Interferometric Sensor System Research Articles

Improvement of Dynamic Range in a Time-Division Multiplexing-Based Linear Sagnac Interferometric Sensor System

Improvement of Dynamic Range in a Time-Division Multiplexing-Based Linear Sagnac Interferometric Sensor System

Bending classification from interference signals of a fiber optic sensor using shallow learning and convolutional neural networks

Bending monitoring is critical in engineering applications, as it helps determine any structural deformation caused by load action or fatigue effect. While strain gauges and accelerometers were previously used to measure bending magnitude, optical fiber sensors have emerged as a reliable alternative. In this work, a machine-learning-based model is proposed to analyze the interference signal of an interferometric fiber sensor system and characterize the bending magnitude and direction. In particular, shallow learning-based and convolutional neural network-based (CNN) models have been implemented to perform this task. Furthermore, given the repeatability of the interference signals, a synthetic dataset was created to train the models, whereas real interferometric signals were used to evaluate the models’ performance. Experiments were conducted on a flexible rod in fixed–free and fixed–fixed ends configurations for bending monitoring. Although both models achieved mean accuracies above 91%, only the CNN-based model reached a mean accuracy above 98%. This confirms that monitoring bending movements through interference signal analysis by means of a CNN-based model is a viable approach.

Characterization of Receptor Binding Affinity for Vascular Endothelial Growth Factor with Interferometric Imaging Sensor.

Wet Age-related macular degeneration (AMD) is the leading cause of vision loss in industrialized nations, often resulting in blindness. Biologics, therapeutic agents derived from biological sources, have been effective in AMD, albeit at a high cost. Due to the high cost of AMD treatment, it is critical to determine the binding affinity of biologics to ensure their efficacy and make quantitative comparisons between different drugs. This study evaluates the in vitro VEGF binding affinity of two drugs used for treating wet AMD, monoclonal antibody-based bevacizumab and fusion protein-based aflibercept, performing quantitative binding measurements on an Interferometric Reflectance Imaging Sensor (IRIS) system. Both biologics can inhibit Vascular Endothelial Growth Factor (VEGF). For comparison, the therapeutic molecules were immobilized on to the same support in a microarray format, and their real-time binding interactions with recombinant human VEGF (rhVEGF) were measured using an IRIS. The results indicated that aflibercept exhibited a higher binding affinity to VEGF than bevacizumab, consistent with previous studies using ELISA and SPR. The IRIS system's innovative and cost-effective features, such as silicon-based semiconductor chips for enhanced signal detection and multiplexed analysis capability, offer new prospects in sensor technologies. These attributes make IRISs a promising tool for future applications in the development of therapeutic agents, specifically biologics.

Optimization of VGG16 Algorithm Pattern Recognition for Signals of Michelson–Sagnac Interference Vibration Sensing System

Signal recognition accuracy and recognition time are the two most important parameters of pattern recognition in a fiber optic vibration sensing system. To obtain high recognition accuracy and short recognition time, this paper optimized the VGG16 algorithm and carried out VGG16-1D and VGG16-2D recognition on big data signals generated by a Michelson–Sagnac interferometric vibration sensor system. The results indicate that VGG16-1D has a higher accuracy of 98.44% and a shorter recognition time of 0.03 s. The proposed method is a more accurate and faster pattern recognition method for big data signals from optical fiber vibration sensing systems, which is helpful in promoting further applications of optical fiber sensing systems.

The Phase Noise Transfer Model in the Phase-Generated-Carrier-Based Interferometric Fiber-Optic Sensor

The phase-generated-carrier (PGC) method is one of the popular interrogation methods for the interferometric fiber-optic sensor systems. Among varieties of specifications, the noise characteristic is a key one that determines the minimum detectable signal. However, the mechanism of the noise transfer process in the PGC-based interferometric fiber-optic sensor has not been reported to the best knowledge. In this paper, the influences of three different types of noise sources on the noise floor of the PGC-based interferometric fiber-optic sensor system are studied systematically. On the basis of that, the phase noise transfer model is built and verified experimentally. The results depict that the theoretical model can well predict the experimental result. With the proposed theoretical model, the prediction and analysis of the output phase noise in the PGC-based interferometric fiber-optic sensor is available. In addition, the proposed model provides a potential support for locking the initial phases to suppress the common-mode noise in the PGC-based system. In this sense, the proposed model is a significant tool for the noise-target design and construction of the PGC-based in terferometric fiber-optic sensor system.

Improved multi-channel interferometric fiber-optic sensor demodulation based on the Goertzel algorithm.

In a multi-channel interferometric fiber-optic sensor system using space-division multiplexing (SDM) and phase-generated-carrier (PGC) demodulation, the phase delay and phase modulation depth fluctuation of each channel will affect the amplitude consistency and harmonic distortion of the demodulation results. In this paper, an improved demodulation scheme based on the Goertzel algorithm is proposed to calculate the multi-channel phase delay and phase modulation depth and to compensate for their fluctuations simultaneously. First, the carrier's 1st to 6th harmonic amplitudes in the interference fringe are extracted using the Goertzel algorithm. Then, the phase delay is calculated using the real and imaginary components of the 1st harmonic amplitude. The phase modulation depth is calculated with a combinatorial operation of the 1st to 6th harmonic amplitudes. In addition, a reference channel is introduced to implement phase delay and modulation depth feedback control. The experimental results demonstrate that the improved scheme can effectively suppress the harmonic distortion and improve the amplitude consistency of multi-channel interferometric fiber-optic sensors with low resource consumption.

Sensitive and real-time detection of IgG using interferometric reflecting imaging sensor system

Considering the limitations of well-known traditional detection techniques, innovative research studies have focused on the development of new sensors to offer label-free, highly sensitive, real-time, low-cost, and rapid detection for biomolecular interactions. In this study, we demonstrate immunoglobulin G (IgG) detection in aqueous solutions by using real-time and label-free kinetic measurements of the Interferometric Reflectance Imaging Sensor (IRIS) system. By performing kinetic characterization experiments, the sensor's performance is comprehensively evaluated and a high correlation coefficient value (>0.94) is obtained in the IgG concentration range of 1–50 μg/mL with a low detection limit (0.25 μg/mL or 1.67 nM). Moreover, the highly sensitive imaging system ensures accurate quantification and reliable validation of recorded binding events, offering new perspectives in terms of direct biomarker detection for clinical applications.

A Reliable, Label Free Quality Control Method for the Production of DNA Microarrays with Clinical Applications.

The manufacture of a very high-quality microarray support is essential for the adoption of this assay format in clinical routine. In fact, poorly surface-bound probes can affect the diagnostic sensitivity or, in worst cases, lead to false negative results. Here we report on a reliable and easy quality control method for the evaluation of spotted probe properties in a microarray test, based on the Interferometric Reflectance Imaging Sensor (IRIS) system, a high-resolution label free technique able to evaluate the variation of the mass bound to a surface. In particular, we demonstrated that the IRIS analysis of microarray chips immediately after probe immobilization can detect the absence of probes, which recognizably causes a lack of signal when performing a test, with clinical relevance, using fluorescence detection. Moreover, the use of the IRIS technique allowed also to determine the optimal concentration of the probe, that has to be immobilized on the surface, to maximize the target recognition, thus the signal, but to avoid crowding effects. Finally, through this preliminary quality inspection it is possible to highlight differences in the immobilization chemistries. In particular, we have compared NHS ester versus click chemistry reactions using two different surface coatings, demonstrating that, in the diagnostic case used as an example (colorectal cancer) a higher probe density does not reflect a higher binding signal, probably because of a crowding effect.

Common-Mode Noise Suppression Technique in Interferometric Fiber-Optic Sensors

Efficient suppression of common-mode noises (CMNs) is significant for the performance of interferometric fiber-optic sensor system. To suppress CMNs, a reference interferometer is normally required as noise canceller. In this paper, we firstly report a detailed correlation analysis between the outputs of the sensing and reference interferometers. By using a band-limited noise decomposing method, we show that the correlation coefficient of the two interferometer outputs is a strong function over their mean phase difference, which appears as the limiting factor of the CMN suppression effect. Based on the analysis, we propose a novel CMN suppression technique by locking the mean phase value of the sensing interferometer using a reference interferometer with a 3 × 2 coupler. Experimental results show that our technique can increase the correlation coefficient between the outputs of sensing and reference interferometers by 6% (to 0.93) and reduce its standard deviation by $\sim$ 70% compared to traditional method. The CMNs suppression factor is measured as $-$ 8.49 dB in the frequency range from 300 Hz to 1 kHz, comparing to $\sim -$ 6 dB achieved by traditional method of simple subtraction. Our results set a new benchmark on the noise level of interferometric fiber-optic sensors.

Design of an Optical Pressure Measurement System for Intraocular Pressure Monitoring

This paper studies the design and application of an interferometric sensor system intended for measuring intraocular pressure. The system consists of a hermetically sealed, biocompatible, wireless, and powerless interferometric pressure sensor and a portable handheld reader. The interferometric pressure sensor consists of a 200 nm silicon nitride diaphragm, a $10~\mu \text{m}$ SU-8 spacer, and a $200~\mu \text{m}$ glass substrate. As monochromatic light is directed towards the sensor cavity, interference fringes between the silicon nitride diaphragm and the glass substrate form as a function of the applied pressure. In-vitro measurements show pressure in the range of 0–60 mmHg can be determined reliably with an accuracy of ±0.3 mmHg, while ex-vivo experiments using rabbit cornea showed an accuracy of ±0.6 mmHg. The resolution of the sensor is 0.2 mmHg. These results demonstrate the ability of the system to measure small changes in pressure, including intraocular pressure of glaucoma patients.

Efficient Common-Mode Noise Suppression for Fiber-Optic Interferometric Sensor Using Heterodyne Demodulation

Common-mode noises (CMNs) are frequently encountered in all types of fiber sensor systems. Through involving a reference interferometer, here we report the application of a differential delay heterodyne scheme to suppress CMNs in fiber-optic interferometric sensor systems. The contributions of CMNs are shared by both sensing and reference interferometers and are further suppressed by heterodyne demodulation. For the first time, we develop the full theoretical model describing this method, and experimental results are also presented to confirm the theory. Theoretical analysis shows that the CMN suppression effect (SE, defined as the ratio of the noise floor of the sensing interferometer after and before suppression) is sensitive to several key parameters, including the mean phase difference, the ratio of the visibility, and ac amplitude between the two interferometers. Experimental results show that the proposed method can suppress CMNs by ~24 dB within the frequency range of 20 Hz to 1 kHz. The measured CMN SE agrees well with the theory. The CMN suppression method and the theory reported here can also be extended to other interferometric systems.

Investigation on the maximum signal handling capability of fiber optic interferometric sensor based on the digital heterodyne demodulation scheme

The maximum signal handling capability (MSHC) is an important parameter for the fiber optic interferometric sensor (FOIS) system. It is restricted by the heterodyne frequency (HF) and the digital quadrature demodulation algorithm (DQDA) in the digital heterodyne demodulation scheme. In this paper we systematically investigate the MSHC of the FOIS based on the digital heterodyne demodulation scheme through comparison of the HF-determined MSHC and DQDA-determined MSHC. When discussing the DQDA-determined MSHC, two widely used methods are included, which are arctangent and differential-cross multiply (DCM). The comparison results reveal that the arctangent-determined MSHC is 12dB larger than the DCM-determined MSHC. The HF-determined MSHC is between the two types of DQDA-determined MSHC. If the DQDA is arctangent, the MSHC of the system is the HF-determined MSHC. If the DQDA is DCM, the MSHC of the system is the DCM-determined MSHC. Experiments are carried out and the results are consistent with the theoretical analysis. The conclusion in this paper can help us to estimate the MSHC of the FOIS system based on the digital heterodyne demodulation scheme more accurately and provide a useful guideline for the design of the FOIS system with large demodulation dynamic scale.

Erratum to “Interferometric Sensor System for Blade Vibration Measurements in Turbomachine Applications” [Aug 13 2297-2302

Erratum to “Interferometric Sensor System for Blade Vibration Measurements in Turbomachine Applications” [Aug 13 2297-2302

Treatment of MZI sensor signal with an improved wavelet neighboring coefficients

In order to gain the wavelength drift of Mach–Zehnder interferometer (MZI) sensor system, achieve the measurement of ambient environment parameters precisely, so, need to treatment optical fiber sensing signal with noise. Firstly, introduce the method of neighborhood wavelet coefficient by analyzing the drawback of traditional wavelet de-noising methods. Secondly, an improved threshold is putted forward based on neighboring coefficients in this paper which is to overcome the shortcomings of traditional wavelet methods. Finally, the threshold function proposed by this paper deal with MZI sensing noisy signal together with improved threshold. The simulation result shows that the new method can get the better signal-to-noise ratios (SNR) and root of mean square error (MSE) simultaneously and gain the reconstruction signal of the higher correlation coefficient (CC). Compared with the soft and hard threshold method, its SNR increases by 2–4db, and compared with NeighCoeff, its SNR improves by 1.2db. The peak error is 1.6pm. So, the system can meet the requirement of improving sensor detection precision.

Application of the Spectrum Peak Positioning Technology Based on BP Neural Network in Demodulation of Cavity Length of EFPI Fiber Optical Sensor

An Extrinsic Fabry-Perot Interferometric (EFPI) fiber optical sensor system is an online testing system for the gas density. The system achieves the measurement of gas density information mainly by demodulating the cavity length of EF- PI fiber optical sensor. There are many ways to achieve the demodulation of the cavity length. For shortcomings of the big intensity demodulation error and complex structure of phase demodulation, this paper proposes that BP neural net-work is used to locate the special peak points in normalized interference spectrum and combining the advantages of the unimodal and bimodal measurement achieves the demodulation of the cavity length. Through online simulation and actual measurement, the results show that the peak positioning technology based on BP neural network can not only achieve high-precision demodulation of the cavity length, but also achieve an absolute measurement of cavity length in large dynamic range.

Self-calibrated non-contact fibre-optic Fabry–Perot interferometric vibration displacement sensor system using laser emission frequency modulated phase generated carrier demodulation scheme

In this paper, the principle of a self-calibrated non-contact fibre-optic Fabry–Perot interferometric vibration displacement sensor (FOFPIVDS) system is described and experimentally demonstrated. According to the principle, the Fabry–Perot cavity, constituted by placing the end face of a gradient-index lens in parallel with the measured vibration surface, is used to translate the vibration displacement of the measured vibration surface into phase shifts in the interference signal output from the FOFPIVDS, and the laser emission frequency modulated phase generated carrier (FMPGC) demodulation scheme based on the arctangent (Arctan) algorithm is adapted to demodulate the phase shifts. After eliminating the optical power modulation in the laser emission frequency modulation, the sensing model for the FOFPIVDS system using the FMPGC–Arctan demodulation scheme is established. On these bases, the FOFPIVDS is designed and fabricated, and the prototyping FOFPIVDS system is built and experimentally tested. The research results indicate that the fabricated FOFPIVDS system possesses the characteristics as follows: (1) the sensitivity is only determined by the laser wavelength and the vibration displacement measurement is self-calibrated, (2) the nonlinearity is 0.29% and (3) the resolution is less than 2.06 nm.

Resolution and sensitivity enhancements in strong grating based fiber Fabry–Perot interferometric sensor system utilizing multiple reflection beams

We investigate an asymmetric intensive fiber Bragg grating (FBG) defined Fabry–Perot (F–P) sensor system decoded by a multiple-path-matched Michelson interferometer. The interrogation of higher order reflection beams cannot only solve the problem of the degraded resolution induced by the spectral mismatch of the FBGs, but also amplify the effect of the fiber strain on the phase of the light. We demonstrate multiple reflection beams in the F–P cavity based on the concept of the FBG effective length for constructing respective interrogation interferometers, and present a cost function with optimized system parameters to improve noise properties. The performances of interrogating the second, third and fourth order reflection beams are compared in a strain sensing experiment arrangement. Under the condition of the same optical path length mismatch, the interrogation of the fourth order reflection beam can achieve 9.8dB sensitivity enhancement and 3dB resolution promotion compared with the result using the second order reflection beam.

High sensitive extrinsic fabry-perot interferometric sensor system with low cost

A high-sensitive fiber optic strain sensor system with low cost is demonstrated. The strain sensor is a microlens based high finesse Fabry-Perot interferometer, and a low-cost wavelength division coupler is used as a wavelength discriminator. A minor fluctuation of strain is changed to a power change at the output. Static strain and dynamic strain are successfully measured using the system. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 1491-1493, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26057

Dual Fiber-Optic Fabry–Perot Interferometer Temperature Sensor with Low-Cost Light-Emitting Diode Light Source

A dual fiber-optic Fabry–Perot interferometer (FFPI) sensor system with a low-coherence communication-system light-emitting diode (LED) as a light source is investigated to detect temperature variation signals. In this system, there are two FFPIs: the sensing and reference FFPIs. When the perturbation of interest, such as that of temperature, disturbs the sensing FFPI to produce a phase shift, the light reflected from the sensor is demodulated by the reference FFPI to extract the measurand. A low-power (sub-nW) optical signal is converted into an electrical signal and processed by a designed optical receiver. This setup is availably applied in biosensors to compensate the temperature variation in a sensing environment or sense the temperature effect in a certain measurement on an interior local site.

Composite-cavity-based Fabry-Perot interferometric strain sensors

A composite-cavity-based Fabry-Perot interferometric strain sensor system is proposed to gain the minimum cross sensitivity to temperature and a high multiplexing capability at the same time. The interrogation of the sensor system is based on a white-light interferometric technology, and the demodulation is achieved by analyzing the coherence spectra. A demonstration system with two sensors is presented and tested.