Microwave and Optical Technology Letters最新文献

In this paper, all optical 2 × 4 decoder (AODEC) is provided using threshold switching method in 2D photonic crystal (PC) structures which has low optical loss and most widely used in photonic integrated circuits (PICs). The proposed optical decoder is designed using silicon pillars with a refractive index of 3.46 perforated in the air background in a cubic lattice with a lattice constant of 585 nm. The proposed structure is composed of seven optical waveguides and three nonlinear ring resonators. Plane wave expansion (PWE) and finite difference time domain (FDTD) methods have been used to obtain and analyze the photonic band gap (PBG) range and performance of the designed AODEC, respectively. The proposed optical device achieves a contrast ratio (CR) of 8.98 dB, time delay of 2 ps and switching speed of 500 GHz at the optical wavelengths of 1550 nm. According to results, high data bit rate and contrast ratio, compactness, low power consumption and ultra-fast operation are the main advantages of designed 2 × 4 AODEC compared with the previous structures.

Carbon monoxide (CO) and carbon dioxide (CO₂) are products of incomplete combustion and complete combustion, respectively. Time-resolved knowledge of CO and CO₂ exhaust concentrations will aid in improving combustion strategies, control, and efficiency. To achieve online high-precision simultaneous measurement of CO and CO₂, a tunable diode laser absorption spectroscopy-based sensor is designed and constructed. Two diode lasers with central wavelengths of 2.3 and 2.0 μm are multiplexed in time-division to cover the absorption spectral lines of CO at 4285.00 cm⁻¹ and CO₂ at 4989.96 cm⁻¹, respectively. Wavelength modulation spectroscopy with second harmonic detection normalized by the first harmonic (WMS-2f/1f) is employed. A software lock-in amplifier and inversion algorithm are implemented for data processing and concentration acquisition. The entire measurement system is based on the idea of a virtual instrument and is carried out using a high-speed data acquisition card and a computer. Experimental verification demonstrates that the measurement accuracies of CO and CO₂ were 2.47% and 2.56%, respectively, with a time resolution of 20 ms. Dynamic measurement experiments with an alcohol blast burner validate the feasibility of measuring CO and CO₂ in actual combustion environments. The developed sensor demonstrates the potential for real-time and in situ carbon emission measurement for combustion diagnosis.

The performance of an active near-infrared laser heterodyne system using a supercontinuum light source as the light signal for trace species detection is experimentally demonstrated. The characteristics of the supercontinuum light source and the data processing methods used in heterodyne detection are described. The measurement of methane (CH₄) and carbon dioxide (CO₂) absorption spectra was carried out in the laboratory to evaluate the active laser heterodyne system, and high-resolution absorption spectra of CO₂ and CH₄ were recorded simultaneously. The stability of the active laser heterodyne system is analyzed using Allan variance analysis of long-term observation data. The active near-infrared laser heterodyne detection system demonstrated in this paper has great potential for the development of industrial parks' gas monitoring.

By using the finite-difference time-domain (FDTD) method and a two-port network model, this letter investigates the response of a uniformly moving resistive sheet to illuminating electromagnetic plane waves, at normal incidence. The numerical Doppler frequency shifts and scattering matrix are matched with curve-fitting expressions. The effects of motion on the impedance matrix, the chain matrix, and the continuity equations are analyzed. Moreover, the total energy of the transferred and reflected waves are studied for the cases of a resistive sheet moving toward or away from the plane wave source.

A spoof surface plasmon polariton superstrate structure-based decoupling method is proposed in this paper to reduce mutual coupling between two tightly coupled quarter-mode substrate integrated waveguide antenna elements. This superstrate is a periodic structure suspended over the antenna elements with an inter-element spacing of 0.02 λ₀ (1 mm) at 6 GHz. It has been demonstrated that the isolation can be improved from 6.5 dB to more than 39 dB within the operation band in measurement. Further, it has been shown that the proposed method can improve both the total efficiency (by 25%) and gain (1.4 dBi) of the multiple-input multiple-output antenna.

In this paper, we present a tunable bandpass frequency-selective surface (FSS) with wide tuning range. The FSS consists of a metallic rectangular waveguide array integrated into the double-sided printed circuit board (DSPCB) and an array of embedded varactors with a bias network on the backside of the DSPCB. The waveguide array exhibits a frequency-selective transmission peak due to the tunneling effect, and the transmission frequency can be adjusted by modifying the capacitance of varactors using different bias voltages. One benefit of this setup is that the varactors, along with the bias network, are situated on the same layer, resulting in a significant reduction in overall thickness to just 0.006λ_c (where λ_c represents the free-space wavelength at the highest transmission frequency). Additionally, the insertion loss related to the parasitic resistance of varactors is notably reduced due to the innovative integrated design of biasing lines with varactors and the nearly full-metal waveguide array. A prototype has been manufactured and tested, demonstrating that by varying the varactor capacitance from 0.12 to 1 pF, the passband showcases a frequency tuning range of 2.32:1, spanning from 5.8 to 2.5 GHz with an insertion loss ranging from 0.2 to 2.6 dB.

A compact dual-band omnidirectional antenna with folded microstrip lines and slotlines is proposed. The antenna is composed of a substrate and a superstrate. The superstrate is employed to broaden the antenna bandwidth. The radiating patch is situated on the upper surface of the substrate and consists of folded microstrip lines. The performance of the high-frequency band can be optimized based on the analysis of the current distribution intensity. The bottom of the substrate is composed of a ground plane with slotlines. The introduction and improvement of the low-frequency band are achieved by modifying the ground plane structure with characteristic modal analysis. The antenna demonstrates omnidirectional radiation characteristics across both frequency bands. The dimensions of the antenna are π × 0.178 λ₀ × 0.178 λ₀ × 0.049 λ₀ (π × 22 × 22 × 6 mm). The antenna achieves a maximum gain of 3.37 dBi at 2.5 GHz and 2.74 dBi at 5.8 GHz. The measured impedance bandwidths for the two frequency bands are 17.3% and 21.7%, respectively.

In this work, a V₂AlC-based saturable absorber (SA) was applied to a 2 μm band passively mode-locked (PML) laser. The saturation intensity and modulation depth of the V₂AlC-based SA were detected by the I-scan method, which were 225.05 MW/cm² and 7.68%, respectively. In the PML mode, an average power of 2.12 W at 1939 nm and a pulse width of 1077 ps at 82.49 MHz were obtained from the Tm:YAP laser. In addition, the laser exhibited a good beam quality factor (M²) which was measured to be less than 1.2. These results will pave the way for the application of V₂AlC-based SA in ultrafast lasers.