Fiber Fabry-Perot Research Articles

Effect of PMMA Removal Methods on Opto-Mechanical Behaviors of Optical Fiber Resonant Sensor With Graphene Diaphragm

Regarding the dependence of the treatment of removing polymethyl methacrylate (PMMA) from graphene upon the prestress in the film, two typical PMMA removal methods including acetone-vaporing and high-temperature annealing were investigated based on the opto-mechanical behaviors of the developed optical fiber Fabry-Perot (F-P) resonant sensor with a 125-µm diameter and ∼10-layer-thickness graphene diaphragm. The measured resonant responses showed that the F-P sensor via annealing process exhibited the resonant frequency of 481 kHz and quality factor of 1 034 at ∼2 Pa and room temperature, which are respectively 2.5 times and 33 times larger than the acetone-treated sensor. Moreover, the former achieved a high sensitivity of 110.4 kHz/kPa in the tested range of 2 Pa–2.5 kPa, apparently superior to the sensitivity of 16.2 kHz/kPa obtained in the latter. However, the time drift of resonant frequency also mostly tended to occur in the annealed sensor, thereby shedding light on the opto-mechanical characteristics of graphene-based F-P resonant sensors, along with an optimized optical excitation and detection scheme.

Numerical Analysis of Radiation Effects on Fiber Optic Sensors.

Optical fiber sensors (OFS) are a potential candidate for monitoring physical parameters in nuclear environments. However, under an irradiation field the optical response of the OFS is modified via three primary mechanisms: (i) radiation-induced attenuation (RIA), (ii) radiation-induced emission (RIE), and (iii) radiation-induced compaction (RIC). For resonance-based sensors, RIC plays a significant role in modifying their performance characteristics. In this paper, we numerically investigate independently the effects of RIC and RIA on three types of OFS widely considered for radiation environments: fiber Bragg grating (FBG), long-period grating (LPG), and Fabry-Perot (F-P) sensors. In our RIC modeling, experimentally calculated refractive index (RI) changes due to low-dose radiation are extrapolated using a power law to calculate density changes at high doses. The changes in RI and length are subsequently calculated using the Lorentz–Lorenz relation and an established empirical equation, respectively. The effects of both the change in the RI and length contraction on OFS are modeled for both low and high doses using FIMMWAVE, a commercially available vectorial mode solver. An in-depth understanding of how radiation affects OFS may reveal various potential OFS applications in several types of radiation environments, such as nuclear reactors or in space.

Microwave photonics interrogation for multiplexing fiber Fabry-Perot sensors.

A microwave photonics interrogation system for multiplexing fiber Fabry-Perot (FP) sensors is demonstrated in this paper. Different from previous FP demodulation schemes, this system aims at quasi-distributed sensing networks composed of FP sensors with a short effective cavity length less than 1 mm. With the help of a dispersion element, the superimposed reflected spectrum from FP sensors based on a hollow core fiber (HCF) can be converted into separate response passbands in the frequency domain simultaneously, whose center frequency will shift linearly with the variations of environment. The experimental results exhibit high linearity and interrogation ability for both the all-FP multiplexing system and hybrid multiplexing system. A strain interrogation sensitivity of 0.938 kHz/µɛ and temperature sensitivity of -0.699 MHz/°C have been realized, corresponding to a FP cavity length demodulation sensitivity of 1.563 MHz/µm. Furthermore, numerical studies about the impacts of the HCF-FP spectrum envelope on the RF response passband, as well as the theoretical minimum detectable cavity length and multiplexing capacity of the system, are also carried out.

Characteristics and Analysis of fiber Fabry-Perot Force Sensor

In this paper, a new optical fiber Fabry-Perot force sensor structure was designed based on the extrinsic optical fiber Fabry-Perot sensor. The sensor had the advantages of small size, high temperature and high pressure resistance, and had good resistance to strong electromagnetic interference. It can measure the friction force on the heat transfer pipe of steam generator in the harsh environment. The transmission characteristics of the sensor were analysed, and the performance of the sensor was simulated. Theoretically, the sensitivity of the sensor can reach 2.591 nm/N, and the minimum resolution can reach 11.309 N.

Finesse Limits in Hollow Core Fiber based Fabry-Perot interferometers

Due to their low sensitivity to changes to the external environment, low optical nonlinearity, low chromatic dispersion, and compatibility with fiber systems, hollow-core optical fibers (HCFs) represent an ideal medium for fiber Fabry-Perot interferometers (FPs). Many applications can benefit from the availability of FPs with high finesse or high finesse-length product. However, the mechanisms that limit the performance of HCF-based FPs are yet to be fully elucidated to the best of our knowledge. In this paper, we present a comprehensive analysis of several factors that impact HCF-FP performance and limit their finesse, e. g., mirror tilt, the distance between the HCF end-face and mirror, HCF cleave angle and HCF attenuation. In a sequence of experiments, we built and characterized five HCF-FPs with lengths ranging from 0.65 m to 9.25 m. By fitting the experimental data with derived analytical expressions, we found the mirror-assisted coupling loss to be below -0.0028 dB (corresponding to a coupling efficiency of 99.94%), which should allow finesse values greater than 5000 to be achieved. Experimentally, we demonstrate here a value of 2400, limited by the parameters of the mirrors available to us presently. We then show that the low coupling loss and high repeatability of mirror alignment and HCF cleave quality allows the effective use of such high-finesse FP for reliable measurements of HCF attenuation, even with short fiber length samples (10 m in our demonstration).

Optical Fiber Fabry-Perot Acoustic Sensors Based on Corrugated PET Diaphragms

In this manuscript, optical fiber Fabry-Perot acoustics sensors based on corrugated PET diaphragms were proposed, fabricated and tested. Corrugations of different depths were introduced into the PET by simple hot-embossing process. The performances of the fabricated acoustics sensors were tested and analyzed. The results showed the corrugations could effectively improve the performances of the sensors. The proposed fabrication method of the corrugated diaphragm showed the advantages of simplicity and low-cost, and the acoustic sensors showed flexible control of corrugated structure, which were suitable for weak acoustic sensing.

A PDMS Film Structured Optical fiber Ultrasonic Sensor with high Sensitivity and Wide Response Range characteristics

This paper proposes an implementation method of the optical fiber FP pressure ultrasonic sensor with a controllable cavity length and a variable membrane, in order to effectively improve the sensitivity and response range of the optical fiber Fabry-Perot (FP) ultrasonic sensor. The optical fiber FP ultrasonic sensor with PDMS film structure proposed in this paper has obvious advantages in improving sensitivity and response range.

Modeling of Fabry-Perot Micro Cavities Under Partial Spatial Coherence Illumination Using Multimode Optical Fibers

Extrinsic Fiber Fabry-Perot Interferometers (EFFPIs) are used for a wide range of applications such as sensors and optical filters. They are usually built using single mode (SM) fibers as they provide better performance and sensitivity when compared to multi-mode (MM) fibers. However, SM fibers are more sensitive to misalignment and MM fiber has a much higher capacity to handle wide spectral range optical power. In this work, a model is developed and experimentally examined for MM fibers based EFFPIs. The model is based on considering the MM fiber as a partial coherent source emitting a Gaussian-Schell beam. The model is used to predict the EFFPIs response and extracted parameters such as finesse, visibility and insertion loss and to study their variation with the cavity length. It can be used for both low and high reflectivity cavities. An experimental setup is formed using two Bragg-coated MM fibers having a numerical aperture (NA) of 0.22 and a core diameter of 62.5 μm, the coating has a high reflectivity above 0.98 over a wavelength range extending from 1490 nm to 1600 nm. The model output is compared with the experimental results and a good agreement is observed.

Stable and narrow linewidth linear cavity CW-active Q-switched erbium-doped fiber laser

A stable and narrow-linewidth, continuous wave and active Q-switching erbium-doped fiber laser, incorporating a fiber Bragg grating and a fiber Fabry-Perot tunable filter, was designed and experimentally implemented. Here, we proposed combining three approaches to suppress the mode hopping and improve both the output power stability and narrow the linewidth: first, two narrow-band optical filters, fiber Bragg grating and Fabry-Perot tunable filter were utilized in the laser cavity; second, the cavity configuration was optimized as a function of the output coupling ratio; finally, a 1.5 m long segment of unpumped erbium-doped fiber was inserted in the cavity to act as an induced virtual long and weak fiber Bragg grating. Using a 90% output coupling ratio, and monitoring over 120 min at room temperature, the 3 dB linewidth and power fluctuation of the fiber laser emission at 1550 nm were 16 kHz and 0.0025 dB respectively. Also, an optical signal to noise ratio (OSNR) of 82 dB was obtained. Keeping the same fiber laser configuration, laser pulses were also obtained using the Q-switching technique, realized by using dynamic spectral overlapping between the Bragg grating and the tunable filter. A stable output peak power of 5.6 W was achieved with a pulse width of 450 ns at a repetition rate of 1 kHz.

Hollow-Core Fiber-Tip Interferometric High-Temperature Sensor Operating at 1100 °C with High Linearity.

Over decades, fiber-optic temperature sensors based on conventional single-mode fibers (SMF) have been demonstrated with either high linearity and stability in a limited temperature region or poor linearity and thermal hysteresis in a high-temperature measurement range. For high-temperature measurements, isothermal annealing is typically necessary for the fiber-optic sensors, aiming at releasing the residual stress, eliminating the thermal hysteresis and, thus, improving the high-temperature measurement linearity and stability. In this article, an annealing-free fiber-optic high-temperature (1100 °C) sensor based on a diaphragm-free hollow-core fiber (HCF) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The proposed sensor exhibits an excellent thermal stability and linearity (R2 > 0.99 in a 100–1100 °C range) without the need for high-temperature annealing. The proposed sensor is extremely simple in preparation, and the annealing-free property can reduce the cost of sensor production significantly, which is promising in mass production and industry applications.

An optical Fiber Pressure Sensor With Ultra-Thin Epoxy Film and High Sensitivity Characteristics Based on Blowing Bubble Method

In this paper, an implementation method of high sensitivity thin film fiber optic pressure sensor based on air blowing method is proposed. The utility model is characterized in that a film ultra-thin microbubble structure is firstly formed on the surface of the AB epoxy glue solution by using high-pressure air, and then the film portion of the end portion of the microbubble is transferred to a single-mode fiber head with a hollow glass tube at the top. Finally, a thin film structure fiber Fabry-Perot fiber pressure sensor is formed. The experimental results show that the thickness of the thin film layer at the end of the FP sensor is only 16 μm. Correspondingly, the maximum pressure sensitivity can reach 263.15 pm/kPa. Meanwhile, due to the decrease of film thickness, the sensor's resistance to temperature interference is improved. The prepared fiber Fabry-Perot pressure sensor has the advantages of ultra-thin film thickness, high-pressure sensitivity, low cost and good repeatability. Therefore, it has good application value in high sensitivity pressure and sound wave detection.

Correlation-Like Demodulation of Fiber Fabry–Perot Sensor Based on Blackbody Radiation Light Source

The blackbody radiation can provide light source for the fiber Fabry-Perot sensor system, but the output signal is difficult to demodulate. Because the signal of Fabry-Perot sensor is modulated by spectrum of blackbody radiation and SNR of signal is low. In this paper, the characteristics of the fiber Fabry-Perot sensor signal based on the blackbody light source were investigated. Effect of spectrum of blackbody radiation and low SNR on demodulation was analyzed. Strain experimental results show that correlation-like algorithm can accurately demodulate the signal when the temperature of the blackbody light source is equal to or higher than 800 °C. The maximum mean square error is $8.375~\mu \varepsilon $ after separating influence of temperature by the relationship between center wavelength of blackbody radiation and temperature. Higher the temperature, higher the demodulation accuracy.

Resonant fiber-optic strain and temperature sensor achieving thermal-noise-limit resolution.

In the area of fiber-optic sensors (FOSs), the past decade witnessed great efforts to challenge the thermal-noise-level sensing resolution for passive FOS. Several attempts were reported claiming the arrival of thermal-noise-level resolution, while the realization of thermal-noise-level resolution for passive FOSs is still controversial and challenging. In this paper, an ultrahigh-resolution FOS system is presented with a sensing resolution better than existing high-resolution passive FOSs. A fiber Fabry-Perot interferometer as the sensing element is interrogated with an ultra-stable probe laser by using the Pound-Drever-Hall technique. Both strain and temperature measurements are carried out to validate the performance of the sensor. The measured noise floor agrees with the theoretical thermal noise level very well.

Demodulation algorithm for optical fiber fabry-perot interference sensor

In view of resolution of optical fiber Fabry-Perot (FP) interference sensor, this paper analyses and researches high resolution demodulation algorithms including fast Fourier transform demodulation algorithm, cross-correlation calculation demodulation algorithm, vernier demodulation algorithm. Through continuous improvement, the vernier demodulation algorithm has achieved a resolution of 0.084nm. And it has a resolution of 2.3Pa when the vernier demodulation algorithm was applied to osmotic pressure measurement.

Design of low frequency fiber optic Fabry–Perot seismometer based on transfer function analysis

We develop a low frequency fiber Fabry–Perot (F-P) seismometer based on transfer function analysis. The seismometer structure and demodulation system accuracy are limitations of low frequency seismic monitoring. The transfer function of the F-P seismometer is analyzed, and the mass displacement spectrum (MDS) is introduced. MDS provides guidance for mechanical structure design and optical interferometer analysis to achieve low noise. The F-P seismometer prototype is built. The experiment shows that the prototype has an average noise of 6.74 ng/√ Hz below 50 Hz, and its noise is less than that of the global new high noise model within 0.16–50 Hz, whose potential is considerable.

Design of optical wedge demodulation system for fiber Fabry-Perot sensor

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Polymer Waveguides for Improved Sensitivity in Fiber Fabry-Perot Ultrasound Detectors

This paper presents a fabrication method and results from optical and acoustic characterization of a miniature fiber Fabry-Perot ultrasound detector. A high Q-factor was achieved by creating a self-aligned polymer waveguide within the resonator cavity to restrict diffraction losses. As a result of the improved optical Q-factor upon introduction of the waveguide, a high acoustic sensitivity was achieved. The device presented in this paper demonstrates an optical resonator Q-factor of >2000, and a Noise Equivalent Pressure of 350 Pa over a 25MHz bandwidth on a 125 μm fiber with a 9 μm waveguide. Sensitivity can be further improved significantly with the use of dielectric mirrors. The high sensitivity of these waveguided fiber Fabry-Perot ultrasound detectors makes them suitable for detection of both ultrasound and photoacoustic signals, while their small size makes this technology suitable for adoption in applications requiring small form factor, such as in interventional cardiology.

Design and simulation of a novel fungus-shaped center embossed diaphragm for fiber optic pressure sensors

A novel structure with a fungus-shaped center embossed diaphragm (FCED) geometry has been proposed to modify in diaphragm-based Fabry-Perot fiber optic pressure sensors (FP-FOPS). The proposed FCED geometry was obtained by adding a pillar between the mesa and diaphragm. Before the simulation analysis of FCED, we derived mathematical equations of attenuation factor widening the acceptance radius. The attenuation factor is defined to understand sensor loss, which is neglected in the literature. With this derived formula, the light reflected from the deflected diaphragm and the light unguided in the fiber was detected. Since the deformation angle is zeroized in the FCED structures, the sensor loss due to the attenuation factor is eliminated. All the incident light being re-guided in the fiber. With FCED design’s help, the decreasing sensitivity in the center embossed diaphragms (CED) has been prevented. Moreover, the deviation of the frequency response of FCED remains lower than 1% compared with the results of conventional diaphragms. As a result, it produces a more stable sensor, and the FCED structure is less affected by manufacturing errors. The researchers can benefit from the use of our presented results when designing and producing new diaphragm-based FP-FOPS.

A high-temperature resistant photonic crystal fiber sensor with single-side sliding Fabry-Perot cavity for super-large strain measurement

A photonic crystal fiber (PCF) Fabry-Perot (F-P) sensor capable of super-large strain measurement under high temperatures has been proposed and investigated in this paper. Two PCFs have been inserted inside of both sides of a quartz capillary with laser welding fixed and freely suspended layouts, respectively. Such configuration leads to a single-side sliding F-P cavity with a large measurement range. The designed sensor is compact and support a simple fabrication procedure with low cost. The sensing principle and validation experiments have been derived and implemented, respectively. Experiments results demonstrate that the sensor has an excellent resistance for the temperature within the range of 28 ºC ∼ 1100 ºC. A large mechanical-induced strain of 9436.66 με can be accurately detected under a high-the temperature reaching 1000 ºC. These merits enable the designed sensor to detect the super-large strain of turbine blades under a high-temperature environment.

Twice-FFT demodulation for signal distortion in optical fiber FP acoustic sensor

A Twice-FFT demodulation method for signal distortion state is proposed and experimentally demonstrated in an optical fiber Fabry-Perot (FP) acoustic sensor. Here the fiber FP acoustic sensor element is build with fiber end face and combination of diaphragms which is composed of a small round aluminum foil and a polymer PET film. The hypotenuse intensity demodulation method is applied to acquire the acoustic signal in time domain assisted with a Photodetector (PD) and an oscilloscope. The first Fast Fourier transform (FFT) processing results show harmonic distortion on the frequency domain spectrum. To demodulate the acoustic frequency and amplitude information, twice-FFT processing is preformed. Experimental results reveal an accuracy up to 95.6% of acoustic signal in the frequency range 2–100 Hz. Our scheme provides a new option for signal demodulation of optical fiber acoustic sensors (OFAS).