Fabry-Perot Cavity Research Articles

Research on a signal demodulation algorithm for fiber optic acoustic sensors based on the amplitude ratio of harmonic components

Fiber optic sensing technology's performance is crucially influenced by the choice of demodulation algorithms. Traditional intensity demodulation methods rely on precisely controlling the working point to the quadrature point (Q point) by adjusting the laser wavelength. However, issues like laser wavelength adjustment accuracy and laser power variations with wavelength affect demodulation accuracy, limiting its application in complex scenarios. Additionally, this method requires sensitivity calibration and has a limited dynamic range. To address these limitations, this paper proposes an amplitude ratio of harmonic components (ARHC) demodulation algorithm. It analyzes the harmonic components of the interference light intensity output by the sensor to calculate Fabry-Perot cavity length changes, achieving real-time demodulation of dynamic signals. Compared to traditional methods, the ARHC algorithm simplifies system adjustment, has a larger demodulation range and higher accuracy, and is more adaptable to environmental changes. Simulations and experiments demonstrate its effectiveness and high-precision, large-dynamic-range signal demodulation capabilities under different interference conditions. The EFPI ultrasonic sensitivity based on the ARHC algorithm is 2.5 nm/Pa@23kHz, and it can linearly demodulate up to a vibration amplitude of 372.8 nm for the sensitive diaphragm, with a demodulation error of less than or equal to 0.8 nm.

In-phase collective unconventional photon blockade and its stability in asymmetrical cavity containing N bosonic atoms

Abstract We present a work of cavity-driven QED system combined an asymmetrical Fabry-Perot cavity and N two-level atoms (TLAs) and show the convenience of simplifying from distinguishable atoms to undistinguishable bosons when atoms are prepared in the same initial state. Such simplification is valid even when the atoms are not prepared in the in-phase condition, since any partial in-phase initial state will evolve into the ground state through a relaxation process. Thus, we get a reduced group of differential equations by introducing the Dicke states, and the under-zero Lyapunov exponents verify its stability. We also work out the collective unconventional photon blockade (UCPB) and get two kinds of giant nonreciprocal UCPBs (NUCPBs) in the weak-driving approximation. Results show that we can employ N non-interacting bosonic atoms to generate a collective UCPB instead of a monoatomic UCPB as UCPB conditions do not vary with the number of atoms. Furthermore, the forward giant NUCPB only occurring for N larger than a certain number, as well as the backward giant NUCPB, are controllable by the cavity asymmetry and by the number of atoms. Our findings suggest a prospective approach to the generation of quantum nonreciprocity by N identical atoms.

Two-photon 3D printed fiber-optic Fabry–Perot probe for triaxial contact force detection of guidewire tips

The demand for real-time feedback and miniaturization of sensing elements is a crucial issue in the treating vascular diseases with minimally invasive interventions. Here, Fabry–Perot microcavities fabricated via direct laser writing using a two-photon polymerization technique on fiber tips are proposed, designed, simulated, and experimentally demonstrated as a miniature triaxial force sensor for monitoring real-time interactions between the tip of a guidewire and human blood vessels and tissues during minimally invasive surgeries. The sensor contains four fiber tip-based Fabry–Perot cavities, which can be seamlessly integrated into medical guidewires and achieves three-axis force decoupling through symmetrically arranged flexible structures. The results showed that the proposed sensor achieved a cross-sectional diameter of 890 μm and a high sensitivity of about 85.16 nm/N within a range of 0 to 0.5 N with a resolution of hundreds of micro-Newtons. The proposed triaxial force sensor exhibits high resolution, good biocompatibility, and electromagnetic compatibility, which can be utilized as an efficient monitoring tool integrated into minimally invasive surgical intervention devices for biomedical applications.

Broadband Light Harvesting from Scalable Two-Dimensional Semiconductor Multi-Heterostructures.

Broadband absorption in the visible spectrum is essential in optoelectronic applications that involve power conversion such as photovoltaics and photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic structures that maximize absorption using surface plasmons and/or Fabry-Perot cavities, which limits the weight efficiency of the device. Here, we show the theoretical and experimental realization of an unpatterned/planar semiconductor thin-film absorber based on monolayer transition-metal dichalcogenides. We experimentally demonstrate an average total absorption in the visible range (450-700 nm) of >70% using <4 nm of semiconductor absorbing materials scalable over large areas with vapor phase growth techniques. Our analysis suggests that a power conversion efficiency of 15.54% and a specific power >300 W g-1 may be achieved in a photovoltaic cell based on this metamaterial absorber.

Watt-level long-term stable ultra-narrow linewidth 1064 nm single-longitudinal-mode ring cavity fiber oscillator

This study presents a high-power, single-longitudinal-mode (SLM) fiber oscillator with a ring cavity design, operating at 1064 nm. Utilizing a double-cladding ytterbium-doped fiber as the gain medium, the system incorporates a fiber Bragg grating Fabry-Perot cavity and a dual coupler ring for step-by-step filtering to achieve SLM operation. With a pump power of 4.19 W, the oscillator delivered an output power of 1.01 W and narrowed the linewidth to 147 Hz, with the potential for further power increase. The oscillator demonstrated excellent longitudinal-mode stability, maintaining mode-hop-free operation for 8.7 hours after temperature stabilization. To the best of our knowledge, this work represents the longest duration of mode-hop-free operation and the narrowest laser linewidth achieved by a free-running ring-cavity SLM fiber oscillator at watt-level output powers.

Influencing factors of self-aligned imaging in near-field lithography for the Fabry-Perot cavity effect

Influencing factors of self-aligned imaging in near-field lithography for the Fabry-Perot cavity effect

Optimization of stacked Fabry-Perot cavities for VO₂-based broadband adaptive thermal radiators

Optimization of stacked Fabry-Perot cavities for VO₂-based broadband adaptive thermal radiators

Reliable fabrication of 3D freestanding nanostructures via all dry stacking of incompatible photoresist

Three-dimensional (3D) free-standing nanostructures based on electron-beam lithography (EBL) have potential applications in many fields with extremely high patterning resolution and design flexibility with direct writing. In numerous EBL processes designed for the creation of 3D structures, the multilayer resist system is pivotal due to its adaptability in design. Nevertheless, the compatibility of solvents between different layers of resists often restricts the variety of feasible multilayer combinations. This paper introduces an innovative approach to address the bottleneck issue by presenting a novel concept of multilayer resist dry stacking, which is facilitated by a near-zero adhesion strategy. The poly(methyl methacrylate) (PMMA) film is stacked onto the hydrogen silsesquioxane (HSQ) resist using a dry peel and release technique, effectively circumventing the issue of HSQ solubilization by PMMA solvents typically encountered during conventional spin-coating procedures. Simultaneously, a dry lift-off technique can be implemented by eschewing the use of organic solvents during the wet process. This pioneering method enables the fabrication of high-resolution 3D free-standing plasmonic nanostructures and intricate 3D free-standing nanostructures. Finally, this study presents a compelling proof of concept, showcasing the integration of 3D free-standing nanostructures, fabricated via the described technique, into the realm of Fabry-Perot cavity resonators, thereby highlighting their potential for practical applications. This approach is a promising candidate for arbitrary 3D free-standing nanostructure fabrication, which has potential applications in nanoplasmonics, nanoelectronics, and nanophotonics.

Ultrafast, Fano resonant colorimetric sensor with high chromaticity beyond standard RGB

Fast-responsive colorimetric sensors with a wide color gamut have garnered significant attention for real-time atmospheric monitoring observable to the naked eye. Although swelling medium-based Fabry–Perot cavities, which enable linear resonance shifts with high Q-factors, have been widely suggested, they face limitations such as a restricted color gamut within standard RGB due to subtractive colors and slow response times caused by the top layer blocking, delaying the swelling medium’s equilibrium time. Here, we present two-dimensionally nanostructured Fano resonant colorimetric sensors using a swelling medium with significantly improved responsiveness and color representation beyond standard RGB. The nanostructured Fano resonator is elaborately designed to transform the spectral line shape into a Lorentz state in terms of reflectance, resulting in additive color through controlled coupling parameters of the resonator systems. In addition, the nanostructuring of the surface provides direct channels to water vapors, ensuring fast and strong interaction with the swelling medium. Consequently, the fabricated sensor exhibits a wide color gamut, covering 141% of standard RGB and 105% of Adobe RGB, and demonstrates rapid responsiveness with response and recovery times of 287 ms and 87 ms, respectively.

Electrically switchable behavior in coupled EIT-like meta-molecule and Fabry-Pérot cavity

In this paper, we propose a microstrip Fabry–Pérot (FP) cavity embedded with an active electromagnetically-induced-transparency-like (EIT-like) meta-molecule to investigate the electrically switchable behavior. The phenomenon of EIT is achieved by coupling a ‘bright’ comb-line resonator with a ‘dark’ split-ring resonator. The FP cavity is fabricated by etching two narrow slots on a microstrip line. With two different resonance mechanisms working together, the proposed composite EIT-cavity design is shown to exhibit the enhanced EIT-like transmission characteristics, accompanied by two sharp Fano-type line-shapes. By incorporating PIN diodes into the composite EIT-cavity structure, we can dramatically modulate the transmission spectrum via external DC voltage. In particular, we show the multi-band unity modulations through biasing the proposed active samples. Moreover, the slow light on-to-off switching processes are also obtained with modifying the state of PIN diode from dielectric to conductive. Our results may open important opportunities for fabricating dynamic functional photonic devices in the future.

Second harmonic generation based on graphene hyperstructure for higher resolution and performance on top of achieving fundamental wave detection in theory

In this paper, an innovative one-dimensional graphene hyperstructure (GHS) is proposed, allowing for the concurrent detection of multiple physical parameters in both the fundamental and second harmonic generation. The sensing characteristics of GHS pertaining to magnetic field strength (B), incident electromagnetic wave angle (θ), and graphene thickness (dgt) are systematically investigated. Moreover, through the incorporation of second harmonic generation alongside fundamental detection, higher resolution and performance are achieved. The findings indicate an expansion of the measurement range for B, θ, and dgt, from 0.3∼0.5 T, 35∼55°, and 1∼6 layers to 0.3∼1 T, 35∼65°, and 1∼10 layers, providing increased flexibility and adjustability. Additionally, by leveraging nonlinear effects and widening the Fabry-Perot cavity width, this structure effectively enhances the quality factor (Q) from 2.94 × 102 to 1.95 × 105, resulting in a substantial improvement in sensing performance. This development holds tremendous promise in surpassing the diffraction limit and addressing high-Q value sensing requirements. In comparison to conventional detectors, the GHS not only enhances detection efficiency but also harbors the potential for multiple physical quantities detection. This forward-looking research is pivotal in its successful resolution of detector performance limitations, ushering in novel possibilities across diverse domains.

Observation of widely separated soliton molecules in a mode-locked Yb-doped fiber laser operating with net anomalous dispersion

This paper investigates the generation and characterization of soliton molecules (SM) in a semiconductor saturable absorber mirror (SESAM) mode-locked Yb-doped fiber laser with a linear cavity. By adjusting the pump power, both single-pulsing (SP) and double-pulsing (DP) states can be achieved. The observed soliton molecules are highly stable, with minimal temporal jitter despite being separated by 1.56ns. While SM have been observed in many different cavities this is one of the few reports in a Fabry–Perot cavity rather than a ring cavity and again most previous observations of soliton molecules having been in the anomalous dispersion regime. This configuration thus provides detailed and valuable insights into the behaviour of SM, shedding light on their formation, stability, and dynamics. This study contributes to understanding long range soliton interactions in fiber lasers, with potential implications for applications such as multi-bit transmission, bit storage, and pump-probe experiments to study the dynamics of chemical reactions.

Ultracompact all-fiber self-transceiving ultrasonic probe with an enhanced working distance.

All-optical ultrasonic probes exhibit notable benefits in ultrasonic detection and imaging. Typically, two separate optical fibers are used for excitation and detection, yet limited research has explored the integration of both functionalities within a single fiber. In this Letter, to our knowledge, a new method for fabricating an all-fiber self-transceiving ultrasonic probe is proposed with a lateral dimension of less than 500 µm. Double cladding fiber (DCF) is spliced with a short segment of thin-diameter single-mode fiber (TDSMF), which is then embedded into a fiber bubble to form a Fabry-Perot cavity, and the bubble surface is coated with a composite material layer. The pulsed laser propagates through the inner cladding of DCF and leaks from the splicing point of DCF-TDSMF, inducing the material excitation for efficient ultrasound generation. The core-guided detection laser is directed to the TDSMF end, entering the bubble microcavity and inducing an optical interference for weak echo detection. The emitting functionality produces an ultrasound with a -6 dB bandwidth of 17.5 MHz and a peak frequency of 6.29 MHz, which is well-matched with the fiber microcavity's response frequency of 3.29 MHz. Through self-transceiving experiments, low-noise pulse-echo signals are captured at varying working distances of up to 3.78 cm. The proposed probe exhibits great potential in biomedical and industrial fields due to its all-fiber miniaturization and enhanced-distance detection capability.

Circumventing the polariton bottleneck via dark excitons in 2D semiconductors

Efficient scattering into the exciton polariton ground state is a key prerequisite for generating Bose–Einstein condensates and low-threshold polariton lasing. However, this can be challenging to achieve at low densities due to the polariton bottleneck effect that impedes phonon-driven scattering into low-momentum polariton states. The rich exciton landscape of transition metal dichalcogenides (TMDs) provides potential intervalley scattering pathways via dark excitons to rapidly populate these polaritons. Here, we present a theoretical and fully microscopic study exploring the time- and momentum-resolved relaxation of exciton polaritons supported by a MoSe2 monolayer integrated within a Fabry–Perot cavity. By exploiting phonon-assisted transitions between momentum-dark excitons and the lower polariton branch, we demonstrate that it is possible to circumvent the bottleneck region and efficiently populate the polariton ground state. Furthermore, this intervalley pathway is predicted to give rise to, yet unobserved, angle-resolved phonon sidebands in low-temperature photoluminescence spectra that are associated with momentum-dark excitons. This represents a distinct signature for efficient phonon-mediated polariton-dark-exciton interactions.

Bridging the Fabry–Perot cavity and asymmetric Berreman mode for long-wave infrared nonreciprocal thermal emitters

Bridging the Fabry–Perot cavity and asymmetric Berreman mode for long-wave infrared nonreciprocal thermal emitters

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.

Cavity Lasing of Thioflavin T in the Condensed Phase for Discrimination between Surface Interaction and β-Sheet Groove Binding in Alzheimer-Linked Peptides.

This study investigates the lasing effects in a Fabry-Perot cavity to discern the binding interactions of thioflavin T (ThT) with various peptides associated with Alzheimer's disease, including Aβ(1-42), KLVFFA, and diphenylalanine (FF) in the condensed phase. Utilizing kinetic lasing measurements, the research explores ThT emission enhancements due to specific groove binding in β-sheet structures and highlights additional contributions from weak surface interactions and solvent-solute interactions. Lasing spectroscopy reveals a lack of transition of the FF system from its native state to an amyloid-like structure, challenging traditional ThT assay interpretations. These findings show the potential of lasing spectroscopy in elucidating the molecular basis of amyloid fibril formation and the development of diagnostic tools for amyloidogenic diseases.

An efficient and miniaturized ultra-thin tunable UWB graphene metasurface absorber for terahertz gap regime

This work introduces an ultra-thin tunable ultra-wideband (UWB) metasurface absorber (MSA) for the terahertz (THz) gap. The polarization-insensitive MSA provides an absorptivity (A(f)) ≥ 90% from 0.1 to 11.5 THz, corresponding to 196.6% fractional bandwidth. The usage of resonant slots engraved on top patterned graphene sheet (Gpat) and strong plasmonic coupling in the Fabry-Perot cavity formed between top Gpat and bottom continuous graphene (Gcont) in bilayer stack configuration ensures absorptivity over a UWB THz spectrum. An equivalent circuit model (ECM) closely follows the A(f) response of the proposed MSA. The proposed DC-biasing mechanism can regulate the chemical potential (μc) of the connected Gcont efficiently. A DC bias voltage of 0 to 6.1 V is adequate to vary μc of Gcont from 0 to 0.6 eV for achieving tunable A(f). The structure maintains its ultra-thin nature and has a thickness of only λ0/1500, where λ0 is the free space wavelength calculated at 0.1 THz. In addition, the periodicity is only λ0/300. The MSA also provides stable absorption response from 0.1 to 11.5 THz with A(f) ≥ 80% for incidence angle (θ) up to 60∘ under both transverse magnetic (TM) and transverse electric (TE) polarization.

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A method is described to measure the thermal expansion coefficient of fused quartz glass. The measurement principle is to monitor the change in resonance frequency of a Fabry–Perot cavity as its temperature changes; the Fabry–Perot cavity is made from fused quartz glass. The standard uncertainty in the measurement was less than 0.6 (nm·m-1)·K-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\ extrm{nm}{\\cdot } \ extrm{m}^{-1}){\\cdot }\ extrm{K}^{-1}$$\\end{document}, or 0.15 %. The limit on performance is arguably uncertainty in the reflection phase-shift temperature dependence, because neither thermooptic nor thermal expansion coefficients of thin-film coatings are reliably known. However, several other uncertainty contributors are at the same level of magnitude, and so any improvement in performance would entail significant effort. Furthermore, measurements of three different samples revealed that material inhomogeneity leads to differences in the effective thermal expansion coefficient of fused quartz; inhomogeneity in thermal expansion among samples is 24 times larger than the measurement uncertainty in a single sample.

Phase signal analysis for high-sensitive temperature fiber-optic external Fabry-Perot-cavity sensor

We experimentally demonstrate a highly temperature-sensitive external Fabry-Perot cavity. The interferometric structure is composed of an air-microcavity; its fabrication uses a microcapillary and UV polymer. A temperature sensitivity close to 5.7 nm/ºC is achieved with suitable linearity (0.9896) and minimal hysteresis; a phase analysis technique is proposed and applied to overcome the trade-off between sensitivity and range of operation. This technique provides a competitive sensitivity (0.84 rad/ºC), good linearity (0.9934), and a range of operation from 25 °C to 41 °C.