Fabry-Perot Research Articles

Maximizing light absorption and photocurrent in organic solar cells by aligning intrinsic absorption peaks with Fabry-Perot resonances

We provide a physical interpretation of the mechanism by which maximum light absorption is achieved in organic solar cells (OSCs) through the tailoring of Fabry-Perot (FP) resonances. Overlapping the intrinsic absorption peaks of the active layer with the FP resonances in a planar OSC structure maximizes light absorption, leading to the highest short-circuit current density (JSC). The OSC with a 119 nm-thick active layer of PTB7-Th:IEICO-4F, where intrinsic absorption peaks occur at wavelengths of 715 nm and 885 nm, exhibits fundamental FP resonant modes at wavelengths of 500, 715, 750, and 850 nm. The strong electric field intensity generated by the FP resonance coincides with the intrinsic absorption peaks of the active layer at 715 nm and 885 nm, leading to an experimentally observed JSC of 26.50 mA/cm2. Optical admittance analyses are conducted to investigate the reduced reflection associated with enhanced light absorption. These results provide a deeper understanding of the fundamental mechanism for designing multilayer photonic and optoelectronic devices. This design principle is general and can be applied to various optoelectronic devices, such as photovoltaics, sensors, and photodetectors across a wide range of wavelengths.

All-optical infrasound sensor based on a Fabry-Perot interferometer

Recent demands for infrasound measurement, whether for detecting violent atmospheric events or evaluating the environmental impact of wind farms, require new acoustic calibration standards in the frequency range below 2Hz. Expanding the frequency bandwidth of microphones remains a limited strategy since they are designed to filter out continuous components. An alternative method for measuring infrasound is proposed, which relies on a Fabry-Perot interferometer. This technique has been studied extensively for static pressure measurements with success. Therefore, adapting a Fabry-Perot refractometer to perform acoustic measurements is not only a technical challenge but also an opportunity to bridge the gap between static pressures and acoustic metrology. As acoustic movement involves both small pressure and temperature variations, it is important to account for their coupled effects in interferometer measurement results. Since the temperature variation field in the measurement system cannot be characterised experimentally, an analytical model has been developed. The chosen theoretical and technical solutions are validated by the good agreement between experimental results obtained with the refractometer carried out and other calibrated sensors in the frequency range from 40mHz to 1.5Hz. These results also highlight the improvements required to bring the device up to the level of an infrasound reference instrument.

MZI-based high intensity responsive sandwiched multi-layer fiber optic humidity sensor

This paper presents a multi-layer optical fiber humidity sensor based on dual-beam Mach-Zehnder interference (MZI) for optical intensity sensitivity. The sensor is fabricated using a large-scale axial offset fusion technique between a multimode fiber (MMF) and an offset hole two-core fiber (OHTC), making it suitable for agricultural and health monitoring applications. The 27 μm axial offset enables tilted light incidence, enhancing environmental sensitivity. With a single-cycle Graphene oxide (GO) coating of approximately 22 nm, the MMF-OHTC structure achieves high humidity sensitivity (0.39 dB/%RH) over the 25 %-80 % RH range with excellent linearity (R2≈0.99). The sensor exhibits stable, rapid response (2.52 s/0.46 s) and low temperature cross-sensitivity (0.06 %RH/°C). When combined with a hollow-core fiber Fabry-Perot interferometer (HCF-FPI), the system allows zero cross-talk simultaneous humidity and temperature measurements, expanding the potential applications of multi-layered structures in multifunctional detection systems.

A Hybrid GAN-Inception Deep Learning Approach for Enhanced Coordinate-Based Acoustic Emission Source Localization

In this paper, we propose a novel approach to coordinate-based acoustic emission (AE) source localization to address the challenges of limited and imbalanced datasets from fiber-optic AE sensors used for structural health monitoring (SHM). We have developed a hybrid deep learning model combining four generative adversarial network (GAN) variants for data augmentation with an adapted inception neural network for regression-based prediction. The experimental setup features a single fiber-optic AE sensor based on a tightly coiled fiber-optic Fabry-Perot interferometer formed by two identical fiber Bragg gratings. AE signals were generated using the Hsu-Nielsen pencil lead break test on a grid-marked thin aluminum plate with 35 distinct locations, simulating real-world structural monitoring conditions in bounded isotropic plate-like structures. It is demonstrated that the single-sensor configuration can achieve precise localization, avoiding the need for a multiple sensor array. The GAN-based signal augmentation expanded the dataset from 900 to 4500 samples, with the Wasserstein distance between the original and synthetic datasets decreasing by 83% after 2000 training epochs, demonstrating the high fidelity of the synthetic data. Among the GAN variants, the standard GAN architecture proved the most effective, outperforming other variants in this specific application. The hybrid model exhibits superior performance compared to non-augmented deep learning approaches, with the median error distribution comparisons revealing a significant 50% reduction in prediction errors, accompanied by substantially improved consistency across various AE source locations. Overall, this developed hybrid approach offers a promising solution for enhancing AE-based SHM in complex infrastructures, improving damage detection accuracy and reliability for more efficient predictive maintenance strategies.

MEMS Fabry-Perot sensor for accurate high pressure measurement up to 10 MPa.

Microelectromechanical system (MEMS) Fabry-Perot fiber-integrated pressure sensor exhibits a compact size, intrinsic safety, and high precision measurement. Here, a MEMS Fabry-Perot interferometer sensor is presented. The sensor is fabricated using a standard microfabrication process with a uniformity of 80%. The sensor enables a pressure measurement range of 0-10 MPa with a full-scale nonlinearity error of 1.44% and a repeatability error of 2.14%. A limit of detection of 1.74 kPa and a pressure resolution of 0.017% are achieved. The comparative experiment is conducted to verify the wavelength tracking method is more robust than cavity length demodulation method in this configuration. Moreover, the temperature drift is alleviated by combining a fiber Bragg grating sensor for compensation in a range of -35-88 °C, which is reduced by 15 times to 2.88 ppm/°C. The proposed sensor has wide potential applications, such as downhole environments and petroleum pipeline pressure monitoring.

Ultracompact and Uniform Nanoemitter Array Based on Periodic Scattering.

As emerging gain materials, lead halide perovskites have drawn considerable attention in coherent light sources. With the development of patterning and integration techniques, a perovskite laser array has been realized by distributing perovskite microcrystals periodically. Nevertheless, the packing density is limited by the crystal size and the channel gap distance. More importantly, the lasing performance for individual laser units is quite random due to variation of size and crystal quality. Herein an ultracompact perovskite nanoemitter array with uniform emission has been demonstrated. Individual emitters are formed via scattering evanescent components from a shared Fabry-Perot laser, ensuring uniform lasing emission in a unit cell with a side length of 160 nm and lattice constant of 400 nm. And the periodic silicon scatterers do not deteriorate the lasing threshold dramatically. In addition, the surface emitting efficiency increased significantly. The direct integration of a densely packed nanoemitter array with a silicon platform promises high-throughput sensing and high-capacity optical interconnects.

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water.

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

An optical fiber high sensitivity temperature sensor with MZI and FPI parallel connection

Accurate detection of temperature is of great significance in the field of medical research. The focal point of this article centers around an optical fiber sensor that integrates Fabry Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) and Mach Zehnder interferometer (MZI), leveraging the principle of the vernier effect. By introducing the vernier effect principle, the sensitivity is 31.09 nm/°C in the detection range of 36 ∼ 40°C, and the maximum temperature measurement error is about 0.55 %. In addition, good linear response and longtime stability make it suitable for application in various scenarios where accurate temperature measurement is required.

PbS-based SWIR micro-spectrometer with on-chip Fabry-Perot filter array.

Miniaturized and portable on-chip spectrometers have been widely explored to facilitate many applications including chemical analysis, environmental monitoring, medical diagnostics, and astronomical observations. However, the optical spectra of micro-spectrometers are mostly within the visible range. Here, we develop high-performance short-wave infrared (SWIR) micro-spectrometers through the integration of wafer-scale uniform lead sulfide (PbS) thin films with an on-chip Fabry-Perot filter array. The optoelectronic performance of PbS-based detectors could be markedly improved through the optimization of chemical bath deposition (CBD) conditions. The high-sensitivity PbS detectors based on the Fabry-Perot filter array demonstrate chemical analysis application.

Growth of VO2-ZnS thin film cavity for adaptive thermal emission

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. In this study, we used a thin film coating with the Fabry–Pérot (FP) effect to enhance emissivity contrast (Δε) between VO2 phase-change states. This coating utilizes a hybrid material architecture that combines VO2 with a mid- and long-wave infrared transparent chalcogenide, zinc sulfide (ZnS), as a cavity spacer layer. We simulated the design parameter space to obtain a theoretical maximum Δε of 0.63 and grew prototype devices. Using x-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), we determined that an intermediate buffer layer of TiO2 is necessary to execute the crystalline growth of monoclinic VO2 on ZnS. Through temperature-dependent FTIR measurements, our fabricated devices demonstrated FP-cavity enhanced adaptive thermal emittance.

Low frequency vibration monitoring of wind turbine tower based on optical fiber sensor and its potential for internet of things

Among all renewable energy sources, wind energy is a cost-effective alternative energy source. The majority of wind turbines are built in harsh environments due to their power generation characteristics, which is one of the prime reasons resulting in frequent failures of wind turbine. Among various failures, the vibration of wind turbine tower cannot be ignored because it is a precursor of the failure of the wind turbine. The electrical vibration sensors have the problems of power supply and electromagnetic interference for the condition assessment of wind turbine tower. A vibration sensor based on optical Fabry-Perot (F-P) interference principle with high sensitivity is designed, fabricated and characterized to further meet the requirements of vibration detection of wind turbine tower. The mechanical simulation model of the diaphragm and optical vibration platform is constructed to verify the sensing characteristic of the F-P optical fiber vibration sensor (OFVS). The experiment results indicate a resonant frequency of the F-P OFVS of 223 Hz, an output sensitivity of 122.22 mV/m·s−2 at 10 Hz, and a horizontal output of less than 6 %. In addition, the designed F-P OFVS possesses the superiorities of compact structure, passive and excellent anti-electromagnetic interference, and has a wide application prospect in the vibration detection of the wind turbine tower.

DC current sensor based upon a fused fiber optic Fabry-Perot interferometer (FPI) and copper wire

In order to meet the demand for direct current (DC) current measurements in industrial production, a new type of fiber optic DC current sensor, combining thin copper wire and fiber optic Fabry-Perot interferometer (FPI), is reported. FPI is a sandwich structure formed by splicing a single-mode fiber (SMF) and a quartz capillary, with a cavity length of approximately 200 μm. The copper wire, with a length of 3.2 cm and a diameter of 1 mm, is attached to the FPI to form the sensor. Due to the excellent thermal conductivity of copper, the results showed that the sensor increased the sensitivity from 4.1 pm/°C to 11 pm/°C. After applying direct current to the sensor, a large quantity of heat generated by the copper wire was absorbed by the FPI, resulting in a significant shift in the resonant wavelength of FPI, which can indirectly measure the current. Three current experiments were performed, and parabolic curves have been used in fitting of the Dip wavelength and the square of the current. The results provide high correlation coefficients with values exceeding 0.99. Therefore, this curve may be used to measure the square of the current, further obtaining the current. In summary, the sensor is compact and durable, easy to manufacture, and provides high correlation coefficients, providing an alternative for measuring DC current.

Highly sensitive push-pull differential pressure sensor with multi-parameter measurement capabilities

A multi-parameter sensor comprising of a Fabry–Perot (FP) pair and a fiber-optic FP microcavity was proposed for simultaneous measurement of differential pressure (DP), static pressure (SP) and temperature. The push-pull FP pair is used to measure the differential pressure, and wide measurement range can be achieved by adjusting the dimensions of the diaphragm. The self-enclosed fiber-optic microcavity is utilized to measure the static pressure. For multi-parameter measurement, a matrix equation is proposed to solve the differential pressure, static pressure and temperature by fully considering the relationship of the FP cavity lengths and measurands. The performance of multi-parameter sensing is verified experimentally. The sensitivities of differential pressure, static pressure and temperature are 294.4822 nm/KPa, 353.08 nm/MPa and 42.4056 nm/°C, respectively, in variation of cavity lengths. The sensing characteristics show good linearity. Such a sensor could find important applications in the fields of process industry and oil industry, etc.

Flexible FPI sensor fabricated by fiber end photopolymerization and integration for high sensitivity gas pressure sensing

This work presents a new design framework for highly sensitive fiber gas pressure sensor. We construct a Flexible Fabry–Perot Interferometer (F-FPI), which consists of three polymer pillars and an end cap, on a fiber end face. A unique fiber-end photopolymerization and integration (FEPI) technique is adopted for fabricating the device. The varied gas pressure in the enclosed space not only changes the refractive index (RI) of the gas but also the length of the pillars. Therefore the difference in the optical path length of the FPI is more sensitive to pressure changes. Experimental results indicate that the F-FPI realizes a gas pressure sensitivity up to 79.0 pm/kPa in the range of 0–200 kPa. In addition, the Vernier effect is introduced to amplify the sensitivity to −409.7 pm/kPa. The temperature compensation is achieved by cascading a Fiber Bragg Grating (FBG) behind the F-FPI. Such a design framework provides a new idea for highly sensitivity gas pressure sensing.

Optical Fibers Use in On-Chip Fabry–Pérot Refractometry to Achieve High Q-Factor: Modeling and Experimental Assessment

This paper investigates the integration of optical fibers into an on-chip Fabry–Pérot (FP) resonator to achieve high-quality (Q) factors, which is favorable in sensing applications. Initially designed for high-speed data transmission, optical fibers are now utilized in sensing applications because of their flexibility and sensitivity to optical phenomena. This article focuses on the role of single-mode fibers (SMF) and the geometry of different structures in enhancing light confinement within FP resonators. Two distinct on-chip designs utilizing SMFs are demonstrated, modeled, and experimentally evaluated. One achieves a Q-factor higher than 5200, demonstrating significant improvement in light confinement, while the other maximizes the spectral range between the resonant modes’ peaks, maximizing the sensing range through the wavelength shift. This is supported by visualized simulation and coupling efficiencies calculations for fundamental and higher-order modes for comprehensive analysis. Comparison with existing literature is also made, underscoring the advancements achieved by the presented approaches. The findings contribute to the development of microscale refractive index sensing applications, highlighting the vital role of optical fiber integration for high-performance sensing.

SU-8-meta-phenylenediamine-conjugated thin film for temperature sensing.

Polymers have distinctive optical properties and facile fabrication methods that have been well-established. Therefore, they have immense potential for nanophotonic devices. Here, we demonstrate the temperature-sensing potential of SU8-meta-phenylenediamine (SU8-mPD), produced by epoxy amination of the SU-8 polymer. Its properties were examined through a series of molecular structural techniques and optical methods. Thin layers have demonstrated optical emission and absorption in the visible range around 420 and 520 nm, respectively, alongside a strong thermal responsivity, characterized by the 18 ppm °C-1 expansion coefficient. A photonic chip, comprising a thin 5-10 μm SU8-mPD layer, encased between parallel silver and/or gold thin film mirrors, has been fabricated. When pumped by an external light source, this assembly generates a pronounced fluorescent signal that is superimposed with the Fabry-Pérot (FP) resonant response. The chip undergoes mechanical deformation in response to temperature changes, thereby shifting the FP resonance and encoding temperature information into the fluorescence output spectrum. The time response of the device was estimated to be below 1 s for heating and a few seconds for cooling, opening a new avenue for optical sensing using SU8-based polymers. Thermoresponsive resonant structures, encompassing strong tunable fluorescent properties, can further enrich the functionalities of nanophotonic polymer-based platforms. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Part-per-Billion (Ppb)-Level Acetylene Sensor Employing Optical Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) with an Erbium-Doped Fiber Amplifier (EDFA) and a Fiber-Optic Fabry–Perot Interferometer

An all-optical double-pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for the detection of acetylene (C2H2) at part-per-billion (ppb) levels was developed and experimentally validated. By employing an erbium-doped fiber amplifier (EDFA) capable of emitting up to 1 W of optical power, a commercial quartz tuning fork (QTF) resonating at 30.7 kHz, and double-pass acoustic microresonators, the amplitude of the QEPAS signal was significantly enhanced, thereby improving the sensitivity of the C2H2-QEPAS sensor. Instead of using piezoelectric detection in conventional QEPAS, a highly sensitive fiber-optic Fabry–Perot interferometer (FPI) was employed to measure the vibration of the QTF prong. A working point self-stabilizing technique was exploited to improve the demodulation sensitivity and stability. The linear response of the sensor to laser power and C2H2 concentration confirmed that no saturation occurred. With an excitation laser power of 1 W and a C2H2 absorption line of 1532.83 nm, a C2H2 minimum detection limit (MDL) of 19.1 ppb was achieved, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.58 × 10−8 cm−1∙W∙Hz−1/2. Owing to its high sensitivity, long-term stability, and immunity to electromagnetic interferences, the QEPAS sensor provides considerable potential for remote gas sensing in environmental monitoring and other applications.

Development of a high-sensitivity and fast-response fiber temperature sensor utilizing Ti3C2TX MXene/PDMS composites and Vernier effect.

Precisely measuring temperature holds great significance for human daily life and industrial production. A high-sensitivity and fast-response optical fiber temperature sensor based on the vernier effect is proposed. A Fabry-Perot interferometer (FPI) filled with Ti3C2TX MXene and polydimethylsiloxane (PDMS) composites is employed as a sensing probe for the first time, and a cascaded Mach-Zender interferometer (MZI) as a reference unit due to its insensitivity to temperature. The temperature sensitivity of the FPI filled with Ti3C2TX MXene/PDMS composites is 1.63 nm/°C owing to the excellent thermal expansion characteristics of PDMS, and the response time is shortened from 3.021 s to 719 ms compared to that of the FPI filled with pure PDMS attributed to the high thermal conductivity of MXene. The cascading of FPI and MZI with similar free spectral ranges generates the vernier effect. The sensitivity is magnified by 19.44 times, reaching up to 31.62 nm/°C in the range of 36.5 - 37.2 °C, and the response time is 721 ms. Furthermore, experimental results demonstrate the sensor's good stability, implying its potential applications of the sensor in medical diagnosis, environmental monitoring and biosensing.

Observational Evidence for the Neutral Wind Responses in the Mid‐Latitude Lower Thermosphere to the Strong Geomagnetic Activity

AbstractBased on two meteor radars in mid‐latitudes of China, the mid‐latitude lower thermospheric neutral wind responses to the 2015 St. Patrick's Day great storm are investigated. The AE and PCN indices presented the similar quasi‐5‐hour oscillations during the storm. Interestingly, the analogous and close‐correlated storm‐time quasi‐5‐hour oscillations were also observed in both the meridional wind differences at 90–102 km derived from meteor radars. The meridional wind disturbances in the lower thermosphere also showed the extension toward the lower latitudes. It has been found that the enhanced equatorward wind disturbances at 250 km estimated by the Horizontal Wind Model‐14 and Fabry‐Perot Interferometer (FPI) emerged accordingly with the increases of AE and PCN with a time delay. And the enhancements of equatorward (poleward) wind disturbances at 250 km were accompanied by the increments of equatorward (poleward) wind disturbances at 94 km with a time lag of a few hours. It is thus suggested that the multiple intensified Joule heating events with quasi‐5‐hour time intervals were triggered by the successive substorm expansions during the storm. Then the Joule heating events led to the vertical wind and temperature disturbances in the mid‐latitude lower thermosphere via disturbing the thermospheric meridional circulation, which consequently induced the quasi‐5‐hour meridional wind disturbances therein.