We present a new computational algorithm of phase-shifting interferometry that can effectively eliminate the uncertainty errors of reference phases encountered when we obtain multiple interferograms. The algorithm treats the reference phases as additional unknowns and we determine their exact values by analyzing interferograms using the numerical least-squares technique. A series of simulations prove that this algorithm can improve measuring accuracy because it is unaffected by the nonlinear and random errors of phase shifters.

광위상간섭법에서 기준위상의 수치해석 보정 = Numerical correction of reference phases in phase-shifting interferometry

Flexible and stable demodulation techniques of large-scale fiber-optic Fabry–Perot (FP) acoustic sensors are highly desirable for accelerating their industrial applications. In this paper, we report a novel self-calibrating wavelength shifting interferometry (WSI) technique that enables simultaneous multi-point acoustic detection using diaphragm based fiber-optic FP acoustic sensors. A widely tunable modulated grating Y-branch (MG-Y) laser (1527∼1567 nm) performs high-speed wavelength switching, introducing phase-shifts in the wavelength domain for real-time phase retrieval. The proposed self-calibrating WSI is easily extended for multiplexing FP acoustic sensors by calibrating the corresponding phase-shift step of each sensor probe. Based on a modified Hariharan 5-step phase shifting algorithm, the phase-shift step for each channel can be calibrated in real-time, making the system robust in applications involving large environmental perturbations. An all-optical multi-point acoustic detection system based on WSI is proposed and experimentally demonstrated for the first time. Sound source localization experiments show that the multi-point acoustic detection system works stably and the positioning accuracy is about 2.42 cm.

Multiplexing fiber-optic Fabry-Perot acoustic sensors using self-calibrating wavelength shifting interferometry

A novel design method for fiber-optic Fabry-Perot (FP) acoustic sensor based on flywheel-like diaphragm has been proposed and experimentally demonstrated. Through theory analysis and simulation, we have established a sensing model based on the flywheel-like diaphragm and illustrated the acoustic sensor's resonant frequency regulation method. A flywheel-like diaphragm-based acoustic sensor has been fabricated and a dual-wavelength system is used to demodulate the phase fluctuation caused by acoustic wave. Experimental results show that the proposed acoustic sensor has an acoustic pressure sensitivity of 1.3967rad/Pa and noise-limited minimum detectable pressure (MDP) of ~16.43μPa/√Hz. The signal to noise ratio (SNR ) of 1kHz, 9kHz, and 20kHz are achieved to be 10.39dB, 60.51dB, and 37.14dB, respectively. Over a fairly broad response range (1 kHz to 20 kHz), the average SNR is up to 45.57dB. Moreover, our acoustic sensor's directivity map approximates to a heart shape. Its excellent frequency response characteristics, sensitivity, and directivity pattern is believed to have a bright application prospect.

https://iopscience.iop.org/article/10.1088/1361-6463/ab95bc/pdf

Flywheel-like diaphragm-based fiber-optic Fabry-Perot frequency tailored acoustic sensor

Fast interrogation of dynamic low-finesse Fabry-Perot interferometers: A review

A modified solid fiber-optic integrated Mach-Zehnder interferometer (IMZI) assisted with a thin piezoelectric sheet (TPS, ~130 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {\mathrm{ m}}$ </tex-math></inline-formula> thickness) and phase generated carrier (PGC) demodulation is proposed and investigated theoretically and experimentally. The IMZI’s two arms are respectively molded with epoxy resin (EP) and silicone rubber (SI). These two materials are with distinctly different elastic modulus and Poisson ratios, which guarantees the high sensitivity of the IMZI. As for PGC, different modulation frequencies and amplitudes are generated and the corresponding modulation depths are calculated to obtain the optimal modulating parameters. Furthermore, a pair of complementary photodetectors are used to remove unwanted DC component and only the first harmonic is utilized to recover the phase, which can effectively avoid signal fading. In the experiments, where the IMZI is put under the mattress, activity monitoring is addressed and subjects are recruited to investigate the vital signs monitoring performance. The consistency check analysis results show the calculated heart rate variability (HRV) and breath rate variability (BRV) results are highly correlated with reference results, and the Pearson’s r reaches 0.99. Moreover, reliability, post-exercise, and Valsalva Maneuver test are further conducted to verify the repeatability and dynamic monitoring capability. In conclusion, the proposed system is unobtrusive, cost-effective, robust, and convenient, which has great potential in future homecare and hospitalization. 

Thin Piezoelectric Sheet Assisted PGC Demodulation of Fiber-Optic Integrated MZI and its Application in Under Mattress Vital Signs Monitoring

In this paper, the optical fiber Fabry-Perot (F-P) interferometer based on phase-shifting technique and birefringence crystals is proposed and demonstrated. We use the characteristics of birefringence and four birefringence crystals with different thicknesses to obtain the quadrature phase-shifted signals, which are demodulated by phase-shifting technique. Two types of sensing interferometers are used in the experiment. One is the optical fiber F-P sensor and the other is composed of the fiber end face and the glass surface fixed on the nanopositioning stage. The experimental results show that the normalized standard deviation (SD) of the calibration microphone centerline is 1.97 and 2.63 times larger than the optical fiber F-P interferometer under the sinusoidal sonic signals of 21 kHz and 40 kHz, and the interferometer is effective in avoiding phase ambiguity. The proposed interferometer has high stability and can adapt to a larger measurement range.

Optical fiber Fabry-Perot interferometer based on phase-shifting technique and birefringence crystals.

In this paper, we propose and demonstrate the optical fiber Fabry-Perot (F-P) interferometer based on birefringent crystals and polarization technology. For recovering the variation signals, the orthogonal signals are obtained based on the birefringent crystal characteristics and the proposal thickness difference between the two crystals. The differential cross multiplication (DCM) algorithm is utilized to demodulate the orthogonal signals to obtain the phase variation of the optical fiber F-P sensor. The proposed interferometer has a minimum detection phase of 0.014 $\text{rad}/\sqrt {\text{Hz}} $ at the frequency of 25 kHz. In the experiment, two kinds of vibration signals with frequencies of 25 kHz and 15 kHz are used and the proposed interferometer SNR is 70 dB and 75 dB under the corresponding reference environment respectively. The experiment results show that the proposed interferometer can realize the measurement of large dynamic signals and has high stability. The proposed interferometer has the advantages of fast demodulation and good environmental adaptability.

/pdf/orthogonal-phase-demodulation-of-optical-fiber-fabry-perot-2rtlras8a8.pdf

Orthogonal Phase Demodulation of Optical Fiber Fabry-Perot Interferometer Based on Birefringent Crystals and Polarization Technology

The invention discloses an optical fiber Fabry-Perot strain sensor based on a single-mode optical fiber, a manufacturing method and a measuring method. An integral structure is formed by a transmission single-mode optical fiber (1), a hollow core optical fiber (2) and a sensing single-mode optical fiber (3), and a Fabry-Perot cavity (4) is formed in the structure, wherein the transmission single-mode optical fiber (1) is used for transmitting incident light and emergent light; the hollow core optical fiber (2) and the rear end face of the transmission single-mode optical fiber (1) are tightlywelded to form a heterogeneous optical fiber-micro tube welding point, and the sensing single-mode optical fiber (3) is used for sensing strain; and the Fabry-Perot cavity (4) serves as a strain sensitive element, and the refractive index and the sensing length of the sensing single-mode optical fiber (3) are caused to be changed, so that the interference phase of the Fabry-Perot cavity (4) is changed. The optical fiber Fabry-Perot strain sensor has a long sensing length and can effectively measure strain with a large distribution range; the manufacturing cost is low, and mass manufacturing isfacilitated; and simultaneously, the measurement of temperature parameters can be realized on the basis of strain measurement.

Optical fiber Fabry-Perot strain sensor based on single-mode optical fiber, manufacturing method and measuring method

The invention discloses a birefringent crystal-based optical fiber Fabry-Perot acoustic vibration sensing device and a demodulation method. Optical signals emitted by an SLD broadband light source aretransmitted to an optical fiber Fabry-Perot acoustic vibration sensor and are modulated under the effect of external acoustic vibration signals; the modulated optical signals are reflected back to a1*2 coupler and are split into four paths of signals by a 1*4 coupler; the four paths of signals pass through an optical fiber collimator array used for emitting, and are modulated by a polarizer array, a birefringent crystal array and an analyzer array; the modulated signals enter an optical fiber collimator array for receiving; the four paths of the optical signals are converted into electricalsignals through a photodetector array; four birefringent crystals in the birefringent crystal array have different thicknesses, so that a quadrature phase difference exists between each paths of signals, so that four paths of interference signals are acquired; and phase information is obtained on the basis of four-quadrant arc tangent, so that the demodulation of the acoustic vibration signals canbe realized. Compared with the prior art, the birefringent crystal-based optical fiber Fabry-Perot acoustic vibration sensing device and the demodulation method of the present invention can ensure measurement accuracy.

Birefringent crystal-based optical fiber Fabry-Perot acoustic vibration sensing device and demodulation method

The invention discloses a demodulation device and a demodulation method of a double-path quadrature phase optical fiber acoustic vibration sensor. According to the demodulation method, a light signalemitted by a light source (1) enters the optical fiber acoustic vibration sensor (3) through an optical fiber circulator (2), an external vibration signal causes vibration of a diaphragm of the optical fiber acoustic vibration sensor (3), and a modulated light signal is returned and divided into two signals through an optical fiber coupler (4); the two signals enter a birefringent crystal (6) through a double-path polarizer (5) to become two signals with a quadrature phase; the two signals are analyzed through a double-path analyzer (7); detection of the two optical signals is performed through a double-path photoelectric detector (8); a digital collection card (9) is adopted to perform signal collection; and cavity length change information is obtained finally after processing. Through the demodulation device and the demodulation method, effective demodulation of the optical fiber acoustic vibration sensor is realized, and the defects of previous relevant demodulation methods are overcome; and demodulation of high-frequency acoustic signals can be realized, the two signals with the stable quadrature phase are created, and the precision of a measurement result is guaranteed.

Huang Yi

Papers

Optical fiber Fabry-Perot interferometer based on phase-shifting technique and birefringence crystals.

Orthogonal Phase Demodulation of Optical Fiber Fabry-Perot Interferometer Based on Birefringent Crystals and Polarization Technology

Optical fiber Fabry-Perot strain sensor based on single-mode optical fiber, manufacturing method and measuring method

Birefringent crystal-based optical fiber Fabry-Perot acoustic vibration sensing device and demodulation method

Demodulation device and demodulation method of double-path quadrature phase optical fiber acoustic vibration sensor