferometric wide mode acquisitions captured from May 1 to 17 September 2018 and applied a coherent change detection (CCD) technique to detect minute changes in the target structure. A time series of coherence maps provided detailed spatial information on the movement of the lava flow fields in the ERZ. The overall lava flow map had an area of approximately 33.3 km2 and was verified with a lava thickness map provided by the United States Geological Survey that was generated by two digital elevation models using airborne light detection and ranging observations. Excellent agreement (>90%) among the lava flow observations suggests that the CCD technique is effective in monitoring lava flows during a volcanic eruption.

Editorial: The Sun seen with the Atacama Large mm and sub-mm array (ALMA)—First results1

et al. comes next, where the results on the temperature structure of the chromosphere, the chromospheric Figure 1. ALMA images of the Sun at 1.3 mm (band 6). Left: Full disk image obtained by scanning with a single dish; the spatial resolution is 30 . Right: High resolution (1 ) image of the region around the sunspot, obtained in interferometric mode with mosaicking. Both images were obtained on December 18, 2015, during the commissioning period and were processed by the authors for better visibility of the disk features.network and spicules are presented, followed by the research article by Tarr et al., which compares the 23 3 mm brightness temperature with the Hα line width in the weak solar network. (Rutten, 2017), with brilliant ideas and acute but constructive criticism. He will be remembered by the 45 entire solar physics community, and we dedicate this Research Topic to his memory.This work makes use of the following ALMA data: ADS/JAO.ALMA.2011.0.00020.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC 48 (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic

Three-Dimensional-Printed Fabrication of POFs Using Different Filaments and Their Characterization for Sensing Applications.

This paper presents the development and sensor applications of 3D-printed polymer optical fibers (POFs) using commercially available filaments. The well-known intensity variation sensor was developed using this fiber for temperature and curvature sensing, where the results indicate a linear response in the curvature analysis, with a coefficient of determination (R2) of 0.97 and sensitivity of 4.407 × 10-4 mW/∘, whereas the temperature response was fitted to an R2 of 0.956 with a sensitivity of 5.718 × 10-3 mW/∘C. Then, the POF was used in the development of a modal interferometer by splicing the POF in-between two single-mode fibers (SMFs), which result in a single-mode-multimode-single-mode (SMS) configuration. The such interferometer was tested for temperature and axial strain responses, where the temperature response presented a linear trend R2 of around 0.98 with a sensitivity of -78.8 pm/∘C. The negative value of the sensitivity is related to the negative thermo-optic coefficient commonly obtained in POFs. Furthermore, the strain response of the SMS interferometer showed a high sensitivity (9.5 pm/μϵ) with a quadratic behavior in which the R2 of around 0.99 was obtained. Therefore, the proposed approach is a low-cost, environmentally friendly and straightforward method for the production of highly sensitive optical fiber sensors.

High sensitivity all-fiber bend sensor based on modal interferences in a ring core fiber

We proposed and experimentally demonstrated an all-fiber sensor for measuring bend with high sensitivity based on a ring core fiber (RCF) modal interferometer. The sensor was fabricated by splicing a segment of RCF between two pieces of multimode fiber (MMF) and single-mode fiber (SMF) at the ends of the MMF as lead-in and lead-out. Due to the first segment of the MMF, the transmitted light is coupled into the ring core, silica center, and cladding of the RCF, exciting multiple modes in the RCF. By the modal interferences in the structure, bending sensing can be realized by interrogating the intensity of the interference dip. Experimental results show a high bending sensitivity of -25.63 dB/m-1 in the range of 1.0954 m-1 to 1.4696 m-1. In addition, the advantages of the bend sensor, such as small size, low temperature sensitivity, and simple fabrication process, can be used for curvature measurement in building health monitoring.