Fabry-Perot optical binary switch for aircraft applications

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.

Based on the mechanism of the liquid flow caused by charged particles and dielectrophoresis under electric field-induced forces, an optical fiber Fabry-Perot interferometer for measuring high voltage is proposed and demonstrated. A second-order equation is established to express the relationship between the voltage signal and the output light signal. In our experiment, both sinusoidal signal with 7 kV, 50 Hz, and instantaneous pulse signal with dozens of kilovolts are employed as testing voltage sources. The results show that when the pulse voltage is applied, the output light signal exhibits a waveform near to the impulse response of a second-order system. A formula is derived to reveal the feature of linear and quadratic voltage effects in the experiment. As for ac voltage response of 50 Hz, the output light waveforms show only ~0.1 ms delay. There is a good agreement between the theory and the experimental result. Moreover, there is no need to use expensive materials and polarization devices in the scheme. Our proposed sensing technique has the potential to measure high pulse voltage or the periodic high voltage.

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.

In low-coherence reflectometry, the light scattered back from a scattering medium is expected to carry information about the spectral properties of the medium as well as range information about the reflective boundaries and backscattering sites. We built and evaluated a white-light interferometry system that gives the range and spectral information about the medium using the white-light continuum. The white-light continuum gives an extremely bright and broad spectrum. Experimental results on multi-layered media are presented.

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.

Liquid level sensing is nowadays a relevant issue in a broad range of applications, forcing the sensors performance and cost to be evaluated in parallel. This paper proposes a fiber optic-based liquid level sensor system using a fiber Fabry-Perot interferometer (FPI) embedded into a polyurethane resin diaphragm. The FPI is based on microcavities generated upon catastrophic fuse effect, enabling the fiber recycling and sensors fabrication in a cost-effective way, compared to traditional methods. To enable the simultaneous temperature control, a fiber Bragg grating was used as thermal reference sensor to compensate the temperature cross-sensitivity. The sensor prototype was tested in a field application, using two different configurations, an open chamber configuration, where the diaphragm is in contact with the atmosphere, and a closed chamber configuration revealing the sensitivities of 4.4 ± 0.1 pm/mm and 1.57 ± 0.04 pm/mm, respectively. These sensitivity values are within the figures of merit for diaphragm-based sensors as reported recently.

An opto-microfluidic static pressure sensor based on a fiber Fabry-Perot Interferometer (FPI) with extended air cavity for enhancing the measuring sensitivity is proposed. The FPI is constructed in a microfluidic channel by the combination of the fixed fiber-end reflection and floating liquid surface reflection faces. A change of the aquatic pressure will cause a drift of the liquid surface and the pressure can be measured by detecting the shift of the FPI spectrum. Sensitivity of the sensor structure can be enhanced significantly by extending the air region of the FPI. The structure is manufactured by using a common single-mode optical fiber, and a silica capillary with the inner wall coated with a hydrophobic film. A sample with 3500 μm air cavity length has demonstrated the pressure sensitivity of about 32.4 μm/kPa, and the temperature cross-sensitivity of about 0.33 kPa/K.

A highly sensitive, compact, and low-cost trace gas sensor based on photothermal effect in a hollow-core fiber Fabry-Perot interferometer (FPI) is described. The Fabry-Perot sensor is fabricated by splicing a piece of hollow-core photonic bandgap fiber (HC-PBF) to single-mode fiber pigtails at both ends. The absorption of a pump beam in the hollow core results in phase modulation of probe beam, which is detected by the FPI. Experiments with a 2 cm long HC-PBF with femtosecond laser drilled side-holes demonstrated a response time of less than 19 s and noise equivalent concentration (NEC) of 440 parts-per-billion (ppb) using a 1 s lock-in time constant, and the NEC goes down to 117 ppb (2.7×10-7 in absorbance) by using 77 s averaging time.

This work presents a novel, simple and sensitive air-gap fiber Fabry-Perot (FP) interferometer (AG-PPFI) which is based on an Sn-overlaying process. Various air-gaps for the FP interferometric cavities are formed between the fiber endface and Sn metal.

The sensing characteristics of irradiated fiber Bragg gratings (FBGs) and Fabry-Perot interferometers (FPIs) were investigated under a 2 MGy dose of gamma radiation. The study found that the pressure sensitivity of FP sensors after irradiation was stable, while the temperature sensitivity of FBG sensors was unstable, and both wavelengths displayed a shift. These findings offer the possibility for the application of FP pressure sensors in the gamma radiation environments, and FBG sensors require further research to be suitable for application in the nuclear radiation environments.

In this paper, we demonstrate a method about designing a tunable and multiple-channel filter. The filter is a combination of a fiber Fabry-Perot interferometer (FPI) and fiber Bragg gratings (FBGs). Through utilizing different period fiber gratings, we can attain a larger free spectral range, and keep the FWHM small in the meantime, so over 30 nm of free spectral range and 0.058 nm of FWHM of this filter are achieved.

A novel monitoring system for a fiber Fabry-Perot interferometer (FFPI) temperature sensor has yielded a resolution of 0.013 degrees C (0.0025 fringe). Light from a broadband source passes through a scanned Michelson interferometer and is reflected from a FFPI to produce a fringe pattern, the temporal position of which is proportional to a change in the optical length of the fiber interferometer. A second Michelson interferometer with a distributed-feedback laser source is used to correct for variations in the translation rate of the motor-driven scanning mirror. Coherence multiplexing of three such sensors has also been demonstrated.

In this paper, we report a sensitivity-controllable refractive index (RI) sensor based on a reflective θ-shaped microfiber resonator cooperated with Vernier effect. The θ-shaped microfiber resonator is a reflective all-fiber device with comb spectrum under weak coupling condition. By cascading it with a fiber Fabry-Perot interferometer, Vernier effect is generated to demodulate surrounding RI with enhanced sensitivity. Theoretical analysis reveals that RI sensitivity of the combined structure with Vernier effect is m times higher than the sensitivity of singular θ-shaped microfiber resonator. Moreover, by adjusting cavity length of the θ-shaped microfiber resonator, magnification factor M = (m + 1) can be tuned which enables the RI sensitivity to be controlled. Experimental result demonstrates that the RI sensitivity can be widely tuned from 311.77 nm/RIU (Reflective index unit) to 2460.07 nm/RIU when the cavity length of the θ-shaped microfiber resonator is adjusted from 9.4 mm to 8.7 mm. The θ-shaped microfiber resonator based all-fiber RI sensor featuring controllable sensitivity and compact size can be widely used for chemical and biological detections. The proposed scheme of generating Vernier effect also offers a universal idea to increase measurement sensitivity for optical fiber sensing structures with comb spectrum.