Cascaded Fabry-Perot Interferometers Research Articles

Magnetic field sensing with in-fiber cascaded Fabry-Perot interferometers (FPIs) using femtosecond laser direct writing

A magnetic field sensor made with femtosecond laser direct writing was built and characterized. The sensor makes use of the Vernier effect (VE) via a cascade of two Fabry-Perot interferometers (FPIs) with similar free spectra ranges (FSRs). The sensor cavity FPI 1 and the reference cavity FPI 2 are made by writing reflective surfaces directly onto the core of a single-mode fiber (SMF) with a femtosecond laser. FPI 1 is secured to a magnetostrictive material. A single FPI 1 has a sensitivity of 6 pm/mT in the 10–50 mT range, but two cascaded FPIs have a sensitivity of −117.1 pm/mT and an amplification of 19.5. The sensor’s temperature properties are studied, and cross-sensitivity to temperature is eliminated. This sensor is easy to fabricate, compact, simple, and structurally stable, making it highly promising for magnetic field sensing applications.

Ultra-sensitive fiber-optic temperature sensor based on UV glue-based FPI and Vernier effect

In this paper, compact cascaded Fabry-Perot interferometers (FPI) for fiber-optic temperature sensors are proposed and verified. The sensors are prepared by combining the properties of temperature-sensitive material ultraviolet glue (UV glue) and the basic principle of the traditional Vernier effect (TVE), first-order harmonic Vernier effect (HVE), and second-order HVE. The sensing cavity FPIs is made up of UV glue filling the gap between two single-mode fibers (SMF) with flat cut ends. The reference cavity FPIr is composed of SMF-capillary-SMF structure. The temperature sensitivity of the FPIs is up to 1.01 nm/°C by the high thermal expansion coefficient of the UV glue. By changing the free spectral range (FSR) of the FPIr, high detection sensitivities achieved are −10.14 nm/°C, 15.22 nm/°C, and 22.24 nm/°C, corresponding the situation of TVE, first-order HVE, and second-order HVE, respectively. The experimental results indicate that temperature sensors based on UV glue possess a simple and compact structure and strong resistance to electromagnetic interference, making them suitable for temperature measurement in various environments.

Fiber Temperature Sensor Based on Cascaded Fabry–Perot Interferometers and Harmonic Vernier Effect

Fiber Temperature Sensor Based on Cascaded Fabry–Perot Interferometers and Harmonic Vernier Effect

Two-dimensional displacement (bending) sensor based on cascaded Fabry-Perot interferometers fabricated in a seven-core fiber.

We demonstrated a two-dimensional vector displacement (bending) sensor with high angular resolution based on Vernier effect generated by two cascaded Fabry-Perot interferometers (FPI) in a seven-core fiber (SCF). To form the FPI, plane-shaped refractive index modulations are fabricated as the reflection mirrors in the SCF using slit-beam shaping and femtosecond laser direct writing. Three pairs of cascaded FPIs are fabricated in the center core and the two non-diagonal edge cores of the SCF and applied to the vector displacement measurement. The proposed sensor exhibits high displacement sensitivity with significant direction dependence. The magnitude and direction of the fiber displacement can be obtained via monitoring the wavelength shifts. Moreover, the source fluctuations and the temperature cross-sensitivity can be referenced out by monitoring the bending-insensitive FPI of the center core.

High-sensitivity gas pressure sensor with low temperature cross-talk based on Vernier effect of cascaded Fabry-Perot interferometers

A gas pressure sensor composed of cascaded Fabry-Perot interferometers (FPIs) based on Vernier effect was demonstrated. Two hollow silica tubes (HSTs) with different inner diameters were used to construct the FP cavities, and spliced with single-mode fiber (SMF) to make a gas pressure sensor with a closed cavity FPI and an open cavity FPI in series. The experimental results show that the proposed sensor achieves a high gas pressure sensitivity of −44.31 nm/MPa in the range of 0–2.2 MPa due to the Vernier amplification effect and a very low temperature cross-sensitivity of −0.6 KPa/℃. This sensor has high sensitivity, wide measurement range, small temperature crosstalk, good robustness and low production cost in gas pressure measurement.

Highly sensitive temperature sensing probe based on two cascaded Fabry–Perot interferometers and Vernier effect

AbstractIn this paper, a temperature sensing probe is designed using two cascaded Fabry‐Perot interferometers (FPIs). FPI1 is made by splicing single‐mode optical fiber (SMF)‐no‐core optical fiber‐capillary‐SMF in turn, and then drilling a micro‐hole on the capillary wall of FPI1 with femtosecond laser, and injecting dimethyl silicone oil (DSO) into the capillary through the micro‐hole with immersion method. FPI2 is made by splicing SMF‐capillary‐SMF sequentially. Due to the thermal sensitivity of DSO, the temperature sensitivity of a single FPI1 reaches −0.3674 nm/°C. When the free spectral ranges of FPI1 and FPI2 are close, their cascaded sensor will produce a Vernier effect for improving the sensitivity. The experimental results show that the sensitivity of the sensing probe is as high as 1.8456 nm/°C. In addition, the sensor has a compact structure and can be used flexibly in confined space temperature measurement.

Highly Sensitive Strain Sensor by Utilizing a Tunable Air Reflector and the Vernier Effect.

A highly sensitive strain sensor based on tunable cascaded Fabry–Perot interferometers (FPIs) is proposed and experimentally demonstrated. Cascaded FPIs consist of a sensing FPI and a reference FPI, which effectively generate the Vernier effect (VE). The sensing FPI comprises a hollow core fiber (HCF) segment sandwiched between single-mode fibers (SMFs), and the reference FPI consists of a tunable air reflector, which is constituted by a computer-programable fiber holding block to adjust the desired cavity length. The simulation results predict the dispersion characteristics of modes carried by HCF. The sensor’s parameters are designed to correspond to a narrow bandwidth range, i.e., 1530 nm to 1610 nm. The experimental results demonstrate that the proposed sensor exhibits optimum strain sensitivity of 23.9 pm/με, 17.54 pm/με, and 14.11 pm/με cascaded with the reference FPI of 375 μm, 365 μm, and 355 μm in cavity length, which is 13.73, 10.08, and 8.10 times higher than the single sensing FPI with a strain sensitivity of 1.74 pm/με, respectively. The strain sensitivity of the sensor can be further enhanced by extending the source bandwidth. The proposed sensor exhibits ultra-low temperature sensitivity of 0.49 pm/°C for a temperature range of 25 °C to 135 °C, providing good isolation for eliminating temperature–strain cross-talk. The sensor is robust, cost-effective, easy to manufacture, repeatable, and shows a highly linear and stable response for strain sensing. Based on the sensor’s performance, it may be a good candidate for high-resolution strain sensing.

Relative humidity sensor based on cascaded Fabry-Perot interferometers and Vernier effect

We study and experimentally demonstrate a highly sensitive humidity sensor, whose sensitivity has an amplification effect, through the use of the Vernier effect produced by a cascaded Fabry-Perot interferometer (FPI). A section of capillary was spliced with single-mode optical fiber, and then the capillary was immersed in polyimide (PI) solution to form PI film to construct the structure of the sensor. The proposed sensor comprises an air cavity, a PI cavity, and an air-PI mixing cavity. Owing to the approximate free spectral range of the air cavity and air-PI mixing cavity, the sensor produces a Vernier effect. Theoretical analysis shows that the relative humidity sensitivity of the sensor is only related to PI film. The experimental results show that in the range of 40~85% relative humidity, the sensitivity of the spectral envelope of the sensor can reach ~344.4 pm/% RH, which is 3.77 times higher than that measured by the sensor interference fringe. The experimental results are basically consistent with the theoretical analysis.

High-Sensitivity Gas Pressure Sensor with Low Temperature Cross-Crosstalk Based on Vernier Effect of Cascaded Fabry-Perot Interferometers

High-Sensitivity Gas Pressure Sensor with Low Temperature Cross-Crosstalk Based on Vernier Effect of Cascaded Fabry-Perot Interferometers

Microfiber sensor probe integrated with a cascaded Fabry-Perot interferometer.

Developing micrometer-nanometer size optical fiber sensors has promising application prospects in microenvironments, such as biological cells, micro robots, and microfluids. We propose a new strategy to fabricate a microfiber sensor probe (MSP). A femtosecond laser was applied to integrate cascaded Fabry-Perot interferometers (FPIs) into a silica microfiber. And a MSP with diameter of ∼8µm, extinction ratio of 15 dB, fitness of 24.6, and Q-factor of 2310 was demonstrated in the experiment. In addition, the MSP was applied for the refractive index and thermal measurement and the sensitivity was observed to be 10 pm/°C and 18.5 nm/RIU. The two-beam approximation model was applied to analyze the spectrum, and simulations were taken to research the refractive index sensitivity influenced by the fiber size.

Simultaneous temperature and bending sensor based on Fabry-Perot interferometer with Vernier effect

We proposed and verified a sensor based on Fabry-Perot interferometer with Vernier effect for the simultaneous measurement of temperature and bending. The sensor mentioned is composed of eccentric-core fiber (ECF) and dual-side-hole fiber (DSHF). The ECF and DSHF are sequentially connected to form two cascaded Fabry-Perot interferometers (FPIs). The free spectral range (FSR) of the two interferometers are approximately equal, the Vernier effect can be occurs. Experimental results show that the temperature sensitivities of the high-frequency spectrum and the envelope spectrum are 6.76 pm/℃ and 57.2 pm/℃, which are amplified by about 8.46 times. In addition, the sensor of the structure has no obvious effect on the amplification of the bending sensitivity with the influence of the Vernier effect. Therefore, the amplification effect of the sensor temperature and the bending sensitivity can be simultaneously achieved.

High-Sensitive Temperature Sensor Based on Cascaded Polymer-Air Cavities

A cascaded Fabry-Perot interferometers (FPIs) structure based on polymer-air cavities is proposed and demonstrated. The structure can be easily manufactured by inserting a section of single-mode fiber (SMF) with a flat end-face into the silica capillary tube (SCT), then filling the SCT with polymer under capillary action, and last inserting another segment of SMF from the other end of the SCT. Thus, a cascaded FPIs structure based on polymer-air cavities are formed. Through tracing the dip wavelengths of superimposed spectra resulting from the two FPIs in temperature change, experimental results show that the spectral dip fringes have clearly linear blue-shifts with the increase of temperature. The linearity of fitting curve exceeds to 0.99, and the temperature sensitivity of sensor is -6.76 nm/°C in temperature range of 29~ 35 °C. Furthermore, it is pointed out for the first time that a closed air-cavity will have a certain inhibitory effect on the thermal expansion of the polymer. Due to serial merits of higher temperature sensitivity and ease of fabrication, the proposed sensor is more potentially competitiveness in practical applications.

Microwave–photonic low-coherence interferometry for dark zone free distributed optical fiber sensing

A microwave-photonic low-coherence interferometry (MPLCI) system is proposed for fully distributed optical fiber sensing. Assisted by an unbalanced Michelson interferometer, a low-coherence laser source is used to interrogate cascaded Fabry-Perot interferometers along with an optical fiber for a dark zone free (or spatially continuous) distributed measurement. By combining the advantages of microwaves and photonics, the MPLCI system can synergistically achieve high sensitivity and high spatial resolution. Our tests have confirmed a strain resolution of 95 nε at the spatial resolution of 10 cm.

Vernier Effect based Strain Sensor with Cascaded Fabry-Perot Interferometers

Highly sensitive cascaded FPI based strain sensor with Vernier Effect is proposed and experimentally demonstrated. This FPI structure is fabricated by simple and cost-effective techniques such as, cleaving, splicing and tapering. Experimental results show that the proposed structure can provide a high strain sensitivity of 37.3 pm/ ${\mu \varepsilon }$ , that is 13.3 times higher than the sensitivity of the single sensing FPI, which is 2.8 pm/ ${\mu \varepsilon }$ . Proposed sensor also exhibits very low temperature cross sensitivity of 0.7 pm/C°. This design can provide simple fabrication, stable and linear output response over a large range of applied strain and brings numerous prospects for sensing applications.

High-Sensitivity Gas Pressure Fabry–Perot Fiber Probe With Micro-Channel Based on Vernier Effect

In this paper, we propose and demonstrate a gas pressure fiber probe with high sensitivity magnified by Vernier effect. The probe is composed of two cascaded Fabry–Perot interferometers based on a SMF–SOHST–OFC structure (SMF: single-mode fiber; SOHST: side-opened hollow silica tube; OFC: optical fiber column). The high-frequency CO2 laser drilling method for hollow silica tube can effectively maintain the transient balance of the air pressure inside and outside the cavity without destroying the reflective ends of the optical fibers. Experimental results show that the prepared fiber probe with the SOHST length of 375.2 μ m and column length of 247.3 μ m has high gas pressure sensitivity of 80.3 pm/kPa by demodulating Vernier envelope, and it has relatively low temperature cross-sensitivity of –1.33 kPa/°C. This sensor is highly sensitive and of compact size, which not only can be applied in gas pressure sensing but also has the potential for application in microfluidic detection.

Ultra-Sensitive Strain Sensor Based on Femtosecond Laser Inscribed In-Fiber Reflection Mirrors and Vernier Effect

One of the efficient techniques to enhance the sensitivity of optical fiber sensor is to utilize Vernier effect. However, the complex system structure, precisely controlled device fabrication, or expensive materials required for implementing the technique creates the difficulties for practical applications. Here, we propose a highly sensitive optical fiber strain sensor based on two cascaded Fabry–Perot interferometers and Vernier effect. Of the two interferometers, one is for sensing and the other for referencing, and they are formed by two pairs of in-fiber reflection mirrors fabricated by femtosecond laser pulse illumination to induce refractive-index-modified area in the fiber core. A relatively large distance between the two Fabry–Perot interferometers needs to be used to ensure the independent operation of the two interferometers. The fabrication of the device is simple, and the cavity's length can be precisely controlled by a computer-controlled three-dimensional micromachining platform. Moreover, as the device is based on the inner structure inside the optical fiber, good robustness of the device can be guaranteed. The experimental results obtained show that the strain sensitivity of the device is ∼28.11 pm/μϵ, while the temperature sensitivity achieved is ∼278.48 pm/°C.

Construction of cascaded Fabry-Perot interferometers by four in-fiber mirrors for high-temperature sensing.

An optical fiber high-temperature sensor is proposed and demonstrated by use of cascaded Fabry-Perot interferometers based on four in-fiber mirrors fabricated by femtosecond laser inscription. The output fringe pattern of the device exhibits dominant/highly distinguishable dip wavelength, which helps in unambiguous measurement beyond the free spectral range. The device has excellent thermal stability in high temperature up to 1100°C, and the temperature sensitivity obtained is 9.91pm/°C within the temperature range of 100°C to 400°C, and 15.88pm/°C within the temperature range of 400°C to 1100°C, respectively. The device features compact size, simple fabrication, and convenient operation, which make it attractive for monitoring of extreme environment.

Relative humidity sensor based on Vernier effect with GQDs-PVA un-fully filled in hollow core fiber

A new relative humidity (RH) sensor based on two cascaded Fabry-Perot interferometers (FPIs) and Vernier effect is proposed and developed. The two cascade FPIs are constructed by splicing a section of photonic crystal fiber (PCF) between a section of single mode fiber and a section of hollow core fiber (HCF), where the length of PCF is 281.43μm and the length of HCF is 490.83μm. The hollow core fiber is un-fully filled with Graphene quantum dots and polyvinyl alcohol. By adjusting the filling time, FPIs with different free spectral ranges are got. We study the three sensors whose filling time are 5 min, 10 min and 15 min, respectively. Among them, the FPI with 15mins’ filling has the highest sensitivity, which is 0.456 nm/%RH with RH changing from 19.63%RH to 78.86%RH. In addition, the experimental results indicate it has good reversibility and stability. What’s more, the sensitivity is about 4.8 times higher than that of our previous work. In brief, the compact configuration, easy fabrication, high sensitivity and good RH resolution imply the proposed sensor has good potential for RH measurement application.

Ultrasensitive Temperature Sensor With Cascaded Fiber Optic Fabry–Perot Interferometers Based on Vernier Effect

We have proposed and experimentally demonstrated an ultrasensitive fiber-optic temperature sensor based on two cascaded Fabry-Perot interferometers (FPIs). Vernier effect that significantly improves the sensitivity is generated due to the slight cavity length difference of the sensing and reference FPI. The sensing FPI is composed of a cleaved fiber end-face and UV-cured adhesive while the reference FPI is fabricated by splicing SMF with hollow core fiber. Temperature sensitivity of the sensing FPI is much higher than the reference FPI, which means that the reference FPI need not to be thermally isolated. By curve fitting method, three different temperature sensitivities of 33.07, -58.60, and 67.35 nm/°C have been experimentally demonstrated with different cavity lengths ratio of the sensing and reference FPI, which can be flexibly adjusted to meet different application demands. The proposed probe-type ultrahigh sensitivity temperature sensor is compact and cost effective, which can be applied to special fields, such as biochemical engineering, medical treatment, and nuclear test.

Transformation algorithm and analysis of the Fourier transform spectrometer based on cascaded Fabry-Perot interferometers.

The Fourier transform spectrometer based on cascaded Fabry-Perot interferometers is analyzed, where one of the interferometers has a fixed length, while the other is scanning. We propose a method to reconstruct the spectrum correctly based on solving the integral equation of the overall response of the cascaded interferometers. The method is tested for different design parameters and noise conditions. Low reconstruction error below -80 dB is found to be achievable.