Fiber-optic Fabry-Perot Pressure Sensor Research Articles

A Large-Range and High-Sensitivity Fiber-Optic Fabry-Perot Pressure Sensor Based on a Membrane-Hole-Base Structure.

In the field of in situ measurement of high-temperature pressure, fiber-optic Fabry-Perot pressure sensors have been extensively studied and applied in recent years thanks to their compact size and excellent anti-interference and anti-shock capabilities. However, such sensors have high technological difficulty, limited pressure measurement range, and low sensitivity. This paper proposes a fiber-optic Fabry-Perot pressure sensor based on a membrane-hole-base structure. The sensitive core was fabricated by laser cutting technology and direct bonding technology of three-layer sapphire and develops a supporting large-cavity-length demodulation algorithm for the sensor's Fabry-Perot cavity. The sensor exhibits enhanced sensitivity, a simplified structure, convenient preparation procedures, as well as improved pressure resistance and anti-harsh environment capabilities, and has large-range pressure sensing capability of 0-10 MPa in the temperature range of 20-370 °C. The sensor sensitivity is 918.9 nm/MPa, the temperature coefficient is 0.0695 nm/(MPa∙°C), and the error over the full temperature range is better than 2.312%.

Parallel Cross-Correlation Algorithm for the Fast Interrogation of High-Finesse Fiber-Optic Fabry-Perot Sensors

It is still a challenge to realize the absolute optical path difference (OPD) demodulation of the high-finesse fiber-optic Fabry-Perot (FP) sensors with a high resolution and high speed. This paper proposes an improved parallel cross-correlation (PCC) algorithm for the absolute OPD interrogation of the high-finesse FP sensors. The proposed demodulation algorithm is simulated and analyzed to verify the feasibility of the algorithm for sensors with different reflectivity or OPDs with large dynamic range. A high-finesse fiber-optic FP pressure sensor with a cavity length of about 1500 µm and reflectivity of 62.5% has been used to carry out the experiment. Results show that the measurement resolution of the PCC algorithm can reach the sub-nanometer level, the sensor' sensitivity is about 3.93 nm/KPa, which is similar to the theoretical value. By exploring the effect of reflectivity on the demodulation results, it is found out that accurate results are still obtainable even though the exact reflectivity is unknown. In addition, thanks to the multi-threading of computers and the parallel computing method proposed in this paper, the demodulation speed would be further improved.

A MEMS-Based High-Fineness Fiber-Optic Fabry-Perot Pressure Sensor for High-Temperature Application.

In this paper, a high-fineness fiber-optic Fabry–Perot high-temperature pressure sensor, based on MEMS technology, is proposed and experimentally verified. The Faber–Perot cavity of the pressure sensor is formed by the anodic bonding of a sensitive silicon diaphragm and a Pyrex glass; a high-fineness interference signal is obtained by coating the interface surface with a high-reflection film, so as to simplify the signal demodulation system. The experimental results show that the pressure sensitivity of this sensor is 55.468 nm/MPa, and the temperature coefficient is 0.01859 nm/°C at 25~300 °C. The fiber-optic pressure sensor has the following advantages: high fineness, high temperature tolerance, high consistency and simple demodulation, resulting in a wide application prospect in the field of high-temperature pressure testing.

A High Precision Fiber Optic Fabry–Perot Pressure Sensor Based on AB Epoxy Adhesive Film

This paper proposes a Fabry–Perot pressure sensor based on AB epoxy adhesive with ultra-high sensitivity under low pressure. Fabry–Perot interference, located between single-mode fiber (SMF) and hollow-core fiber (HCF), is an ultra-thin AB epoxy film formed by capillary action. Then the thick HCF was used to fix the HCF and SMF at both ends with AB epoxy adhesive. Experimental results show that when the thickness of AB epoxy film is 8.74 μm, and the cavity length is 30 μm, the sensor has the highest sensitivity. The sensitivity is 257.79 nm/MPa within the pressure range of 0–70 kPa. It also investigated the influence of the curing time of AB epoxy on the interference spectrum. Experiments showed that the interference spectrum peak is blue-shifted with the increase of curing time. Our study also demonstrated the humidity stability of this pressure sensor. These characteristics mean that our sensor has potential applications in the biomedical field and ocean exploration.

Impact of support material deformation in MEMS bulk micromachined diaphragm pressure sensors

In this work, experimental data and finite element analysis reveals deflection in diaphragm supporting material leading to non-linear pressure-reflection response. These results are contrary to the standard assumptions presented in literature, where modelling of deflection response in diaphragm pressure sensors is primarily carried out assuming a rigid supporting structure. An extrinsic fiber-optic Fabry–Perot pressure sensor, based on micro-electromechanical system, is developed and used to investigate optical deflection response. While the sensor is not novel, a series of experiments to validate support deflection phenomena are designed and carried out using a silicon membrane at gauge pressures from 0 to 1000 PSI in ambient temperature. The device is packaged with an industry standard stainless-steel housing typically used in plastic injection moulding. Sensor performance is compared to analytical and finite element modelling. Results suggest that the device is experiencing greater deflection than analytically predicted at pressures above 200 PSI, where a rigid support is assumed in existing literature. Based on these results, a modified analytical model is proposed to correct for this behaviour. The modified model is created through addition of a nonlinear component to an existing model, which is then fitted to the experimental data using least-square methods. Prediction of the experimental deflection results is improved from 81% error using a fixed-support analytical model to 4% error using the presented adjusted model. It is demonstrated that nonlinear effects are present and optically measurable in cases where deflection is lower than 1% of the membrane thickness. This work will aid in the implementation of high-resolution pressure sensors operating in harsh environment conditions.

MgO Single Crystals MEMS-Based Fiber-Optic Fabry–Perot Pressure Sensor for Harsh Monitoring

A single crystalline magnesium oxide (MgO) MEMS-based fiber-optic Fabry-Perot (FP) pressure sensor was designed, fabricated and tested for 800 °C high-temperature environmental applications. In this article, MgO was selected as the sensitive materials of the optical sensor owing to its high melting point, and excellent mechanical and optical properties at elevated temperatures. The sensor head was constructed by combining wet chemical etching with direct bonding. This MEMS process technique realized all-MgO sensor head structure, which is beneficial to reduce the temperature gradient within the sensor structure, and avoid sensor failures. In addition, a non-scanning cross-correlated interrogation method is used to realize the demodulation of FP pressure cavity length having multiple reflectors. The experimental tests demonstrate that the proposed sensor can stably operate at an ambient environment of 22-800 °C and 0-0.6 MPa with a pressure sensitivity of 5.21 μm/MPa (room temperature), a repeatability error of 1.67% and a zero drift of 0.00353 μm/°C. In addition, the high-temperature testing proves that the adhesive-free well-sealed pressure cavity is conducive to improve the operating temperature and the performance of the sensor. To our best knowledge, this is the first research to realize fabrication of high-temperature pressure sensor by developing MgO micromachining technology. Our work is of fundamental importance in realization of pressure detecting in harsh environments.

Adhesive-free bonding fiber optic Fabry–Perot pressure sensor based on oxy-hydrogen flame welding and spiral tube

In this paper, a fiber optic Fabry–Perot (F–P) cavity high pressure sensor used in oil wells is presented. An F–P cavity probe encapsulated by silica capillary was fabricated through oxy-hydrogen flame welding, and the F–P cavity was fully sealed with adhesive-free bonding. A spiral tube filled with silicone oil was chosen to prevent the probe from directly contacting with down-hole corrosion fluid and to transfer pressure. A fiber Bragg grating was linked with the F–P cavity probe to measure ambient temperature for the probe’s temperature compensation. The sensing pressure can be as high as 82 MPa with a sensitivity of 241 nm/MPa, a repeatability of 0.05% F.S.(full scale), a resolution of 0.0004 MPa with the temperature ranging from room temperature to 175 °C. Besides, the maximum fluctuation of the F–P cavity length can be as small as about 0.0072 MPa within 40 days at the pressure and temperature of 42 MPa and 130 °C. In addition, this kind of sensor has been used in Shengli Oil Field.

Implantable self-aligning fiber-optic optomechanical devices for in vivo intraocular pressure-sensing in artificial cornea.

Artificial cornea is an effective treatment of corneal blindness. Yet, intraocular pressure (IOP) measurements for glaucoma monitoring remain an urgent unmet need. Here, we present the integration of a fiber-optic Fabry-Perot pressure sensor with an FDA-approved keratoprosthesis for real-time IOP measurements using a novel strategy based on optical-path self-alignment with micromagnets. Additionally, an alternative noncontact sensor-interrogation approach is demonstrated using a bench-top optical coherence tomography system. We show stable pressure readings with low baseline drift (<2.8 mm Hg) for >4.5 years in vitro and efficacy in IOP interrogation in vivo using fiber-optic self-alignment, with good initial agreement with the actual IOP. Subsequently, IOP drift in vivo was due to retroprosthetic membrane (RPM) formation on the sensor secondary to surgical inflammation (more severe in the current pro-fibrotic rabbit model). This study paves the way for clinical adaptation of optical pressure sensors with ocular implants, highlighting the importance of controlling RPM in clinical adaptation.

An Optimized PDMS Thin Film Immersed Fabry-Perot Fiber Optic Pressure Sensor for Sensitivity Enhancement

To effectively control the critical thickness of a polydimethylsiloxane (PDMS) film and enhance the sensitivity characteristics of the fiber pressure sensor, we propose a new method to optimize the thickness of the PDMS film in a fiber tube. It is characterized by analyzing the relationship between the diffusion rate of the PDMS and its viscosity, and using an oven to solidify the PDMS to a certain extent to accurately control the diffusion rate and diffusion length of the PDMS in the fiber tube. We also used multiple transfer methods to control the volume of the PDMS in the fiber tube to minimize the thickness of the formed PDMS film. Fabry-Perot interference occurs when the surface of the PDMS film layer filled into the fiber tube and the adjacent single mode fiber/fiber tube form a joint surface. This method forms a new fiber-optic Fabry-Perot pressure sensor that is very sensitive to external pressure parameters. The experimental results show that the optimized film thickness will be reduced to an order of 20 μm. Correspondingly, the fiber-optic pressure sensor has a sensitivity of up to 100 pm/kPa, which is about 100 times that reported in the literature. The structure also has better resistance to temperature interference. To our knowledge, this is the first in-depth study of the effects of the PDMS viscosity coefficient, diffusion rate, and fiber pressure sensitivity in fiber. The film thickness optimization method has some advantages, including a low cost, good controllability, and good application value in high sensitivity pressure and sound wave detection.

Miniature All-Silica Microbubble-Based Fiber Optic Fabry-Perot Pressure Sensor with Pressure Leading-In Tube

A novel all-silica fiber optic Fabry-Perot (FP) pressure sensor with pressure leading-in tube based on microbubble structure is developed and experimentally demonstrated. The FP cavity is formed by fixing the end face of the single-mode fiber (SMF) parallel to the outer surface of the microbubble, in which the microbubble with a diameter of about 318 μm is constructed at the end of silica hollow tube. When external pressure is transmitted on the inner surface of the microbubble by the pressure leading-in tube, the FP cavity length changes with the diameter of microbubble. Experimental results show that such a sensor has a linear sensitivity of approximately 4.84 nm/MPa at room temperature over the pressure range of 1.1 MPa; the sensor has a very low temperature coefficient of approximately 2 pm/°C from room temperature to 600°C. The sensor has advantages of extremely low temperature coefficient, compact structure, and small size, which has potential applications for measuring pressure in high-temperature environment.

Fiber-optic Fabry-Perot pressure sensor based on sapphire direct bonding for high-temperature applications.

In this study, a fiber-optic Fabry-Perot (FP) high-temperature pressure sensor based on sapphire direct bonding is proposed and experimentally demonstrated. The sensor is fabricated by direct bonding of two-layer sapphire wafers, including a pressure diaphragm wafer and a cavity-etched wafer. The sensor is composed of a sensor head that contains a vacuum-sealed cavity arranged as an FP cavity and a multimode optical fiber. The external pressure can be measured by detecting the change in FP cavity length in the sensor. Experimental results demonstrate the sensing capabilities for pressures from 20kPa to 700kPa up to 800°C.

短腔长复合式光纤法布里-珀罗压力传感器椭圆拟合腔长解调算法

短腔长复合式光纤法布里-珀罗压力传感器椭圆拟合腔长解调算法

Fiber Optic Fabry-Perot Pressure Sensor With Embedded MEMS Micro-Cavity for Ultra-High Pressure Detection

A fiber-optic Fabry–Perot pressure sensor with embedded micro-electromechanical system (MEMS) micro-cavity for ultra-high pressure detection is demonstrated. The embedded-type structure (ETS) is first proposed and analyzed to meet the requirements of ultra-high pressure detection. The geometry parameters of sensor have been optimized by analyzing mechanical and optical characteristics. From the analysis results based on the ETS, an ultra-high pressure sensor is fabricated and experimentally demonstrated for ultra-high pressure detection. The ultra-high pressure experiment illustrated response relationship between the absolute phase and pressure in the range of 2–120 MPa, and full-scale (FS) errors less than 0.079% F.S. at room temperature. The other characteristics index of sensor such as pressure sensitivity, hysteresis error, and temperature's influence factor are superior to 1.071 rad/MPa, 1.397%, and $\text{2.665} \times {\text{10}^{ - \text{3}}}{\text{ rad}}/^\circ {\text{C}}$ , respectively. The transient response time of system is 0.27 s. The sensor can be used for ultra-high pressure detections, which is necessary in deep-sea and oil exploration.

Batch-producible MEMS fiber-optic Fabry-Perot pressure sensor for high-temperature application.

A fiber-optic Fabry-Perot pressure sensor based on a micro-electro-mechanical system (MEMS) and CO2 laser fusion technology is developed and experimentally demonstrated for high-temperature application. The sensing heads are batch-fabricated by anodically bonding the micromachined Pyrex glass wafer and local gold-plated silicon wafer. The separated sensing head and the single-mode fiber are fused together to form the Fabry-Perot cavity using the CO2 laser. In order to improve the measurement accuracy in a high-temperature environment, a fiber Bragg grating is used as a temperature sensor for temperature decoupling. The experimental results show that the fiber-optic Fabry-Perot pressure sensor has a maximum nonlinearity of 0.4%. The maximal error of the pressure after temperature decoupling is less than 1.05% over a pressure range of 0-0.5MPa and a temperature range of 20°C-350°C. The batch fabrication technology makes the sensors low cost and high uniformity.

Fiber-optic Fabry-Perot pressure sensor based on low-temperature co-fired ceramic technology for high-temperature applications.

In this study, a novel batch-producible fiber-optic Fabry-Perot (FP) pressure sensor based on a low-temperature co-fired ceramic technology is proposed and experimentally demonstrated for high-temperature applications. The sensor is fabricated by inserting a well-cut single-mode fiber (SMF) into a zirconia fiber ferrule, followed by insertion of the overall structure into an alumina sensor head. The FP cavity in the sensor is formed by placing the end face of the SMF in parallel to the diaphragm. The external pressure can be detected by demodulating the FP cavity length of the sensor. A theoretical analysis indicates that the pressure sensitivity can be designed flexibly by adjusting the parameters of the ceramic diaphragm, radius, and thickness. Experimental results demonstrate that the pressure sensor exhibits a high linear sensitivity of approximately 0.1μm/kPa at room temperature in the pressure range up to 160kPa. The repeatability error and nonlinear error of three repeatable experiments are approximately 2.60% and smaller than 0.101%, respectively. The temperature coefficient and coefficient of the pressure-sensitivity changes with temperature are 0.023μm/°C and 0.205nm/(kPa°C) in the temperature range of 20°C-300°C.

Microbubble-based fiber-optic Fabry-Perot pressure sensor for high-temperature application.

Using arc discharge technology, we fabricated a fiber-optic Fabry-Perot (FP) pressure sensor with a very low temperature coefficient based on a microbubble that can be applied in a high-temperature environment. The thin-walled microbubble can be fabricated by heating the gas-pressurized hollow silica tube (HST) using a commercial fusion splicer. Then, the well-cut single-mode fiber (SMF) was inserted into the microbubble, and they were fused together. Thus, the FP cavity can be formed between the end of the SMF and the inner surface of the microbubble. The diameter of the microbubble can be up to 360μm with the thickness of the wall being approximately 0.5μm. Experimental results show that such a sensor has a linear sensitivity of approximately -6.382 nm/MPa, -5.912 nm/MPa at 20°C, and 600°C within the pressure range of 1MPa. Due to the thermal expansion coefficient of the SMF being slightly larger than that of silica, we can fuse the SMF and the HST with different lengths; thus, the sensor has a very low temperature coefficient of approximately 0.17pm/°C.

Fiber optic Fabry–Perot pressure sensor based on lensed fiber and polymeric diaphragm

A novel optical fiber-based Fabry–Perot pressure sensor fabricated with a lensed fiber and a polymeric diaphragm is proposed for application in the medical field. The lensed fiber was constructed at the tip of a single mode fiber, for use with a deformable flexible polymeric diaphragm. The sensor can reduce the loss of optical power of the back-reflected light, and the flexible diaphragm can increase deformation sensitivity. The lensed fiber was fabricated from a coreless silica fiber attached to a single mode fiber by splicing using a fusion splicing method, and arc discharge. The polymeric diaphragm consists of layered PDMS, parylene and gold mirror. The intermediate parylene layer is helpful to prevent cracking of the mirror when the diaphragm is deformed by external pressure. The polymeric diaphragm was fabricated by MEMS processing including spin-coating, vaporization, and sputtering. The deformation of the polymeric diaphragm was evaluated through numerical simulation. The change in cavity length between the lensed fiber and the polymeric diaphragm with external pressure was estimated using the interference generated from two reflected lights. Experimental results showed that the proposed pressure sensor has a sensitivity of 1.41μm/kPa over a pressure range from 0kPa to 4kPa with good linearity, and its minimum detection resolution is less than 0.03kPa. The proposed sensor could be used for reliable low-pressure measurement, especially in medical applications.

Fiber optic Fabry–Perot pressure sensor with low sensitivity to temperature changes for downhole application

Pressure and temperature are two important parameters in reservoir engineering. The fiber optic sensors can be used for permanent downhole monitoring. In this paper, we propose an extrinsic fiber Fabry–Perot interferometer (EFPI) sensor for pressure measurement with low sensitivity variation. The pressure sensitivity of EFPI sensor and of the fiber Bragg grating (FBG) sensors have been measured. The experimental pressure sensitivity for EFPI and FBG sensors are measured to be 2.75×10−81/kPa and 1.52×10−81/kPa, respectively. The temperature cross-sensitivity problem of the EFPI sensor has been solved by a new technique. The temperature sensitivity of EFPI sensor has been decreased to 1.2×10−6/°C, while the temperature sensitivity of non-compensated EFPI sensor has been measured to be 16.4×10−6/°C. The results show that the EFPI sensor has a higher pressure sensitivity and good capability to decrease temperature sensitivity in comparison to FBG sensor.

High-sensitivity intrinsic fiber-optic Fabry–Perot pressure sensor

A new configuration for a pressure sensor in which the motion of a diaphragm produces strain in a fiber Fabry-Perot interferometer (FFPI) is described. The single-mode fiber containing the interferometer is bonded at one end to the stainless-steel diaphragm. The fiber is also attached beyond the interferometer to the sensor housing in such a manner that it is always under tension and experiences a strain in proportion to the deflection of the diaphragm. An analysis relating the expected interferometer phase change to pressure is presented, and the dynamic response of the FFPI sensor to pressure changes produced by an air pump is in good agreement with that measured with a conventional pressure sensor.