Fabry-Perot Research Articles

Realization of an Adaptive Radiative Cooler with a Multilayer-Filter VO2-Based Fabry–Pérot Cavity

A high-performance adaptive radiative cooler comprising a multilayer-filter VO2-based Fabry–Pérot (FP) cavity is proposed. The bottom FP cavity has four layers, VO2/NaCl/PVC/Ag. Based on the phase transition of VO2, the average emissivity in the transparent window can be switched from 3.7% to 96.3%. Additionally, the average emissivity can also be adjusted with external strain to the PVC layer, providing another way to attain the desired cooling effect. An upper filter is included to block most of the solar radiation and provide a transmittance of 96.7% in the atmospheric window. At high temperature, the adaptive emitter automatically activates radiative cooling. The net cooling power is up to 156.4 W⋅m−2 at an ambient temperature of 303 K. Our adaptive emitter still exhibits stable selective emissivity at different incident angles and heat transfer coefficients. At low temperature, the radiative cooling automatically deactivates, and the average emissivity decreases to only 3.8%. Therefore, our work not only provides new insights into the design of high-performance adaptive radiative coolers but also advances the development of intelligent thermal management.

The Brillouin linewidth in water as a function of temperature and salinity: the missing empirical relationship

Brillouin scattering in water has been proposed as a method to measure temperature profiles in the ocean. Spontaneous Brillouin scattering can be understood as light scattering on phonons in the water originating from thermal fluctuations. The scattering signal usually features three peaks in its spectrum, of which one is attributed mainly to scattering from suspended particles and shows no frequency shift from the incident light, while the other two are shifted by the phonon frequency leading to a linear dependency of this Brillouin shift to the speed of sound. The speed of sound is dependent on temperature and salinity. To measure temperature and salinity independently, a second measurement parameter is necessary. The spectral width of the Brillouin lines constitutes a measure for the phonon lifetime and depends on various macroscopic water properties. This linewidth was investigated in a laboratory using a scanning FPI (Fabry-Perot interferometer) over a temperature range from 1.8 °C to 35 °C and 13 salinities from 0 ppt to 36 ppt. A strong temperature dependence was confirmed and a weaker, nonlinear dependency on salinity was found. An empirical model was created to describe the data for the purpose of enabling remote sensing of water temperature profile and salinity simultaneously in the future.

Highly sensitive fiber force sensor based on cascaded Fabry-Perot cavities and Vernier effect

In this article, we introduce a new concept for an in-line optical fiber force sensor probe, which is based on two cascaded Fabry-Perot (F-P) cavities to generate the Vernier effect and enhance sensitivity. Due to the significantly low Young’s modulus of UV-cured adhesive within the sensing cavity, extremely high force sensitivity is obtained. In our initial sample, we achieved an impressive force sensitivity of −61,301 nm/N. To improve that, the optical path difference between the two cavities is further reduced, exhibiting a remarkable increased force sensitivity of −140,813 nm/N. As an application, we conducted an experiment using this highly sensitive force sensor probe to measure the evaporation rate of ethanol, a common solvent, which is 7.79 × 10−5 g/s at room temperature. The proposed sensor features advantages of high sensitivity, simple structure, ease of fabrication, compactness, which is an ideal fiber sensor probe for sensitive force measurement.

Fabry-Perot parallel type high sensitivity fiber optic temperature sensor based on vernier effect beyond free spectral range measurement

Accurate detection of temperature is crucial in industry, agriculture, the military, etc. In our paper, using the vernier effect of fiber optic interference, we demonstrate a temperature sensoru, in parallel with a grating, to improve the sensitivity of the probe while expanding the measurement range. The probe consists of a combination of a temperature-sensitive polymer Fabry-Perot interferometer (SFPI) and a temperature-insensitive 3D printed reference Fabry-Perot interferometer (RFPI). The innovative combination of femtosecond-induced two-photon polymerization provides a reference cavity with determinable cavity length for vernier effects. Innovative use of fiber Bragg grating (FBG) for vernier effect to determine the temperature interval and extend the range. This experiment concluded that the average sensitivity of the parallel probe reached −22.52 nm/°C in the temperature detection interval of 31°C to 37°C, a 16.8-fold increase in sensitivity, based on which the temperature outside the six free spectral ranges (FSR) can be measured in the interval of 31°C to 51°C using the FBG.

High pressure-sensitive and stable fiber Fabry-Perot interferometer with nano-diaphragm assembled by H-O catalysis bonding.

Herein, a high pressure-sensitive and stable fiber Fabry-Perot (FP) interferometer with nano-diaphragm assembled by H-O catalysis bonding is proposed and demonstrated. In order to assemble a nano-diaphragm-based fiber FP interferometer by H-O catalysis bonding technique, a SiO2 film, introduced as a bridging layer on the nano-diaphragm, can be regarded as a solid adhesive to bridge hollow-core fiber end-face and nano-diaphragm. As thus, by depositing bonded layers on different diaphragm materials, this H-O catalysis bonding technology can be used to for assembling FP interferometer with different materials nano-diaphragms. Experimentally, Si nano-diaphragm is transferred to hollow-core fiber end-face to build a stable fiber FP interferometer without polymeric adhesive. Experimental results reveal that this Si nano-diaphragm-based fiber FP interferometer has a high (79.6 pm/kPa) pressure sensitivity and a low (17.3 pm/°C) temperature sensitivity. Besides that, different materials nano-diaphragm also can be assembled by using this H-O catalysis bonding technique, and the functional FP interferometer can be realized by using functional nano-diaphragm material. Thus, a Pd nano-diaphragm is successfully assembled to build a FP interferometer with a hydrogen concentration measurement capacity. Further investigation will focus on exploitation of multi-material nano-film patterning transfer and different nano-film integration by using this H-O catalysis bonding transfer.

Multiplexed FBG-FFPI strainmeter array for field observation

Mining mass data of the earth's surface deformation is a promising approach for earthquake early-warning, raising an urgent demand for developing large-scale optical fiber strainmeters. This paper presents the implementation and results of large-scale, ultrahigh-resolution, real-time multiplexed fiber Bragg grating-based Fabry-Perot interferometer (FBG-FFPI) strainmeter arrays for field observation. The Pound-Drever-Hall technique locks master and slave single-sideband lasers onto the FBG-FFPI resonance peaks for precise strain measurement. A 10-channel array was successfully utilized for field observation at Lijiang National Seismic Station, which accurately recorded over 100 earthquakes and the earth's daily tide signal. The FBG-FFPIs have a strain resolution of 4.80 pε/√Hz @ 30 Hz with a 0.22-m cavity length. A 4-channel array with a longer cavity length of 1.4 m was also established at Heqing Seismic Station, showing advantageous performances. These results demonstrate the significant potential of FBG-FFPI strainmeter arrays in providing geophysical data for earthquake early-warning and hazard mitigation.

Ultrahigh-sensitivity optical fiber sensor based on the virtual harmonic vernier effect

This paper proposes a fiber-optic sensor based on the virtual harmonic Vernier effect (VHVE). The VHVE is obtained by processing the spectrum of the traditional Vernier effect (TVE). We demonstrate that the periodic outer envelope and the high-frequency fringes in the TVE can be used as the spectra of the virtual interferometer and sensing interferometer of the VHVE, respectively. Thus, the VHVE-based spectrum will be viewed as a “superposition” of the spectra of the virtual interferometer and sensing interferometer. The optical path length of the virtual interferometer is multiple times different from that of the sensing interferometer, they meet the excitation condition of the HVE, and they can use the same spectral demodulation method. Thus, this is called the “VHVE.” A novel parallel-structured dual Fabry–Perot interferometer fiber-optic sensor is employed to detect gas refractive index. The spectral demodulation methods of the VHVE and TVE are used to track the same set of spectral data, and the obtained sensitivities are 1,158,000 nm/RIU and 39,000 nm/RIU, respectively. Experimental results show that through the VHVE, the sensitivity of the sensor is increased to 106 orders of magnitude. Compared with the HVE, the VHVE can easily increase the harmonic order. In this experiment, the harmonic order reaches 28. Meanwhile, based on the proposed VHVE principle, any sensor based on the TVE can be converted into a VHVE-based sensor to significantly enhance the sensitivity without changing the existing sensor structure. This new sensing mechanism has significant potential in improving sensor sensitivity.

Experimental demonstration of a photonic reservoir computing system based on Fabry Perot laser for multiple tasks processing

Abstract Photonic reservoir computing (RC) is a simple and efficient neuromorphic computing framework for human cortical circuits, which is featured with fast training speed and low training cost. Photonic time delay RC, as a simple hardware implementation method of RC, has attracted widespread attention. In this paper, we present and experimentally demonstrate a time delay RC system based on a Fabry Perot (FP) laser for multiple tasks processing. Here, the various tasks are attempted to perform in parallel in the multiple longitudinal modes of the FP laser. It is found that the time delay RC system based on the FP laser can successfully handle different tasks across multiple longitudinal modes simultaneously. The experimental results demonstrate the potential of the time delay RC system based on the FP laser to achieve multiple tasks processing, providing various possibilities for improving the information processing ability of neural morphology RC systems, and promoting the development of RC systems.

Optical pH Sensor Based on a Long-Period Fiber Grating Coated with a Polymeric Layer-by-Layer Electrostatic Self-Assembled Nanofilm.

An optical fiber pH sensor based on a long-period fiber grating (LPFG) is reported. Two oppositely charged polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), were alternately deposited on the sensing structure through a layer-by-layer (LbL) electrostatic self-assembly technique. Since the polymers are pH sensitive, their refractive index (RI) varies when the pH of the solution changes due to swelling/deswelling phenomena. The fabricated multilayer coating retained a similar property, enabling its use in pH-sensing applications. The pH of the PAA dipping solution was tuned so that a coated LPFG achieved a pH sensitivity of (6.3 ± 0.2) nm/pH in the 5.92-9.23 pH range. Only two bilayers of PEI/PAA were used as an overlay, which reduces the fabrication time and increases the reproducibility of the sensor, and its reversibility and repeatability were demonstrated by tracking the resonance band position throughout multiple cycles between different pH solutions. With simulation work and experimental results from a low-finesse Fabry-Perot (FP) cavity on a fiber tip, the coating properties were estimated. When saturated at low pH, it has a thickness of 200 nm and 1.53 ± 0.01 RI, expanding up to 310 nm with a 1.35 ± 0.01 RI at higher pH values, mostly due to the structural changes in the PAA.

Miniature Optical Fiber Fabry-Perot Interferometer Based on a Single-Crystal Metal-Organic Framework for the Detection and Quantification of Benzene and Ethanol at Low Concentrations in Nitrogen Gas.

This study reports for the first time, to the best of our knowledge, a real-time detection of ultralow-concentration chemical gases using fiber-optic technology, combining a miniaturized Fabry-Perot interferometer (FPI) with metal-organic frameworks (MOFs). The sensor consists of a short and thick-walled silica capillary segment spliced to a lead-in single-mode fiber (SMF), housing a tiny single crystal of HKUST-1 MOF, imparting chemoselectivity features. Ethanol and benzene gases were tested, resulting in a shift in the FPI interference signal. The sensor demonstrated high sensitivity, detecting ethanol gas concentrations (EGCs) with a sensitivity of 0.428 nm/ppm between 24.9 and 40.11 ppm and benzene gas concentrations (BGCs) with a sensitivity of 0.15 nm/ppm between 99 and 124 ppm. The selectivity study involved a combination of three ultralow concentrations of ethanol, benzene, and toluene gases, revealing an enhancement factor of 436% for benzene and 140% for toluene, attributed to the improved miscibility of these conjugated ring molecules with the alkane chains of the ethanol-modified HKUST-1. Experimental tests confirmed the sensor's viability, demonstrating significantly improved response time and spectral characteristics through crystal polishing, indicating its potential for quantifying and detecting chemical gases at ultralow concentrations. This technology may prevent energy resource losses, and the sensor's small size and robust construction make it applicable in confined and hazardous locations.

Design and fabrication of poly-Si/SiO2 Fabry–Perot filter for nondispersive IR CO2 sensors

The relationship between the transmittance and FWHM of a Fabry–Perot filter for a nondispersive carbon dioxide (CO2) sensor was investigated as a function of the number of distributed Bragg reflector (DBR) pairs consisting poly-Si and SiO2 thin films. Given the significant prior research on the fabrication of high-performance Fabry–Perot filters, this study is focused on the relationship between the transmittance and FWHM that can be achieved by controlling the reflectance of the DBR pairs. Each layer of the filter was simulated adequately as the poly-Si and SiO2-based DBR pairs, and poly-Si and SiO2 were deposited on the soda–lime substrate by RF sputtering and low-pressure chemical vapor deposition based on the simulation results. The fabricated filter showed a transmittance of 43.7% and FWHM of 125 nm at 4.26 μm. The NDIR CO2 sensor with Fabry–Perot filter showed enhanced selectivity to CH4 and CO compared with normalized CO2 response.

Nano-Displacements Tests for a Motorized Linear Translation Stage With a Fabry-Perot Interferometer

Nano-Displacements Tests for a Motorized Linear Translation Stage With a Fabry-Perot Interferometer

Stellar feedback impact on the ionized gas kinematics in the dwarf galaxy Sextans B

ABSTRACT We investigated the ionized and atomic gas kinematics and excitation state in the central region of ongoing star formation of the nearby low-metallicity dwarf galaxy Sextans B. The analysis is based on the new observations performed in the H α emission line with high resolution (R ∼ 16 000) scanning Fabry–Perot interferometer at the 6-m BTA Special Astrophysical Observatory of the Russian Academy of Sciences telescope, and on the long-slit spectral observations at the 9.2-m SALT and 2.5-m Caucasian Mountain Observatory of Sternberg Astronomical Institute of Moscow State University telescopes. Strong non-circular gas motions detected in the studied regions probably resulted from the off-plane gas motions and impact of stellar feedback. We identified six regions of elevated H α velocity dispersion, five of which exhibit asymmetric or two-component H α line profiles. Three of these regions are young (<1.1 Myr) expanding ($V_\mathrm{exp} \sim 25-50 \, \mbox{km}\, \mbox{s}^{-1}$) superbubbles. We argue that at least three regions in the galaxy could be supernova remnants. We conclude that supernovae feedback is the dominant source of energy for superbubbles in Sextans B, which is expected for such a low metallicity, although we cannot rule out a strong impact of pre-supernova feedback for one superbubble.

Characterization of Thin AlN/Ag/AlN-Reflector Stacks on Glass Substrates for MEMS Applications

Thin metal layers such as silver (Ag) are being utilized for various optical and plasmonic applications as well as for electrical purposes, e.g., as transparent electrodes in display devices or solar cells. This paper focuses on optical MEMS applications such as the Fabry–Pérot interferometer (FPI). Within such filters, reflector materials such as distributed Bragg reflectors (DBRs) or subwavelength gratings (SWGs) have been widely used so far, whereas metallic thin films (MTFs) were limited in application due to their comparatively higher absorption. In this paper, thin sputtered Ag layers with thicknesses of 20, 40 and 60 nm on glass substrates have been investigated, and it is shown that the absorption is very low in the visible spectral range (VIS) and increases only in near-infrared (NIR) with increasing wavelength. Thus, we consider Ag-thin layers to be an interesting reflector material at least for the VIS range, which can be easily fabricated and integrated. However, Ag is not inert and stable when exposed to the atmosphere. Hence, it needs a passivation material. For this purpose, AlN has been chosen in this contribution, which can be deposited by sputtering as well. In this contribution, we have chosen thin AlN layers for this purpose, which can also be deposited by sputtering. Thus, various AlN/Ag/AlN-reflector stacks were created and patterned by lift-off technology preferably. The fabricated reflectors were characterized with respect to adhesion, stress, cohesion, homogeneity, and most importantly, their optical properties. It was found that the thickness of the AlN can be used to adjust the reflectance–transmittance ratio in the VIS range, and influences the adsorption in the NIR range as well. Based on the measured values of the reflectors with 40 nm Ag, an exemplary transmission filter characteristics has been predicted for a wavelength range from 400 to 800 nm. Both the maximum transmittance and the full width at half maximum (FWHM) can be tuned by variation of the AlN thickness from 20 to 60 nm.

Resonance theory of vibrational polariton chemistry at the normal incidence

Abstract We present a theory that explains the resonance effect of the vibrational strong coupling (VSC) modified reaction rate constant at the normal incidence of a Fabry–Pérot (FP) cavity. This analytic theory is based on a mechanistic hypothesis that cavity modes promote the transition from the ground state to the vibrational excited state of the reactant, which is the rate-limiting step of the reaction. This mechanism for a single molecule coupled to a single-mode cavity has been confirmed by numerically exact simulations in our recent work in [J. Chem. Phys. 159, 084104 (2023)]. Using Fermi’s golden rule (FGR), we formulate this rate constant for many molecules coupled to many cavity modes inside a FP microcavity. The theory provides a possible explanation for the resonance condition of the observed VSC effect and a plausible explanation of why only at the normal incident angle there is the resonance effect, whereas, for an oblique incidence, there is no apparent VSC effect for the rate constant even though both cases generate Rabi splitting and forming polariton states. On the other hand, the current theory cannot explain the collective effect when a large number of molecules are collectively coupled to the cavity, and future work is required to build a complete microscopic theory to explain all observed phenomena in VSC.

Motional Narrowing through Photonic Exchange: Rational Suppression of Excitonic Disorder from Molecular Cavity Polariton Formation.

Maximizing the coherence between the constituents of molecular materials remains a crucial goal toward the implementation of these systems into everyday optoelectronic technologies. Here we experimentally assess the ability of strong light-matter coupling in the collective limit to reduce energetic disorder using porphyrin-based chromophores in Fabry-Pérot (FP) microresonator structures. Following characterization of cavity polaritons formed from chemically distinct porphyrin dimers, we find that the peaks corresponding to the lower polariton (LP) state in each sample do not possess widths consistent with conventional theories. We model the behavior of the polariton peak widths effectively using the results of spectroscopic theory. We correlate differences in the suppression of excitonic energetic disorder between our samples with microscopic light-matter interactions and propose that the suppression stems from photonic exchange. Our results demonstrate that cavity polariton formation can suppress disorder and show researchers how to design coherence into hybrid molecular material systems.

Photonic comb: a stabilized single-mode fiber etalon for wavelength calibration

We present a low-cost alternative to more complex laser metrology systems that uses a single-mode fiber Fabry–Perot etalon to generate an emission spectrum of evenly spaced lines with similar intensities, ideal for calibrating spectrographs (both in terms of wavelength and image quality). The system uses the hyperfine transition lines of 87Rb near 780.24 nm as an absolute reference. By controlling the cavity dimensions by small changes in temperature, we can tune and thus stabilize the transmission spectrum. A 20 Hz PID loop controls the etalon temperature and locks it to the 87Rb transitions. Through this method, we achieve a centroid error/precision of <1m/s (2.6 fm or 1.3 MHz) for 1 s integrations and 1 cm/s (0.026 fm or 13 kHz) for 30 min integrations of the reference line. We also show that a solution can be found to mathematically describe the spectrum. With the correct calibration and environmental controls in place, we show that this setup has the potential to be competitive with the best existing methods based on expensive and cumbersome laser combs.

Tunable VO2 cavity enables multispectral manipulation from visible to microwave frequencies

Optical materials capable of dynamically manipulating electromagnetic waves are an emerging field in memories, optical modulators, and thermal management. Recently, their multispectral design preliminarily attracts much attention, aiming to enhance their efficiency and integration of functionalities. However, the multispectral manipulation based on these materials is challenging due to their ubiquitous wavelength dependence restricting their capacity to narrow wavelengths. In this article, we cascade multiple tunable optical cavities with selective-transparent layers, enabling a universal approach to overcoming wavelength dependence and establishing a multispectral platform with highly integrated functions. Based on it, we demonstrate the multispectral (ranging from 400 nm to 3 cm), fast response speed (0.9 s), and reversible manipulation based on a typical phase change material, vanadium dioxide. Our platform involves tandem VO2-based Fabry–Pérot (F-P) cavities enabling the customization of optical responses at target bands independently. It can achieve broadband color-changing capacity in the visible region (a shift of ~60 nm in resonant wavelength) and is capable of freely switching between three typical optical models (transmittance, reflectance, and absorptance) in the infrared to microwave regions with drastic amplitude tunability exceeding 0.7. This work represents a state-of-art advance in multispectral optics and material science, providing a critical approach for expanding the multispectral manipulation ability of optical systems.

Three-dimensional sound source localization system based on fiber optic sensor array with an adaptive algorithm

Sound Source Localization (SSL) based on microphone arrays nowadays is widely used in the fields of machinery rattle localization, weapon navigation, and robot hearing. However, there is also a need for SSL in some special environments, such as long-distance gas pipelines where there is a risk of leakage. In these environments, arrays built with ordinary microphones can be a safety hazard, which can be compensated by the External Fabry-Perot interferometer (EFPI) fiber-optic sensor's advantages of being uncharged, inexpensive, and highly sensitive. To expand the application areas of microphone array-based SSL techniques, this paper using four EFPI fiber-optic sensors to constructs a 1 m × 1 m × 1 m sensor array, which is used for real-time localization of sound sources based on three-wavelength adaptive intensity demodulation methods and Time Difference Of Arrival (TDOA) localization techniques. An improved method is proposed for the three-wavelength adaptive intensity demodulation method to avoid the occurrence of signal flips. Finally, formulas are provided for this sensor array to quickly calculate the sound source position based on the arrival delay. Several experiments show that the system can achieve sound source localization over a wide range with an average error of less than 3 cm.

Synchronous filtering method for improving the optical signal-to-noise ratio of a tunable laser based on the Fabry-Pérot interferometer.

Optical measurements are closely related to the optical signal-to-noise ratio (OSNR) of the laser, which can be improved using a tunable optical filter (TOF) to suppress frequency noise. For an external-cavity tunable laser with a tuning range larger than the TOF bandwidth, the wavelength at the center of the TOF passband must be varied based on the laser tuning. This study proposes a tunable-laser OSNR-enhancement method based on the Fabry-Pérot (FP) interferometer. The FP signal contains the wavelength information of the swept laser, which can be used to determine the real-time driving voltage of the TOF. Notably, the laser needs to be continuously tunable without mode hopping, and the free spectral range of the FP interferometer must be smaller than the TOF bandwidth.