Fiber-optic Interferometry Research Articles

Nonlinearity-suppressed micro-probe fiber optic interferometer for accurate long-range displacement measurements

Fiber-optic interferometry technology has advanced rapidly in recent years. However, accurate measurement of the displacement over long ranges remains a challenge. This study reveals that fiber interferometers with Fabry–Perot cavities experience non-elliptic multi-order nonlinear errors due to parasitic interference, leading to nonlinearity correction failures in the case of reflectivity mismatch. We proposes a nonlinearity-suppressed microprobe fiber interferometer to measure long-range displacement with high accuracy. The proposed microprobe interferometer structurally avoids non-elliptic nonlinearities from higher-order harmonics and ensures the effectiveness of the nonlinearity correction method. Moreover, we optimized the micro-sensing probe parameters based on an established multimedia transmission interference model to further improve the measurement accuracy of long-range displacement. Nonlinear errors are reduced from 2.3 nm to 0.92 nm in the application range 0–700 mm. The findings of this study demonstrate that the proposed nonlinearity-suppressed microprobe fiber interferometer is suitable for sub-nanometer accuracy measurements over displacements of several hundred millimeters, especially in limited-space scenarios. It has great potential for industries seeking breakthroughs in long-range displacement measurement, such as robotics, medical devices and manufacturing.

A Mach–Zehnder Fabry–Perot Hybrid Fibre-Optic Interferometer for a Large Measurement Range Based on the Kalman Filter

To solve the short working distance and small measurement range of an all-fibre interferometer, we proposed a Mach–Zehnder Fabry–Perot hybrid fibre-optic interferometry system based on sinusoidal phase modulation. In this paper, a low-finesse fibre interferometer with a larger linear operating range for displacement measurement is realised using a self-collimating probe and incorporating a Kalman filter-based phase demodulation algorithm. Through experimental comparisons, it is demonstrated that the interferometer proposed in this paper can effectively reduce the phase delay, compensate for the depth of modulation drift, and correct the error due to parasitic interference introduced by the optical path structure through the algorithm. A linear large measurement working range of 20 cm is realised.

Dynamic Profiling and Prediction of Antibody Response to SARS-CoV-2 Booster-Inactivated Vaccines by Microsample-Driven Biosensor and Machine Learning.

Knowledge of the antibody response to the third dose of inactivated SARS-CoV-2 vaccines is crucial because it is the subject of one of the largest global vaccination programs. This study integrated microsampling with optical biosensors to profile neutralizing antibodies (NAbs) in fifteen vaccinated healthy donors, followed by the application of machine learning to predict antibody response at given timepoints. Over a nine-month duration, microsampling and venipuncture were conducted at seven individual timepoints. A refined iteration of a fiber optic biolayer interferometry (FO-BLI) biosensor was designed, enabling rapid multiplexed biosensing of the NAbs of both wild-type and Omicron SARS-CoV-2 variants in minutes. Findings revealed a strong correlation (Pearson r of 0.919, specificity of 100%) between wild-type variant NAb levels in microsamples and sera. Following the third dose, sera NAb levels of the wild-type variant increased 2.9-fold after seven days and 3.3-fold within a month, subsequently waning and becoming undetectable after three months. Considerable but incomplete evasion of the latest Omicron subvariants from booster vaccine-elicited NAbs was confirmed, although a higher number of binding antibodies (BAbs) was identified by another rapid FO-BLI biosensor in minutes. Significantly, FO-BLI highly correlated with a pseudovirus neutralization assay in identifying neutralizing capacities (Pearson r of 0.983). Additionally, machine learning demonstrated exceptional accuracy in predicting antibody levels, with an error level of <5% for both NAbs and BAbs across multiple timepoints. Microsample-driven biosensing enables individuals to access their results within hours of self-collection, while precise models could guide personalized vaccination strategies. The technology's innate adaptability means it has the potential for effective translation in disease prevention and vaccine development.

Precise detection of trace level protein using MIP-MoS2 nanocomposite functionalized PCF based interferometer.

Fiber optic interferometry combined with recognizing elements has attracted intensive attention for the development of different biosensors due to its superior characteristic features. However, the immobilization of sensing elements alone is not capable of low-concentration detection due to weak interaction with the evanescent field of the sensing transducer. The utilization of different 2D materials with high absorption potential and specific surface area can enhance the intensity of the evanescent field and hence the sensitivity of the sensor. Here, a biosensor has been fabricated using an inline hetero fiber structure of photonic crystal fiber (PCF) and single-mode fiber (SMF) functionalized with a nanocomposite of molybodenum di-sulfide (MoS2) and molecular imprinting polymer (MIP) to detect trace levels of bovine serum albumin (BSA). The sensor showed a wide dynamic detection range with a high sensitivity of 2.34 × 107 pm/µg L-1. It shows working potential over a wide pH range with a subfemtomolar detection limit. The compact size, easy fabrication, stable structure, long detection range, and high sensitivity of this sensor would open a new path for the development of different biosensors for online and remote sensing applications.

High-Resolution Measurement of Magneto-Shape Effect Based on Fiber Optic Interferometry Ranging

High-Resolution Measurement of Magneto-Shape Effect Based on Fiber Optic Interferometry Ranging

High-resolution micro-cavity filling sensing by fiber optic interferometry.

In the last decade, new potential applications of micro- and nano-products in telecommunication, medical diagnostics, photovoltaic, and optoelectronic systems have increased the interest to develop micro-engineering technologies. Injection molding of polymeric materials is a recent method being adapted for serial manufacturing of optic components and packaging at the micro- and nano-scale. Quality assurance of replication into small cavities is an important but underdeveloped factor that is needed to ensure high production efficiency in any micro-fabrication industry. In this work, we introduce a fiber-based interferometric measurement sensor to monitor the cavity filling of optical microstructures fabricated into a macroscopic molding die. The interferometer was capable of resolving melt front motion into the microcavity to the point of complete filling as verified by atomic force microscopy. Despite the low reflectivity of the transparent polymer and unoptimized reflected light collection optics, this system is capable of monitoring polymer movement during the course of filling and detecting the completion of the process. The simplicity and flexibility of the technology could allow eventual instrumentation of injection molds, embossing, and nanoimprint tooling suitably modified with a small optical window to accommodate light from an optical fiber. This would provide a solution to the challenging problem of monitoring local, nanometer scale filling processes.

Impact of Soil-Based Insulation on Ultrahigh-Resolution Fiber-Optic Interferometry.

High resolution optical interferometry often requires thermal and acoustic insultation to reduce and remove environment-induced fluctuations. Broader applications of interferometric optical sensors in the future call for low-cost materials with both low thermal diffusivity and good soundproofing capability. In this paper, we explore the feasibility and effectiveness of natural soil as an insulation material for ultrahigh-resolution fiber-optic interferometry. An insulation chamber surrounded by soil is constructed, and its impact on the noise reduction of a Mach-Zehnder Fabry-Perot hybrid fiber interferometer is evaluated. Our results indicate that soil can effectively reduce ambient noise across a broad frequency range. Moreover, compared to conventional insulation materials such as polyurethane foam, soil shows superior insulation performance at low frequencies and thereby affords better long-term stability. This work demonstrates the practicability of soil as a legitimate option of insulation material for precision optical experiments.

Gupta-Bleuler quantization of optical fibers in weak gravitational fields

The theory of gauge-fixed Maxwell equations in linear isotropic dielectrics is developed using a generalization of the standard ${R}_{\ensuremath{\xi}}$ gauge-fixing term. In static space times, the theory can be quantized using the Gupta-Bleuler method, which is worked out explicitly for optical fibers either in flat space time or at a constant gravitational potential. This yields a consistent first-principles description of gravitational fiber-optic interferometry at the single-photon level within the framework of quantum field theory in curved space times.

Narrow-band multi-component gas analysis based on photothermal spectroscopy and partial least squares regression method

In spectroscopic multi-component gas sensing, the crosstalk in the overlapping region of gas absorption spectra will affect the measurement accuracy. This paper reports a new multi-component gas analyzing method based on partial least squares regression (PLSR), which can retrieve target gas concentration and the composition and concentration of interfering gas from an overlapping narrow-band spectrum. Two overlapping absorption spectra (acetylene and ammonia) around 1530 nm are selected to simulate the absorption crosstalk phenomenon. We built a fiber-optic photothermal interferometry system to verify the method on two-component gases in the overlapping region. The training of the PLSR model was based on 63 sets of photothermal second-harmonic signals, which acquired from the gases composed by 100–700 ppm ammonia and 100–900 ppm acetylene. The prediction error of PLSR model achieved 3.84 % when tested by extra data.

Limits and prospects for long-baseline optical fiber interferometry

Today’s most precise optical instruments—gravitational-wave interferometers and optical atomic clocks—rely on long storage times for photons to realize their exquisite sensitivity. Optical fiber technology is the most widely deployed platform for realizing long-distance optical propagation. Yet, its application to precision optical measurements is sparse. We review the state of the art in the noise performance of conventional (solid-core) optical fibers from the perspective of precision optical measurements and quantum technology that rely on precise transfer of information over long distances. In doing so, we highlight the limitations of this platform and point to the opportunities that structured fiber technology offers to overcome some of these limitations.

In situ ground settlement sensor for oil-tank monitoring by combining a fiber-optic low-coherent interferometry with a fine mechanical design.

An in situ robust ground settlement (IR-GS) sensor was designed to meet the requirements for oil-tank health monitoring by combining a low-coherent fiber-optic interferometry with a fine mechanical spline shaft. A floating mirror was mounted on the shaft and moved up and down along with the liquid surface. The liquid-contained chambers were hydraulically connected at the bottom by using a liquid-filled tube. The liquid level inside each chamber was initially at equal level. One of the chambers was fixed on a steady ground point, which was chosen in a surveying point of view and served as a reference. The others were distributed around an oil tank and separated the tank's perimeter into eight equal spans. Thereby, the health states of the oil tank were able to be evaluated based on these sensing results. Interrogation of the sensor was employed via a low-coherent fiber-optic Michelson interferometer. One path of the interferometer was composed by the floating mirror, whereupon a light was reflected. The other path was projected to a mirror that was fixed on a stepping motor. Therefore, the corresponding liquid level could be optically surveyed. Differential settlements between each chamber and the reference served as a measure of how much the liquid level was changed from its initials. Experimental tests demonstrated that this IR-GS design, with the optimized shape and weights of the spline shaft, could overcome the error caused by dust, hysteresis, temperature, etc. and meet the practical requirement in the accuracy of ±0.5mm. A practical application was carried out, and its long-term stability has been proved.

On-Site Biolayer Interferometry-Based Biosensing of Carbamazepine in Whole Blood of Epileptic Patients.

On-site monitoring of carbamazepine (CBZ) that allows rapid, sensitive, automatic, and high-throughput detection directly from whole blood is of urgent demand in current clinical practice for precision medicine. Herein, we developed two types (being indirect vs. direct) of fiber-optic biolayer interferometry (FO-BLI) biosensors for on-site CBZ monitoring. The indirect FO-BLI biosensor preincubated samples with monoclonal antibodies towards CBZ (MA-CBZ), and the mixture competes with immobilized CBZ to bind towards MA-CBZ. The direct FO-BLI biosensor used sample CBZ and CBZ-horseradish peroxidase (CBZ-HRP) conjugate to directly compete for binding with immobilized MA-CBZ, followed by a metal precipitate 3,3′-diaminobenzidine to amplify the signals. Indirect FO-BLI detected CBZ within its therapeutic range and was regenerated up to 12 times with negligible baseline drift, but reported results in 25 min. However, Direct FO-BLI achieved CBZ detection in approximately 7.5 min, down to as low as 10 ng/mL, with good accuracy, specificity and negligible matric interference using a high-salt buffer. Validation of Direct FO-BLI using six paired sera and whole blood from epileptic patients showed excellent agreement with ultra-performance liquid chromatography. Being automated and able to achieve high throughput, Direct FO-BLI proved itself to be more effective for integration into the clinic by delivering CBZ values from whole blood within minutes.

Photon force microelectromechanical system cantilever combined with a fibre optic system as a measurement technique for optomechanical studies

In this paper we present a metrological measurement technique that is a combination of fibre optic interferometry and a microelectromechanical system (MEMS) sensor for photon force (PF) measurement with traceability via an electromagnetic method. The main advantage of the presented method is the reference to the current balance, which is the primary mass/force metrological standard. The MEMS cantilever transduces the PF to a deflection that can be compensated with the use of the Lorentz force. This movement is measured with the use of the interferometer and does not require any mechanical calibration. Combining the MEMS current balance system with interferometry is a unique and fully metrological solution. The resolution of the proposed measurement technique is calculated to be 4 pN Hz–0.5 (2% uncertainty). The PF–MEMS used for the investigation is a cantilever with a resolution of 46 fN Hz–0.5, which was calculated from the thermomechanical noise and is far below the resolution limit of the whole system. Because the whole construction is based on a fibre optic system, it does not require any complex adjustment procedure and may work as an optomechanical reference in any metrological laboratory.

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.

Artificial Receptor‐Based Optical Sensors (AROS): Ultra‐Sensitive Detection of Urea

The combined approach of optical fiber interferometry with molecular imprinting technology has shown a tremendous potential for developing a specific and sophisticated bio‐detection system with high degree of resolution and sensitivity. However, the specificity limitation of the fiber optic sensors renders them unsuitable for several key applications. Molecular imprinted polymer (MIP), an indispensable artificial molecular receptor with a complementary structure and functionality for the target analyte, possesses the ability to overcome the limitations of specificity. Therefore, a new class of artificial receptor‐based optical sensors (AROS) constructed from an optical fiber interferometer integrated with artificial MIP for selective and ultrasensitive sensing of urea is demonstrated. The sensor device shows an unprecedented sensitivity of 0.584 × 1011 nm m −1 and a lower detection limit of 17.1 fM with a wide dynamic range of 10−11–10−4 m. This demonstration of an ultrasensitive, selective, and accurate AROS system is bound to find potential applications that requires remote sensing in harsh environmental conditions with large fluctuations in the temperature, pressure, and humidity.

Vibration insensitive THz wave interferometry for characterizing optical phase shifter

Optic interferometry is a well-known measurement technique with high precision attained through the optical interference caused by the superposition of lightwaves. However, with fiber-optic interferometry, the phases of the lightwaves are susceptible to interference via the fiber fluctuation that is unavoidably induced by the environmental vibration, which makes the measurement result unstable and limits the usage scenarios of the interferometric installation. In this paper, a fiber-optic THz wave interferometer aiming for vibration isolation is presented. Due to the longer wavelength of the THz wave, the influence of optical fiber fluctuation on the phase noise is considerably suppressed. For verifying the feasibility of the fiber-optic THz wave interferometer, it is used here to measure the optical phase shift at a fiber-pigtailed thermo-optic phase shifter. The experimental results show that, compared with an all-fiber interferometer, the fiber-optic THz interferometer enables accurate measurement of an optical phase shift as well as an improved signal-to-noise ratio of interference with 6dB gain.

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

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.

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

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.

Application Research of Frequency-Modulated Continuous-Wave Displacement Sensor Based on Zero-Crossing Phase Detecting Algorithm

Frequency-modulated continuous-wave (FMCW) interference, as a new technology of laser interferometry, has the advantages of length traceability, large range, high accuracy, simple structure, and optical fiber transmission. Based on the formula of FMCW laser interference displacement, a zero-crossing phase detection algorithm is proposed, which can accurately calculate the initial phase of a cosine signal in a modulation period, and it is successfully applied to the contact laser interference displacement sensor. The experimental results show that the FMCW technology based on the zero-crossing phase detection algorithm can achieve the technical specifications of the contact displacement sensor with a measurement range greater than 15 mm and the standard deviation is less than 0.01 μm. The conversion of noncontact measurement to contact measurement can realize the direct measurement of workpieces with complex surface conditions on the production line, breaking through the limitation of optical measurement and expanding the application of optical fiber interferometry.

Ultra-Sensitive Microwave-Photonic Optical Fiber Interferometry Based on Phase-Shift Amplification

This paper proposes phase-shift-amplified optical fiber interferometry based on microwave photonics (MWP) for sensing applications with substantially-improved sensitivity. The principal idea of the system combines a destructive interference-based phase-shift amplification technique with optical carrier-based microwave interferometry (OCMI). The phase sensitivity of the OCMI system is significantly improved due to the phase amplifier, and more importantly, can be adjusted by simply varying the amplitude ratio of the two beams used in the interferometer. The amplification of the phase sensitivity is numerically investigated and experimentally demonstrated using a Mach-Zehnder interferometer for temperature and strain measurements. The measurement results accurately match theoretical predictions. Moreover, we demonstrate that light-scattering dots in the optical fiber core, created by tightly-focused femtosecond laser pulses, can be used to precisely tune the amplitude ratio of the two-beam interferometer. We postulate that amplification of several orders of magnitude in phase sensitivity can be achieved in the OCMI system by employing micromachining methods.