Fabry-Perot Research Articles

Pressure and liquid depth sensing using a Fabry–Perot probe based on a silica capillary fiber and an agar membrane

The continuous evolution of fiber optics technology drives the photonics community to explore novel sensing configurations, aiming at developing optical sensors with enhanced capabilities. Among these efforts, Fabry–Perot interferometers (FPIs) emerge as a promising strategy for building fiber sensors due to their simplicity, miniature size, resolution tunability, and capability of acting as platforms for humidity, temperature, and pressure sensors. In addition to traditional materials for constructing FPIs, agar appears as a promising photonic material, offering biocompatibility, flexibility, and ease of preparation. In this manuscript, we present the development of a FPI sensing probe based on a silica capillary and an agar membrane for pressure and liquid depth sensing. Our report encompasses the description of the probe preparation procedure, the FPI spectral characterization, and the sensing measurements. Our efforts allowed us to demonstrate sensors with sensitivities of (− 4.9 ± 0.1) nm/bar and (− 5.9 ± 0.2) pm/mm. We consider that our work expands the application scenario of agar within photonics and offers a new avenue for realizing biocompatible pressure and liquid depth sensors.

Single photonic reservoir dual-task simultaneous computing based on a semiconductor ring laser with filtered optical feedback

A single photonic reservoir based on a semiconductor ring laser with filtered optical feedback (FOF) is proposed to achieve simultaneous reservoir computing (RC) through multiplexing of the two directional modes and enhance the robustness of RC operations by using a Fabry-Perot filter. Numerical investigations of laser dynamics reveal that the FOF successfully provides RC-preferred dynamically stable, steady state for both directional modes simultaneously. Moreover, the FOF can expand the parameter ranges of the RC-preferred state when the filter bandwidth is smaller than twice the transient response frequency of the laser. Furthermore, such expansion can be enhanced by optimizing the detuning frequency between the filter and the free-running laser. In addition to the advantages in laser dynamics, the positive effects of FOF on RC operations are further verified by benchmark tasks of complex time series prediction and pattern classification. The results show that the robustness of RC operations against parameter fluctuations is significantly enhanced not only in single-task computing independent of task types but also in dual-task simultaneous computing without significant degradation of performances independent of task combinations.

Monolithically integrated passive photonic silicon chip for nano-g level acceleration tri-axial detection

This paper proposes a nano-g level monolithically integrated tri-axial passive photonic accelerometer chip using uniform silicon-based micromachining with a low-frequency band. The silicon sensing units are designed with compact gradient-type and asymmetric S-type spring beams, allowing superior sensitivity in low-frequency band and tri-axial consistency. The spring-mass structures behave with uniform 460 μm thickness, significantly simplifying the silicon micromachining and improving process yield. A fiber-based Fabry-Perot interferometer (FPI) is utilized to retrieve the acceleration signal by demodulating optical phase change. In the operating bandwidth of 1 to 80 Hz, the sensitivity of the X-axial and Y-axial sensing units surpasses 43.6 dB with linear responses, while the Z-axial unit exhibits a sensitivity of over 42.8 dB. The average minimum detectable accelerations (MDAs) of the tri-axis directions are measured to be 21.80 ng/Hz1/2, 24.77 ng/Hz1/2, and 32.47 ng/Hz1/2, with the transverse crosstalk below 1.32%, 1.43%, and 2.07%, respectively. These results show that the proposed tri-axial photonic accelerometer is a perspective for detecting low-frequency acceleration vector signals.

Fiber Fabry–Perot Sensor Based on Ion-Imprinted Sodium Alginate/Graphene Oxide Hydrogel for Copper Ion Detection Using Vernier Effect

This work proposes an optical fiber copper ion sensor, which is fabricated by an ion-imprinted sodium alginate/graphene oxide (SA/GO) hydrogel and single-mode fiber (SMF). This sensing Fabry–Perot Interferometer (FPI) achieves −1.98 nm/(mg/L) sensitivity with 0.998 linearity. To achieve higher sensitivity, we add a reference FPI to create a Vernier effect. We achieve 19.58 nm/mg/L sensitivity and 0.989 linearity at a concentration range of 0 mg/L–1.4 mg/L. It was 9.9 times higher than that of a single-sensing FPI. The experimental results also demonstrate that when the FSR values of two FPIs are closer, the higher response sensitivity is achieved. The sensor also has good measurement repeatability and dynamic response. In addition, the experimental results of response selectivity show that its response sensitivity to copper ions is significantly higher than other six types of ions, including iron ions, lead ions, magnesium ions, manganese ion, zinc ions, chromium ions. The copper ion is also mixed with six types of ions to deeply investigate the response selectivity. Good response selectivity and cross-responding are demonstrated by experimental results.

A Spatiotemporal Tunable Filter Array Chip for Video-Rate Hyperspectral Imaging.

Existing miniaturized spectral imagers have mutual restrictions among spatial, temporal, and spectral resolutions, making them inadequate to meet practical needs. Here, we demonstrate a spatiotemporal filter array chip to tackle the trade-off among the three resolutions for miniaturized hyperspectral imaging. A 2 × 2 Fabry-Perot filter array is embedded inside a tunable liquid crystal spectral modulator, increasing the number of filtering channels spatiotemporally in hardware, which empowers the spectral imager with high spatial, temporal, and spectral resolutions simultaneously. The tunable filter is of transmission type with the advantages of easy fabrication and large modulation. Experimental results show the proposed spectral imager has a spectral resolution of around 0.5 nm in the visible range, with a frame rate of 60 Hz and a spatial resolution of up to 25 lp/mm without postinterpolation. The proposed filter gives the best balanced performance for spectral imaging in terms of spatial, temporal, and spectral resolutions.

Bandwidth Enhancement of Epsilon‐Near‐Zero Supercoupling with Inverse‐Designed Metamaterials

AbstractEpsilon‐near‐zero (ENZ) materials exhibit unique electromagnetic properties that enable efficient wave transmission through channels of arbitrary geometry, which is known as ENZ supercoupling or tunneling. However, the supercoupling effect is typically confined to an inherent narrow bandwidth, which significantly restrict its practical applications. In this paper, a feasible method is proposed that enhanced the bandwidth of ENZ supercoupling. By optimizing the structure of an inverse‐designed pixel metamaterial inserted into the ENZ channel, multiple Fabry‐Perot (FP) modes are properly regulated and coupled, facilitating multimode superposition to enhance the bandwidth for high‐efficiency signal transmission in ENZ channels with arbitrary geometry. Furthermore, a prototype is constructed at microwave frequency to validate the performance of the proposed method, which opens new avenues for the development of broadband and geometry‐independent electromagnetic devices with the benefit of ENZ materials.

Secure space division multiplexing system based on multi-channel chaos random encryption with synchronized Fabry-Perot lasers

Secure space division multiplexing system based on multi-channel chaos random encryption with synchronized Fabry-Perot lasers

Self-injection-locked near-visible laser at 781 nm by frequency-doubling in a quasi-singly resonant high-Q micro-cavity.

Based on a quasi-singly resonant plane-concave Fabry-Perot (FP) micro-cavity with a high Q-factor of 9.1 M and a volume of <0.12 mL, we have demonstrated self-injection-locked (SIL) second-harmonic generation (SHG) at near-visible frequencies. With an incident SIL pump power of 80 mW at 1561.8 nm, the maximum output SHG power at 780.9 nm reached 16.9 mW, achieving a high conversion efficiency of 21.1%. The intrinsic linewidth of the SIL pump laser was reduced from 1.1 MHz to about 130 Hz, and the corresponding linewidth of the SIL-SHG light was about 520 Hz as expected. Most importantly, high SHG efficiency was observed at any pump frequency of the corresponding FP resonant modes. Compared to the recently reported results of SIL-SHG using microring cavities, our SIL-SHG design with a quasi-singly resonant FP cavity offers higher conversion efficiency and output SIL-SHG power, along with a potential of continuous tunability of the SHG frequency. Thanks to its significantly larger mode-field volume, it can handle higher input power without incurring unwanted nonlinear effects.

Fiber-Optic Photoacoustic Gas Microprobe Based on Linear Spot-Type Multipass Cell.

A linear spot-type multipass cell-enhanced fiber-optic photoacoustic gas microprobe is proposed. To further reduce the volume of the gas chamber and enhance the photoacoustic signal, we designed the cross section of the photoacoustic tube as a slit with a height of 10 mm and a width of 1.5 mm. The volume of the gas chamber is only 210 μL. Through theoretical analysis and multiphysical field simulation, the photoacoustic intensity of the slit cross section is more than 6 times that of traditional circular cross section. A cantilever beam is integrated into the photoacoustic microprobe and forms a Fabry-Perot (FP) interferometer with an optical fiber, achieving enhanced photoacoustic detection. By adjusting the angle of the collimator, the light passes through the photoacoustic cell 26 times, and 13 linear spots are formed on the reflecting surface. The photoacoustic signal with multiple linear reflections is 12.4 times that of a single reflection. The gas enters the sensor in a freely diffused manner, and the response time of the sensing system is 54 s. When the averaging time is 400 s, the detection limit of the designed sensor for acetylene gas reaches 1.5 ppb. The minimum detectable absorption coefficient (αmin) and the normalized noise equivalent absorption coefficient (NNEA) are 1.7 × 10-8 cm-1 and 1.9 × 10-9 Wcm-1/Hz1/2, respectively.

Parameter Study on Ultraviolet Rayleigh–Brillouin Doppler Lidar with Dual-Pass Dual Fabry–Perot Interferometer for Accurately Measuring Near-Surface to Lower Stratospheric Wind Field

To suppress the influence of aerosols scattering on the double-edge detection technique and achieve high-accuracy measurement of the wind field throughout the troposphere to the lower stratosphere, an ultraviolet 355 nm Rayleigh–Brillouin Doppler lidar technology based on a dual-pass dual Fabry–Perot interferometer (FPI) is proposed. The wind speed detection principle of this technology is analyzed, and the formulas for radial wind speed measurement error caused by random noise and wind speed measurement bias caused by Mie scattering signal contamination are derived. Based on the detection principle, the structure of the lidar system is designed. Combining the wind speed measurement error and measurement bias on both sides, the parameters of the dual-pass dual-FPI are optimized. The free spectral range (FSR) of the dual-pass dual-FPI is selected as 12 GHz, the bandwidth as 1.8 GHz, and the peak-to-peak spacing as 6 GHz. Further, the detection performance of this new type of Rayleigh–Brillouin Doppler lidar with the designed system parameters is simulated and analyzed. The simulation results show that at an altitude of 0–20 km, within the radial wind speed dynamic range of ±50 m/s, the radial wind speed measurement bias caused by aerosol scattering signal is less than 0.17 m/s in the cloudless region; within the radial wind speed dynamic range of ±30 m/s, the bias is less than 0.44 m/s and 0.91 m/s in the simulated cumulus cloud at 4 km where aerosol backscatter ratio Rβ = 3.8 and cirrus cloud at 9 km where Rβ = 2.9, respectively; using a laser with a pulse energy of 350 mJ and a repetition frequency of 50 Hz, a 450 mm aperture telescope, setting the detection zenith angle of 30°, vertical resolution of 26 m@0–10 km, 78 m@10–20 km, and 260 m@20–30 km, and a time resolution of 1 min, with the daytime sky background brightness taking 0.3 WSr−1m−2nm−1@355 nm, the radial wind speed measurement errors of the system during the day and night are below 2.9 m/s and 1.6 m/s, respectively, up to 30 km altitude, below 0.28 m/s at 10 km altitude, and below 0.91 m/s at 20 km altitude all day.

Unveiling the relationship between Fabry-Perot laser structures and optical field distribution via symbolic regression

Unveiling the relationship between Fabry-Perot laser structures and optical field distribution via symbolic regression

Multimode dynamics of a monolithically integrated, tunable, bidirectional, gain switched optical comb source.

A three-sectioned, bidirectionally coupled, tunable, optical comb source is presented. The photonic integrated circuit (PIC) consists of a gain section, a slotted mirror section and a Fabry-Perot (FP) section. Optical frequency combs (OFCs) are produced by gain switching the FP section via a high power radio frequency (RF) signal. An investigation into the effect of the RF frequency on the quality of the OFC is performed. Multimode behavior is observed with OFCs produced in multiple modes as well as the overall degradation in the quality of the combs in each mode. A minimal extension multimode rate equation model is presented that reproduces the experimental results extremely well using experimentally determined values for numerical parameters. The appearance of multimode behavior is interpreted as relating to the modified relaxation oscillation frequency of the bidirectionally coupled system.

Attraction of microbubble at a fiber end face by the solute Marangoni force and its application as a tunable interferometer based on optical control.

In this Letter, we show the attraction of a microbubble at a fiber end face by the solute Marangoni force. The microbubble is formed by partial filling of an ethanol-water mixture in the microcavity that is spliced to the end face of a single-mode fiber. Due to different surface tension of ethanol and water, the uneven temperature gradient induced by a laser causes the non-uniform distribution of ethanol-water molecules on the bubble surface. As a result, the solute Marangoni force that is much larger than the buoyancy is generated and it presses the microbubble against the fiber end face. The microbubble forms a high-quality Fabry-Perot (FP) interferometer, and the interferometric phase can be adjusted by changing the solute Marangoni force that is influenced by the laser power. This Letter gives a new method to achieve a tunable interferometer based on optical control.

Silicon photonic modulators with a 2 × 1 Fabry–Perot cavity

Abstract Silicon photonics modulators based on a 2 × 1 Fabry–Perot (FP) cavity, which is circulator-free, are proposed and demonstrated by introducing two asymmetric multimode-waveguide grating (AMWG) reflectors and a short straight modulation section with interleaved PN junctions. In particular, the straight modulation section in the FP cavity is broadened to be far beyond the single-mode regime, alleviating the inherent sensitivity to the variations of waveguide dimensions and thus reducing stochastic resonance-wavelength variations. The Q factor of the FP cavity is manipulated by optimally manipulating the reflection of the AMWGs, and the modulation bandwidth is enhanced to be over 40 GHz by utilizing the optical peaking enhancement effect, which happens when operating at the wavelength slightly detuning to its resonance wavelength. Eye diagrams for high-speed modulation with 50 Gbps are also demonstrated in experiments. Finally, wafer-level measurement is conducted by characterizing the silicon photonic modulators based on the 2 × 1 FP cavity and a conventional microring fabricated on the same chip, experimentally revealing an average improvement of 43 % in minimizing the random resonance-wavelength variation, which is attributed to the implementation of broadening the straight modulation section in the FP cavity.

Enhanced broadband quantum efficiency in LWIR T2SL detectors with guided-mode resonance structure.

Type-II superlattice (T2SL) detectors are emerging as key technologies for next-generation long-wavelength infrared (LWIR) applications, particularly in the 8-14 µm range, offering advantages in space exploration, medical imaging, and defense. A major challenge in improving quantum efficiency (QE) lies in achieving sufficient light absorption without increasing the active layer (AL) thickness, which can elevate dark current and complicate manufacturing. Traditional methods, such as thickening the absorber, are limited by the short carrier lifetime in T2SLs, necessitating alternative solutions. In this study, we introduced a guided-mode resonance (GMR) structure into T2SL LWIR detectors to enhance QE while maintaining a thin AL for efficient carrier collection. The GMR structure was fabricated by introducing a grating array on the surface of the detector and an Au mirror beneath the absorber. This configuration enhanced light trapping, which introduced additional resonance modes. The optimized grating design, with a 5 µm period and a fill factor of 0.6, significantly increased absorption, as predicted by finite-difference time-domain (FDTD) simulations and confirmed experimentally. The GMR-enhanced T2SL detector demonstrated a 2.58-fold improvement in QE over conventional LWIR detectors and a 1.33-fold increase compared to Fabry-Pérot (FP) resonance-based detectors in the 6-11 µm range. Despite exhibiting an almost identical dark current density, the GMR LWIR detector demonstrated superior performance, featuring a broader cut-off wavelength of 9.3 µm and higher QE compared to FP LWIR detectors.

3D printing fiber-tip integrated Fabry-Perot interferometers for ultrasensitive RI sensing with an enhanced Vernier effect.

An ultrasensitive refractive index (RI) sensing technology based on an enhanced Vernier effect is proposed, which integrates a polymer Fabry-Perot interferometer (FPI) with an open cavity FPI on the tip of a seven-core optical fiber. Interference spectra of the polymer FPI and the open cavity FPI shift to opposite directions as the ambient RI changes, thus leading to the enhanced Vernier effect. Investigations of RI sensitivity and temperature dependence of the proposed fiber sensors are carried out. Taking advantage of the enhanced Vernier effect, we demonstrate a remarkable sensitivity of 19742.86 nm/RIU within the RI range from 1.39 to 1.395. The sensor exhibits substantial advantages such as ease of fabrication, compact structure, high sensitivity, and good repeatability, providing a practical and competitive solution for RI sensing.

Realization and simulation of silicon-on-sapphire mid-infrared one-dimensional photonic crystal cavities

The mid-infrared (MIR) waveband is significant for chemical and biological sensing since it covers several atmospheric windows and molecular fingerprint regions. On-chip photonic integrated one-dimensional (1D) microcavities have great potential for high-performance mid-IR sensing because of their high sensitivity and compact structure. However, high-performance 1D microcavities based on the promising silicon-on-sapphire (SoS) MIR platform have not yet been designed or realized. Based on the photonic band structure induced by 1D photonic crystals (PhC), a high-performance Bragg reflector, an inward apodized Bragg grating, and a free spectral range (FSR)-free PhC microcavity integrated system operating in the MIR waveband were developed on the SoS platform. By carefully designing the period and penetration depth of the corrugation in the Bragg reflector, a stopband of 45 nm and an extinction ratio of −12 dB were achieved. The inward apodized Bragg grating was optimized by adjusting the apodization depth and the number of periods, resulting in a quality factor of 1043 at a wavelength of 3088.4 nm. Furthermore, introducing a Fabry–Pérot (F-P) cavity between two Bragg reflectors (with side-coupled light) and precisely tuning the stopband of the Bragg reflector and the FSR of the F-P cavity enabled the realization of an FSR-free PhC microcavity. This microcavity exhibited a single deep resonance dip with subnanometer bandwidth across a record-wide operational waveband from 3025 to 3200 nm, achieving a quality factor of approximately 5090. The MIR 1D PhC microcavities on the SoS platform hold great promise for high-performance gas detection and molecular sensing in future applications.

Color variations of silicon-on-insulator wafers with silicon device layer thickness.

The perceived colors of silicon-on-insulator (SOI) wafers with etched Si surface layers of thickness 90 nm to 30 nm vary from turquoise to purple to golden. Measured reflectance curves spanning ultraviolet, visible, and near infrared wavelengths have an amplitude modulated oscillatory pattern. Multilayer reflectance calculations indicate the oscillatory pattern results from the 2 µm thick buried SiO2 layer which functions as a nearly lossless reflective Fabry-Perot etalon in the near infrared where SiO2 and Si are transparent. The amplitude modulation of the oscillatory pattern in the visible region where Si is absorbing results from thin-film effects in the Si surface layer. The changing modulation with Si thickness and wavelength results in the observed color variations. It is therefore possible to estimate the Si thickness based on the etched SOI wafer color observed visually. This ability is useful when initially optimizing the etching process to produce a specific thin Si layer, for example when fabricating photodiodes or other photonic devices on SOI wafers. Accurate measurements of the Si thickness and the buried SiO2 thickness can be performed by analyzing the modulated oscillatory reflectance curve using multilayer reflectance calculations.

Partial Discharge Detection from Large Motor Stator Slots Using EFPI Sensors.

This study addresses the challenges of electromagnetic interference and unstable signal transmission encountered by traditional sensors in detecting partial discharge (PD) within stator slots of large motors. A novel Extrinsic Fabry-Perot Interferometer (EFPI) sensor with a vibration-coupling air gap was designed to enhance the narrowband resonant detection sensitivity for PD ultrasonic signals by optimizing the diaphragm structure and coupling interface. The sensor features a quartz diaphragm with a thickness of 20 μM, an effective constrained radius of 0.9 mm, a vibration-coupling air gap depth of 100 μM, and a first-order natural resonant frequency of 66 kHz. Simulation and experimental analyses revealed the distribution characteristics and propagation paths of ultrasonic signals within stator slots. The results demonstrate that the EFPI sensor effectively detects PD ultrasonic signals at its resonant frequency of 66 kHz with a localization error of less than 5 mm, meeting engineering requirements. This study provides theoretical and practical insights into the efficient detection and precise localization of insulation faults in large motor stators.

Ultra-short stripe microlasers fabricated with a focused ion beam etching technique.

Fabry-Perot (FP) lasers with a cavity length shorten down to 50 µm were investigated. One or two laser mirrors were formed by focused ion beam etching. InGaAs quantum dots of high density were used as the laser active region. The lasers operate in a pulsed regime up to at least 105°С. A comparison with lasers formed by the facet cleaving method (minimum length is 100 µm) reveals the similarity of the emission wavelength and the threshold current depending on the cavity length. This allows us to conclude that the etched facets do not significantly affect the non-radiative recombination rate and provide a reflection coefficient close to that of the cleaved facet. The maximum modal gain was estimated to be not less than 240 cm-1. No evidence of the excited-state lasing was found.