In-fiber Fabry-Perot Interferometer Research Articles

Compact Harmonic Vernier Sensor Based on an In-Fiber FPI with Three Reflector System for Simultaneous Gas Pressure and Temperature Measurement.

In this work, we proposed a sensitivity-enhanced temperature sensor, a compact harmonic Vernier sensor based on an in-fiber Fabry-Perot Interferometer (FPI), with three reflective interfaces for the measurement of gas temperature and pressure. FPI consists of air and silica cavities formulated by single-mode optical fiber (SMF) and several short hollow core fiber segments. One of the cavity lengths is deliberately made larger to excite several harmonics of the Vernier effect that have different sensitivity magnifications to the gas pressure and temperature. The spectral curve could be demodulated using a digital bandpass filter to extract the interference spectrum according to the spatial frequencies of resonance cavities. The findings indicate that the material and structural properties of the resonance cavities have an impact on the respective temperature sensitivity and pressure sensitivity. The measured pressure sensitivity and temperature sensitivity of the proposed sensor are 114 nm/MPa and 176 pm/°C, respectively. Therefore, the proposed sensor combines ease of fabrication and high sensitivity, making it great potential for practical sensing measurements.

Enhancing the Performance of FBG Accelerometers by Using In-Fiber Fabry Perot Interferometers

An in-fiber Fabry–Perot interferometer (FPI) is proposed and designed for performance improvement of a fiber Bragg grating (FBG) accelerometer. It consists of two FBGs which are inscribed using the femtosecond laser point-by-point technology. The spectral characteristics of the FBG Fabry–Perot (FBG-FP) were studied. Edge filter interrogation configuration was employed in the vibration measurement system. In contrast to the conventional FBG accelerometer used in wavelength interrogation or edge filter interrogation configurations, the scheme has a higher sensitivity and lower detection threshold which are achieved improving the optical properties of the accelerometer. We fabricated a high-frequency accelerometer and experiments were carried out to verify its performance. The sensitivity and detection threshold were 27.3 mV/g and 1.5 mg, respectively. This study presents a feasibility analysis of the short cavity FBG-FP, as opposed to a single FBG, for the vibration accelerometer.

Tunable multiwavelength Erbium-doped fiber laser based on in-fiber Fabry-Perot interferometer fiber Bragg gratings in linear and ring cavity configurations

Multiwavelength Erbium-doped fiber laser (MWEDFL) in the ring and linear cavities operating at 1.5-μm wavelength region was demonstrated. The multiwavelength fiber laser comprises a 3-m Erbium-doped fiber as an active gain medium, an in-fiber Fabry-Perot interferometer Fiber Bragg Gratings (FPI FBG) as a filter, and a 10-km dispersion compensating fiber (DCF) as a nonlinear gain medium. A comparison investigation was conducted. The MWEDFL in the linear cavity generates 12 stable lasing lines, with an optical signal-to-noise ratio (OSNR) of 45 dB. In the case of MWEDFL operated in a ring cavity, 8 stable lasing lines were generated, with an OSNR of 47 dB. The free spectral range (FSR) of 0.08 nm was measured for the FPI FBG in both linear and ring cavities MWEDFL spectrum. Besides, the stability measurement was conducted for 150 min for both MWEDFL cavities. Both lasers had a peak power fluctuation of less than 1.0 dB and negligible wavelength drifts below 0.1 nm. Furthermore, the wavelength tunability of MWEDFL in both configurations was performed by heating the FPI FBG from 28 °C to 100 °C. At the temperature of 100 °C, the MWEDFL shows a wavelength shift of 1.0 nm, and this can be further increased by heating the FPI FBG to its highest temperature limit. This MWEDFL employs in-fiber FPI FBG offers a compact, highly tunable, and simple design applicable for optical communications and optical sensing applications.

Discriminative measurement for temperature and humidity using hollow-core Fabry-Perot interferometer

In this work, an in-fiber Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated for ambient relative humidity (RH) and temperature measurements. The FPI is manufactured from short segments of hollow-core fiber (HCF) and photonic crystal fiber (PCF). The air-cavity in the HCF segment enables a strong light-air interaction whereas the air holes of the PCF serve as vents which enable the exchange of air between the air-cavity and the surrounding medium. Our findings show that the dip intensity is solely sensitive to the change in RH with a linear sensitivity of 0.06273 dB/%RH in the range of 35–71%RH whereas the dip wavelength is solely sensitive to the ambient temperature with a linear sensitivity of 10.64 pm/°C in the range of 25–70 °C. The cross-sensitivity between the two measurands can be disregarded, therefore no sophisticated equation is required for the discriminative measurement of humidity and temperature.

In-fiber Fabry Perot interferometer with narrow interference fringes for enhanced sensitivity in elastic wave detection

Abstract In this work, we have demonstrated using a pair of in-fiber Fabry-Perot interferometer (FPI) with matched Bragg wavelength and free spectral range (FSR) for elastic wave detection based on matched filter interrogation configuration. The cavity lengths of the FPI structures are deliberately made long to achieve small FSR to enhance their sensitivity to elastic wave pressure. It is found that the sensitivity of sensor to elastic wave pressure is linearly proportional to the FPI cavity length. This finding is in agreement with the theoretical analysis.

Dual micro-holes-based in-fiber Fabry-Perot interferometer sensor

A kind of dual micro-holes-based in-fiber Fabry-Perot interferometer sensor is proposed in this paper. The theoretical model of the reflection spectrum of proposed sensor is established based on the interference among four light beams, where both the relationships of the spectrum intensity with the length of micro-hole, refractive index (RI) of medium in cavity, transmission loss and reflection loss, and the characteristic parameters of fiber are demonstrated, and the temperature and RI responses of reflection spectra are also simulated. Through machining two micro-holes in single-mode fiber with 193 nm excimer laser, we fabricate the proposed fiber sensor which can be used for measuring the multi-physical quantities, and the corresponding experiments are demonstrated simultaneously. The results show that the sensor has better linear responses to temperature and RI change, and the corresponding linearity is superior to 99%. Due to having two sets of different temperature and RI sensitivities (i.e.-0.172 nm/℃ and 1050.700 nm/RIU; 0.004 nm/℃ and 48.775 nm/RIU) and better linearity, this kind of sensor can be used for measuring the temperature, the ambient RI and even the simultaneous discrimination of temperature and ambient RI. The RI and temperature resolutions are 1.010-5 RIU and 0.2℃, respectively. Furthermore, the sensor can also be used for sensing the gas pressure, and its measurement accuracy can reach to. 3 kPa. Owing to its high sensitivity, stability, small volume and easy fabrication, the sensor will be widely used in sensing technology.

In-fiber Fabry-Perot interferometer for strain and magnetic field sensing.

In this paper we discuss the results obtained with an in-fiber Fabry-Perot interferometer (FPI) used in strain and magnetic field (or force) sensing. The intrinsic FPI was constructed by splicing a small section of a capillary optical fiber between two pieces of standard telecommunication fiber. The sensor was built by attaching the FPI to a magnetostrictive alloy in one configuration and also by attaching the FPI to a small magnet in another. Our sensors were found to be over 4 times more sensitive to magnetic fields and around 10 times less sensitive to temperature when compared to sensors constructed with Fiber Bragg Grating (FBG).

High-Sensitivity Gas Pressure Sensor Based on Fabry–Pérot Interferometer With a Side-Opened Channel in Hollow-Core Photonic Bandgap Fiber

We demonstrate a high-sensitivity gas pressure sensor by use of an in-fiber Fabry-Perot interferometer (FPI) based on hollow-core photonic bandgap fiber (HC-PBF) with a side-opened channel. The FPI was constructed by splicing a thin piece of HC-PBF between two stander single-mode fibers. Then, a side-opened channel was drilled through the hollow core of the HC-PBF by use of a femtosecond laser. Such an FPI with a side-opened channel greatly enhanced the gas pressure sensitivity up to 4.24 nm/MPa, which is two orders of magnitude higher than that of FPI with an enclosed cavity. In addition, the effects of cavity length on the gas pressure sensing performance were also studied. A shorter cavity gives rise to broader measurement range while offering larger detection limit, and vice versa. The structure size is tens of micrometers, which makes it possible to develop an ultracompact high-sensitivity gas pressure sensor.

High-sensitivity strain sensor based on in-fiber improved Fabry–Perot interferometer

We demonstrated a high-sensitivity strain sensor based on an in-fiber Fabry-Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers. The sensitivity of this strain sensor was enhanced to 6.0 pm/με by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.1 pm/°C, which reduces the cross sensitivity between tensile strain and temperature.

Optical Fiber Vibration Sensor Using FBG Fabry–Perot Interferometer With Wavelength Scanning and Fourier Analysis

An in-fiber Fabry-Perot interferometer with fiber Bragg grating (FBG) mirrors (FBG-FPI) yields extremely narrow transmission peaks within the FBG reflection wavelength range. Periodical scanning of the laser light source wavelength produces a train of optical pulses and the occurrence time of the pulse is modulated as the FBG-FPI is under influence of strain. When dynamic strain due to mechanical vibration is applied to the FBG-FPI, the detected signal of the pulse train is Fourier transformed and processed to reproduce the waveform of the vibration-induced strain. Furthermore, an inexpensive DFB laser can be utilized as a light source because the narrowness of the transmission peaks does not require broad wavelength scanning.