Stably suppressing laser relative intensity noise on a 3 × 3 coupler interferometric system.

A 3 × 3 coupler multiphase demodulation scheme is proposed to eliminate the impact of working point drifting and the laser relative intensity noise (RIN) on a 3 × 3 coupler interferometric system. An ellipse-fitting algorithm (EFA) is applied to fit the two interference signals of the 3 × 3 coupler in order, then the ATAN algorithm is applied to obtain three noise-containing signals with specific trigonometric relationships. By averaging the three signals, the demodulated phase noise induced from RIN can be effectively eliminated.

Nonlinear error elimination using the fusion of PGC-DCM, geometric fitting, and Atan algorithms.

A phase generated carrier (PGC) demodulation scheme is always accompanied by nonlinear errors. We propose a fusion of PGC differential and cross multiplying (PGC-DCM), geometric fitting, and arctangent (Atan) algorithms for fiber optic interferometric sensors to eliminate nonlinear errors. The output amplitude of the PGC-DCM algorithm is used to judge whether the Lissajous figure of quadrature signals is larger than 1/2 ellipse arc.

Ameliorated 3 × 3 coupler-based demodulation algorithm using iteratively reweighted ellipse specific fitting.

Passive demodulation scheme using 3 × 3 coupler has been widely used in phase-sensitive optical time-domain reflectometry (φ-OTDR), interrogation of fiber Bragg gratings or fiber optic interferometric sensors, and sensor multiplexing. However, the asymmetry of the 3 × 3 coupler in real applications affects the demodulation performance seriously. We proposed an ameliorated 3 × 3 coupler-based demodulation algorithm using iteratively reweighted ellipse specific fitting (IRESF) to overcome the drawback.

Phase noise suppression technique based on an improved reference interferometer scheme.

The reference interferometer scheme is an effective noise reduction method, but the optical path length difference (OPD) of the two interferometers must be strictly equal, which limits its application in practical environments. In this paper, an improved reference interferometer demodulation technique without strictly equal OPDs is proposed to suppress phase noise. By introducing a reference interferometer, the phase noise can be removed from the demodulation results.

Improved topography measurement with a high dynamic range using phase difference sensing technology.

Phase difference sensing technology (PDST) is employed for topography measurement, and two interference structures are proposed to achieve upper-limit adjustment and high resolution in the measurement range: a dual-wavelength system with a single Fabry-Perot (FP) cavity and a single-wavelength system with dual FP cavities. The phase difference between the two interference signals is determined by an elliptic fitting algorithm (EFA), and this change in phase difference is utilized to characterize the step height. Experimental results indicate that the measurement upper-limit can be adjusted to either 410 µm, 187 µm, or 108 µm by varying the wavelength difference in the dual-wavelength system, which gives a measurement error of 2.

Improved ellipse-fitting phase demodulation technique to suppress the effect of light source intensity noise in interferometric system.

An improved ellipse-fitting algorithm phase demodulation (EFAPD) technique is proposed to reduce the influence of light source intensity noise on a system. In the original EFAPD, the sum of the intensities of coherent light (ICLS) is an important part of the interference signal noise, which makes the demodulation results suffer. The improved EFAPD corrects the ICLS and fringe contrast quantity of the interference signal by an ellipse-fitting algorithm, and then calculates the ICLS based on the structure of pull-cone 3 × 3 coupler, so as to remove it in the algorithm.

Fiber optic temperature and strain sensor using dual Mach-Zehnder interferometers.

A fiber optic temperature and strain sensor using dual Mach-Zehnder interferometers (MZIs) is proposed. The dual MZIs were fabricated by fusion splicing of two different fibers between two single-mode fibers. The two fibers of thin-core fiber and small-cladding polarization maintaining fiber were fusion spliced with a core offset.

Ameliorated PGC demodulation technique based on the ODR algorithm with insensitivity to phase modulation depth.

For the optical fiber sensing system using phase generated carrier (PGC) technology, it is very important to eliminate the nonlinear effect of phase modulation depth (C) fluctuation on the demodulation results in the actual environment. In this paper, an ameliorated phase generated carrier demodulation technique is presented to calculate the C value and suppress its nonlinear influence on the demodulation results. The value of C is calculated out by the fundamental and third harmonic components with the equation fitted by the orthogonal distance regression algorithm.

Cardiac damage in autoimmune diseases: Target organ involvement that cannot be ignored.

Autoimmune diseases are diseases that cause damage to the body's own tissues as a result of immune dysfunction, often involving multiple organs and systems. The heart is one of the common target organs of autoimmune diseases. The whole structure of the heart can be affected, causing microcirculatory disorders, arrhythmias, pericardial damage, myocarditis, myocardial fibrosis, and impaired valvular function.

Highly sensitive temperature and strain sensor based on an antiresonant hollow core fiber probe with the Vernier effect.

A highly sensitive temperature and strain sensor based on an antiresonant hollow core fiber (ARHCF) probe with the Vernier effect is proposed and experimentally demonstrated. The ARHCF probe is used as a reference interferometer by sandwiching an ARHCF, which is insensitive to temperature, strain, and refractive index, between a single-mode fiber (SMF) and a polarization-maintaining fiber (PMF). The polarization mode interferometer (PMI), fabricated by splicing a section of PMF with a fiber polarizer at a 45-degree angle, works as a sensing interferometer.

High-stability PGC demodulation technique with an additional sinusoidal modulation based on an auxiliary reference interferometer and EFA.

In the reference interferometer demodulation scheme, it's difficult to guarantee in practice that both interferometers have the same optical path length difference (OPD), which makes the phase modulation depth different in different interferometers with the same laser modulation. The random shift of phase modulation depth also affects the demodulation results. An improved phase-generated carrier (PGC) technique is proposed based on an auxiliary reference interferometer and the ellipse fitting algorithm (EFA).

Large-range phase-difference sensing technology for low-frequency strain interrogation.

Phase-difference sensing technology (PDST) has been applied to strain measurement, but its completeness is destroyed by the phase-difference measurement range. A scheme that can realize the completeness of the PDST for low-frequency strain interrogation is proposed. It is built on dual-interferometers and the elliptic-fitting algorithm.

Phase-shifted demodulation technique with additional modulation based on a 3 × 3 coupler and EFA for the interrogation of fiber-optic interferometric sensors.

A phase-shifted demodulation technique with a 3×3 coupler and ellipse fitting algorithm (EFA) for the interrogation of interferometric sensors is proposed. To reduce the error of the EFA as to measure small phase signals, additional phase modulation is introduced. The additional modulation provides a walk of the operating point along the Lissajous ellipse large enough to permit calculation of the ellipse parameters at every moment.

Simultaneous measurement of refractive index and temperature or temperature and axial strain based on an inline Mach-Zehnder interferometer with TCF-TF-TCF structure.

A refractive index (RI) and temperature or a temperature and axial strain sensor based on an inline Mach-Zehnder interferometer with thin core fiber (TCF)-thin fiber (TF)-TCF structure is proposed and experimentally demonstrated, requiring only the cleaving and fusion splicing methods. The operation principle depends on the effect that the TF cladding modes interfere with the core mode as an optical coupler. The RI, temperature, or axial strain variations can lead to resonance dip variations in the interferometer spectra, and the RI, temperature, or axial strain sensitivity can be measured by monitoring the wavelength shifts of resonance dips.

Axial strain applied in-fiber Mach-Zehnder interferometer for acceleration measurement.

We present an axial strain applied in-fiber Mach-Zehnder interferometer (MZI) for acceleration measurement. A thin core fiber is sandwiched between two single-mode fibers with core offset to form the MZI. A controlled high fringe visibility in the transmission spectrum is obtained by applying an axial strain, leading to a large slope at the quadrature point.

Thin fiber-based Mach-Zehnder interferometric sensor for measurement of liquid level, refractive index, temperature, and axial strain.

An all-fiber Mach-Zehnder interferometric sensor capable of measuring liquid level, refractive index (RI), temperature, and axial strain is proposed and experimentally demonstrated. The proposed sensor is based on a fiber ball-thin fiber (TF)-core-offset structure sandwiched between two standard single-mode fibers. The variations of ambient liquid level, RI, temperature, and axial strain cause the change of phase difference between the cladding modes and the core mode, which leads to the shift of interference spectrum.

Miniaturized Fabry-Perot probe utilizing PMPCF for high temperature measurement.

We propose a miniaturized optical fiber Fabry-Perot probe for high temperature measurement (up to 1000°C). It is simply fabricated by fusion splicing a short section of polarization-maintaining photonic crystal fiber (PMPCF) with a single-mode fiber (SMF). The interface between the core of the SMF and air holes of the PMPCF, and the end face of the PMPCF work as the mirrors.

High temperature Vernier probe utilizing photonic crystal fiber-based Fabry-Perot interferometers.

This study proposes a highly sensitive and stable optical fiber probe based on Vernier effect for high temperature measurement (up to 1000 °C), utilizing photonic crystal fiber (PCF)-based Fabry-Perot interferometers (FPIs). The cascaded FPIs are fabricated by fusion splicing a section of polarization maintaining PCF to a lead-in single-mode fiber, and then a section of temperature-insensitive hollow core PCF is spliced between the PMPCF and a multi-mode fiber. The shift of the spectral envelope is monitored to measure the temperature variation.

Enhanced sensitivity of fiber laser sensor with Brillouin slow light.

We proposed and experimentally demonstrated a new scheme for enhancing the sensitivity of a fiber laser sensor using Brillouin slow light. The Brillouin laser was exposed to environmental vibrations, producing fluctuations at 408 kHz frequency, which were then interrogated using a Mach-Zehnder interferometer. By introducing Brillouin slow light into one arm of the interferometer, the sensitivity increased by 1.

Real-time acceleration sensing with an arctan algorithm based on a modal interferometer.

This study proposes a fiber-optic accelerometer for low-frequency vibration signal detection. The phase velocities of the polarization eigenmodes are affected differently by signals, leading to a polarization rotation of the transmitted lights. The orthogonal square roots of the photovoltages are utilized for an arctan demodulation scheme.