Fabry-Perot Cavity Research Articles

High-Speed Directly Modulated Widely Tunable Hybrid Square/Rhombus-Rectangular Coupled Cavity Lasers

We report the latest development in high-speed directly modulated tunable laser based on simple and compact hybrid square/rhombus-rectangular laser (HSRRL), aiming for low-cost deployment in next generation high-throughput optical interconnects, intra-/inter-data center networks, and optical fiber communication system. The HSRRL is composed of a deformed square whispering gallery mode (WGM) microcavity and a Fabry–Pérot (FP) cavity, and the WGM microcavity is used as an end face of the FP cavity with mode selection. A deformable WGM microcavity is designed to obtain a high reflectivity. The HSRRL, fabricated with deep-etching processing steps similar to FP laser without grating or epitaxial regrowth, has achieved 7-mA threshold current, 0.4-mW/mA slope efficiency, above 52-dB side mode suppression ratio (SMSR), and 16.2-GHz modulation bandwidth with injection currents of 34.3 mA and 60 mA for WGM microcavity and FP cavity, respectively. A wavelength tuning from 1537.40 nm to 1570.42 nm is realized by adjusting the injection currents simultaneously. In the tuning range, the laser has an SMSR greater than 40 dB, a linewidth less than 4 MHz, and a 3-dB modulation bandwidth greater than 14 GHz.

High-Gain Fabry–Perot Cavity Antenna With an Artificial Magnetic Conductor Side Wall

We propose a novel design method for a Fabry–Perot (FP) cavity antenna with an artificial magnetic conductor (AMC) side wall intended to provide a high gain in the tilted target direction. However, multiple reflections in the FPC caused by the AMC side wall make it extremely difficult to design the antenna. To solve this problem, we suggest a new design method based on a more generalized image theory, which transforms our antenna into a regular FPC problem that is more straightforward to analyze. The AMC unit cells of the AMC side wall and the ground plane are deliberately designed to have the antenna satisfy the FP resonance condition, which is required to produce a high gain. As a result, the antenna provides a relatively high gain of 12.6 dBi in the target direction of 30° and has reasonable aperture efficiency of 29%, which were validated experiments.

Statically Multiple Colors and Dynamically Infrared Emissivity Modulation Compatible Electrochromic Devices via Simple Fabry–Perot Photonic Structures

AbstractThe development of electrochromic devices (ECDs) that can dynamically modulate infrared (IR) emissivity while maintaining a wide color gamut distribution for visible (VIS)‐IR compatible spectral manipulation has been a long‐standing challenge. Current ECDs are limited by simultaneous changes in IR emissivity and VIS colors when subjected to external potential, restricting their potential applications. This work presents, for the first time, VIS–IR compatible ECDs capable of displaying VIS multicolor and dynamically modulating IR emissivity via a Ge/HfO2 Fabry–Perot cavity structure. The all‐solid‐state VIS‐IR compatible ECD with the structure of ITO/NiO/Ta2O5/Li/WO3/ITO/Ge/HfO2 achieves not only emissivity modulation of 0.20 at potentials of −2.5 V and +2.5 V in the wavelength range of 2.5–25 µm, but also, due to the presence of Fabry–Perot cavity, the novelty compatible device structure achieves static multicolor modulation, thus decoupling VIS and IR emissivity modulation. Additionally, a flexible VIS‐IR compatible ECD based on polyaniline is also constructed. This novel approach offers a promising possibility for multispectral compatible manipulation, VIS multicolor, and IR signal processing applications.

Improved topography measurement with a high dynamic range using phase difference sensing technology.

Phase difference sensing technology (PDST) is employed for topography measurement, and two interference structures are proposed to achieve upper-limit adjustment and high resolution in the measurement range: a dual-wavelength system with a single Fabry-Perot (FP) cavity and a single-wavelength system with dual FP cavities. The phase difference between the two interference signals is determined by an elliptic fitting algorithm (EFA), and this change in phase difference is utilized to characterize the step height. Experimental results indicate that the measurement upper-limit can be adjusted to either 410 µm, 187 µm, or 108 µm by varying the wavelength difference in the dual-wavelength system, which gives a measurement error of 2.96%. In contrast, while offering a measurement resolution of 3.47 nm, the single-wavelength system exhibits a measurement error of 5.38%. The proposed method is capable of satisfying the measurement requirements during micro-electromechanical system (MEMS) processing with proficiency.

PDMS-filled micro-spring Fabry-Perot cavity for temperature sensing.

A highly sensitive fiber-tipped temperature sensor based on polydimethylsiloxane (PDMS)-filled spring Fabry-Perot (FP) cavity has been proposed and experimentally demonstrated. The spring FP cavity is first fabricated on the fiber endface by the two-photon polymerization lithography. After that, PDMS is filled into the cavity to drive the elongation of the flexible spring and thus to functionalize high-performance temperature sensing. Benefiting from the large thermal expansion coefficient of PDMS, the proposed sensor exhibits a maximal temperature sensitivity of 704.3 pm/°C with excellent operating repeatability and stability. Besides, by selecting a proper spring constant k, the FP sensitivity can be precisely adjusted in the range of 100-700 pm/°C. Thanks to the advantages of high fabrication accuracy and designable property, the proposed sensor could promote numerous usages for customizable temperature sensing.

On-chip electro-optically tunable Fabry-Perot cavity laser on erbium doped thin film lithium niobate

We demonstrate an on-chip electro-optically tunable Fabry-Perot (FP) cavity laser on Er3+-doped thin film lithium niobate (Er: TFLN). The FP cavity consists of two Sagnac loop reflectors at the two ends with a loaded quality factor of 1.3 × 105 and a free spectral range of 68 pm. The fabricated Er: TFLN FP laser structure is integrated with microelectrodes designed for electro-optically tuning, and a continuous laser wavelength tuning with 24 pm around 1544 nm is achieved by applying a driving voltage from −6 V to 6 V.

Spin-dependent and tunable perfect absorption in a Fabry-Perot cavity containing a multi-Weyl semimetal.

Spin-dependent absorption has been widely studied in metamaterials and metasurfaces with chirality since it develops significant applications in multiplexed holograms, photodection, and filtering. Here, the one-dimensional photonic crystal Fabry-Perot (FP) cavity containing a multi-Weyl semimetal (mWSM) defect is proposed to investigate the spin-dependent perfect absorption. Results denote that the distinct refractive indices of right hand circularly polarized (RCP) and left hand circularly polarized (LCP) waves are present due to the nonzero off-diagonal term of mWSM, thus supporting the perfect absorption of RCP and LCP waves at distinct resonant wavelengths. The different perfect absorption wavelengths of RCP and LCP waves reveal the spin-dependent perfect absorption. By altering the Fermi energy, tilt degree of Weyl cones, Weyl nodes separation, topological charge, and thickness of the mWSM layer, the perfect absorption wavelength of RCP and LCP waves can be regulated conveniently. Particularly, the linear tunable perfect absorption wavelength with thickness of the mWSM layer supports the accurate determination of perfect absorption wavelength at distinct mWSM thicknesses. Our studies develop simple and effective approaches to acquire the spin-dependent and adjustable perfect absorption without the external magnetic field, and can find practical applications in spin-dependent photonic devices.

Cavity Optomechanical Bistability with an Ultrahigh Reflectivity Photonic Crystal Membrane

AbstractPhotonic crystal (PhC) membranes patterned with sub‐wavelength periods offer a unique combination of high reflectivity, low mass, and high mechanical quality factor. Using a PhC membrane as one mirror of a Fabry–Perot cavity, a finesse as high as is demonstrated, corresponding to a record high PhC reflectivity of and an optical quality factor of . The fundamental mechanical frequency is 426 kHz, more than twice the optical linewidth, placing it firmly in the resolved‐sideband regime required for ground‐state optical cooling. The mechanical quality factor in vacuum is , allowing values of the single‐photon cooperativity as high as . Optomechanical bistability is easily observed as hysteresis in the cavity transmission. As the input power is raised well beyond the bistability threshold, dynamical backaction induces strong mechanical oscillation above 1 MHz, even in the presence of air damping. This platform will facilitate advances in optomechanics, precision sensing, and applications of optomechanically‐induced bistability.

Economy and colors based on solution-process rGO-TiO2 dye-sensitized solar cells modulated with organic Fabry-Perot cavity for indoor photovoltaic

This research modified a porous titanium dioxide (TiO2) dye-sensitized solar cell (DSSC) with reduced graphene oxide (rGO) to improve efficiency. A secondary color selectivity effect was obtained by addition of an organic Fabry-Perot (F.P.) cavity. The TiO2 was doped with a variety of rGO including 0, 1, 5, and 10 wt%. Small molecule (McFarland and Tang, 2003; McFarland and Tang, 2003) [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and polymer poly(3,4-ethylenedioxyselenophene): poly (styrene sulfonate) (PEDOS: PSS) were used to create the F.P. cavity. Such organic F.P. cavities on DSSCs can be produced by solution process which is economical, rapid, and produces a large surface area. The devices are suitable for use under low illumination indoor photovoltaic because there is light conversion current under low voltage. The solution process had three parts: (i) using a modified Hummers' method, the rGO was doped onto the porous TiO2 structure in different wt%, (ii) the polymer PEDOT: PSS and small molecule PCBM F.P cavities with different thicknesses were produced, as the thicknesses correspond to different color bands, and (iii) combine the F.P. cavity and rGO-TiO2 to produce a FTO/TiO2-rGO/Dye/Ag/F.P./Ag DSSC. Scanning electron microscope (SEM) images showed that 5 wt% rGO offered the best sheet nano-structure, and this increased the efficiency of DSSC by 28.1% when measured by power conversion efficiency (PCE). The color output advantages of F.P. cavity using PCBM and PEDOT materials are red and blue, respectively. The devices with PEDOT: PSS and PCBM saw a 9 and 12.5% gain compare to DSSC without F.P. cavity. However, two structures of TiO2 doped 5 wt% rGO and colorful PCBM F.P. cavity can increase the efficiency of DSSC by 44.1%.

Accessible interferometric autocorrelator for noise-like pulses based on a Fabry-Perot cavity.

In this work, we develop experimentally a Fabry-Perot fiber optic interferometer applied to the measurement of autocorrelation of complex dynamic pulses generated by a figure-eight fiber laser. The principle is based in the superposition of multiple pulses, which requires two partially reflecting flat surfaces in parallel, resulting in a simple and compact autocorrelator design. The autocorrelation trace obtained exhibits a typical double-scaled structure for noise-like pulses (NLPs), with an ultrashort coherence spur on the order of 100 fs riding upon a broad pedestal of 120 ps. Finally, we show experimentally that the developed Fabry-Perot device is able to measure accurately the autocorrelation of NLPs, as confirmed by comparing the measurement with that of a conventional autocorrelator scheme based on a Michelson interferometer, with the additional advantages of a more compact setup and a much easier alignment procedure compared to the latter.

Bidirectional planar absorber with polarization-selective absorption and reflection capabilities.

In this study, we developed a novel planar bidirectional perfect metamaterial absorber (PMA) with polarization-selective absorption and reflection capabilities. The proposed bidirectional PMA has near-perfect absorption for y- and x-polarized waves propagating in the -z and + z directions. It also reflects x- and y-polarized waves propagating in the -z and + z directions. We used full-wave simulations and Fabry-Perot cavity models to evaluate the performance of the proposed bidirectional PMA. We also used a free-space method to measure the fabricated sample. To demonstrate the potential of the proposed PMA in multiband systems, we extended our PMA design to a dual-band bidirectional absorber.

Novel microspherical fiber Fabry–Pérot interferometer based on the Vernier effect for micro-displacement sensing

A novel optical fiber Fabry–Perot interferometer (FPI) based on the Vernier effect is proposed for micro-displacement sensing. The sensor is composed of an optical fiber microsphere and a section of multimode optical fiber with a flat end surface. The air cavity in the middle is used as the Fabry–Perot cavity. The extinction ratio of the reflection spectrum is significantly improved by the optical fiber microsphere, and the extinction ratio is ∼12 dB. First, a single FPI is tested for micro-displacement. A sensitivity of 2.13 nm/µm and linearity of 99.31% are obtained within the range of 0–1.872 µm via phase demodulation. The fabricated optical fiber FPI is used as the sensing arm and cascaded with the designed analog reference arm. The micro-displacement sensitivity of the sensing arm can be improved to 28.92 nm/µm through the Vernier effect, i.e., 13.58 times that of a single FPI. The fabricated sensor exhibits the characteristics of high sensitivity, contrast, and linearity; a compact structure; and low cost. It can be used for micro-displacement detection. In addition, the analog reference arm is unaffected by the environment, and it can freely adjust sensitivity magnification. Accordingly, it is applicable to micro-displacement detection scenarios under different sensitivity requirements.

Mid-infrared pyroelectric detector with metasurface electrode for broadband enhanced absorption

Pyroelectric photodetectors have continuously been an attractive candidate due to their noncryogenic and easy-to-fabricate specifics. Because the detectivity or resolution of the pyroelectric detector is closely related to the absorptivity to incident radiation, we propose a scheme for a metasurface-based pyroelectric detector (MPPD) by constructing its top electrode with an absorptive metasurface composed of nanogrid-patch units. The resonance modes of Fabry–Perot cavity, magnetic dipole and electric dipole are collectively leveraged for the mid-infrared MPPD with optimal broadband absorption plus three absorptive peaks at 3.13 μm, 3.94 μm and 4.8 μm. The mechanisms and field distributions of these resonance peaks are intensively explored and verified for configuration of the metasurface top electrode with optimized geometries. Finally, our scheme achieves an average absorptivity of 94.2% in the mid-infrared range of 3–5 μm, with its thermal response enhanced by 2.6 times that results in a significantly improved pyroelectric current for the detector.

Temperature-robust optical microphone with a compact grating interferometric module.

The high demand for advanced acoustic sensors has prompted optical microphones to become a current research hotspot; this is especially the case in light of the performance of existing electroacoustic microphones having reached the ceiling. In this work, a thermally stable optical microphone has been developed for sensitive detection of low-frequency acoustic signals. The microphone was prepared using a prestressed nickel diaphragm and a compact grating interferometric module. The adjacent surfaces of the diaphragm and grating form a short Fabry-Perot cavity, which makes the microphone robust to ambient temperature fluctuation due to the reduced thermal drift of its operating point relative to the quadrature point of the interferometer. The cavity length-operating wavelength relationship of the microphone operating at the quadrature point was obtained. The performance of the prepared microphone was tested using various methods. Experimental results show that the microphone enables stable operation at the quadrature point over a wide range of temperatures from 0°C to 60°C with low signal distortion and high sensitivity. The response of the prepared optical microphone to low-frequency drone noise was measured and compared with that obtained with a commercial electret condenser microphone.

Metasurface-Enabled Uncooled Silicon Germanium Oxide Infrared Microbolometers for Long-Wave Infrared Detection

This paper investigated metasurface enabled uncooled silicon germanium oxide (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.425</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.512</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.063</sub> ) infrared (IR) microbolometers. The metasurface was used to engineer the IR absorption to achieve broadband or narrowband spectral response, eliminate the need for Fabry-Perot quarter wave resonant cavity typically used in conventional microbolometer under the pixel, and significantly improve the electrical performance of the temperature-sensing layer. This has facilitated the fabrication of the microbolometer with the supporting arms placed underneath the pixel without disrupting the Fabry-Perot cavity, and as a result, the supporting arms were fabricated with longer length without sacrificing the fill factor. The longer support arms reduced the thermal conductance between the microbolometer pixel and the underlying substrate and thus increased the voltage responsivity. The spectral responsivity and detectivity for the fabricated devices were measured in vacuum and demonstrated tunablility with narrow bands between 7 to 12 μm by changing the metasurface disk diameter and periodicity. The measured voltage responsivity, detectivity and thermal response time were > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> V/W and > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W and 2.01 ms to filtered blackbody infrared radiation between > 2 μm. The voltage noise power spectral density (PSD) of the fabricated devices were reduced by annealing the devices in vacuum.

Tunable, coherent optical comb source via on-chip bidirectional coupling.

A tunable comb source is demonstrated through gain switching on a three-sectioned photonic integrated circuit (PIC). The PIC consists of two mutually coupled lasers connected by a passive waveguide. One of these is a tunable, two-section, single mode laser. The second laser is a simple Fabry-Perot cavity laser which can be phase-locked with the single mode laser via bidirectional coupling. Frequency combs are produced by gain switching the Fabry-Perot laser by applying a high-power radio frequency signal. Combs are generated with line spacings ranging from 3.5 to 8 GHz. The on-chip bidirectional coupling causes the comb to also be generated in the two-section device. Despite the lack of on-chip optical isolation between the lasers, the resulting combs are stable. Numerical simulations using a delay-differential model reproduce the results and reveal the important role played by the short delay times inherent to on-chip integration in this stability.

High-accuracy wide-range refractive index demodulation based on under-sampled fiber F-P cavity length spectrum.

A scheme of fiber Fabry-Perot (F-P) cavity refractive index (RI) demodulation named under-sampled length spectrum retrieval (ULSR) is proposed. Unlike the wavelength spectrum method, ULSR can be used for physical quantity detection with just a monochromatic laser and photodetectors, avoiding the need for wideband lasers or expensive infrared spectrometers. Eight F-P cavities of different lengths were fabricated to sample the cavity length spectrum, and then the obtained under-sampled length spectrum was used to demodulate the RI of F-P cavity fillings. It was demonstrated that the ULSR system can achieve an index measurement accuracy of 1 × 10-4 in the glucose solution index range of 1.3294-1.3746 at wavelength λ = 1.55 µm. An index demodulation with higher accuracy and wider range is expected when more than 8 F-P cavities are used. The proposed scheme, with advantages of low system complexity, low cost, high reliability, high detecting accuracy, and wide detecting range, holds great promise for facilitating the wide application of F-P cavity sensors. Additionally, ULSR liberates wavelength freedom, making it a strong candidate for multiplexed sensing based on wavelength division multiplexing.

Telecom Band Single-Photon Source Using a Grafted Carbon Nanotube Coupled to a Fiber Fabry–Perot Cavity in the Purcell Regime

Telecom Band Single-Photon Source Using a Grafted Carbon Nanotube Coupled to a Fiber Fabry–Perot Cavity in the Purcell Regime

A Compact Fabry–Pérot Acoustic Sensor Based on Silicon Optical Waveguide Bragg Gratings

No membranous optical sensors have excellent development prospects in aerospace and other industrial fields due to their small size and anti-electromagnetic interference. Here, we proposed a novel Fabry–Pérot (FP) cavity acoustic sensor based on silicon optical waveguide Bragg gratings. The FP cavity consists of two Bragg gratings written on the silicon-based optical waveguide and a miniature air groove. When the sound signal acts on the miniature air groove, the sound pressure changes the density of air molecules near the waveguide grating’s evanescent field, causing variation in the air’s refractive index. This results in a shift in the reflection spectrum of the FP cavity to detect the sound signal. The effects of the grating period, grating pitch quantity, and groove depth of the FP cavity on acoustic sensing were studied. The modelling predicts that the sensing sensitivity could be 0.4 nm/Pa. Theoretically, the compact self-designed acoustic sensor can withstand temperatures above 800 °C. Therefore, it has significant potential applications in precision measurement in high-temperature and high-pressure environments.

Broadband quantum-dot frequency-modulated comb laser

Frequency-modulated (FM) laser combs, which offer a quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion, Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of –5 dB allows the QD laser to generate FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs).