Hongkun Zheng

Northeastern University | NEU · College of Computer and Information Science

The phase-sensitive optical time domain reflectometry scheme has attracted great research interest in distributed acoustic sensing (DAS) but suffers from a trade-off between the dynamic range and signal frequency. In this paper, an optical path difference (OPD) demodulation method is applied to an interferometer array composed of an ultra-weak fibe...

Optical fiber sensors have emerged as vital tools in various applications. Among them, Fabry-Perot interferometers (FPIs), have gained prominence due to their compactness and versatility in sensor design. Microwave photonics (MWP) techniques offer enhanced performance and flexibility for developing optical sensor interrogation methods. This paper p...

The measurement of acoustic signals at high frequencies with a large dynamic range remains a challenge for phase-demodulation-based fiber acoustic sensing systems due to the phase wrapping phenomenon. Here, an optical path difference (OPD)-assisted demodulation method aiming at breaking the limitations of phase demodulation is reported. By interrog...

The signal-to-noise ratio (SNR) of fiber-optic distributed acoustic sensing (DAS) systems based on Rayleigh backscattered (RBS) signals can be improved using point-backscattering-enhanced fiber (PBSEF). It is necessary to explore the methods to achieve stable and low noise demodulation for PBSEF-based DAS system. Driven by this, this work theoretic...

To break the π-phase criterion in phase demodulation, POFNet is proposed to fuse the OPD and the phase signal to estimate the unwrapping errors and recover larger phase. The results showcase its superiority performance.

An OPD-based demodulation method for acoustic signal detection is proposed, breaking the limit of phase demodulation. Experiment results demonstrated superior performance at high frequency, and the SNR increases proportionally with the frequency of the signal.

A stable and low noise demodulation for PBSEF based DAS system is explored by theoretical and experimental analysis. The results show that, direct-average and weighted-average, for suppressing the noise level of DAS and the optimal parameters are investigated.

This article reports a multi-point curvature sensor system based on multiplexed optical fiber Fabry-Perot interferometric (FPI) sensor devices and a microwave photonics interrogation technique. The FPI sensor is fabricated with the assistance of a capillary tube, where a short section of the capillary is sandwiched between two single-mode fibers, f...

Vibration sensing is vital in health monitoring of critical structures such as aerospace engines. Although there are many mature vibration techniques in the market, there still lacks simple sensors that are suitable in high temperature with wide-frequency range. In this paper, we proposed a chirped pulse interferometer (CPI) empowered by a pair of...

Optical fiber sensors that have a compact size and the capability for multi-parameter sensing are desired in various applications. This article reports a miniaturized optical fiber Fabry–Perot interferometric sensor with a length of hundreds of µm that is able to simultaneously measure variations of curvature, temperature, and strain. The sensor is...

Fabry-Perot interferometers have found a multitude of scientific and industrial applications ranging from gravitational wave detection, high-resolution spectroscopy, and optical filters to quantum optomechanics. Integrated with optical fiber waveguide technology, the fiber-optic Fabry-Perot interferometers have emerged as a unique candidate for hig...

A novel method is proposed to correct the distortions induced by phase unwrapping error. The method is further validated in processing the data acquired from a field test performed in ocean environments using a DAS system.

An in-fiber optofluidic Michelson interferometer fabricated by femtosecond laser micromachining technology was presented. The interferometer structure was prepared by a special optical fiber with two cores and a microchannel. One core was connected to the core of a single-mode fiber (SMF) and functioned as a sensing arm on the microchannel inner wa...

In this work, an optic-fiber sensor utilizing magneto-shape effect of magnetic fluid (MF) has been put forward to measure magnetic field direction. MF magneto-shape effect has been presented, simulated and verified through experiments as a magneto-optical effect. The sensor consists of a capillary glass tube, two single-mode fibers (SMFs) and MF. T...

For low fineness extrinsic Fabry-Perot inter-ferometer (EFPI) sensors, the discrete gap transform (DGT) algorithm can be usually adopted to acquire the cavity length, and the magnitude of its demodulation error is often larger than several hundred picometer. In this paper, three-parameter cosine fitting (TPCF) method is proposed to compensate for t...

A salinity sensor based on the principle of Mach-Zehnder interferometer (MZI) is presented and verified in this letter, which has certain advantages in the sensitivity and cost of the salinity sensor. This structure consists of a lead-in single-mode fiber (SMF), a small section of C-type micro-structured optical fiber (CMOF), a multi-mode fiber (MM...

A sensing probe based on fiber side-open cavity structure is proposed for the measurement of seawater temperature, which is mainly composed of a lead-in single mode fiber (SMF), a side-open cavity C-type microstructure fiber (SOCTF), a multimode fiber (MMF), a lead-out SMF, and a layer of polydimethylsiloxane (PDMS). It could effectively reduce the...

A reflective optical fiber sensor that is composed of two Fabry Perot cavities is proposed for temperature and salinity measurement. One of the Fabry Perot cavity which is fabricated by offset splicing is exposed to the ambient directly to sense the ambient salinity, the other is employed to compensate for the temperature coupling effect. A thin la...

In this paper, a reflective type optical fiber probe, which can measure the salinity and temperature simultaneously, is proposed. The proposed probe integrates Mach-Zehnder interferometer and Fabry-Perot interferometer in the same channel skillfully and effectively, which makes it possible to integrate more information into the sensor. The reflecte...

A cavity length demodulation method, which is dedicated to solving the frequency spectrum leakage and barrier effect of FFT analysis, is proposed. The signal interception is adopted to improve the demodulation effect, and the curve fitting method is applied to find a more accurate characteristic frequency of the spectrum. Compared with the pre-sett...

A novel magnetic field measurement method based on the magneto-volume effect is proposed. The magnetic field sensing structure fabricated by the proposed measurement method is made by the magnetic fluid (MF) partially filled into the hollow core fiber (HCF). The presence of air provides conditions for the change of MF volume with the magnetic field...

This publisher’s note contains corrections to Opt. Lett. 46, 2714 (2021).OPLEDP0146-959210.1364/OL.428001

For the purpose of monitoring seawater temperature, a novel Mach–Zehnder (MZ) temperature-sensing structure with a wedge-shaped open cavity is presented and experimentally studied in this article. The open-cavity structure realizes the direct contact between the sensing optical path and the external environment, and ensures the high sensitivity of...

A special open-cavity Mach–Zehnder salinity sensor is presented and verified in this Letter, which has obvious advantages in salinity sensitivity and loss. The open-cavity structure is composed of a short section of etched double-side hole fiber spliced between a pair of multimode fibers and connected in series between a pair of single-mode fibers,...

A magnetic field measurement method based on the magneto-volume effect of magnetic fluid (MF) and Fabry-Perot interferometer (FPI) is proposed, which has higher magnetic field sensitivity and shorter response time than the traditional optical fiber methods. The MF is partially injected into the fabricated Fabry-Perot (FP) cavity composed of two sec...

A novel method, which is based on the phase difference between the filtered spectrum and simulated spectrum, is proposed to compensate for the optical path difference (OPD) demodulation error of the interferometer sensors. With applying the phase difference technology, large dynamic range OPD demodulation with high accuracy is realized. Its princip...

A multifunctional optical fiber sensor fabricated by asymmetric offset splicing is proposed in this Letter. The light is divided into several parts at the offset interface, among which the transmitted light forms the Mach–Zehnder interference (MZI) spectrum while the reflected light forms the Fabry–Perot interference (FPI) spectrum. The online moni...

We proposed an ultra-sensitive seawater temperature sensor with extended measurement range by using an optical fiber Bragg grating (FBG) cascaded with a microfiber Mach-Zehnder interferometer (MZI) working at dispersion turning point (DTP). The FBG works as a rough temperature measurement tool, while the ultra-sensitive polydimethylsiloxane (PDMS)-...

A highly sensitive reflective Fabry-Perot (FP) magnetic field sensor using magnetic fluid (MF) based on Vernier effect is presented and experimentally verified. Capillary action acts as an injection of MF into a FP cavity, which is composed of a single mode fiber (SMF), capillary glass tube and a short section of SMF coated with gold film. Vernier...

In this study, an optical fiber pressure sensor based on a thin-walled oval cylinder is proposed. To sense the degree of deformation, a pair of fiber Bragg gratings (FBGs) are fixed on the outer wall of the oval cylinder. A finite element analysis is performed to analyze the sensing characteristic of the sensor. The temperature cross-sensitivity is...

A novel and compact temperature and relative humidity (RH) simultaneously measurement sensor based on compact Mach-Zehnder interferometer (MZI) and Fabry-Perot interferometer (FPI) is proposed and experimental implemented. The sensing structure is made by splicing a 200 μm single mode fiber (SMF) between two 10 cm SMFs with large core-offset. The c...

A compact, stable, low cost and high sensitivity fiber salinity sensor based on single mode fiber-single mode fiber-no-core fiber-single mode fiber-single mode fiber (SSNSS) structure is proposed and demonstrated. It is proved by experiments and simulations that the sensor has high sensitivity to external refractive index (RI) changes, so as to ach...

A new type of two-channel surface plasmon resonance (SPR) sensor based on hollow-core fiber (HCF) for simultaneous measurement of seawater salinity and temperature was presented in this article. One of the SPR channels that are excited on the outer surface of the HCF with Au film coating was used to measure the seawater salinity, while another SPR...

An optical fiber sensor was proposed and studied for the simultaneous measurement of flow rate and temperature. It includes a capillary steel tube, an adjustable target and two fiber Bragg gratings (FBGs). The two fiber Bragg gratings were fixed in the tube by glue, and they could be protected well. One end of the tube was assembled in the protecti...

A novel integrated optical fiber sensor was proposed for temperature, pressure and flow measurement. One fiber Bragg grating (FBG) was fixed in the target for temperature measurement. A couple of FBGs, which were stuck on the inner wall of a hollow cylindrical cantilever, were used to measure flow rate. Another couple of FBGs were fixed on the oute...

A practical FBG pressure sensor on the basis of diaphragm-cantilever was proposed and experimentally demonstrated. The measurement principle and the simulation verification were introduced. The proposed sensor is composed of a diaphragm, a cantilever, a rod and a cover. The rod transfer the deformation of the diaphragm to the cantilever. A pair of...