Fabry-Perot Cavity Research Articles

High reflectance tunable multi-color electrochromic films based on Fabry–Perot cavity

High reflectance tunable multi-color electrochromic films based on Fabry–Perot cavity

Surface Modified Optical Fiber Fabry–Perot Cavity Pressure Sensor With Carbon Film

By the method of pulsed laser deposition of a Ni/C bilayer precursor films and annealing in air, amorphous carbon films were prepared on the surface of the capillary used for fabrication of optical fiber Fabry-Perot (FP) cavity pressure sensors. The surface morphologies of the coated and annealed carbon films were investigated through scanning electron microscopy. The images reveal that surface modification smoothes the irregular particles on the capillary surface and releases the stress induced by carbon and nickel deposition and oxy-hydrogen flame welding. Performance tests showed that the surface modified pressure sensors have good linearity for pressure response and the cavity length variations during the full cycle of pressure change is within 31 nm. Furthermore, thanks to the introduction of carbon films, the long-term stability of the cavity length can be kept within 10 nm during the tested 150 days.

Advanced Design of High-Gain Fabry–Perot Cavity Antenna Offering Wide Common Impedance and Gain Bandwidth

An advanced design of a Fabry-Perot cavity antenna (FPCA) is proposed to achieve wide common impedance and gain bandwidth along with high gain. A compact and lightweight FPCA is achieved by employing a printed primary radiator and superstrate with superior manufacturing capabilities. A wideband primary radiator is employed for the first time to realize such a wideband FPCA. Superstrate dimensions are estimated by using the aperture field theory and the proposed design is validated through both EM simulation and experiment. The measured broadside gain is shown to be better than 11.5 dBi over an impedance bandwidth of 63% (8.2−15.6 GHz). About 40% common impedance and gain bandwidth is achieved while the broadside gain attains a maximum value of 17.4 dBi. To the best of our knowledge, this has never been achieved before from an FPCA made of a printed superstrate and a primary radiator. The cross-polar (XP) radiation remains under −40dB whereas the front-to-back ratio (FBR) remains above 35dB, over the desired bandwidth.

Extremely High-Quality Periodic Structures on ITO Film Efficiently Fabricated by Femtosecond Pulse Train Output from a Frequency-Doubled Fabry-Perot Cavity.

This study developed a novel frequency-doubled Fabry-Perot cavity method based on a femtosecond laser of 1030 nm, 190 fs, 1 mJ, and 1 kHz. The time interval (60-1000 ps) and attenuation ratio (0.5-0.9) between adjacent sub-pulses of the 515 nm pulse train were able to be easily adjusted, while the efficiency was up to 50% and remained unchanged. Extremely high-quality low-spatial-frequency LIPSS (LSFL) was efficiently fabricated on an indium tin oxide (ITO) film using a pulse train with a time interval of 150 ps and attenuation ratio of 0.9 focused with a cylindrical lens. Compared with the LSFL induced by the primary Gaussian pulse, the uniformity of the LSFL period was enhanced from 481 ± 41 nm to 435 ± 8 nm, the divergence of structural orientation angle was reduced from 15.6° to 3.7°, and the depth was enhanced from 74.21 ± 14.35 nm to 150.6 ± 8.63 nm. The average line edge roughness and line height roughness were only 7.34 nm and 2.06 nm, respectively. The depths and roughness values were close to or exceeded those of resist lines made by the interference lithography. Compared with the common Fabry-Perot cavity, the laser energy efficiency of the pulse trains and manufacturing efficiency were enhanced by factors of 19 and 25. A very colorful "lotus" pattern with a size of 30×28 mm2 was demonstrated, which was covered with high-quality LSFLs fabricated by a pulse train with optimized laser parameters. Pulse trains can efficiently enhance and prolong the excitation of surface plasmon polaritons, inhibit deposition particles, depress ablation residual heat and thermal shock waves, and eliminate high-spatial-frequency LIPSS formed on LSFL, therefore, producing extremely high-quality LSFL on ITO films.

Growth of InGaAs/InAlAs superlattices for strain balanced quantum cascade lasers by molecular beam epitaxy

This study investigated the molecular beam epitaxy (MBE) growth conditions of strain-balanced (SB) In0.669GaAs/In0.362AlAs superlattices (SLs) for SB quantum cascade lasers (QCLs). The growth modes and properties of SB SLs are strongly affected by the growth conditions. The properties of the SB SLs were evaluated using atomic force microscopy (AFM) and high-resolution X-ray diffraction (HRXRD) analysis. Following the establishment of optimized conditions for SB SLs growth, SB QCL were grown. The HRXRD analysis and transmission electron microscopy (TEM) measurements showed that the grown samples exhibited abrupt interfaces and good structural quality. An epitaxial wafer was processed into a Fabry-Perot cavity with a ridge structure. The device operated in pulsed mode emitting ∼4.7 µm at room temperature with a peak power of 650 mW and a slope efficiency of 870 mW/A.

Regulation of Recombinase Polymerase Amplification by Vibrational Strong Coupling of Water

Vibrational strong coupling (VSC) between molecular transitions and photonic structures can be used to tune the reactivity of molecules, and hybrid polariton states have been employed to modify the energy landscape of molecular systems in an optical cavity. To investigate how to modulate life reactions with VSC, herein we selected an in vitro model bioreaction, DNA replication, i.e., recombinase polymerase amplification (RPA), to couple with the typical Fabry–Pérot (FP) cavity mode. Known as an isothermal enzymatic reaction, RPA well satisfies the VSC study within FP cavities. Through tuning the resonance coupling strength between water molecules and FP cavity modes, we can regulate the efficiency of RPA as the cavity modes change from 3100 to 3550 cm–1. The results showed that O–H-based VSC can significantly inhibit the efficiency of RPA by ∼58%. Due to the key role of water in life, O–H stretching vibrational coupling with photonic structures could be a novel tool to regulate life in turn.

Multidimensional structural coloration from hierarchically designed plasmonic structures

We propose a photonic strategy for multidimensional structural coloration that responds to varying illumination conditions. Both theoretical and experimental results verified that the combination of a metal/dielectric/metal cavity with a one-dimensional (1D) metal grating can increase the degree of freedom of structural coloration. We fabricated Ag/MgF2/Ag cavities coupled to 1D Ag gratings (pitches of 400, 570, and 800 nm) and obtained their photonic band dispersions (i.e., angle-resolved reflectance spectra) to unravel their mode characteristics. The 1D Ag grating and Ag/MgF2/Ag cavity induced surface plasmon polariton (SPP) and Fabry–Perot cavity modes, respectively. Notably, only a cavity mode emerged in the s-polarization and gradually blueshifted with increasing angle, whereas in the p-polarization, both SPP and cavity modes appeared and shifted oppositely with changes in the angle, leading to intricate color patterns at different wavelengths, angles, and polarizations. To further understand the effect of each mode upon structural coloration, we obtained the distribution of electric field intensity using rigorous coupled-wave analysis simulation, which identified multiple photonic bands in the p-polarization as various SPP-mediated hybrid modes.

Lasing features of the ultra-short Fabry–Perot cavity on the basis of a photosensitive Er/Yb-doped multimaterial fiber with a silicophosphate core

The lasing properties of a short-cavity laser based on the Er/Yb composite fiber with a silicophosphate core in a silica cladding were investigated in detail. A Fabry–Perot cavity was manufactured on a 25 mm long fiber segment using the ultraviolet (UV) (λ=193nm) excimer laser radiation and phase-mask technique of Bragg grating inscription. The laser with an effective cavity length of 11 mm generated single-frequency radiation centered at 1554.45 nm. This laser demonstrated strictly continuous-wave operation under 974 nm pumping but self-Q-switched operation under 1485 nm pumping. Under 974 nm pumping, the slope efficiency was as high as 4%, and the output power reached 17 mW—a level comparable with the characteristics of commercial single-frequency laser diodes.

Grayscale-patterned integrated multilayer-metal-dielectric microcavities for on-chip multi/hyperspectral imaging in the extended visible bandwidth.

Pixelated filter arrays of Fabry-Perot (FP) cavities are widely integrated with photodetectors to achieve a WYSIWYG ("what you see is what you get") on-chip spectral measurements. However, FP-filter-based spectral sensors typically have a trade-off between their spectral resolution and working bandwidth due to design limitations of conventional metal or dielectric multilayer microcavities. Here, we propose a new idea of integrated color filter arrays (CFAs) consisting of multilayer metal-dielectric-mirror FP microcavities that, enable a hyperspectral resolution over an extended visible bandwidth (∼300 nm). By introducing another two dielectric layers on the metallic film, the broadband reflectance of the FP-cavity mirror was greatly enhanced, accompanied by as-flat-as-possible reflection-phase dispersion. This resulted in balanced spectral resolution (∼10 nm) and spectral bandwidth from 450 nm to 750 nm. In the experiment, we used a one-step rapid manufacturing process by using grayscale e-beam lithography. A 16-channel (4 × 4) CFA was fabricated and demonstrated on-chip spectral imaging with a CMOS sensor and an impressive identification capability. Our results provide an attractive method for developing high-performance spectral sensors and have potential commercial applications by extending the utility of low-cost manufacturing process.

Control, Modulation, and Analytical Descriptions of Vibrational Strong Coupling

Here, we review the design of optical cavities, transient and modulated responses, and theoretical models relevant to vibrational strong coupling (VSC). While planar Fabry-Perot cavities remain the most common choice for experiments involving vibrational polaritons, other choices including plasmonic and phononic nanostructures, extended lattice resonances, and wavelength-scale three-dimensionally confined dielectric cavities have unique advantages, which are discussed. Next, we review the nonlinear response to laser excitation of VSC systems revealed by transient pump-probe and 2DIR techniques. The assignment of various features observed in these experiments has been an important topic with significant recent progress and controversy. The modulation of VSC systems by various means such as ultrafast pulses and electrochemical methods is also described. Finally, theoretical approaches to understanding the physics and chemistry of VSC systems are reviewed with an eye toward their applicability and usefulness. These fall into two main categories: (1) solving for the eigenmodes of the system and (2) evolutionary techniques including the transfer-matrix method and its generalizations. The need for quantum optical methods of describing VSC systems is critically evaluated in light of current experimental work, and we discuss circumstances which necessitate consideration of the full in-plane dispersion of the Fabry-Perot cavities.

Highly Efficient Single-Exciton Strong Coupling with Plasmons by Lowering Critical Interaction Strength at an Exceptional Point.

The single-exciton strong coupling with the localized plasmon mode (LPM) at room temperature is highly desirable for exploiting quantum technology. However, its realization has been a very low probability event due to the harsh critical conditions, severely compromising its application. Here, we present a highly efficient approach for achieving such a strong coupling by reducing the critical interaction strength at the exceptional point based upon the damping inhibition and matching of the coupled system, instead of enhancing the coupling strength to overcome the system's large damping. Experimentally, we compress the LPM's damping linewidth from about 45nm to about 14nm using a leaky Fabry-Perot cavity, a good match to the excitonic linewidth of about 10nm. This method dramatically relaxes the harsh requirement in mode volume by more than an order of magnitude and allows a maximum direction angle of the exciton dipole relative to the mode field of up to around 71.9°, significantly improving the success rate of achieving the single-exciton strong coupling with LPMs from about 1% to about 80%.

Fabry-Perot Cavity Control for Tunable Raman Scattering.

The Fabry-Perot (FP) resonator is an intuitive and versatile optical structure owing to its uniqueness in light-matter interactions, yielding resonance with a wide range of wavelengths as it couples with photonic materials encapsulated in a dielectric cavity. Leveraging the FP resonator for molecular detection, a simple geometry of the metal-dielectric-metal structure is demonstrated to allow tuning of the enhancement factors (EFs) of surface-enhanced Raman scattering (SERS). The optimum near-field EF from randomly dispersed gold nano-gaps and dynamic modulation of the far-field SERS EF by varying the optical resonance of the FP etalon are systematically investigated by performing computational and experimental analyses. The proposed strategy of combining plasmonic nanostructures with FP etalons clearly reveals wavelength matching of FP resonance to excitation and scattering wavelengths plays a key role in determining the magnitude of the SERS EF. Finally, the optimum near-field generating optical structure with controlled dielectric cavity is suggested for a tunable SERS platform, and its dynamic SERS switching performance is confirmed by demonstrating information encryption through liquid immersion.

Design of a switchable bifunctional terahertz metamaterial absorber from ultra-broadband to 10-band

A bifunctional absorber with hybrid graphene–vanadium dioxide (VO2) is proposed and numerically investigated in the paper. Simulation results indicate that the absorber behaves as a broadband absorber with absorptance of more than 90% from 3.15 THz to 8.45 THz, when VO2 is in the metallic state. When VO2 is in the insulating state, the design exhibits a 10-band absorber, whose peak absorptances are above 90%. Broadband absorption is investigated by the impedance matching theory, and detailed physical studies indicate that it arises from electromagnetic resonance based on VO2 patches. Ten-band absorption originates from graphene plasmon (GP) resonance and Fabry–Perot cavity resonance. By adjusting the conductivity of VO2 and the Fermi level of graphene, the designed absorber not only can be independently tuned, but also has 91.9% modulation depth under broadband absorptance. Furthermore, the effect of incident angle on absorptance is investigated, and the absorber is polarization insensitive due to the symmetry of the structure. Benefiting from the above excellent performance, the bifunctional absorber offers great potential in terahertz applications, such as modulating, switching, and electromagnetic energy harvesting.

Optical switching in molybdenum trioxide (MoO3)-doped vanadium pentaoxide (V2O5) thin films using Fabry–Perot cavity

Optical switching in molybdenum trioxide (MoO3)-doped vanadium pentaoxide (V2O5) thin films using Fabry–Perot cavity

Advances in Fiber-Optic Extrinsic Fabry–Perot Interferometric Physical and Mechanical Sensors: A Review

Fabry–Perot interferometers (FPIs) have found a multitude of scientific and industrial applications ranging from gravitational wave detection, high-resolution spectroscopy, and optical filters to quantum optomechanics. Integrated with optical fiber waveguide technology, the fiber-optic FPIs have emerged as a unique candidate for high-sensitivity sensing and have undergone tremendous growth and advancement in the past two decades with their successful applications in an expansive range of fields. The extrinsic cavity-based devices, i.e., the fiber-optic extrinsic FPIs (EFPIs), enable great flexibility in the design of the sensitive Fabry–Perot cavity combined with state-of-the-art micromachining and conventional mechanical fabrication, leading to the development of a diverse array of EFPI sensors targeting at different physical quantities. Here, we summarize the recent progress of fiber-optic EFPI sensors, providing an overview of different physical and mechanical sensors based on the FPI principle, with a special focus on displacement-related quantities, such as strain, force, tilt, vibration and acceleration, pressure, and acoustic. The working principle and signal demodulation methods are shown in brief. Perspectives on further advancement of EFPI sensing technologies are also discussed.

Broadband actively tunable metamaterial absorber based on vanadium dioxide and Fabry-Perot cavity

The dynamic tunable broadband perfect absorber based on vanadium dioxide (VO2) is proposed in this paper. And the VO2 conductivity can be changed by temperature, thus changing the absorption characteristics of the absorber. Under normal incident conditions, absorption is more than 90% of the absorber in the range of 5.8–17.2 THz (THz), with an average absorption rate of more than 96%. And impedance matching theory and magnetic resonance theory are used to illustrate the mechanism of operation. The effect of the incidence angle on the absorption performance was studied, and the results show that the absorbers still maintain excellent absorption when the incidence angle is less than 45∘. In addition, the absorption characteristics of the absorber working in water are also studied. We demonstrate that the absorber's absorption is more than 90% in the range of 5–18 THz with an absorption bandwidth of 13 THz at a water depth of 5.2 μm. And by adjusting the VO2 conductivity, the average absorption rate can be adjusted from 2.5% to 96.1% with a water depth of 5.2 μm. The proposed structure has potential significant applications in the design of heat emitters, optical switches, cloaking devices, and energy harvesting devices.

Transparent microfiber Fabry-Perot ultrasound sensor with needle-shaped focus for multiscale photoacoustic imaging

Photoacoustic tomography emerged as a promising tool for noninvasive biomedical imaging and diseases diagnosis. However, most of the current piezoelectric ultrasound transducers suffer optical opacity and tissue-mismatched acoustic impedance, hindering the miniaturization and integration of the system for multiscale and multimodal imaging. Here, a transparent polydimethylsiloxane (PDMS) encapsulated optical microfiber ultrasound sensor was demonstrated for photoacoustic imaging with scalable spatial resolution and penetration depth. The sensor comprised a microfiber loop sandwiched by a pair of in-line Bragg gratings, which formed an ultrasound-sensitive Fabry-Perot cavity allowing free delivery of ultrasound/light beams and unique needle-shaped ultrasound focusing along the penetration depth. The sensor with a detection limit of ∼ 700 Pa and a bandwidth of ∼ 10 MHz was applied for multiscale photoacoustic imaging of mouse ear and brain vasculatures. With advantages of flexibility, optical transparence and focusing capability, the sensor offers new opportunities for developing photoacoustic/ultrasound imaging devices for biomedical and clinic applications.

Interlayer exciton polaritons in homobilayers of transition metal dichalcogenides

Transition metal dichalcogenides integrated within a high-quality microcavity support well-defined exciton polaritons. While the role of intralayer excitons in 2D polaritonics is well studied, interlayer excitons have been largely ignored due to their weak oscillator strength. Using a microscopic and material-realistic Wannier–Hopfield model, we demonstrate that MoS2 homobilayers in a Fabry–Perot cavity support polaritons that exhibit a large interlayer exciton contribution, while remaining visible in linear optical spectra. Interestingly, with suitable tuning of the cavity length, the hybridization between intra- and interlayer excitons can be ‘unmixed’ due to the interaction with photons. We predict formation of polaritons where % of the total excitonic contribution is stemming from the interlayer exciton. Furthermore, we explore the conditions on the tunneling strength and exciton energy landscape to push this to 100%. Despite the extremely weak oscillator strength of the underlying interlayer exciton, optical energy can be effectively fed into the polaritons once the critical coupling condition of balanced radiative and scattering decay channels is met. These findings have a wide relevance for fields ranging from nonlinear optoelectronic devices to Bose–Einstein condensation.

Modelling and design of ultra-high stable Fabry–Pérot cavity

Lasers having sub-Hz linewidth and long-term stability better than a few parts in 1016 is an unavoidable requisite to achieve unprecedented accuracy in the optical atomic clocks, intercomparing distributed atomic clocks and their networking, establishing coherent optical fibres, precision time & frequency transfer, production of optical qubits, and many more. For these wide ranges of applications, ultrastable Fabry–Pérot (FP) cavities, which act as the reference optical resonator, have got lots of attention. Designing such a FP cavity is a challenge due to the requirements of suppressing instabilities from all the thermo-mechanical noise sources at the highest degree. In this article, we report a comprehensive study to elucidate detailed design steps and associated numerical analysis procedures to build such a FP cavity. For this, we considered all sources of noises arising from: improper optical and opto-mechanical settings, ground vibrations transmitted to the cavity, deformations due to self-weight as it worsens the stability due to acoustic noise coupled to it, and temperature fluctuation. We present quantitative assessments of the instabilities for different shapes, geometries, and constituent materials of the cavities. In order to model the vibration-induced instability, we developed a novel forced-vibration based technique for accurate estimation of the instabilities, that reciprocates the experimental results reported in the literature, and the method is found to be superior compared to the other approaches, therefore estimating the overall cavity stability more accurately. We found in short term (¡ 10 s), the instability of the cavity is limited by temperature fluctuation, and in the long term (¿ 10 s), Brownian noise dominates the instability, therefore demands adequate precautions to reach the desired level of stability. Through systematic simulations, we have identified the best criteria for minimization of all these noises and obtain stabilities of 8.5×10−17 and 5.1×10−17 using dielectric and crystalline mirror coatings, respectively, which are similar to the best-reported results among its homologue cavities.

Investigation of the cap layer for improved GeSn multiple quantum well laser performance.

The study of all-group-IV SiGeSn lasers has opened a new avenue to Si-based light sources. SiGeSn heterostructure and quantum well lasers have been successfully demonstrated in the past few years. It has been reported that, for multiple quantum well lasers, the optical confinement factor plays an important role in the net modal gain. In previous studies, adding a cap layer was proposed to increase the optical mode overlap with the active region and thereby improve the optical confinement factor of Fabry-Perot cavity lasers. In this work, SiGeSn/GeSn multiple quantum well (4-well) devices with various cap layer thicknesses, i.e., 0 (no cap), 190, 250, and 290 nm, are grown using a chemical vapor deposition reactor and characterized via optical pumping. While no-cap and thinner-cap devices only show spontaneous emission, the two thicker-cap devices exhibit lasing up to 77 K, with an emission peak at 2440 nm and a threshold of 214 kW/cm2 (250 nm cap device). The clear trend in device performance disclosed in this work provides guidance in device design for electrically injected SiGeSn quantum well lasers.