Current Issue : July-September Volume : 2025 Issue Number : 3 Articles : 5 Articles
An all-optical single-longitudinal-mode (SLM) forward Brillouin microwave oscillator (FB-MO) with an unbalanced Fiber Mach–Zehnder interferometer (UF-MZI) for microwave photonics (MWP) generation is proposed and experimentally investigated. UF-MZI consists of an optical coupler (OC), a polarization controller (PC), and two asymmetric length arms with 5 km and 500 m single-mode fibers (SMFs), which implements two unbalanced length feedback rings that are connected to one another. One long-length ring with a forward Brillouin gain cooperates with the other short-length ring to maintain a spectral Vernier effect and improve the effective free spectral range (FSR). By contrast with traditional optoelectronic oscillators (OEOs), this design does not require any photoelectric conversion devices and additional modulation, avoids external electromagnetic interference, and side-mode suppression and linewidth are favorable. Experimental results reveal that the 3-dB linewidth of the all-optical SLM FB-MO with UF-MZI is about 140 Hz. The acoustic-mode and side-mode suppression ratios are 26 dB and 31 dB.Within 60 min of the stability experiment, the power and frequency stability fluctuation were ±1 dB and ±100 Hz. Thanks to its long main ring cavity length, our all-optical SLM FB-MO with UF-MZI maintains good phase-noise performance. The measurement shows that a phase noise as low as −120 dBc/Hz at an offset frequency of 100 kHz is achieved. This SLM MWP generation technology holds great potential for applications in radar monitoring and wireless communication systems....
The acceptance of biodiesel, specifically fatty acid methyl esters, as an alternative to petroleum diesel has increased significantly. Traditional feedstocks used to produce biodiesel include various seed oils and used frying oils, but there is growing interest in low-cost alternatives like pumpkin seed oil. As a byproduct of cucurbits processing, a significant number of seeds often remains with a high oil content suitable for biodiesel production. In the search for new low-cost alternative feedstocks for biodiesel production, the evaluation of pumpkin seed oil was emphasized. Using a modified microwave oven for transesterification, this study optimized the key parameters of reaction temperature, catalyst concentration (KOH), and reaction time using a Box–Behnken design. The results showed a maximum biodiesel yield of 91.5%. Microwave irradiation significantly accelerated the process, reducing reaction times from an hour to minutes. The biodiesel produced met international physicochemical standards, demonstrating the potential of pumpkin seed oil as a sustainable biodiesel source....
Cloud liquid water (CLW) and total precipitable water (TPW) are two important parameters for weather and climate applications. These parameters are typically retrieved at 23.8 GHz and 31.4 GHz. Historically, the CLWand TPW physical retrievals always required the sea surface temperature (SST) and sea surface wind speed (SSW), which are difficult to obtain from conventional measurements. This study employs the multilayer perceptron (MLP) model to retrieve SST and SSW from FY-3F Microwave Radiometer Imager (MWRI) observations. Collocated with ERA5 reanalysis data, the MLP model predicts SST well, with a correlation coefficient of 0.98, the root mean squared error (RMSE) of 1.10, and mean absolute error (MAE) of 0.70 K. For SSW, the correlation coefficient is 0.82, RMSE is 1.80, and MAE is 1.30 m/s, respectively. The SST and SSW parameters derived from MWRI are then used to retrieve CLW and TPW based on the observations from the Microwave Temperature Sounder (MWTS) onboard the FY-3F satellite. The spatial distributions of CLW and TPW derived from this new algorithm agree well with those from ERA5 data. Cloud liquid water (CLW) and total precipitable water (TPW) are crucial parameters for weather and climate applications. The integration of physical and AI-based algorithms enables the retrieval of CLW and TPW directly from FY-3F satellite observations. This approach overcomes the limitations imposed by the need for other data sources, such as ERA5 reanalysis data, and offers distinct advantages in terms of data processing timeliness....
This paper presents a combined theoretical and experimental method for noise suppression in the repetition frequency (fr) locking of erbium-doped ber optical frequency combs (OFCs). This study proposed a novel mathematical model to bridge the noise relationship of fr between the free-running and locked modes, and analyzed this relationship from two perspectives: the additional phase noise and the frequency stability. In addition, to integrate theoretical modeling with experimental validation, this study designed fr locking strategy that uses a phase-locked loop (PLL) with PFD + PIID (a phase frequency detector and a proportional, rst-order integer, second-order integer, rstorder dierential controller). Under synchronization of the fr with a microwave reference (REF), this study achieved OFC additional frequency stabilities of 2.81 × 1015@1 s and 8.08 × 1019@10,000 s at 200 MHz fundamental frequency locking and 4.25 × 1016@1 s and 1.91 × 1019@10,000 s at 1200 MHz harmonic locking. The simulated and experimental results are in good agreement, conrming the consistency of the theoretical model and experiment. This work provides a reliable theoretical model that can be used to predict stability for OFC locking and signicantly improves the additional frequency stability of OFCs....
In this study, a model of a double-quantum-dot system driven by two-mode microwave photons is presented. The quantum master equation is derived from the system’s Hamiltonians, and the expression for the steady-state current is obtained. Electronic tunneling properties are then analyzed. The results revealed that different twomode quantum microwave photons have varying effects on the tunneling current within the double-quantum-dot system, with a steplike current trend emerging. The tunneling current showed pronounced negative differential conductance for both coherent and squeezed microwave photons. Furthermore, the tunneling current was significantly influenced by changing the squeezing coefficient and phase. The asymmetric evolution of the tunneling current under varying bias voltages also depends on the asymmetry in system parameters. These findings are crucial for manipulating the transport properties of double-quantum-dot systems in nanostructured devices....
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