Fabry-Perot Research Articles

Fiber-optic semi-distributed Fabry-Perot interferometer for low-limit label-free detection of CCL5 cancer biomarker

Fiber-optic semi-distributed Fabry-Perot interferometer for low-limit label-free detection of CCL5 cancer biomarker

Accurate and fast calibration for FBG demodulation based on deep learning and ensemble learning

Accurate and rapid demodulation plays a crucial role in fiber Bragg grating (FBG) sensing systems. The Fabry-Perot (F-P) filter is a dependable demodulation technique with excellent accuracy. However, the F-P filter suffers from demodulation error drift in a temperature-changing environment. The non-repeatable wavelength scanning affects the accuracy and stability of demodulation. To solve the problem, an accurate and rapid calibration approach is proposed for FBG demodulation. First, the temporal convolutional network (TCN) is utilized to extract the hidden information and long-term temporal relationships in the input features including temperature, a temperature changing rate, and shift of reference grating. Second, a state-of-the-art light gradient boosting machine (LightGBM) capable of forecasting demodulation error is adopted for rapid forecasting. To demonstrate the effectiveness of the proposed approach, the traditional TCN model and the composited-residual-block TCN (CTCN) model are both discussed, and the temperature-drift experiments are designed and conducted in two temperature-changing environments. The experimental results show that, compared to the widely applied long short-term memory (LSTM) model, the TCN-LightGBM model achieves higher prediction accuracy and reduces computation time by at least 59.68%. The proposed approach is an affordable and effective alternative to the existing hardware-based calibration techniques.

Development of a miniaturized PZT-based MEMS Fabry-Perot interferometer with eutectic wafer bonding and its interface electronics

A miniaturized lead zirconate titanate (PZT)-actuated Fabry-Perot interferometer (FPI) was developed for an 850 nm light beam selection by modulating the air gap between two refractive mirrors. The developed FPI consists of mirrors, a PZT actuator for air gap modulation, metal electrodes, and interface electronics capable of applying a square voltage at a frequency of 0.1 Hz. Eutectic wafer bonding method was employed to bond two mirrors through rapid thermal annealing (RTA) and applying mechanical pressure for a short time to minimize the interdiffusion between layers. The PZT actuator and metal electrodes serve as a thickness spacer to create an air gap between the two mirror plates. Alternating high and low dielectric layers (TiO2 and SiO2) with precise thickness and high crystallization quality were utilized for the formation of the refractive mirror because these layers offer high reflectivity and low absorption loss, enabling effective transmission of a specific wavelength in the incident light beam. By applying 0.1 Hz square pulses to the PZT actuator, the air gap was modulated, resulting in significant shifts in the center wavelength of the filtered beam at the desired wavelength. The study demonstrates the successful modulation and optimization of transmission peaks, ensuring a sharp full width at half maximum (FWHM) and high transmission rate. It also provides comprehensive experimental process factors for optimizing heat treatment conditions for PZT and refractive mirrors, minimizing metal interdiffusion between the dielectric layers, and ensuring mirror plate flatness. The device parameter effects such as cavity length orders, sequence of refractive indices for dielectric layers, and the extent of elongation of PZT with applied voltage were systematically studied to achieve optimal performance of FPI filter. The developed interface electronics allow voltage modulation up to 21.9 V at a frequency of 0.1 Hz, while preserving the elasticity of the PZT actuator.

Fiber-Optic Hydraulic Sensor Based on an End-Face Fabry–Perot Interferometer with an Open Cavity

The paper describes the design and manufacturing process of a fiber optic microphone based on a macro cavity at the end face of an optical fiber. The study explores the step-by-step fabrication of a droplet-shaped macro cavity on the optical fiber’s end surface, derived from the formation of a quasi-periodic array of micro-cavities due to the fuse effect. Immersing the end face of an optical fiber with a macro cavity in liquid leads to the formation of a closed area of gas where interfacial surfaces act as Fabry–Perot mirrors. The study demonstrates that the macro cavity can act as a standard foundational element for diverse fiber optic sensors, using the droplet-shaped end-face cavity as a primary sensor element. An evaluation of the macro cavity interferometer’s sensitivity to length alterations is presented, highlighting its substantial promise for use in precise fiber optic measurements. However, potential limitations and further research directions include investigating the influence of external factors on microphone sensitivity and long-term stability. This approach not only significantly contributes to optical measurement techniques but also underscores the necessity for the continued exploration of the parameters influencing device performance.

Optical fiber acoustic sensor with gold diaphragm based Fabry-Perot interferometer

This work proposes an optical fiber acoustic sensor using a Fabry-Perot interferometer (FPI), which consists of an optical fiber end face and a gold diaphragm with an effective diameter of 75 µm and a thickness of 20 nm. The sensor has contrast of up to 34 dB and achieves audible acoustic signal sensing over a broad frequency response range from 70 Hz to 20 kHz with a linear response to sound pressure. The minimum detectable sound pressure is 815.5 μPa/Hz1/2 at 70 Hz. The sensor made of a pure gold diaphragm has stable performance and can work consistently over a long period, promising to be applied as an optical microphone for real-time communication in some extreme environments.

A high-sensitivity strain sensor based on the core-offset fiber with a micro air bubble

A highly sensitive optic-fiber strain sensor based on the air-microbubble Fabry–Perot interferometer (FPI) formed in a core-offset tapered fiber is proposed. By drawing tapers on the staggered spliced single-mode fibers, micro air bubbles with an average wall thickness of 2.6 μm are formed. The experimental results show that the sensor has a high strain sensitivity of 17.24 pm/με and good linear response in the range of 0–1500 με. A numerical simulation model is developed to study the axial strain response, and the results show that the core-offset structure increases the strain sensitivity by 46 %. In addition, the sensor has a temperature sensitivity of 3.43 pm/°C and a cross-sensitivity with strain as low as 0.199 με/°C over the range of 50–350 °C.

A dual-wavelength demodulation-based sensor for magnetic fields

This work presents a magnetic field sensor based on a Fabry–Perot interferometer (FPI) doped with a magnetic fluid. The FPI consists of multiple reflective end surfaces. The tail end of the FPI is wrapped with a magnetic fluid, and the external magnetic field adjusts the complex refractive index of the magnetic fluid, which influences the reflectivity of the tail end face of the interferometer and influences the spectral interferogram. The sensor possesses a small size, ease of fabrication, and potential for multiplexing. Additionally, a dual-wavelength intensity demodulation method is employed, which reduces the system cost compared to the spectrometer measurements approach. The measurement accuracy can achieve a value of 2.62 Gs under weak magnetic fields. According to the experimental results, the measurement range can span from 0 to 150 Gs, with a sensitivity of 4.58×10−5 mw/mT.

(Invited) Applications of Electrochemistry Toward Blue/Green and SWIR-Wavelength VCSELs

Unlike the more established edge-emitting lasers (EELs) with a horizontal Fabry-Perot (FB) cavity, VCSELs have a vertical cavity with highly reflective top and bottom mirrors sandwiching the active region. This design enables wafer-level testing, one- and two-dimensional arrayed integration, and scalability for low- and high-power applications. VCSELs are poised to surpass EELs as a more versatile and intelligent option for semiconductor lasers in the future.Currently commercially available VCSELs only cover the red to near-infrared (NIR) range of 700-1100nm, whereas EELs offer products across a wide spectral range. The optimal active regions for blue and short-wavelength infrared (SWIR) spectra are only supported on GaN and InP substrates, respectively. Lattice-matched, epitaxial mirrors compatible with these two substrates remain major challenges. As a solution, we propose the use of electrochemistry to engineer the refractive index of the material. The innovation is based on the recognition that nanoporous (NP) semiconductor layers can be considered a nanocomposite with nanoscale voids of air uniformly dispersed in a single-crystalline semiconductor, thus rendering a unique way to control the effective optical index with a tunability that is typically un-attainable through epitaxy.We have studied the electrochemistry of semiconductors for applications in photonics, beginning with GaN and most recently with InP. In both material systems, we have discovered a selective porosification process based on the doping concentration. Due to the doping selectivity in EC etching, layers with high doping concentration will be converted to low index nanoporous material with an unprecedented tunability in the refractive index depending on the porosity. Meanwhile, the lightly doped layers remain intact. As a result, highly reflective mirrors were fabricated on GaN and InP substrates with wide stopbands. In this talk, we will provide latest updates in the VCSEL performances in the blue/green and long-wavelength region.

Enhanced sensitivity of temperature and magnetic field sensor based on FPIs with Vernier effect.

A kind of temperature and magnetic field sensor using Fabry-Perot interferometers (FPIs) and Vernier effect to enhance sensitivity is proposed. The sensor structure involves filling the FP air cavities with polydimethylsiloxane (PDMS) and magnetic fluid (MF) to create the PDMS and MF cavities for temperature and magnetic field detection, respectively. The two cavities are reflective structures, which are interconnected in series through a fiber-optic circulator. Experimental data demonstrates that the Vernier effect effectively enhances the sensor sensitivity. The average temperature sensitivity of the sensor is 26765 pm/°C within the range of 35∼39.5°C. The magnetic field intensity sensitivity is obtained to be -2245 pm/mT within the range of 3∼11 mT. The sensitivities of the temperature and magnetic field using the Vernier effect are about five times larger than those of the corresponding single FP cavity counterparts.

Ultrasensitive Magnetic Field Sensor Based on Fabry–Perot Interferometer and Magnetostrictive Material

Ultrasensitive Magnetic Field Sensor Based on Fabry–Perot Interferometer and Magnetostrictive Material

High-sensitivity optical fiber probe for simultaneous measurement of chloride ions and temperature

A fiber optic probe for the simultaneous measurement of chloride ions and temperature is presented. The Ag/alginate composite film is used as the reflective surface of the Fabry–Perot interferometer (FPI) and is a sensitive film for the adsorption of chloride ions. The experimental results show that the Fabry–Perot (FP) response sensitivity is approximately 1.4689 nm/µM as the chloride ion concentration changes from 1 to 9 µM, but the fiber Bragg grating (FBG) is insensitive to chloride ions. When the temperature is changed from 35°C to 80°C, the response sensitivities of the FP and the FBG are about 0.7 and 0.01115 nm/°C, respectively.

Integration of (Poly‐Si/Air)n Distributed Bragg Reflectors in a 150 mm Bulk Micromachined Wafer‐Level MOEMS Fabrication Process

This paper reports the development and integration of (Poly‐Si/Air)n Distributed BRAGG Reflectors (DBR) in a MOEMS Fabry‐Pérot‐Interferometer (FPI) concept. The realized reflectors constitute a promising and resource‐efficient alternative to complex Ion‐Assisted Deposition based DBRs while maintaining their advantages. Compared to state of the art MOEMS FPIs the (Poly‐Si/Air)n DBRs can be integrated into two moveable reflector carriers based on two individually fabricated wafers which are bonded. The (Poly‐Si/Air)n DBRs are investigated as (HL) and (HL)2 reflector stacks showing a reflectance above 91% within the wavelength range of 2.8–5.7 μm. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Multi-Physics and Multi-Objective Optimization for Fixing Cubic Fabry–Pérot Cavities Based on Data Learning

The Fabry–Pérot (FP) cavity is the essential component of an ultra-stable laser (USL) for gravitational wave detection, which couples multiple physics fields (optical/thermal/mechanical) and requires ultra-high precision. Aiming at the deficiency of the current single physical field optimization, a multi-physics and multi-objective optimization method for fixing the cubic FP cavity based on data learning is proposed in this paper. A multi-physics coupling model for the cubic FP cavity is established and the performance is obtained via finite element analysis. The key performance indices (V, wF, wF) and key design variables (d, l, F) are determined considering the features of the FP cavity. Different data learning models (NN, RSF, KRG) are established and compared based on 49 sets of data acquired by orthogonal experiments, with the results showing that the neural network has the best performance. NSGA-II is adopted as the optimization algorithm, the Pareto optimal front is obtained, and the optimal combination of design variables is finally determined as {5,32,250}. The performance after optimization proves to be greatly improved, with the displacement under the fixing force and vibration test both decreased by more than 60%. The proposed optimization strategy can help in the design of the FP cavity, and could enlighten other optimization fields as well.

S0 Galaxies: Outer Gas Accretion through Tidal Interaction and Minor Merging

To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the Hα emission line by using the scanning Fabry–Perot interferometer of the 6m telescope of the Special Astrophysical Observatory RAS. We find perspective accretion flows seen as ionized-gas emission filaments between the galaxies. We discuss the whole kinematics and origin of these flows.

Colorful Semitransparent Organic Photovoltaics with Record Key Parameters by Optimizing Photon Utilization and Fabry‐Pérot Resonator Electrode

AbstractDonor PM6 and acceptor L8‐BO are employed to build semitransparent organic photovoltaics (ST‐OPVs). Opaque OPVs are fabricated by tuning the spin‐coating speed of PM6:L8‐BO solution to optimize the photon utilization by balancing photon harvesting and photogenerated carrier collection. The optimal opaque OPVs exhibit relatively high fill‐factor (FF) of 77.58% and power conversion efficiency (PCE) of 15.07%, the average visible transmittance (AVT) of corresponding PM6:L8‐BO films arrives to 53.25%, indicating great potential in realizing efficient ST‐OPVs. ST‐OPVs are built with 1 nm Au/(10, 15, 20, 25 nm) Ag as cathode, exhibiting the PCE/AVT of 11.53%/22.57%, 13.20%/14.24%, 14.28%/9.34%, and 14.71%/6.77%, respectively. Colorful ST‐OPVs are achieved by coupling different Ag/LiF/Ag Fabry‐Pérot (F‐P) resonator microcavity. Green ST‐OPVs with varied color coordinates are achieved by fixing LiF layer thickness as 110 nm and varying Ag layers′ thickness, originating from the adjusted transmittance spectra of green ST‐OPVs. Upon fixing Ag layers′ thickness as 15/25 nm and varying LiF layer thickness as 90, 110, and 145 nm, ST‐OPVs present colors of blue, green, and red with corresponding transmittance peak at 474, 553, and 657 nm. The corresponding PCE/peak transmittance (Tpeak) values arrive to 13.80%/37.8%, 13.31%/28.4%, and 13.20%/27.7%, which should be the best performance among reported colorful ST‐OPVs.

Protonation reaction at the air/water interface monitored by a bubble Fabry-Perot interferometer

A novel interferometric technique for studies of exothermal chemical reactions at the water surface is presented. The key feature of the technique is the use of an air bubble as the interface which hosts coating molecules and at the same time acts as a subnanometer-sensitive Fabry-Perot interferometer which follows the bubble radius change after a chemical reaction with coating molecules. As an example we report measurements of a protonation reaction with dodecyl-amine (DA). A monolayer of the DA surfactant is formed at the gas-liquid interface of a millimeter-sized bubble immersed in a 10.6 pH solution. After the monolayer formation, the residual DA is removed from the bulk by gentle rinsing. Interference with the DA bulk reaction is avoided. Protonation is induced by HCl injection. The reaction in the thin DA coating layer generates a non-trivial evolution of the bubble radius with amplitude oscillations of the order of 10−3 of the bubble radius with persisting time of a few hundred seconds. Measurements are performed at different DA coverages of the bubble surface, always below the maximum coverage. Control experiments with non-coated bubble show no amplitude radius oscillations. Formation and stability of the DA monolayer are precisely monitored by measurements of the lowest-frequency bubble capillary mode. A possible interpretation of the experiments is given in terms of heat effects, vapor production and surface modification. Molecular Dynamics simulations provide a mechanistic understanding of surface effects triggered by the protonation reaction which promotes desorption of positively charged DA micelles.

Optical fiber Fabry-Perot strain sensor based on metal welding

This paper presents a strain sensor based on Fabry-Perot (F-P) interference. The F-P strain sensor is composed of a single-mode fiber (SMF) and a silica capillary, which are encapsulated by metal welding. The relationship between the cavity length and sensitivity is analyzed theoretically, then the F-P strain sensor is calibrated and tested. The experiment results show that the strain sensitivity of the fabricated sensor reaches 4.4 pm/με when the length of the silica capillary is 12 mm and the F-P cavity length is 436 μm. In addition, the temperature sensitivity of the F-P sensor is 11.7 pm/°C. With the increase of the capillary, the strain sensitivity increases. When the capillary length is 20 mm and the cavity length is 341 μm, the sensitivity of the sensor reaches 9.11 pm/με. The sensor proposed fabricated by metal welding, has the advantages of high sensitivity, simple fabrication, simple structure, and low cost.

Ultraviolet-induced sensitivity enhancement of a fiber tip temperature sensor based on adhesive-TiO2 double-cavity composite Fabry-Perot interferometer

A composite fiber Fabry-Perot interferometer (FPI) -based optical fiber temperature sensor is theoretically proposed and practically demonstrated in this work, in which the composite FPI is formed by covering the end face of single-mode fiber with ultraviolet (UV) adhesive and nano-TiO2 coating using the dip-coating method. With the superior thermo-optic characteristic of UV adhesive and the UV absorption of nano-TiO2, the sensitivity of the composite FPI temperature sensor can be effectively enhanced by UV irradiation. After five times of TiO2 dip-coating processes, the composite FPI has a higher temperature sensitivity of 75.3 pm/°C (R2 = 0.9754) under 365 nm UV light, in which the measurement range is from 25 °C to 130 °C and the detection accuracy is 0.66 °C. The proposed sensor has a simple structure and preparation process, competitive sensitivity, high linearity, and satisfactory repeatability and stability, which can be an appropriate candidate to realize high-precision temperature sensing in industrial, chemical, biological, and environmental applications.

Research on Transformer Omnidirectional Partial Discharge Ultrasound Sensing Method Combining F-P Cavity and FBG.

To achieve omnidirectional sensitive detection of partial discharge (PD) in transformers and to avoid missing PD signals, a fiber optic omnidirectional sensing method for PD in transformers combined with the fiber Bragg grating (FBG) and Fabry-Perot (F-P) cavity is proposed. The fiber optic omnidirectional sensor for PD as a triangular prism was developed. The hollow structure of the probe was used to insert a single-mode fiber to form an F-P cavity. In addition, the three sides of the probe were used to form a diaphragm-type FBG sensing structure. The ultrasound sensitization diaphragm was designed based on the frequency characteristics of PD in the transformer and the vibration model of the diaphragm in the liquid environment. The fiber optic sensing system for PD was built and the performance test was conducted. The results show that the resonant frequency of the FBG acoustic diaphragm is around 20 kHz and that of the F-P cavity acoustic diaphragm is 94 kHz. The sensitivity of the developed fiber optic sensor is higher than that of the piezoelectric transducer (PZT). The lower limit of PD detection is 68.72 pC for the FBG sensing part and 47.97 pC for the F-P cavity sensing part. The directional testing of the sensor and its testing within a transformer simulation model indicate that the proposed sensor achieves higher detection sensitivity of PD in all directions. The omnidirectional partial discharge ultrasound sensing method proposed in this paper is expected to reduce the missed detection rate of PD.

Indoor Self-Powered Perovskite Optoelectronics with Ultraflexible Monochromatic Light Source.

Self-powered skin optoelectronics fabricated on ultrathin polymer films is emerging as one of the most promising components for the next-generation Internet of Things (IoT) technology. However, a longstanding challenge is the device underperformance owing to the low process temperature of polymer substrates. In addition, broadband electroluminescence (EL) based on organic or polymer semiconductors inevitably suffers from periodic spectral distortion due to Fabry-Pérot (FP) interference upon substrate bending, preventing advanced applications. Here, ultraflexible skin optoelectronics integrating high-performance solar cells and monochromatic light-emitting diodes using solution-processed perovskite semiconductors is presented. n-i-p perovskite solar cells and perovskite nanocrystal light-emitting diodes (PNC-LEDs), with power-conversion and current efficiencies of 18.2% and 15.2cd A-1 , respectively, are demonstrated on ultrathin polymer substrates with high thermal stability, which is a record-high efficiency for ultraflexible perovskite solar cell. The narrowband EL with a full width at half-maximum of 23nm successfully eliminates FP interference, yielding bending-insensitive spectra even under 50% of mechanical compression. Photo-plethysmography using the skin optoelectronic device demonstrates a signal selectivity of 98.2% at 87bpm pulse. The results presented here pave the way to inexpensive and high-performance ultrathin optoelectronics for self-powered applications such as wearable displays and indoor IoT sensors.