Extrinsic Fabry-Perot Interferometric Optical Fiber Research Articles

Extrinsic Fabry–Pérot Underwater Acoustic Sensor Based on Micromachined Center-Embossed Diaphragm

Most research works emphasized on the acoustic sensor miniaturization are not optimized for applications under high surrounding pressure. For underwater acoustic sensing, measuring the small acoustic pressure from the huge hydrostatic pressure makes the design of the sensor challenging. In this paper, we attempt to solve the problem by adopting a center-embossed diaphragm as the sensitive structure. The deformation angular error is defined to evaluate the optical performance degradation and the optical sensitivity reduction under hydrostatic pressure. Simulations indicate that the central embossment is beneficial to maintain optics-related properties, although the structural sensitivity is reduced. Then, the diaphragm design guideline for underwater acoustic sensing is regulated. An optical fiber extrinsic Fabry-Perot interferometer probe based on the diaphragm, which was micromachined by double-side etching of the silicon on insulator, was designed and assembled. Experimental results show that the interferometric fringe preserves similar shapes at any tested depth from 0 (in air) to 50 cm. The recovered signal detected by the sensor coincides well with the corresponding transmitted signal. The pressure sensitivity response is flat in frequency range from 10 to 2 kHz, of which value is about -154.6 dB re. 1/μPa. It agrees well with the theoretical predication. These results demonstrated that the designed sensor according to the guideline can be used as an underwater acoustic sensor. Moreover, the sensor has potential applications in smart unmanned platforms and swiftly deployable arrays.

Large temperature sensitivity of fiber-optic extrinsic Fabry–Perot interferometer based on polymer-filled glass capillary

A novel and low cost fiber-optic extrinsic Fabry–Perot interferometer (EFPI) is proposed. The EFPI is fabricated at the fiber tip by inserting a single mode fiber (SMF) into a partially polymer-filled glass capillary to form an air micro-cavity, which can be precisely controlled with a three-dimensional translation stage. The optimal EFPI has a loss less than 10dB and a fringe visibility more than 30dB. Application of the EFPI for temperature measurement is experimentally demonstrated. Due to the high thermal expansion coefficient (TEC) of the polymer, the sensor exhibits a good linear response and large temperature sensitivity of ∼5.2nm/°C, which is almost three orders larger than that of the current F-P temperature sensors. Therefore, it may be applied to the surrounding temperature sensing.

通过改进非本征法布里-珀罗干涉型光纤传感器结构实现温度补偿的新方法

通过改进非本征法布里-珀罗干涉型光纤传感器结构实现温度补偿的新方法

High-sensitivity Fabry–Perot interferometric pressure sensor based on a nanothick silver diaphragm

We present a fiber-optic extrinsic Fabry-Perot interferometer pressure sensor based on a nanothick silver diaphragm. The sensing diaphragm, with a thickness measured in a few hundreds of nanometers, is fabricated by the electroless plating method, which provides a simple fabrication process involving a high-quality diaphragm at a low cost. The sensor exhibits a relatively linear response within the pressure variation range of 0-50 kPa, with a high pressure sensitivity of 70.5 nm/kPa. This sensor is expected to have potential applications in the field of highly sensitive pressure sensors.

一种光纤EFPI高温传感器

A fiber optic Extrinsic Fabry-Perot Interferometer(EFPI) high-temperature sensor based on steel capillary encapsulation is demonstrated.By using different materials with different coefficients of thermal expansion,the cavity length of the sensor is sensitive to the change of temperature,and the sensor can be used in high temperature situations.The sensor has many characteristics such as simple structure,high sensitivity,high-temperature durability and so on.Experimental results show that it has a sensitivity of 0.3837μm/℃,linearity of 0.9956,and a resolution of 0.26℃.Its normal operating temperature range is 0-400℃.

Optical fiber ultrasonic sensor networks based on WDM and TDM

An optical fiber sensor network for ultrasonic measurement based on wavelength division multiplexing (WDM) and time division multiplexing (TDM) technology is presented. Each of the sensor probes is an optical fiber extrinsic Fabry-Perot interferometer (EFPI) which is composed of the fiber's end face and the aluminum thin diaphragm. The sensors are arranged in different wavelength domains formed by a wavelength division multiplexer. Each wavelength division multiplexer, with a group of the sensors, is connected to one of the output ports of optical switch to realize TDM. The signal of each sensor is exported sequentially from a tunable narrowband optical filter (TNOF) that queries every sensor though scanning mode. The principle of the phenomenon of phase induced signal fade in interferometric fiber-optic sensors is also analyzed. Nicely, the detection method above implements the operation of anti-phase induced signal fade detection. The system is interrogated by broadband light source. The scanning range of TNOF is full of the bandwidth of the light source. The result of experiment in water show that the sensor sensitivity reaches −162dB(0dB=1rad/μPa), the frequency response range is from 10KHz to 5 MHz. The number of multiplexing sensors based on WDM and TDM reaches to 64.

Pressure sensor based on the fiber-optic extrinsic Fabry-Perot interferometer

Pressure sensors based on fiber-optic extrinsic Fabry-Perot interferometer (EFPI) have been extensively applied in various industrial and biomedical fields. In this paper, some key improvements of EFPI-based pressure sensors such as the controlled thermal bonding technique, diaphragm-based EFPI sensors, and white light interference technology have been reviewed. Recent progress on signal demodulation method and applications of EFPI-based pressure sensors has been introduced. Signal demodulation algorithms based on the cross correlation and mean square error (MSE) estimation have been proposed for retrieving the cavity length of EFPI. Absolute measurement with a resolution of 0.08 nm over large dynamic range has been carried out. For downhole monitoring, an EFPI and a fiber Bragg grating (FBG) cascade multiplexing fiber-optic sensor system has been developed, which can operate in temperature 300 °C with a good long-term stability and extremely low temperature cross-sensitivity. Diaphragm-based EFPI pressure sensors have been successfully used for low pressure and acoustic wave detection. Experimental results show that a sensitivity of 31 mV/Pa in the frequency range of 100 Hz to 12.7 kHz for aeroacoustic wave detection has been obtained.

Extrinsic Fabry–Perot interferometric optical fiber hydrogen detection system

We present a new hydrogen sensor system based on the use of an optical fiber extrinsic Fabry-Perot interferometer coated with palladium silver (Pd-Ag) film. The sensing mechanism of such a sensor is based on the mechanical stress that is induced in the Pd-Ag film when it absorbs hydrogen. To obtain the absolute length of the air gap, a modified cross-correlation signal processing method is introduced. Results are presented for a comparison between two Pd-Ag films of different thicknesses. A temperature compensation method based on an optical switch is presented. The sensor is suitable for monitoring concentrations of hydrogen below the lower explosive limit.

Optical fiber sensor for tensile and compressive strain measurements by white-light Fabry–Perot interferometry

Based on the theory of optical fiber coupling and Fabry–Perot interference, a model of extrinsic Fabry–Perot interferometric (EFPI) optical fiber sensor for measuring strain is analyzed, and the theoretical model is demonstrated. A formula of white-light interfered EFPI optical fiber strain sensor is obtained. The system of the optical fiber sensor is designed using an LED source as light source to obtain reflected spectrum. The experimental results show that it coincides well with the computational simulation of theoretical model, which means the model is accurate.

Diaphragm-based extrinsic Fabry-Perot interferometric optical fiber sensor for acoustic wave detection under high background pressure

A new structure for diaphragm-based extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensors is presented. This structure introduces a through hole in a conventional diaphragm-based EFPI sensor and significantly reduces the effect of operating point drift due to the background pressure and fluctuations. This structure also potentially has high temperature stability.

Fiber temperature sensor for high-pressure environment

We describe a fiber optic extrinsic Fabry-Perot interferometer EFPI based temperature sensor that incorporates a pressure isolation fixture. The sensor has high temperature sensitivity and low pressure- induced crosstalk. The detailed analysis and discussion of the sensor design, the signal demodulation algorithm, and the sensor fabrication as well as the sensor performance are presented. © 2005 Society of Photo-Optical

Parameter design of signal processing for transmission/reflection-type hybrid extrinsicFabry–Perot interferometric optical fiber sensors

A transmission/reflection-type hybrid extrinsic Fabry–Perot interferometric (TRHEFPI)optical fiber sensor presents transmission-type and reflection-type sensor signalssimultaneously, and measurement directions can be robustly distinguished withthe phase lead or lag of the linear combination signal from the original sensorsignal. This sensor principle compensates for the ambiguous distinction of themeasurement directions and direction changes of conventional interferometric optical fibersensors, including extrinsic Fabry–Perot interferometric optical fiber sensors, dueto the exclusive use of fringe counting in signal processing. Designing a sensorcoefficient in the linear combination signal is one of the most important works insignal processing for the TRHEFPI optical fiber sensor because the magnitudeof the phase shifts depends on the sensor coefficient. A design method of thesensor coefficient is presented in this research. The method was verified withexperimental sensor signals and applied to strain measurement experiments. A method ofabsolute measurement using the TRHEFPI optical fiber sensor is also presented.

Phase-shifted transmission/reflection-type hybrid extrinsic fabry-perot interferometric optical fiber sensors

Conventional interferometric optical fiber sensors, including the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor, have the drawback of ambiguous measurement directions and direction changes, because their signal processing using only fringe counting cannot present measurement direction information, such as tension/compression of strain or increment/decrement of temperature. An EFPI optical fiber sensor constructed with a transmission-type structure (TEFPI optical fiber sensor) can successfully compensate for this problem. However, it has low interferometric fringe visibility and requires somewhat sophisticated signal processing to detect the measurement direction changes. In this research, a hybrid EFPI optical fiber sensor is presented from which transmission-type and reflection-type sensor signals can be simultaneously acquired. The linear combination of the actual transmission-type and reflection-type signals is shown to have a shifted phase from the reflection-type signal according to measurement directions, and thus the phase behavior of lead/lag can present the measurement direction information. Because the hybrid sensor uses separated signals for the measurement quantity and direction, its signal processing is more robust than that of the TEFPI sensor. The sensor and signal processing algorithm were verified with the strain measurement experiments.

Fiber-optic extrinsic Fabry-Perot interferometer strain sensor with <50 pm displacement resolution using three-wavelength digital phase demodulation

A fiber-optic extrinsic Fabry-Perot interferometer strain sensor (EFPI-S) of ls = 2.5 cm sensor length using three-wavelength digital phase demodulation is demonstrated to exhibit <50 pm displacement resolution (<2nm/m strain resolution) when measuring the cross expansion of a PZT-ceramic plate. The sensing (single-mode downlead-) and reflecting fibers are fused into a 150/360 microm capillary fiber where the fusion points define the sensor length. Readout is performed using an improved version of the previously described three-wavelength digital phase demodulation method employing an arctan-phase stepping algorithm. In the resent experiments the strain sensitivity was varied via the mapping of the arctan - lookup table to the 16-Bit DA-converter range from 188.25 k /V (6 Volt range 1130 k ) to 11.7 k /Volt (range 70 k ).

Fiber-optic extrinsic Fabry–Perot interferometer sensors with three-wavelength digital phase demodulation

A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry-Perot interferometer vibration, acoustic, and strain sensors. This scheme uses a superluminescent diode light source with interference filters in front of the photodiodes and real-time arctan calculation. Quasi-static strain and dynamic vibration sensing with up to an 80-kHz sampling rate is demonstrated. Periodic nonlinearities owing to dephasing with increasing fringe number are corrected for with a suitable algorithm, resulting in significant improvement of the linearity of the sensor characteristics.

A study on the development of transmission-type extrinsic Fabry-Perot interferometric optical fiber sensor

The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor has good sensitivity and resolution compared with other types of optical fiber sensors. However, they have the disadvantage that the distinction of strain direction of EFPI is difficult because of measurement method by only fringe counting. This paper presents the newly developed transmission-type EFPI (TEFPI) optical fiber sensor, which has been improved by additional functions, and whose measuring system differs from that of the reflection-type EFPI optical fiber sensors using a single-mode fiber (SMF) and multimode (MMF) fibers as light guides and reflectors, respectively. The output signal of the TEFPI optical fiber sensor was analyzed with the uniform plane wave-based model, the SMF power distribution-based model and the splice loss-based model; the analyzed signals were then verified experimentally. Based on the results of analysis, the TEFPI optical fiber sensor was fabricated using two single-mode fibers connected to the light source and optical receiver; this was then used in strain measurement. The strain measured by the TEFPI optical fiber sensor was compared with that measured by the electric strain gauge.

Vibration Responses of CFRP Laminated Beam Containing ER Fluids as a Variable Damper.

A CFRP sandwich composite beam containing electro-rheological (ER) fluids as a variable damper is prepared. The vibration strain responses of the composite beam supported under the cantilevered condition are measured by an Extrinsic Fabry Perot Interferometric (EFPI) optical fiber strain sensor. The experiment is conducted under external sinusoidal excitations. The timing of a sinusoidal electric field supplied to the ER fluids is adjusted by observing vibration strain responses with the EFPI optical fiber strain sensor. It is shown that damping properties of CFRP laminates are changed by controlling phase differences of the sinusoidal electric field from the strain response of the composite beam. The sinusoidal electric field having phase lead difference of 90° from the vibration response is most effective for suppressing the vibration of the composite beam. These experimental results are also explained by using a simplified equation of motion for the composite beam with a variable damping factor considering the strain dependency of ER fluids.

Fiber-optic extrinsic Fabry–Perot vibration-isolated interferometer for use in absolute gravity meters

In an absolute gravity meter, a laser interferometer measures the position of a test mass that is falling ina vacuum. The calculated value of gravity is the average acceleration of the mass during a set ofdrops. Since systematic accelerations of the optical system will bias the measured value of gravity,various interferometer geometries have been implemented in the past to isolate the optical system fromground motion. We have developed and tested a low-finesse fiber-optic extrinsic Fabry-Perotinterferometer that is fixed to the mass of a critically damped seismometer in which the effects ofsystematic ground motion and acoustic vibrations are reduced.

Neural Network Processing of Optical Fiber Sensor Signals for Impact Location

AbstractA system to detect and locate impacts by foreign bodies on a surface was developed and tested. Fiber optic extrinsic Fabry-Perot interferometer (EFPI) strain sensors were attached to or embedded in the surface, so that stress waves emanating from an impact could be detected. By employing an artificial neural network to process the sensor outputs, the impact location could be inferred to centimeter range accuracy directly from the arrival time data. In particular, the network could be trained to determine impact location regardless of material anisotropy. Results demonstrate that a back-propagation network identifiesimpact location for an anisotropic graphite/bismaleimide plate with the same accuracy as that for an isotropic aluminum plate.

Split-cavity cross-coupled extrinsic fiber-optic interferometric sensor

A new configuration of the fiber-optic extrinsic Fabry-Perot interferometer is demonstrated. This configuration utilizes two sensor heads on a single directional coupler in a split-cavity cross-coupled extrinsic fiber interferometric (SCEFI) arrangement to provide a four-beam interference. The need for quadrature phase biasing is eliminated, with a new spectrum analysis detection scheme devised for the SCEFI in a no-feedback condition. Good agreement between the model for interference and the experimental results is demonstrated. Wide applications for fiber sensor multiplexing and split-cavity étalons for filters in wavelength-division-multiplexing systems are indicated.