Multiplexed fiber Fabry–Perot temperature sensor system using white-light interferometry

A fiber Fabry-Perot interferometric (FFPI) temperature sensor system with digital signal processing scheme is introduced. Major functions of this digital processor is to determine the difference between the round trip optical phase shift of the sensor and reference FFPIs as changes occur in the temperature at the sensor location. The interference fringe shift caused by thermally induced chirping of laser diode light source is utilized in this scheme. The system is developed as a stand-alone instrument which has its own LCD display and a control keyboard.

The optical fiber Fabry-Perot interferometer (FPI) has been widely investigated as a potential temperature sensor. To function as a temperature sensor, the cavity of the FPI is typically constructed from either silica fibers or polymers. The silica cavity FPIs can function at temperatures exceeding 1 000 °C. However, their temperature sensitivity is constrained by their relatively low thermal optical coefficients and thermal expansion of silica materials. Although the polymer cavity FPI exhibits high temperature sensitivity, its cavity is susceptible to deterioration in high-temperature environments. Here, to overcome this challenge and achieve high-sensitivity temperature sensing in a high-temperature environment, we propose a new type of temperature FPI sensor by inserting and sealing a section of Cr20Ni80 metal microwire inside a section of a silica hollow core fiber (HCF) spliced to a standard single-mode fiber (SMF). The FPIs exhibit a high degree of temperature sensitivity due to the high thermal expansion of the Cr20Ni80 metal microwire. Since the Cr20Ni80 metal has a high melting temperature of 1 400 °C, such FPIs can function in high-temperature environments. Moreover, the temperature sensitivity of this FPI can be modified without affecting its reflection spectrum by changing the length of the metallic microwire within the hollow core fiber. The experimental results indicate that the proposed FPIs exhibit temperature sensitivity of greater than −0.35 nm/°C within the temperature range of 50 °C to 440 °C. Our proposed metal microwire-based FPIs are economical, robust, simple to fabricate, and capable of functioning in high-temperature environments, rendering them appealing options for practical applications.

We demonstrated an ultrasensitive temperature sensor based on a unique fiber Fabry-Perot interferometer (FPI). The FPI was created by means of splicing a mercury-filled silica tube with a single-mode fiber (SMF). The FPI had an air cavity, which was formed by the end face of the SMF and that of the mercury column. Experimental results showed that the FPI had an ultrahigh temperature-sensitivity of up to -41 nm/°C, which was about one order of magnitude higher than those of the reported FPI-based fiber tip sensors. Such a FPI temperature sensor is expected to have potential applications for highly-sensitive ambient temperature sensing.

We have proposed and demonstrated a novel elastic optical fiber Fabry-Perot interferometer (FPI)-based ac magnetic field sensor with high magnetic sensitivity and correction of temperature crosstalk. The elastic FPI is formed by soft splicing using low Young's modulus polydimethylsiloxane material at the joint point of a hollow-core fiber and single-mode fibers and is fixed on a common supermendur rod, a kind of magnetostrictive material. AC magnetic field-induced length change of the magnetostrictive rod results in the obvious change of the FPI cavity length and finally is transduced to the intensity variation of the sensor signal, which makes the sensor highly sensitive to ac magnetic field. Taking advantage of the elastic FPI structure, the magnetic sensitivity (in terms of strain) is improved to 48 ppm/mT (75.01 pm/mT in terms of wavelength), compared with the low intrinsic sensitivity of the conventional magnetostrictive rod (usually below several ppm/mT and 0.39 ppm/mT in our case). Moreover, the impact of temperature cross-sensitivity is removed by retrieving the wavelength shift of the FPI interference spectrum based on the calibrated signal voltage versus wavelength shift. All the ac magnetic fields of different frequencies and intensities have been successfully detected and measured by our FPI sensor without the impact of temperature crosstalk. We believe such a simple, compact, and cost-effective sensor would be a promising candidate for accurate monitoring of ac magnetic field.

A temperature sensor with two cascaded fiber Fabry-Perot interferometers (FPIs) is constructed and demonstrated, which works on envelope-based demodulation and exhibits a high temperature sensitivity. The sensor is fabricated by splicing a short segment of large mode area (LMA) fiber to a short segment of capillary tube fused with a section of single-mode fiber to form a cascaded FPI structure. Experimental results show that the temperature sensitivity achieves up to 249.22 pm/V by using envelope-based demodulation, which is much higher than the one obtained by directly tracing the resonant wavelength in the superposition interference spectrum or the one for a single FPI with air-cavity. Moreover, the proposed sensor is compact with dimension of <;1 mm. All the features make it promising for temperature measuring in many fields.

An optical binary switch for aircraft applications is demonstrated. A fiber Fabry-Perot interferometer (FFPI) bonded to a cantilever is used as the sensing element. A white-light interferometry system with two bulk Michelson interferometers sharing the same motor-driven translation stage is utilized to monitor the elongation of the FFPI. The system exhibits excellent linearity as a force sensor; the experimental results are in good agreement with theoretical calculated values. With a properly set threshold value, the system produces a binary output.

Temperature measuring is a daily procedure carried out worldwide in practically all environments of human activity, but it takes particular relevance in industrial, scientific, medical, and food processing and production areas. The characteristics and performance of the temperature sensors required for such a large universe of applications have opened the opportunity for a comprehensive range of technologies and architectures capable of fulfilling the sensitivity, resolution, dynamic range, and response time demanded. In this work, a highly sensitive fiber optic temperature sensor based on a double-cavity Fabry-Perot interferometer (DCFPI) is proposed and demonstrated. Taking advantage of the Vernier effect, we demonstrate that it is possible to improve the temperature sensitivity exhibited by the polymer-capped fiber Fabry-Perot interferometer (PCFPI) up to 39.8 nm/°C. The DCFPI is sturdy, reconfigured, and simple to fabricate, consisting of a semi-spherical polymer cap added to the surface of the ferrule of a commercial single-mode fiber connector (SMF FC/PC) placed in front of a mirror at a proper distance. The length of the air cavity (Lair) was adjusted to equal the thickness of the polymer cap (Lpol) plus a distance δ to generate the most convenient Vernier effect spectrum. The DCFPI was packaged in a machined, movable mount that allows the adjustment of the air cavity length easily but also protects the polymer cap and simplifies the manipulation of the sensor head.

An interferometric fiber optic sensor employing a light emitting diode (LED) as the optical source and two fiber Fabry-Perot interferometers (FFPI) which were fabricated in continuous length of a single-mode silica fiber is analyzed. The performance as a temperature sensor is demonstrated and the predicted behavior is confirmed.

Two-mode fiber Mach-Zehnder interferometric temperature sensor in the 50 °C – 650 °C range

Biomedical researchers and clinicians have long sought the development of small, low cost and disposable sensors for in-vivo measurements of pressure and temperature. These sensors typically measure static or quasi-static pressure and temperature and are required for direct and accurate measurements over a wide range of operational, enviromental and (especially) handling conditions.

A system is presented for sensing nanometer scale structural disturbances using white light interferometry in conjunction with a tracking controller. A Michelson interferometer is established using a fiber-coupled white light source, a beamsplitter cube, an actuated reference mirror, and a retroreflector attached to the structure of interest. Structural motion is determined by actively tracking the zeroth order white light interference fringe. A multimode controller architecture enables location of the white light fringe packet, coarse tracking of the packet by modulation of the actuated mirror, and fine tracking by locking onto the slope of the zeroth order fringe. Resolution and bandwidth of the measurement system is increased at each successive mode. Experimental results of the system prototype are presented. Applications include position control of optical elements in segmented aperture imaging systems such as the Next Generation Space Telescope and the USAF Research Lab UltraLITE space imager.

A fiber Fabry–Perot interferometer based on a PVA coating for humidity measurement

A novel high-sensitivity Fabry-Perot (FP) interferometer temperature sensor based on liquid crystals (LCs) and the Vernier effect is proposed and demonstrated in this Letter. This sensor is prepared by inserting two cleaved single-mode fibers into a section of a capillary tube to generate an FP cavity. The cavity is filled with LCs, which induces a Vernier effect due to the birefringence of LCs. The refractive indices of the ordinary and extraordinary light have different responses to the temperature changes. As a result, the temperature sensitivity is significantly improved by detecting the peak shifts of a periodic envelope. The experimental results show that the proposed sensor can provide a high-temperature sensitivity of 19.55nm/°C. This sensor offers key features and advantages of the Fabry-Perot interferometer, including low cost and good fringe visibility. Furthermore, such a sensor probe can meet different requirements of temperature sensing in various application areas by using different kinds of LCs.

A temperature-sensor system based on low-coherence interferometry with a fiber Mach-Zehnder interferometer as a phase modulator was implemented. A measurement range of 20 to 800 degrees C with a resolution of 0.025 degrees C (corresponding to 0.0004 fringe) was achieved with a 1-mm-long fiber Fabry-Perot interferometer as the sensing element.

A microfluidic gas flowmeter based on optical fiber Fabry-Perot interferometer(FPI) was proposed and demonstrated. The sensor was formed by two embedded optical fibers with a microfluidic gas channel running across the two end faces. The gas flowrate was first tested by monitoring the shift of the resonancewavelength of the FPI. The intensity demodulation method was then applied to investigate thedynamic response of the sensor, by utilizing a tunable laser and a photodiode. The experimental results show that our proposed microfluidic gas flowmeter has high sensitivity and fast response.