Microwave and Optical Technology Letters最新文献

By incorporating scandium oxide (Sc₂O₃) powder into a PVA film, a Sc₂O₃ saturable absorber (SA) was successfully developed, boasting a modulation depth of 25%. When integrated into a ring erbium-doped fiber laser, the Sc₂O₃-SA facilitated the production of mode-locked dark pulses featuring multi-wavelength emission, leveraging its saturable absorbing ability along with the nonlinear properties inherent in the Sc₂O₃ thin film and the long erbium-doped fiber. Mode-locking operation was achieved within a pumping range of 209.3–239.8 mW, resulting in a peak pulse energy of 0.71 nJ. Operating at 1597.8 nm, the mode-locked laser demonstrated a repetition rate of 10.42 MHz and a pulse width of 23 ns. Domain-wall dark pulse operation was demonstrated in the L-band region, achieving a relative stability with a signal-to-noise ratio of 55.6 dB, utilizing a Sc₂O₃ thin film absorber and an 8-meter-long active fiber. These findings underscore the promising potential of Sc₂O₃ to be used in pulsed laser systems, particularly due to its exceptional nonlinear optical properties.

This article investigates nonidealities of the time modulation function that may affect the measurement accuracy when extracting the direction of arrival (DOA) using the time-modulated array. The types of nonidealities are identified and the fundamental and harmonic Fourier coefficients for each type are calculated theoretically. The measurement DOA error is calculated using these Fourier coefficients, and the allowable bounds of the nonideal parameters guaranteeing the confidence region of the error are proposed. Furthermore, a two-step measurement procedure is proposed to reduce these errors. For a systematic reduction of the measurement errors, a method for characterizing and compensating the nonidealities is investigated. To verify the validity of the proposed theory and measurement method, experiments are conducted to compare the results with and without calibration and compensation.

To realize the wideband and efficient operation of Doherty power amplifier (DPA) in multi-band mode, this paper proposes a tri-band DPA design method based on phase and impedance-constrained optimization. First, the phases required for impedance transformation networks across multi-band are determined based on the impedance required when the DPA operates at back-off power (BOP) and saturation. Then, the impedance judgment method using multiple impedance constraint circles was employed to determine the optimal load impedances. Finally, the phase and impedance constraints at multiple frequencies were used to optimize the carrier and peaking output matching networks. For verification, a tri-band DPA operating at 1.25−1.35, 1.9−2.1, and 2.75−2.85 GHz was designed and fabricated. Measured results show that, for the above three frequency bands, the drain efficiencies (DEs) at saturation reach 59.0%−61.7%, 59.5%−64.2%, and 52.4%−59.8% with corresponding output power exceeding 43 dBm. For 6 dB BOP, the DEs are 46.1%−54.2%, 50.4%−55.2%, and 44.8%−51.9%. Moreover, good linearity can be achieved after linearization for 20 MHz modulated signals.

To achieve low-concentration measurement using near-infrared dual-comb spectroscopy (DCS), this study presents a trace C₂H₂ detection using near-infrared DCS. A multi-pass gas cell is employed to extend the optical path length, improving the sensor's sensitivity. Signal post-processing via interpolation method is applied to reduce noise and achieve a flatter dual-comb. The sensor's sensitivity and transient characteristics are evaluated by selecting absorption lines at 6526.53, 6529.17, and 6531.78 cm⁻¹, with the experimental profile being well-fitted by a Voigt function. The stability of the system is confirmed with a C₂H₂ concentration of 200 ppm over a 2.5 h observation period, showing a stability better than 2.305 × 10⁻². Allan variance analysis indicates an optimal integration time of 597 s, yielding a minimum detection limit of 6.15 × 10⁻⁴ for absorbance and 350 ppb for concentration. Additionally, the detection of nine absorption lines demonstrates the multi-peak measurement capability, with deviations ranging from 0.059% to 12.496%.

Germanium (Ge) has garnered significant attention in the field of silicon-based monolithic light sources as an attractive material. Silicon nitride is widely used in optoelectronic devices due to its excellent optical properties. By using silicon nitride as a stressor to introduce tensile strain into Ge, the band structure of Ge can be tuned, enhancing the radiative recombination of direct bandgap emission. A LED with silicon nitride as a stressor is proposed in this paper. Simulation results demonstrate that the device has been introduced to a 3% uniaxial tensile strain, resulting in peak electroluminescence at 1986 nm and a maximum electro-optical conversion efficiency of 1.94%, indicating excellent performance in the short infrared wavelength range. This work provides a method for achieving more efficient silicon-based group IV light sources.

As a bonding material for bonding the shell and propellant in the combustion chamber of solid rocket motor, the liner plays a protective role for the engine. Only when the liner is in a “semi-solidified state” can the charge quality be guaranteed, and it is easy to cause the phenomenon of unstable bonding interface if the charge is loaded too early or too late. Therefore, noncontact monitoring of the gradual solidification process of the material from liquid state can prevent the problems of unstable bonding interface and significantly improve the safety of solid rocket motors. In this paper, the reflective terahertz time-domain spectroscopy technology is used to monitor the curing process of lining materials, extract the refractive index spectra of samples with different curing degrees, establish the relationship between refractive index and curing reaction time, and compare it with the material loss factor obtained by rheometer to establish the correlation between refractive index and material loss factor. The experimental results show that the refractive index decreases gradually during the curing process, and the correlation coefficient between the refractive index and material loss factor is higher than 0.9. With the curing reaction, the refractive index can accurately reflect the curing process of polyurethane materials. This study provides an effective means for monitoring the curing process of lining materials.

This letter presents a millimeter-wave ultra-wideband compact Wilkinson power divider (WPD) with an impedance compensation technique. For the first time, parallel LC resonance networks are introduced to compensate for the rapidly decreasing real part of the input impedance, resulting in additional matching and lossless frequency points. Besides, this design also leads to a reduction in area by more than 25% compared to traditional lumped-element WPDs. The proposed novel WPD is implemented using 65 nm CMOS technology with a compact core area of 0.022 mm² (0.88 × 10⁻³ λ₀²) and achieves the measured insertion loss of 1.36‒1.56 dB from 62 to 104 GHz, reaching the 0.2 dB-amplitude fraction bandwidth of 70% (42 GHz). Furthermore, the corresponding input-output return loss and isolation are better than 10 and 17 dB, respectively.

In this letter, a novel design for an electrically tunable substrate integrated waveguide (SIW) equalizer that maintains a stable insertion loss at high frequencies, is proposed. The SIW equalizer is composed of various parallel units consisting of microwave resistor (R) and varactor diode (C). Different resistance and capacitance values, forming a complex impedance, are achieved through PIN and varactor diodes under different DC biases, respectively. It results in greater losses in the low-frequency range compared to the high-frequency range, achieving an equalization effect. Moreover, because ideal capacitors do not contribute to signal loss, the loss in the high-frequency range remains minimal and stable under certain conditions. Experimental results indicate that the equalization range in the Ku-band is 0.30–9.75 dB with a DC voltage range of 0–4 V, and the insertion loss change in the high-frequency band is only 0.5 dB. For the equalizer operating in the Ka-band, within a DC voltage range of 6–14 V, the equalization range is 0.30–16.60 dB, with a change in insertion loss of only 0.12 dB at high frequencies. The return losses of equalizers are all better than −12.4 dB and −11.6 dB, respectively, in Ku- and Ka-band.

A polarization rotation second order dual-band aperture coupled based frequency selective surface (FSS) is presented in this letter. It produces different polarization rotation angle for both the bands. The corner truncated square patch resonators are used to examine dual-band responses. The patch resonators are placed back-to-back through metallic aperture coupled layer in the middle. Two passband responses are obtained with sub-patch resonator I (SPR I) and sub-patch resonator II (SPR II) patch resonators. In first passband, two orthogonal component provide $��\; ��18�\; �0^{\circ }��$ phase difference. Similarly, in second passband $��\; ��0^{\circ }��$ phase difference is occur. Thus, rotation in polarization is occurs in both passband. The prototype of the proposed FSS is fabricated and simulation results are verified with measured results.

In this paper, an improved W-band bandpass filter for the W-band synthetic aperture radar (SAR) system with a center frequency of 96 GHz is designed and implemented. Compared with the conventional rectangular waveguide resonator filters, two specially designed oversized rectangular waveguide cavities are combined in the structure to create two transmission zeros (TZs), which improves the sharp cutoff rate of the filter and remains the simplicity of the structure. Meanwhile, the position of each TZ is independently controlled by the dimensions of one specific oversized rectangular resonator, which makes it easier to realize a flexible and accurate design. The improved structure is analyzed, modeled and optimized to obtain a better transmission characteristic. The measured results show that the return loss of the improved W-band bandpass filter is less than −8 dB and the insertion loss is less than 1.4 dB within the passband. Additionally, the two TZs are located at 89.17 GHz and 103 GHz, respectively. These results verify the feasibility of the improved bandpass filter structure.