Search Results (83)

This paper presents a methodology for extracting and simulating arterial pulse waveform signals from Fabry–Perot interferometric measurements, emphasizing a practical approach for noninvasive cardiovascular assessment. A key novelty of this work is the presentation of a complete Python-based processing pipeline, which is made publicly available as open-source code on GitHub (git version 2.39.5). To the authors’ knowledge, no such repository for demodulating these specific interferometric signals to obtain a raw arterial pulse waveform previously existed. The proposed system utilizes accessible Python-based preprocessing steps, including outlier removal, Butterworth high-pass filtering, and min–max normalization, designed for robust signal quality even in settings with common physiological artifacts. Key features such as the rate of change, the Hilbert transform of the rate of change (envelope), and detected extrema guide the signal reconstruction, offering a computationally efficient pathway to reveal its periodic and phase-dependent dynamics. Visual analyses highlight amplitude variations and residual noise sources, primarily attributed to sensor bandwidth limitations and interpolation methods, considerations critical for real-world deployment. Despite these practical challenges, the reconstructed arterial pulse waveform signals provide valuable insights into arterial motion, with the methodology’s performance validated on measurements from three subjects against synchronized ECG recordings. This demonstrates the viability of Fabry–Perot sensors as a potentially cost-effective and readily implementable tool for noninvasive cardiovascular diagnostics. The results underscore the importance of precise yet practical signal processing techniques and pave the way for further improvements in interferometric sensing, bio-signal analysis, and their translation into clinical practice. Full article

A double-cavity Fabry-Perot (F-P) interferometer sensor based on a polymer-filled hollow core fiber (HCF) has been proposed and experimentally verified. The double cavity of the sensor is formed by filling the hollow core fiber with two kinds of polymer materials and curing these materials, with the other end of the hollow core fiber connected to a single-mode fiber (SMF). The three reflective surfaces of the sensor reflect three beams of light, which interfere to form a spectrum with an envelope. By using Fast Fourier Transform (FFT) and a Fourier filter, the spectrum of each cavity can be separated and, based on this, the demodulation matrix of the sensor can be constructed. By controlling the length of the polymer cavity, a single sensor cavity can achieve high temperature and gas pressure sensitivity, with values of 2.05 nm/°C and 17.63 nm/MPa, respectively. More importantly, the sensor can be used under an environment of 40–110 °C and 0–3.0 MPa, with simple fabrication, good robustness, and better stability and repeatability compared to similar sensors. Based on its high sensitivity and large measurement range, this sensor has broad application prospects in industrial manufacturing and harsh environmental monitoring fields. Full article

To meet the pressure measurement requirements of deep earth exploration, we propose an OFPS (optical fiber pressure sensor) with self-temperature compensation based on MEMS technology. A spectral extraction and filtering algorithm, based on FFT (fast Fourier transform), was designed to independently demodulate the composite spectra of multiple FP (Fabry–Pérot) cavities, enabling the simultaneous measurement of pressure and temperature parameters. The sensor was fabricated by etching on an SOI (silicon on insulator) and bonding with glass to form pressure-sensitive FP cavities, with the glass itself serving as the temperature-sensitive component as well as providing temperature compensation for pressure sensing. Experimental results showed that within the pressure range of 0–100 MPa, the sensor exhibited a sensitivity of 0.566 nm/MPa, with a full-scale error of 0.34%, and a linear fitting coefficient (R²) greater than 0.9999. Within the temperature range of 0–160 °C, the temperature sensitivity of the glass cavity is 0.0139 nm/°C and R² greater than 0.999. Full article

The main characteristic of a reflective semiconductor optical amplifier chip (RSOA) is that it does not generate optical resonance under electric pumping and maintains the operation state of spontaneous emission. In this paper, a Nb₂O₅/SiO₂/Nb₂O₅/SiO₂ (four-layer Nb₂O₅/SiO₂) film system is employed as the coating material for the output facet of the RSOA. The 3 dB spectral width of the spontaneous emission spectrum from this RSOA reaches 79.4 nm, with a ripple of less than 1 dB occurring across this wavelength range. Notably, around the 1550 nm wavelength, the ripple is as low as 0.5 dB. This represents the best performance reported for this type of chip. The RSOA is packaged as a narrow-linewidth external cavity laser. Under test conditions of 25 °C and 180 mA, the external cavity laser produces an output power of 12.6 mW and achieves a linewidth of 299.8 Hz. Furthermore, by adjusting the Fabry–Pérot (FP) standard cavity, filtering, and other external cavity parameters, the lasing spectrum of the narrow-linewidth external cavity laser based on the RSOA is tunable across a wavelength range from 1535.83 nm to 1561.42 nm, which shows the usability of the proposed ROSA for a C-band external cavity narrow-linewidth laser. Full article

Demodulation of fiber optic Fabry–Pérot (F-P) acoustic sensors with high sensitivity and a large dynamic range continues to pose significant challenges. In this paper, we propose an advanced phase-generated carrier (PGC) demodulation algorithm, applied innovatively to membrane-free F-P acoustic sensors operating under high sound pressure. The algorithm optimizes acoustic demodulation results by adjusting the mixing phase delay, achieving the best signal to noise and distortion ratio (SINAD) and total harmonic distortion (THD) (<1%). Additionally, by introducing the cosine component of the acoustic signal obtained directly after filtering the interference signal, into the demodulation algorithm process, the sensitivity of the sensor at high sound pressure is significantly improved. The experimental results show that the ameliorated algorithm obtains a demodulation sensitivity of $34.95\mathsf{\mu }$rad/Pa and a THD of 0.87%, both of which are superior to traditional PGC demodulation algorithms under the same experimental conditions. At the same time, the minimum detectable sound pressure of $129.73{\mathrm{mPa/Hz}}^{1/2}$ was obtained, and the sound pressure tested in the experiment at a frequency of 1 kHz was as high as 3169.78 Pa (164 dB). With the proposed algorithm, the flatness of the frequency response is ±0.82 dB from 100 Hz to 33 kHz, and a dynamic range of up to 102.6 dB was obtained, making it relevant in the field of aerospace acoustic measurements. Full article

In this paper, a design of vanadium dioxide for dynamic color gamut modulation based on Fano resonance is proposed. This approach facilitates color modulation by manipulating the phase transition state of vanadium dioxide. The device integrates both broadband and narrowband filters, featuring a structure consisting of a top silver mesh, a layer of vanadium dioxide, and a Fabry–Pérot cavity, which allows for effective modulation of the reflectance spectrum. Simulation results demonstrate that when vanadium dioxide is in its insulating state, the maximum reflectivity observed in the device spectrum, reaching 43.1%, appears at 475 nm. Conversely, when vanadium dioxide transitions to its metallic state, the peak wavelength shifts to 688 nm, accompanied by an increased reflectance peak of 59.3%. Analysis of electric field distributions reveals that the intensity caused by surface plasmonic resonance dominates over the excited Fano resonance while vanadium dioxide is in its insulating state, which is the opposite of when vanadium dioxide transitions to its metallic state. This behavior exhibits an excellent dynamic color-tuning capability. Specifically, the phase transition of vanadium dioxide results in a color difference ∆E₂₀₀₀ of up to 36.7, while maintaining good color saturation. This technique holds significant potential for applications such as dynamic color display and anti-counterfeit labeling. Full article

Hexamethyldisiloxane (HMDSO) is an organosilicon compound with a modifiable bandgap, depending on the deposition conditions. This material has many unique properties due to its stability, low toxicity, and strong adhesion, making it useful as a protective barrier against corrosion, moisture, and oxidation. In this work, HMDSO films were deposited on glass substrates by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique at different deposition times. The optical properties of HMDSO films, such as dielectric permittivity, refractive index, extinction and absorption coefficients, and band gap energy, are inferred from transmission and reflection spectra. As the deposition time increased, the real part of the dielectric constant, the refractive index, and the bandgap energy showed a decrease, dropping from 4.24 to 3.40, from 2.06 to 1.84, and from 2.85 eV to 2.03 eV, respectively. The latter result is determined using classical models such as the O’Leary-Johnson-Lim (‘OJL’) interband transition and the harmonic oscillator model. HMDSO and Silver are used in this study for the fabrication of optical filters using two types of structures, a multiple cavity metal–dielectric (MCMD) and the Fabry–Perot structure. The silver layers are deposited by a sputtering process. The MCMD optical filter shows a higher transmittance of about 30%, but a wide range of wavelengths is transmitted. In contrast, the Fabry–Perot filter showed high contrast but a lower transmittance of about 20%. Full article

Implementation of edge-filter detection for interrogating optical interferometric ultrasonic sensors is often hindered by the lack of cost-effective laser sources with agile wavelength tunability and good noise performance. The detected signal can also be affected by optical power variations and locking-point drift, negatively affecting the sensor accuracy. Here, we report the use of laser single-sideband generation with a dual-parallel Mach–Zehnder interferometer (DP-MZI) for laser wavelength tuning and locking in edge-filter detection of fiber-optic ultrasonic sensors. We also demonstrate real-time in situ calibration of the sensor response to ultrasound-induced wavelength shift tuning. The DP-MZI is employed to generate a known wavelength modulation of the laser, whose response is used to gauge the sensor response to the ultrasound-induced wavelength shifts in real time and in situ. Experiments were performed on a fiber-optic ultrasonic sensor based on a high-finesse Fabry–Perot interferometer formed by two fiber Bragg gratings. The results demonstrated the effectiveness of the laser locking against laser wavelength drift and temperature variations and the effectiveness of the calibration method against optical power variations and locking-point drift. These techniques can enhance the operational robustness and increase the measurement accuracy of optical ultrasonic sensors. Full article

To meet the demands of laser communication, quantum precision measurement, cold atom technology, and other fields for narrow linewidth and low-noise light sources, an external cavity diode laser (ECDL) operating in the wavelength range around 780 nm was set up with a Fabry–Pérot etalon (F–P) and an interference filter (IF) in the experiment. The interference filter type ECDL (IF–ECDL) with butterfly-style packaging configuration has continuous wavelength tuning within a specified range through precise temperature and current control and has excellent single-mode characteristics. Experimental results indicate that the output power of the IF–ECDL is 14 mW, with a side-mode suppression ratio (SMSR) of 54 dB, a temperature-controlled mode-hop-free tuning range of 527 GHz (1.068 nm), and an output linewidth of 570 Hz. Compared to traditional lasers operating at 780 nm, the IF–ECDL exhibits narrower linewidth, lower noise, and higher spectral purity, and its dimensions are merely 25 × 15 × 8.5 mm³ weighing only 19.8 g, showcasing remarkable miniaturization and lightweight advantages over similar products in current research fields. Full article

Tunable filters have many potential applications in diverse fields, including high-capacity communications, dynamic beam shaping and spectral imaging. Although providing a high-performance solution for actively tunable devices, metasurface combined with tunable materials faces the great challenges of limited tuning range and modulation depth. Here, we propose a far-infrared tunable band-stop filter based on Fabry-Perot (FP) resonators and graphene surface plasmons. By switching the wavelength of the critical coupling condition of the filter via the gate voltage applied on graphene, achieving the dynamically tunable band-stop filtering at the central wavelengths from 12.4 μm to 14.1 μm with a modulation depth of more than 99%. Due to the symmetry of the proposed meta-atoms, the filter is insensitive to the polarization direction of the incident light. And it can realize more than 85% filtering efficiency within 60° angle of incidence around the vertical direction. By adjusting the geometry of the meta-atoms structure, it is feasible to move the operational range from the near-infrared to terahertz bands. Full article

The transmission spectrum of a twin-waveguide cavity is systematically analyzed based on coupled mode theory, using the transfer matrix method (TMM). The results show that the traveling-wave transmission spectra of the twin-waveguide cavity is entirely determined by the coherent coupling effect involving the parameters of the effective refractive indices of the upper and lower waveguides, the coupling length Lc, and the ratio of the cavity length L to the coupling length (L/Lc). Filters with single, double, or triple-notch filtering could be obtained by choosing an appropriate L/Lc value. When the facet reflection is taken into consideration, the traveling-wave transmission spectrum is modified by the Fabry––Perot (FP) resonance, making it a standing-wave transmission spectrum. As a result, resonance splitting has been observed in the transmission spectrum of twin-waveguide resonators with high facet reflectivity. Further analysis shows that such an abnormal resonance phenomenon can be attributed to the destructive interference between the two FP resonance modes of the upper and lower waveguide through coherent coupling. In addition, narrow bandwidth amplification has also been observed through asymmetric facet reflections. Undoubtedly, all these unique spectral characteristics should be beneficial to the twin-waveguide cavity, achieving many more functions and being widely used in photonic integration circuits (PICs). Full article

We experimentally demonstrate a scheme for generating massively parallel and real-time physical random bits (PRBs) by using weak-resonant-cavity Fabry-Perot laser diodes (WRC-FPLDs) with optical feedback. By using external optical feedback to modify the nonlinear dynamic behavior of the longitudinal modes in WRC-FPLDs, the chaotic behavior of each channel can be induced under suitable feedback strength. By filtering these longitudinal modes, a real-time PRBs at 10 Gbits/s can be generated by using field programmable gate array (FPGA) board for the real-time post-processing of a single-channel chaotic signal. Considering the presence of up to 70 longitudinal modes within a broad spectral range exceeding 40 nm, each of these modes can be used to extract chaotic time sequences for random number generation. Therefore, our PRB generation scheme has the potential to achieve a data throughput of over 700 Gbits/s. Full article

This work demonstrates the use of an erbium-doped fiber amplifier (EDFA), a tunable bandpass filter (TBF), and a tunable delay line interferometer (TDLI) to form a ring laser that produces multi-format, multi-wavelength laser beams. The TDLI serves as the core of the proposed laser generation system. TDLI harnesses the weak Fabry–Pérot (FP) interferences generated by its built-in 50/50 beamsplitter (BS) with unalterable filtering characteristics and the interferences with free spectral range (FSR) adjustable from each of its two outputs with nearly complementary phases to superpose and generate a variable interference standing wave. The interferometric standing wave and weak FP interferences are used to form a spatial-hole burning to promote the excitation of multi-format and multi-wavelength lasers. The proposed system enables dual-wavelength spacing ranging from 0.3 nm to 3.35 nm, with a switchable wavelength position at approximately 1527 nm to 1535 nm, providing flexible tunability. Full article

In this paper, we construct a near-infrared Fabry–Perot cavity composed of two sodium (Na) layers and an antimony trisulfide (Sb₂S₃) layer. By cascading two Fabry–Perot cavities, the transmittance peak splits into two transmittance peaks due to the coupling between two Fabry–Perot modes. We utilize a coupled oscillator model to describe the mode coupling and obtain a Rabi splitting of 60.0 meV. By cascading four Fabry–Perot cavities, the transmittance peak splits into four transmittance peaks, leading to a near-infrared transparent band. The near-infrared transparent band can be flexibly tuned by the crystalline fraction of the Sb₂S₃ layers. In addition, the effects of the layer thickness and incident angle on the near-infrared transparent band and the mode coupling are investigated. As the thickness of the Na layer increases, the coupling strength between the Fabry–Perot modes becomes weaker, leading to a narrower transparent band. As the thickness of the Sb₂S₃ layer increases, the round-trip propagating of the Sb₂S₃ layer increases, leading to the redshift of the transparent band. As the incident angle increases, the round-trip propagating of the Sb₂S₃ layer decreases, leading to the blueshift of the transparent band. This work not only provides a viable route to achieving tunable near-infrared transparent bands, but also possesses potential applications in high-performance display, filtering, and sensing. Full article

To solve the short working distance and small measurement range of an all-fibre interferometer, we proposed a Mach–Zehnder Fabry–Perot hybrid fibre-optic interferometry system based on sinusoidal phase modulation. In this paper, a low-finesse fibre interferometer with a larger linear operating range for displacement measurement is realised using a self-collimating probe and incorporating a Kalman filter-based phase demodulation algorithm. Through experimental comparisons, it is demonstrated that the interferometer proposed in this paper can effectively reduce the phase delay, compensate for the depth of modulation drift, and correct the error due to parasitic interference introduced by the optical path structure through the algorithm. A linear large measurement working range of 20 cm is realised. Full article