Interference Cavity Research Articles

Optical manipulation of magnetic microspheres Enables high-sensitivity Fiber-optic magnetic field sensors

This study uses single-fiber optical tweezers to capture non-uniform magnetic particles, producing a novel type of magnetic field sensor for implementing the measurement of external magnetic field changes. A tapered fiber optic probe is used to capture magnetic particles as a sensing probe, constituting an Fabry–Pérot (F-P) interferometric structure. When an external magnetic field is applied, the magnetic particles at the tip of the optical fiber are deflected, affecting the length change of the interference cavity. By reconstructing the axial displacement of the particles, the accurate measurement of the magnetic field within the range of 1–10 mT is successfully realized with a sensitivity of 258 nm/mT. The minimum detectable intensity is 1.44 nT/Hz. This method offers a feasible and effective solution for the realization of magnetic field measurements by using the capture of non-uniform magnetic particles, which can play an important role in the fields of medicine and biology.

Quantum interference and controllable magic cavity QED via a giant atom in a coupled resonator waveguide

Quantum interference and controllable magic cavity QED via a giant atom in a coupled resonator waveguide

Simulation study of an x-ray sub-picosecond resolution detection system based on time-domain amplification.

This study proposes what we believe to be a novel x-ray detection system that achieves a temporal resolution of 930fs with photorefractive and four-wave mixing effects. The system comprises two parts: a signal-conversion system and signal-acquisition system. The signal-conversion system is based on the photorefractive effect, which converts x-ray evolution into the variation of infrared interference intensity. The signal-conversion sensor consists of ultra-fast response LT-GaAs and a high-resolution interference cavity, achieving a resolution of 767fs. The signal-acquisition system consists of a time-domain amplification system based on four-wave mixing and a high-resolution signal-recording system with a resolution of 21ps, providing a temporal resolution of 525fs.

Ultrahigh-Resolution and Large-Dynamic-Range Temperature Sensor Based on Fiber-Optic EFPI Cavity

A fiber-optic extrinsic Fabry–Perot interferometric (EFPI) temperature sensor with extremely high resolution and large dynamic range is proposed and demonstrated. The sensor uses a thermally expanded core (TEC) fiber as the first reflective surface of the interference cavity to focus the beam to improve the finesse of the interference fringes, which enables extremely high cavity length resolution and large dynamic range with a multivalley averaging method based on dynamic estimation of the fringe order. Using a borosilicate capillary as the temperature-sensitizing material, a cavity length sensitivity of 79.25 nm/°C as well as a good linearity were obtained in the temperature range of 10 °C–100 °C. A temperature resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.5\times 10^{-{5}}\,\,^{\circ }\text{C}$ </tex-math></inline-formula> was demonstrated. The extremely high-temperature resolution with a large dynamic range has an important application value in the monitoring of weak temperature changes in deep sea and underground fluids.

Probe type TFBG-excited SPR fiber sensor for simultaneous measurement of multiple ocean parameters assisted by CFBG.

The tilted fiber Bragg grating(TFBG), chirped fiber Bragg grating(CFBG), Vernier effect and metal surface plasmon resonance(SPR) effect are effectively combined to form a probe type fiber sensor for simultaneous measurement of seawater salinity, temperature and depth(STD). The SPR effect excited by the TFBG is achieved by covering a gold layer around the TFBG, which is used to measure the refractive index (RI) of seawater. The core mode of TFBG is used to detect the change of seawater temperature and the measurement of TFBG reflection spectrum is realized by inscribing a CFBG after the TFBG, which makes the sensor have a probe type design and more beneficial to practical applications. The fusion of quartz micro-spheres on the end face of the sensing fiber and the parallel connection of an Fabry Perot(F-P) interference cavity enables the use of Vernier effect to detect the depth of the ocean. Femtosecond laser line-by-line method is used to the inscribing of TFBG, which allows the grating parameters to be changed flexibly depending on the desired spectrum. The experimental results show that the temperature sensitivity is 10.82pm/°C, the salinity sensitivity is 0.122nm/g/Kg, the depth sensitivity is 116.85 pm/m and the depth can be tested to 1000 m or even deeper.

High-sensitivity optical fiber magnetic field sensor based on multimode optical fiber multi Fabry-Perot interference cavities.

A high-sensitivity optical fiber magnetic field sensor based on a multi-Fabry-Perot interference (F-P) cavity in an etched multimode optical fiber (MMF) was proposed. The MMF was etched along the fiber axis and a hole with the length of about 250 µm formed in the MMF. The multi-F-P cavity in the MMF is a sandwich structure, which is composed of UV glue, magnetic fluid and UV glue. The refractive index and effective cavity length of the magnetic fluid cavity change with the changing of the external magnetic field, which will result in changes of the reflection spectra of the multi-F-P. Thus, the external magnetic field could be detected by the changes of spectra. Experimental results showed that the high magnetic field sensitivity of 299.7 pm/mT and 0.164 dB/mT were obtained in the range of 0∼8 mT weak magnetic induction intensity by using the wavelength and intensity demodulations, respectively. The proposed sensor shows the potential applications in the magnetic field measurement in the weak magnetic environment.

High sensitivity fiber optic acceleration sensor based on Fabry-Perot interferometer

• This paper proposes a high sensitivity fiber optic acceleration sensor based on Fabry-Perot interference. • The sensitivity of the sensor is 3.81 nm/g at 300 Hz, and the resonance frequency of the sensor is 800 Hz. • The sensor has a simple structure, low cost and easy to fabricate. A high sensitivity fiber optic acceleration sensor based on Fabry-Perot interferometer is proposed and experimentally demonstrated. The proposed sensor is composed of a sensor pedestal, a mass block, elastic diaphragm and two reflectors, wherein the collimating reflector 1 and the reflector 2 constitute a fiber Fabry-Perot (F-P) interference cavity. By analyzing the relevant parameters of F-P interference theory, we modulate the F-P reflection spectrum with high finesse, and demodulate the F-P reflection spectrum by wavelength demodulation method to obtain the acceleration signal. Through simulation analysis and experimental verification, the resonant frequency, sensitivity and lateral anti-interference ability of the sensor have been investigated. The experimental results show that the resonant frequency of the sensor is 800 Hz, the sensitivity is 3.81 nm/g when the frequency is 300 Hz, the resolution is 0.263 mg, and the lateral anti-interference degree is less than 5 %. Furthermore, the proposed acceleration sensor exhibits the advantages of simple structure and low cost, and has great application prospects in the vibration monitoring of the pitch bearing of wind power generation.

Ultralow Emittance Thermal Radiation Barrier Achieved by a High-Contrast Grating Coating

Thermal radiative emission in vacuum is minimized using metal-backed flexible “space blankets” that have a theoretical minimum infrared emittance of 0.03. However, their presence under oxygenated and degradation-prone environments rapidly increases emittance due to metal oxidation, surface pitting, and implantation of contaminants. A monolithic dielectric coating composed of microscale periodic metasurface gratings on multilayers and metal thin film can achieve sub-1% total emittance. The minimum emittance can be tailored to any temperature-function blackbody emission, so long as the selected dielectric coating materials have near-zero absorption. Using computational optimization and theoretical understanding of high-contrast grating phase-shift mode conditions, we identified characteristic at-wavelength germanium gratings and a near-quarter-wave layer above a low-refractive-index infrared-transparent Fabry–Pérot multilayer interference cavity. This dual mechanism can achieve a room-temperature total emittance of 0.0085, paving a new theoretical minimum multilayer insulation effective conductance. As multilayer insulation, this coating offers total effective emittance of 0.0032 per pair of optimally mismatched grating surfaces. This ultrahigh reflection coating design can also be relevant in thermal management of refrigeration and electronic components.

Enhancing the adjustable range of saturation in color reflectors using a phase-change material as an effective absorption base

Structural color technology has garnered extensive attention in the development of ink-free color technology for applications such as color displays, color reflectors, and colorimetric devices. A Fabry–Perot (F–P) structure formed by stacking a metal base, an interference cavity, and a phase change material layer (MIP) is of significant interest as a lithography-free and scalable color-reflecting structure. Such a structure can selectively reflect interfered light over a range of visible wavelengths, resulting in bright colors. However, obtaining a wide range of saturation regulation spaces has become a challenge. In this study, an F–P color reflector based on a phase-change material (PCM) base is proposed, which consists of a PCM base, an interference layer, and a PCM top layer (PIP). The results of the finite element simulation and experimental measurements demonstrated that the PIP reflector had an adjustable saturation range 10.75 times larger than that of the MIP reflector. The effects of the structure size and phase change of the PCM layer on the structural characteristics were further analyzed. In addition, the performance of laser-induced color change and its application in color printing were demonstrated. The present study sheds new light on color reflectors, and the strategy proposed indicates their potential optoelectronic applications based on saturation modulation.

Signal recovery of a Fabry–Pérot interferometric x-ray pulse detector based on the RadOptic effect

The signal recovery of a Fabry–Pérot interferometric x-ray pulse detector based on the RadOptic effect in the non-limiting case was investigated in this research. A Fe-doped InP with an invariant excess carrier recombination mechanism was used as the interference cavity material to achieve a constant temporal instrumental response function (tIRF). A linear and time-invariant detection system described by the convolution of the time-varying x-ray pulse and the constant tIRF was established based on the transient refractive index variation model determined by the three effects of band filling, band shrinkage, and free-carrier absorption. For the non-limiting case, the accumulation of excess carriers enhanced the sensitivity but altered the fluctuations of the real x-ray pulse. To realistically reconstruct the x-ray pulse, two-photon absorption of the infrared ultrashort pulse was used to simulate the ultrashort x-ray excitation to obtain the tIRF. Finally, using the conjugate gradient method, the original signal recorded by the detection system was deconvoluted to recover the signal. The success of signal recovery in the non-limiting case provided the basis for the development of detectors with adjustable sensitivity controlled by carrier lifetime.

Four-wave-cooling to the single phonon level in Kerr optomechanics

Cavity optomechanics has achieved groundbreaking control and detection of mechanical oscillators, based on their coupling to linear electromagnetic modes. Recently, however, there is increasing interest in cavity nonlinearities as resource in radiation-pressure interacting systems. Here, we present a flux-mediated optomechanical device combining a nonlinear superconducting quantum interference cavity with a mechanical nanobeam. We demonstrate how the Kerr nonlinearity of the circuit can be used to enhance the device performance by suppressing cavity frequency noise, and for a counter-intuitive sideband-cooling scheme based on intracavity four-wave-mixing. With a large single-photon coupling rate of up to g0 = 2π ⋅ 3.6 kHz and a high mechanical quality factor Qm ≈ 4 ⋅ 105, we achieve an effective four-wave cooperativity of {{{{{{{{mathcal{C}}}}}}}}}_{{{{{{{{rm{fw}}}}}}}}}, > , 100 and demonstrate four-wave cooling of the mechanical oscillator close to its quantum groundstate. Our results advance the recently developed platform of flux-mediated optomechanics and demonstrate how cavity Kerr nonlinearities can be utilized in cavity optomechanics.

Metallic nanoparticle-on-mirror: Multiple-band light harvesting and efficient photocurrent generation under visible light irradiation

We present a photoanode concept for photoelectrochemical (PEC) water splitting based on metal nanoparticles (Au, Ag, Cu) deposited on a Ti mirror (NPoM) to photosensitize an intermediate TiO2 layer to induce the harvesting of light with sub-bandgap photon energies. The generation of hot electron-hole pairs in metallic nanostructures can occur either by intraband excitation, i.e., plasmon electrons, or by the interband transition of the d-band electrons to the unoccupied conduction band states. Our results demonstrate that the underlying Ti mirror significantly amplifies the PEC activity of such NPoM systems in the visible spectral range. We show that the PEC enhancement in the visible spectral range is not limited to the intraband excitations but is affected mainly by the light trapping pathway within the TiO2 layer, i.e. due to a favorable interplay between thin-film interference cavity modes with both intraband and interband excitations. Among tested metals, Cu and Ag NPs demonstrate a ~3-fold higher enhancement factor than that of Au NPs, while in both former cases the nature of the excited electrons is different. The experimentally determined internal quantum efficiency demonstrates alternating behavior with wavelength showing higher efficiencies at short wavelengths, which is attributed to the reduced Schottky barrier of the NPoMs at constructive interference maxima.

Compact Fabry-Perot microfiber interferometer temperature probe with closed end face

In this paper, a Fabry-Pérot interferometer microprobe was constructed based on microfiber taper and hollow microfiber cone cavity. The interference cavity length of the Fabry-Pérot structure can be flexibly changed by moving the microfiber taper in the hollow microfiber. Polydimethylsiloxane solution was filled into the air cavity of the Fabry-Pérot interferometer to build a Fabry-Pérot temperature-sensitive microprobe with a stable structure by coaxially fixing the microfiber taper in the hollow fiber. The temperature sensitivity reached up to 2.41 nm/°C. The triple-repeated measurements and stability tests were experimentally verified with an excellent sensing performance. This small, compact, and end-sealed temperature-sensitive probe will push forward the development of wearable or implantable sensors.

Dynamic matching of a 300-mm-aperture high-precision interference cavity via a double-ring-point support

The precision of a large-aperture interference cavity is limited by the deformation of the flat owing to support and gravity. In this study, we proposed a double-ring-point support scheme for dynamic matching. The theory was derived from elastic deformation. To obtain an optimal support structure and force operation, the support locations, number of discrete support points, and force distribution were analysed quantitatively using finite element method. Furthermore, matching measurements were analysed in detail, and dynamic matching was implemented by matching different transmission flats to achieve high-precision interference cavity. The identical matching precision demonstrated the effectiveness of the proposed scheme. Finally, with the dynamic matching, the precision of interference cavity is improved from λ/7 to λ/27 (peak-to-valley) for a 300-mm aperture.

Optical phase-shifting methods based on low coherence laser for large aperture Fizeau interferometer

PZT is commonly used as the phase shifter in interferometric systems with small apertures for decades. However, it becomes more difficult to be applied to the system with large aperture. In this paper, the phase shifting procedure is moved to the source module with a low coherence laser, which makes phase shifting independent of the large interference cavity. The path matching procedure based on intensity variation is introduced to compensate the path difference between the two arms. The experiments based on PZT and wavelength tuning methods are both carried out on a 600mm Fizeau interferometer for verification of the proposed method. The difference between the two results is 0.0015λ(PV). Besides, repeated experiments are performed, showing excellent repeatability and stability and the standard deviation of RMS is 0.0011λ via PZT method. The analysis of error sources is also performed, including the poor contrast and the nonlinearity of PZT. Both the experimental results and the error analysis verify the feasibility of the proposed method in large aperture interferometer.

Fabry-Pérot Interference Cavity Length Tuned by Plasmonic Nanoparticle Metasurface for Nanophotonic Device Design

Fabry-Perot (FP) interference cavity for which the interference property is controlled by the tuning of the cavity length is widely used in many fields. However, in nanophotonic device applications...

Research on Two-dimensional Fabry-Perot Ultrasonic Sensing Technology

According to the laser interference method, a two-dimensional Fabry-Perot fiber optic sensor is used as the core, and the difference between the propagation speed of the ultrasonic transverse wave and the longitudinal wave in the solid medium is used to measure the ultrasonic wave propagating in the solid to realize the ultrasonic positioning. An F-P interference cavity is formed with a coated quartz film, the end face of the fiber end, and air. At the same time, the cantilever beam design can be used to simultaneously extract longitudinal ultrasonic waves based on Fabry-Perot cavity interference and transverse ultrasonic signals based on cantilever fibers in a solid rod-shaped acoustic waveguide. In this paper, the position of the ultrasonic wave is determined by the difference of the longitudinal and transverse ultrasonic wave speeds in the detected ultrasonic signals.

An Optical Fiber Fabry–Perot Pressure Sensor with Optimized Thin Microbubble Film Shaping for Sensitivity Enhancement

A pressure-assisted arc discharge method of preparing silicon microbubbles with a glass tube was utilized for decreasing the bubble film’s thickness and improving the bubble’s uniformity. By controlling the arc discharge intensity, discharge time and the position of the fiber carefully, the thickness of the microbubble film was reduced to the micrometer scale. Later, the thin film of the microbubble was transferred to the end the single-mode-fiber/glass-tube structure, for forming the FP (Fabry–Perot) interference cavity. As the thin film is sensitive to the outer pressure, such a configuration could be used for a high-sensitive-pressure measurement. Experimental results show that the sensitivity of this FP (Fabry–Perot) cavity was 6790 pm/MPa when the outer pressure ranges from 100 to 1600 kPa, and the relationship between the structural parameters of the thin film and the outer pressure was theoretically analyzed. Moreover, this special structure made of the end silicon film microbubble is more suitable for high-sensitivity applications.

WITHDRAWN: An air-coupled ultrasonic sensor based on cascaded fibre Bragg grating and Fabry-Perot interference cavity

Abstract In this paper, we proposed and demonstrated experimentally an air-coupled fiber-optic ultrasonic sensor, based on cascaded fibre Bragg grating (FBG) and Fabry-Perot interference (FPI) cavity. Because of the modulation effect of FPI cavity, the sensor’s responses to ultrasonic wave (UW) have been improved. With side-band filtering technology-based intensity interrogation, the voltage responses of 1.2 V and 1.34 V to the continuous and pulse UW at 1 MHz respectively are obtained in air, and its SNR is about 37 dB. Further results of the directivity and stability of the sensor indicate that the sensor has the potential of imaging in air.

3D imaging of mural model in air using sensitivity-improved ultrasonic sensor based on fiber-optic Fabry-Perot interferometer

A sensitivity-improved ultrasonic fiber optic sensor is proposed and demonstrated for ultrasound wave (UW) imaging of mural models. The sensor contains a Fabry-Perot (F-P) cavity at one end of a single-mode fiber (SMF) and a gold-coated ceramic ferrule. Because the gold film is 120 nm thick, the sensor has extremely high ultrasonic sensitivity. Compared to similar sensors in the literature, by changing its package structure, removing the acoustic lens and using a thinner film in the interference cavity, the signal-to-noise ratio (SNR) of the proposed sensor can reach 68.18 dB. Using the sideband filtering method, the echo wave signal can be extracted, the cross sectional image of hollows in the mural model can be obtained by 1D scanning, and 3D images can be reconstructed by 2D scanning. We calculated the thicknesses of the three hollows in the ground layer to be 0.1986 cm, 0.6752 cm, and 0.3873 cm, and the thickest part of the efflorescence area to be 2.857 cm. The ultrasonic sensor helps archaeological conservators to detect information on size of defects in the mural ground layer.