Cavity Length Research Articles

MEMS Fabry-Perot sensor for accurate high pressure measurement up to 10 MPa

Microelectromechanical system (MEMS) Fabry-Perot fiber-integrated pressure sensor exhibits a compact size, intrinsic safety, and high precision measurement. Here, a MEMS Fabry-Perot interferometer sensor is presented. The sensor is fabricated using a standard microfabrication process with a uniformity of 80%. The sensor enables a pressure measurement range of 0–10 MPa with a full-scale nonlinearity error of 1.44% and a repeatability error of 2.14%. A limit of detection of 1.74 kPa and a pressure resolution of 0.017% are achieved. The comparative experiment is conducted to verify the wavelength tracking method is more robust than cavity length demodulation method in this configuration. Moreover, the temperature drift is alleviated by combining a fiber Bragg grating sensor for compensation in a range of -35–88 °C, which is reduced by 15 times to 2.88 ppm/°C. The proposed sensor has wide potential applications, such as downhole environments and petroleum pipeline pressure monitoring.

Исследование изменения геометрии внутренней полости передающих устройств для гидроструйных технологий с целью улучшения их теплового состояния

The paper is devoted to the study of the influence on changes in their thermal balance during operation by improving the cooling conditions of sections of the drill shaft with contact surfaces of changes in geometric characteristics, such as diameter and length, of the internal cavity for supplying working fluid in high-pressure hydro-puller device for hydro-jet technologies. The axisymmetric simulation not on a full-size transmit-ting device was carried out, but on one-eighth part in order to reduce the time of both creating the model itself and the amount of calculations. A model created in the computing environment «Ansys» with a computational grid for calculating equivalent stresses is shown. The stress distributions calculated by the finite element method for various combinations of the geometry of the transfer device revealed the corresponding boundaries for the rational change in the diameter and length of the internal cavity, allowing to ensure its operability of the structural unit in combination with maximum cooling of the most thermally loaded sections of the shaft. Dimensionless geometric parameters (reduced diameter and reduced length of the internal cavity) are introduced for a general description of the geometry of transmitting devices for hydro-jet technologies. Graphs of the dependences of voltage values on the given values were obtained.

Large-energy operation of an Er-doped fiber laser with ZrGeTe4 saturable absorber

ZrGeTe4 as a layered semiconductor material with good stability and optoelectronic properties, and excellent saturable absorption characteristics, but its application in fiber lasers is still insufficient. In order to explore its application in fiber lasers, we prepared ZrGeTe4-PVA thin film by liquid phase exfoliation and performed a series of characterizations. A modulation depth of 13.15 %, a non-saturated loss of 6.4 %, and a saturation intensity of 5.5 MW/cm2 were obtained. Then used the ZrGeTe4-PVA thin film as the saturable absorber (SA) in an Er-doped fiber laser (EDFL), the large-energy operation could be realized. In the case of a cavity length of 234 m, when the pump power was increased to 1229 mW, a maximum single pulse energy of about 32.72 nJ was achieved, with a repetition frequency of 859 kHz. To the best of our knowledge, this is the highest single-pulse energy achieved in an EDFL based on ZrGeTe4-SA. This experiment shows that the ZrGeTe4 is a promising two-dimensional (2D) material with good nonlinear absorption properties, proving that it is a promising pulse modulation of SA and laying a foundation for its subsequent study in fiber lasers.

Compact widely tunable laser integrated on an indium phosphide membrane platform

We present the design, fabrication, and characterization results of a compact, widely tunable laser realized on an indium phosphide membrane-on-silicon (IMOS) platform. The laser features a compact Mach–Zehnder interferometric structure as the wavelength-selective intracavity filter with a footprint of 0.13 mm2. The filter design is optimized to ensure narrow filter transmission and high side-mode-to-main-mode-ratio, enabling single-mode operation for the laser. The high optical confinement on the IMOS platform can support tight waveguide bends. Leveraging this, the laser achieves a short cavity length, further enhancing the single-mode operation. Measurement results indicate a threshold current of 29 mA and a maximum on-chip output power of approximately 3.6 dBm and wall plug efficiency of 1.8%. The side-mode suppression ratio ranges from 30 to 44 dB, with a tuning range spanning 40 nm, from 1555 to 1595 nm. A complete tuning lookup table is generated via an automated setup incorporating a stochastic search algorithm.

DC current sensor based upon a fused fiber optic Fabry-Perot interferometer (FPI) and copper wire

In order to meet the demand for direct current (DC) current measurements in industrial production, a new type of fiber optic DC current sensor, combining thin copper wire and fiber optic Fabry-Perot interferometer (FPI), is reported. FPI is a sandwich structure formed by splicing a single-mode fiber (SMF) and a quartz capillary, with a cavity length of approximately 200 μm. The copper wire, with a length of 3.2 cm and a diameter of 1 mm, is attached to the FPI to form the sensor. Due to the excellent thermal conductivity of copper, the results showed that the sensor increased the sensitivity from 4.1 pm/°C to 11 pm/°C. After applying direct current to the sensor, a large quantity of heat generated by the copper wire was absorbed by the FPI, resulting in a significant shift in the resonant wavelength of FPI, which can indirectly measure the current. Three current experiments were performed, and parabolic curves have been used in fitting of the Dip wavelength and the square of the current. The results provide high correlation coefficients with values exceeding 0.99. Therefore, this curve may be used to measure the square of the current, further obtaining the current. In summary, the sensor is compact and durable, easy to manufacture, and provides high correlation coefficients, providing an alternative for measuring DC current.

Highly sensitive push-pull differential pressure sensor with multi-parameter measurement capabilities

A multi-parameter sensor comprising of a Fabry–Perot (FP) pair and a fiber-optic FP microcavity was proposed for simultaneous measurement of differential pressure (DP), static pressure (SP) and temperature. The push-pull FP pair is used to measure the differential pressure, and wide measurement range can be achieved by adjusting the dimensions of the diaphragm. The self-enclosed fiber-optic microcavity is utilized to measure the static pressure. For multi-parameter measurement, a matrix equation is proposed to solve the differential pressure, static pressure and temperature by fully considering the relationship of the FP cavity lengths and measurands. The performance of multi-parameter sensing is verified experimentally. The sensitivities of differential pressure, static pressure and temperature are 294.4822 nm/KPa, 353.08 nm/MPa and 42.4056 nm/°C, respectively, in variation of cavity lengths. The sensing characteristics show good linearity. Such a sensor could find important applications in the fields of process industry and oil industry, etc.

Enhancing the efficiency of Brown 24 pigment production through continuous microwave heating in conveyor belt and rotary kiln systems: A design and optimization study

In energy intensive industries, the continuous production with microwave technology presents several challenges in achieving high energy efficiency and heating uniformity. In the ceramic pigments sector, the Brown 24 is the ideal candidate for this study due to its susceptibility to thermal runaways and its high temperature to reach total conversion, higher than 1000K. By another hand, most literature related to this field focus on static systems while ignoring the continuous ones which are required by the industry. A coupled model that integrates thermal, electromagnetic and chemical phenomena within an energy system was implemented in COMSOL Multiphysics. Additionally, a MATLAB controller was employed to dynamically adjust the cavity length through a moving plunger, which maximizes the electrical efficiency. The required power is also managed to guarantee a total chemical conversion of the material. The proposed optimization methodology reduces computational costs, and it is applicable to any continuous microwave system processing moving solid materials. In this work, two microwave configurations were optimized. The first one, based on a conveyor belt, achieved a global efficiency close to 70%. While the second one, based on a rotary kiln, achieved a global efficiency of 85% and a production rate of 4.66kg/h, significantly outperforming a previous study by factors of 1.57 and 2.06, respectively. These findings show the potential for substantial improvements in continuous microwave systems.

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.

Self-excited oscillation characteristics and mechanisms of supercritical CO2 flowing in a Helmholtz oscillator for enhancing heat transfer

The drastic variations in thermal properties of supercritical CO2 near its pseudo-critical point induce the formation of complex boundary layer structures within pipelines, rendering it susceptible to heat transfer deterioration under the influence of buoyancy forces. The Helmholtz self-excited cavity can generate self-excited pulsating jets, enhancing the intermixing between fluids inside the heat exchanger tubes, disrupting the thermal boundary layer, and suppressing heat transfer deterioration. In this study, the characteristics and mechanisms of self-excited oscillations of supercritical CO2 flowing vertically upward in the Helmholtz self-excited cavity were investigated using the large eddy simulation (LES) method. A detailed analysis of cavitation and vortex evolution within the cavity was conducted, along with an exploration of the influence of inlet pressure and structural parameters on the frequency characteristics of pulsations. The results indicate a close relationship between cavitation and vortex interactions and the pulsation frequency. An increase in inlet pressure leads to a significant cavitation phenomenon near the jet shear layer and an increase in vortex frequency. Dimensionless cavity length (Lc/d1) enlargement results in an increase in outlet pulsation frequency but a decrease in pulsation amplitude. The critical dimensionless ratio of cavity diameter (Dc/d1) plays a crucial role in maintaining the desired pulsation frequency and amplitude. Within the working range outlined in this paper, practical insights for system design and operation are provided by the optimal parameters of Lc/d1 = 3 and Dc/d1 = 10.

Study of the birefringence noise in high-finesse ULE cavity

High-finesse ultra-low expansion (ULE) cavities are important components in many precision optical experiments, and the cavity length noise in ULE cavities has been intensively studied. However, some experiments, such as vacuum magnetic birefringence measurements, have focused on the phase difference between orthogonal polarizations. To determine the effect of high-reflectivity mirrors on birefringence noise, we investigated the birefringence noise of a ULE cavity with the finesse of 531000(1000) and obtained the noise spectrum of the intrinsic birefringence of the cavity. The single-pass phase difference due to the birefringence of the cavity mirror is (21.3±0.2)μrad and the noise for the birefringent cavity is 81.3prad/Hz at 0.1Hz and 2.6prad/Hz at 40Hz. These results may draw attention when considering noise in cavity-based optical experiments.

Stabilized conformal planar cavity with continuous adjustable resonant frequency

A conformal planar cavity with filling dielectrics is conformally transformed from a concave cavity by transformation optics. The proposed conformal planar cavity offers remarkable advantages, including high stability, high Q factor, tunable resonant frequency, and small mode volume. In contrast to concave cavities, it offers a significant advantage by being integrable onto a chip. Additionally, when compared to planar cavities based on metasurfaces, which lack the capability for continuous resonant frequency adjustment, the proposed conformal cavity offers a tunable resonant frequency that can be continuously adjusted by simply changing the cavity length without the need for redesigning the filling dielectrics. Only dielectrics with permittivity ranging from 1 to 1.7 are required inside the conformal cavity, which can be easily obtained at various frequency bands. The tunability and stability of the conformal planar cavity is numerically verified, and experimental demonstrations at microwave band are performed.

Snapshot computational spectroscopy enabled by deep learning

Abstract Spectroscopy is a technique that analyzes the interaction between matter and light as a function of wavelength. It is the most convenient method for obtaining qualitative and quantitative information about an unknown sample with reasonable accuracy. However, traditional spectroscopy is reliant on bulky and expensive spectrometers, while emerging applications of portable, low-cost and lightweight sensing and imaging necessitate the development of miniaturized spectrometers. In this study, we have developed a computational spectroscopy method that can provide single-shot operation, sub-nanometer spectral resolution, and direct materials characterization. This method is enabled by a metasurface integrated computational spectrometer and deep learning algorithms. The identification of critical parameters of optical cavities and chemical solutions is demonstrated through the application of the method, with an average spectral reconstruction accuracy of 0.4 nm and an actual measurement error of 0.32 nm. The mean square errors for the characterization of cavity length and solution concentration are 0.53 % and 1.21 %, respectively. Consequently, computational spectroscopy can achieve the same level of spectral accuracy as traditional spectroscopy while providing convenient, rapid material characterization in a variety of scenarios.

Impact of polarization and gain control in the optimization of output pulse properties in ultralong ultrafast ring fibre lasers

The application of limited polarization and gain control to the recently demonstrated mode-locked ultralong ultrafast, EDFA-based and Raman-assisted pulsed ring fibre lasers is shown to reduce output pulse duration and noise, as well as to increase pulse peak power in cavities of 10 km with repetition rates as low as 38 kHz and pulse durations below 200 fs FWHM, which remain effectively depolarized at the output in the optimized case, accompanied by improved mode-locking stability. The impact of polarization state optimization prior to the doped-fibre amplification section on these devices is studied for different lengths of fibre, harmonic modes, and Raman amplification values. Peak power is nearly doubled thanks to temporal compression and spectral broadening, with a wide choice of regimes of operation dynamically available for a given cavity length, allowing the modification of laser output towards targeted pulse characteristics.

Improving the air stability of flexible top-emitting organic light-emitting diodes

Flexible organic light-emitting diodes (OLEDs) are promising light sources for biomedical applications. However, the use of these flexible devices has been restricted by their short shelf lifetimes due to poor ambient stability. Here, the fabrication of a long-lived flexible OLED is reported by replacing air-sensitive metals such as aluminum, and alkali metals used as n dopants, with silver. In addition, to achieve stable and efficient flexible OLEDs we tuned the optical cavity length to the second-order interference maximum. The device design has simple encapsulation and leads to an improvement in the air stability of flexible OLEDs which show a shelf lifetime of greater than 130 days whereas the conventional structure exhibits degradation after only 12 days. The proposed design for making flexible OLEDs demonstrates a great potential for using the devices for wearable bioelectronic applications.

Design and wavelength selection of compact dual-wavelength Yb:YAG lasers with a Z-shaped cavity

The compact dual-wavelength Yb:YAG lasers were designed and developed by employing a Z-shaped cavity. The overall cavity length is about 32 cm, which can be packaged in a device size of 15 × 10 cm2. The oscillating beam radius in the laser crystal varied by the cavity length, and stable dual wavelength laser was achieved. The 1050 nm output of 1.44W was obtained at the highest pump power is 10 W when the oscillating beam radius was 125 μm. The balance dual-wavelength output of 0.93W was achieved with the optical to optical conversion efficiency of 9.3%. The output wavelengths of the Yb:YAG laser depended on the oscillating beam radius, which was consistent with the experimental results. Our findings indicated that while stringent mode matching was ideal, there was a degree of flexibility that can be tolerated without significantly compromising the laser's performance, which can be beneficial for the dual-wavelength oscillation in applications.

Transmission Characteristics Analysis of a Twin-Waveguide Cavity

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).

Study on 1550 nm Human Eye-Safe High-Power Tunnel Junction Quantum Well Laser.

Falling within the safe bands for human eyes, 1550 nm semiconductor lasers have a wide range of applications in the fields of LIDAR, fast-ranging long-distance optical communication, and gas sensing. The 1550 nm human eye-safe high-power tunnel junction quantum well laser developed in this paper uses three quantum well structures connected by two tunnel junctions as the active region; photolithography and etching were performed to form two trenches perpendicular to the direction of the epitaxial layer growth with a depth exceeding the tunnel junction, and the trenches were finally filled with oxides to reduce the extension current. Finally, a 1550 nm InGaAlAs quantum well laser with a pulsed peak power of 31 W at 30 A (10 KHz, 100 ns) was realized for a single-emitter laser device with an injection strip width of 190 μm, a ridge width of 300 μm, and a cavity length of 2 mm, with a final slope efficiency of 1.03 W/A, and with a horizontal divergence angle of about 13° and a vertical divergence angle of no more than 30°. The device has good slope efficiency, and this 100 ns pulse width can be effectively applied in the fields of fog-transparent imaging sensors and fast headroom ranging radar areas.

Inverse-designed compact silicon waveguide reflector for on-chip resonators

Waveguide reflectors are crucial components in integrated optics and on-chip resonators, with their efficiency and dimensions significantly impacting system performance and integration. This paper presents an compact silicon on-chip waveguide reflector, designed using photonics inverse design, featuring a footprint of only 1.64μm×1.78μm and a simple, smooth structure. The simulation shows a 1 dB bandwidth over 400 nm and a reflectivity above 97.6% in the 1520–1570 nm wavelength range. Experimental measurements, conducted through Fabry-Pérot resonator spectrum analysis, confirm the excellent performance of the waveguide reflector, attaining a reflectivity over 92.8%. Additionally, the study presents two more waveguide reflectors tailored for the 1.31μm and 2μm wavelength, emphasizing the scalability of the design. The compact size and broadband reflectivity characteristics of the waveguide reflector provide increased flexibility in designing cavity lengths and directional couplers, making it a promising choice for applications in resonators and highly integrated photonics systems.

A quick 3D BEM iterative algorithm for partially cavitating flows over cylindrical bodies at angles of attack

An iterative three dimensional Boundary Element Method (BEM) is formulated to investigate partial cavitating flows around cylindrical bodies at various angles of attack and validation is pursued through comparison with other numerical models. Also, in this article the effect of angle of attack on two types of head (conical and blunt-head) is investigated. The results show that the effect of angle of attack on variation of cavity shape at blunt-head cylinder is more considerable. The need for a very short time (less than 10 min) to reach the desirable convergence and also proper accuracy in calculating the properties of cavitating flows are considerable advantages of this method. Also, in this research, the effect of the length of a cylindrical body on the cavity length has been investigated. The results confirm that if the length of the body is greater than 1.7 times the cavity length, the effects of the negative pressure behind the cylindrical body on the cavity length can be neglected.

A Metamaterial Bandpass Filter with End-Fire Coaxial Coupling

A miniaturized metamaterial (MTM) bandpass filter (BPF) based on end-fire coaxial coupling is proposed. End-fire coaxial coupling is achieved by using the coaxial cavity to connect with the SubMiniature version A connector. The subwavelength characteristics of the MTM lead to the miniaturization advantages of the filter in transverse dimensions. Moreover, the longitudinal length of the coaxial cavity can be sharply reduced by introducing matched blocks. As a result, the proposed filter has miniaturization merit both in transverse and longitudinal dimensions. The full-wave simulation results further reveal that the MTM BPF exhibits the advantages of low loss, low reflection, and low group delay. Additionally, the fractional bandwidth is approximately 13% when |S11| is less than −15 dB. The MTM BPF might have potential applications to array antennas for easily being expanded to two dimensional arrays.