Fiber-based Interferometer Research Articles

Bragg grating etalon-based optical fiber for ultrasound and optoacoustic detection

Fiber-based interferometers receive significant interest as they lead to miniaturization of optoacoustic and ultrasound detectors without the quadratic loss of sensitivity common to piezoelectric elements. Nevertheless, in contrast to piezoelectric crystals, current fiber-based ultrasound detectors operate with narrow ultrasound bandwidth which limits the application range and spatial resolution achieved in imaging implementations. We port the concept of silicon waveguide etalon detection to optical fibers using a sub-acoustic reflection terminator to a Bragg grating embedded etalon resonator (EER), uniquely implementing direct and forward-looking access to incoming ultrasound waves. Precise fabrication of the terminator is achieved by continuously recording the EER spectrum during polishing and fitting the spectra to a theoretically calculated spectrum for the selected thickness. Characterization of the EER inventive design reveals a small aperture (10.1 µm) and an ultra-wide bandwidth (160 MHz) that outperforms other fiber resonators and enables an active detection area and overall form factor that is smaller by more than an order of magnitude over designs based on piezoelectric transducers. We discuss how the EER paves the way for the most adept fiber-based miniaturized sound detection today, circumventing the limitations of currently available designs.

Ultra-sensitive optical fiber ethanol gas sensor based on Vernier effect in cascaded Mach-Zehnder interferometer and Sagnac interferometer

Optical fiber-based sensors, which show the merits of high sensitivity, real-time, and rapid detection, have important research value in the detection of volatile organic compounds (VOCs). In this paper, a novel ethanol gas sensor was experimentally investigated based on the cascaded optical fiber-based Sagnac interferometer and Mach-Zehnder interferometer. The Sagnac interferometer was constructed with an anisotropic nematic liquid crystal (NLC) film which acted as the reactor with ethanol gas. A tapered single-mode fiber (SMF) was used to build the Mach-Zehnder interferometer (MZI). The two interferometers were parallelly and tandemly cascaded respectively to achieve the magnification of measurement sensitivity. Experimental results showed that the sensitivities were 8.561 pm/ppm with a magnification factor of 3.76 for the parallel cascaded structure and 7.924 pm/ppm with a magnification factor of 3.48 for the tandemly cascaded structure. The designed optical fiber-based ethanol gas sensor, showing the advantages of compact structure, high sensitivity, small size, and low cost, could be a competitive candidate for the detection of ethanol gas leakage.

High-order tunable multi-wavelength random Raman fiber laser based on few-mode fiber filter

In recent years, multi-wavelength fiber lasers have become one of the research hotspots and have been extensively applied in optical fiber communication systems. However, the presented multi-wavelength fiber lasers mainly operate in the 1.5 μm band. In this paper, a few-mode fiber filter-based cascaded high-order tunable multi-wavelength random Raman fiber laser (MWRRFL) is demonstrated, for the first time, in which a tuning range covers the 1.1–1.5 μm band. In the half-open MWRRFL, a few-mode fiber-based intermodal interferometer filter is inserted in the point reflector as a wavelength selector. The synergetic effect including high Raman gain and Rayleigh backscattering intensity in the hybrid of dispersion-shifted fiber and standard single-mode fiber is employed. It presents the capability for flat multi-wavelength random lasing stimulation. As a result, the wavelength channel number of the 6th-order random lasing is 6, with a maximum power variation of 4.66 dB and good temporal stability. The proposed cascaded tunable MWRRFL could provide a versatile source for optical fiber communication, optical fiber sensing, spectrum analysis, etc.

Multipath artifacts enable angular contrast in multimodal endoscopic optical coherence tomography.

Multipath artifacts are inherent to double-clad fiber based optical coherence tomography (OCT), appearing as ghost images blurred in the A-line direction. They result from the excitation of higher-order inner-cladding modes in the OCT sample arm which cross-couple into the fundamental mode at discontinuities and thus are detected in single-mode fiber-based interferometers. Historically, multipath artifacts have been regarded as a drawback in single fiber endoscopic multimodal OCT systems as they degrade OCT quality. In this work, we reveal that multipath artifacts can be projected into high-quality two-dimensional en face images which encode high angle backscattering features. Using a combination of experiment and simulation, we characterize the coupling of Mie-range scatterers into the fundamental image (LP01 mode) and higher-order image (multipath artifact). This is validated experimentally through imaging of microspheres with an endoscopic multimodal OCT system. The angular dependence of the fundamental image and higher order image generated by the multipath artifact lays the basis for multipath contrast, a ratiometric measurement of differential coupling which provides information regarding the angular diversity of a sample. Multipath contrast images can be generated from OCT data where multipath artifacts are present, meaning that a wealth of clinical data can be retrospectively examined.

Thin-core fiber-based Mach-Zehnder interferometer sensor for monitoring temperature, pressure, and humidity

A Mach-Zehnder interferometer (MZI) sensor based on thin-core fiber (TCF) is proposed. Sensitive materials such as polydimethylsiloxane (PDMS) or gelatin are coated on the surfaces of MZIs to achieve temperature, pressure, and humidity measurements. MZI is composed of single mode fiber (SMF), TCF, and multimode fiber (MMF) spliced together to form a “SMF-MMF-TCF-MMF-SMF” structure. The core/cladding diameters of TCF are 3.8 µm and 80 µm respectively. When three types of optical fibers with different core diameters are cascaded together, many cladding modes are excited to form MZI. Firstly, two similar MZI structures were fabricated designated by MZI1 and MZI2. In order to improve the sensitivity and mechanical strength, a layer of PDMS film was coated on the TCF surface of MZI1. Then, a layer of gelatin film is covered on the TCF surface of MZI2. PDMS has the high thermal expansion coefficient, thermal optical coefficient, and elasticity, and gelatin has good humidity sensitivity properties. The experimental results showed that the temperature and pressure sensitivity of MZI1 coated with PDMS reached −340 pm/°C and −14.3 nm/MPa, respectively, while the humidity sensitivity of MZI2 coated with gelatin reached −112.57 pm/% RH. When a fiber Bragg grating is cascaded with the MZI1, the sensor can achieve simultaneous measurement of temperature and pressure, eliminating crosstalk. The proposed sensor has an extremely simple structure and manufacturing method, which only involves the splicing of optical fiber and the coating by the film. In addition, the proposed sensor has a robust structure, good repeatability and stability, and high sensitivity, which has broad application prospects.

A static stiffness reference object for instrumented indentation with integrated fiber Fabry–Perot displacement measuring interferometer

Instrumented indentation is a technique used for measuring the mechanical response of materials to deformation. The accuracy of these measurements relies on force and displacement values recorded during the indentation process. This paper presents a miniature fused silica parallelogram flexure to serve as a reference object for calibrating the applied indentation force based on Hooke’s law, F = kz, where k is the stiffness of the reference object and z is the displacement of the flexure under force F. This study discusses two independent experimental approaches to determine the stiffness of the flexure. In both cases, the stiffness was calculated from the measured flexure displacement while known forces are applied. In the first method, the displacement is measured using a built-in fiber-based interferometer while reference masses of 100 mg and 200 mg are placed on the flexure. A stiffness of is determined with this method. The second method uses a commercial indenter to apply a cyclic force of 100 mN magnitude on the flexure while recording the displacement of the indenter probe. Experiments using a 5 μm and a 50 μm conospherical tip estimate the stiffness to be , and respectively.Disclaimer: Certain commercial equipment, instruments are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Fiber-based multichannel heterodyne interferometer for studying the pulsed plasma properties

A fiber-based four-channel heterodyne interferometer has been developed to study the properties of pulsed plasma. The accuracy of phase measurements was 0.03 rad, which corresponds to an error in measuring the concentration of free electrons of ± 1· 1019 m-2. Measurements of the electron density and plasma velocity of the plasma accelerator have been carried out.. Keywords: laser interferometer, fiber-based interferometer.

Волоконный многоканальный гетеродинный интерферометр для исследования свойств импульсной плазмы

A fiber-based four-channel heterodyne interferometer has been developed to study the properties of pulsed plasma. The accuracy of phase measurements was 0.03 rad, which corresponds to an error in measuring the concentration of free electrons of ±1. × 1019 m-2. Measurements of the electron density and plasma velocity of the plasma accelerator have been carried out.

Fiber-based two-wavelength heterodyne laser interferometer.

Displacement measuring interferometry is a crucial component in metrology applications. In this paper, we propose a fiber-based two-wavelength heterodyne interferometer as a compact and highly sensitive displacement sensor that can be used in inertial sensing applications. In the proposed design, two individual heterodyne interferometers are constructed using two different wavelengths, 1064 nm and 1055 nm; one of which measures the target displacement and the other monitors the common-mode noise in the fiber system. A narrow-bandwidth spectral filter separates the beam paths of the two interferometers, which are highly common and provide a high rejection ratio to the environmental noise. The preliminary test shows a sensitivity floor of 7.5pm/Hz at 1 Hz when tested in an enclosed chamber. We also investigated the effects of periodic errors due to imperfect spectral separation on the displacement measurement and propose algorithms to mitigate these effects.

In situ exploring the dynamic behaviors of gas bubbles in liquid by using a tapered dual-hole hollow fiber

Multiphase systems are often accompanied by highly complex gas-liquid-solid interactions and interface behaviors, which are difficult to be captured directly. This work reports theoretically and experimentally the studies on monitoring the dynamic behaviors of the gas bubbles in liquid by using a tapered dual-hole optical fiber-based interferometer. As demonstrated by regulating their size, quantity, and arrangement, gas bubbles touching the waist region of the tapered fiber lead to a spectral response of the interferometer, and the total area of the gas-solid interface between them directly determines the wavelength shift of the output spectrum. Beyond that, the sensor with the uniform tapered waist region (length: 1.5 cm, diameter: Ф 5 μm) is fabricated to explore the gas bubbles’ coalescence. In this case, the gas bubbles contact each other until the waist region of tapered fiber is radially enclosed entirely. When the enclosed gas-solid interface area varies between 16,000 - 24,000 µm2, the wavelength shift responds exponentially to the area, and the sensitivity at the area of 16,000 µm2 is calculated to be 2.42 pm/μm2. The proposed sensing platform could be adapted to in situ and online explore the multiphase dynamics for applications such as cell analysis, energy production, and environmental monitoring.

Temperature Insensitive Delay-Line Fiber Interferometer Operating at Room Temperature

Environmental temperature fluctuations cause phase changes of the light propagating through optical fibers due to their thermal sensitivity. This limits the stability of fiber delay-line interferometers. Here, we present a thermally-insensitive fiber Mach-Zehnder interferometer. It consists of a hollow core fiber (HCF), which has a low thermal sensitivity coefficient, in one branch and a standard single-mode fiber with a thermal sensitivity coefficient about 25 times larger in the other. By setting their associated length ratio to approximately 25:1, the optical phase of the light in both arms changes by the same amount with temperature, making the difference in their optical paths insensitive to temperature and thus producing thermally-insensitive interference. As the thermal sensitivity coefficient of the optical fibers is itself slightly temperature dependent, exactly-zero sensitivity is achieved at a specific temperature only. We show how this zero-sensitivity temperature can be controlled via control of the relative fiber lengths in the two interferometer arms and set it to room temperature. Further, we show that our interferometer is over 100 times less sensitive to temperature than a single-mode fiber-based interferometer over temperature range as large as 25–50 °C. When considering a simple temperature control that keeps the interferometer within ±1 °C, the demonstrated interferometer achieves over 2000 times lower thermal sensitivity than a single-mode fiber-based interferometer and over 100 times lower sensitivity than an HCF-only based interferometer. Finally, we discuss how the thermal sensitivity of such interferometer depends on the light source wavelength.

Storage and analysis of light-matter entanglement in a fiber-integrated system.

The deployment of a full-fledged quantum internet poses the challenge of finding adequate building blocks for entanglement distribution between remote quantum nodes. A practical system would combine propagation in optical fibers with quantum memories for light, leveraging on the existing communication network while featuring the scalability required to extend to network sizes. Here, we demonstrate a fiber-integrated quantum memory entangled with a photon at telecommunication wavelength. The storage device is based on a fiber-pigtailed laser-written waveguide in a rare earth-doped solid and allows an all-fiber stable addressing of the memory. The analysis of the entanglement is performed using fiber-based interferometers. Our results feature orders-of-magnitude advances in terms of storage time and efficiency for integrated storage of light-matter entanglement and constitute a substantial step forward toward quantum networks using integrated devices.

A Review of Sensitivity Enhancement in Interferometer-Based Fiber Sensors.

Optical fiber sensors based on an interferometer structure play a significant role in monitoring physical, chemical, and biological parameters in natural environments. However, sensors with high-sensitivity measurement still present their own challenges. This paper deduces and summarizes the methods of sensitivity enhancement in interferometer based fiber optical sensors, including the derivation of the sensing principles, key characteristics, and recently-reported applications.The modal coupling interferometer is taken as an example to derive the five terms related to the sensitivity: (1) the wavelength-dependent difference of phase between two modes/arms , (2) the sensor length , (3) refractive index difference between two modes/arms , (4) sensing parameter dependent length change , and (5) sensing parameter dependent refractive index change . The research papers in the literature that modulate these terms to enhance the sensing sensitivity are reviewed in the paper.

Realistic model of entanglement-enhanced sensing in optical fibers.

Experimental limitations such as optical loss and noise have prevented entanglement-enhanced measurements from demonstrating a significant quantum advantage in sensitivity. Holland-Burnett entangled states can mitigate these limitations and still present a quantum advantage in sensitivity. Here we model a fiber-based Mach-Zehnder interferometer with internal loss, detector efficiency, and external phase noise and without pure entanglement. This model features a practical fiber source that transforms the two-mode squeezed vacuum (TMSV) into Holland-Burnett entangled states. We predict that a phase sensitivity 28% beyond the shot noise limit is feasible with current technology. Simultaneously, a TMSV source can provide about 25 times more photon flux than other entangled sources. This system will make fiber-based quantum-enhanced sensing accessible and practical for remote sensing and probing photosensitive materials.

Dimensional Stability Ground Test and in-Orbit Prediction of SiC Telescope Frame for Space Gravitational Wave Detection

Telescope is the key element of space brone gravitational wave detector. Its dimensional stability is required to be better than 1 pm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at 0.1 mHz. And SiC is the current most likely material for manufacturing telescope with high dimensional stability. Therefore, a potential SiC telescope frame is designed and tested. In addition, in orbit dimensional stability is predicted by a numerical model. The ground dimensional stability of SiC frame is tested with a fiber-based interferometer, and the temperature change data are collected at the same time. The results of which show that when room temperature fluctuation frequency is greater than 10 mHz, the dimensional stability is about 300 pm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . A numerical model is established which is consistent with the measured data. The in-orbit dimensional stability is evaluated using the numerical model and the thermal environment of Taiji, whose numerical simulation results shows that when space temperature fluctuation frequency is about 0.1 mHz the dimensional stability would be 6.49 pm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> .

A step beyond in steady-state and time-resolved electro-optical spectroscopy: Demonstration of a customized simple, compact, low-cost, fiber-based interferometer system.

Electro-optical spectroscopy is nowadays a routine approach for the analysis of light induced properties and dynamical processes in matter, whose understanding is particularly crucial for the intelligent design of novel synthetic materials and the engineering and optimization of high-impact optoelectronic devices. Currently, within this field, it is the common choice to rely on multiple commercial setups, often costly and complex, which can rarely combine multiple functions at the same time with the required sensitivity, resolution, and spectral tunability (in both excitation and detection). Here, we present an innovative, compact, and low-cost system based on “three in one” components for the simultaneous electro-optical material and device characterization. It relies on compact fiber-coupled Fourier transform spectroscopy, the core of the system, enabling a fast spectral analysis to acquire simultaneously wavelength and time resolved photoluminescence (PL) maps (as a function of the time and wavelength), PL quantum yield, and electroluminescence signal. Our system bypasses conventional ones, proposing a new solution for a compact, low-cost, and user-friendly tool, while maintaining high levels of resolution and sensitivity.

Hyperfine optical vector analysis of ultra- narrowband optical bandpass filters based on coherent two-tone sweeping and fixed low-frequency detection

A hyperfine optical vector analyzer (OVNA) is proposed and experimentally demonstrated to characterize ultra-narrowband optical bandpass filters (OBPFs). In this scheme, a coherent two-tone optical signal (TTOS) with a small frequency interval is generated to act as a probe light. Through finely sweeping the TTOS across the passband of the OBPF via electro-optic modulation, the magnitude and phase responses of the OBPF under test can be measured with a high signal-to-noise ratio based on fixed low-frequency detection. The frequency response measurement is immune to external disturbance. In the experiment, the magnitude and group delay responses of a fiber-based Fabry-Perot tunable filter (FFP-TF) and a fiber-based Fabry-Perot interferometer (FFP-I) with 3-dB bandwidths of 1.5 GHz and 60 MHz, respectively, are successfully measured. In addition, the measurement uncertainty is theoretically and experimentally analyzed. This method paves a way to characterize ultra-narrowband OBPFs with high out-of-band rejection ratios.

Acoustic wave generated by focused nanosecond laser pulse at air–solid interface: Experiment and modeling

Perturbations are induced by focusing a laser pulse (1064 nm, 10 ns duration, and energy ranging from 3.24 to 12.02 mJ) on a ceramic plate in the air. The generated signals are detected with an optical fiber-based Michelson interferometer. The detected waveforms are similar for various pulse energies, but the dimensions differ. Based on the partial differential equation system from linear acoustic theory, a simple model with a symbolic solution is proposed to explain the detected waveforms. Laser-induced wave energies are estimated based on the model.

Optical dosimeter for selective retinal therapy based on multi-port fiber-optic interferometry.

Selective retinal therapy (SRT) employs a micro-second short-pulse lasers to induce localized destruction of the targeted retinal structures with a pulse duration and power aimed at minimal damage to other healthy retinal cells. SRT has demonstrated a great promise in the treatment of retinal diseases, but pulse energy thresholds for effective SRT procedures should be determined precisely and in real time, as the thresholds could vary with disease status and patients. In this study, we present the use of a multi-port fiber-based interferometer (MFI) for highly sensitive real-time SRT monitoring. We exploit distinct phase differences among the fiber ports in the MFI to quantitatively measure localized fluctuations of complex-valued information during the SRT procedure. We evaluate several metrics that can be computed from the full complex-valued information and demonstrate that the complex contour integration is highly sensitive and most correlative to pulse energies, acoustic outputs, and cell deaths. The validity of our method was demonstrated on excised porcine retinas, with a sensitivity and specificity of 0.92 and 0.88, respectively, as compared with the results from a cell viability assay.

Simultaneous measurement of temperature and curvature using ring-core fiber-based Mach-Zehnder interferometer.

In this paper, the Mach-Zehnder interferometer (MZI) based on ring-core fiber was proposed and manufactured. Benefiting from the identical diameters of ring-core fiber, no-core fiber, and single-mode fiber, the MZI fiber sensor can be prototyped by sandwiching the ring-core fiber between the no-core fiber and the single-mode fiber (SMF). With the proposed specific structure of the ring-core fiber, the simultaneous measurement of temperature and curvature was achieved with the MZI sensor by means of monitoring the wavelength shift of interference dips. Experimental results have shown that the sensitivity of curvature sensing could reach up to -3.68 nm/m-1 in the range from 1.3856 m-1 to 3.6661 m-1 with high linearity of 0.9959. Meanwhile, the maximum temperature sensitivity is measured to be 72 pm/°C with a fairly good linearity response of 0.9975. In addition, by utilizing the 2×2 matrix algorithm, the dual demodulation of temperature and curvature can be readily realized for the purpose of direct sensing. It is believed that the proposed special structure-based MZI sensor may show great potential applications in the field of fiber-optics sensing and structural health monitoring (SHM).