Search Results (49)

We demonstrate a sideband Pound–Drever–Hall (SPDH) locking scheme that enables the simultaneous narrow-linewidth stabilization and continuous broadband frequency tuning of a laser referenced to an ultra-stable cavity. The method employs dual-frequency modulation applied to a fiber electro-optic modulator, where high-frequency modulation generates tunable sidebands and low-frequency modulation provides the error signal. We experimentally stabilize a 922 nm seed laser to the cavity and achieve a laser linewidth of 85(1) kHz with frequency noise suppression of up to 25 dB. The residual amplitude modulation (RAM) remains below 0.08% across the full tuning range. In addition, we demonstrate a continuous frequency tuning range of 1.4 GHz for a frequency-doubled 461 nm laser, with scan rates up to 317 MHz/s, while preserving stable locking to the cavity. This approach avoids complex waveform generation and provides a simple and robust solution for broadband laser frequency control. Full article

In this article, a compact wideband three-slot filtering antenna is proposed. The antenna consists of a U-shaped driven slot, a folded resonant slot, and a linear resonant slot. A microstrip feedline with a shorting via is employed to excite the antenna. Mixed electric and magnetic couplings enable the driven slot to couple to the two resonant slots. Three resonant frequencies lie within the passband, resulting in wideband operation. The lowest resonant frequency is determined by the folded resonant slot, while the highest resonant frequency is determined by the linear resonant slot. The center resonant frequency is influenced by the combined effects of the U-shaped driven slot, the folded resonant slot, and the linear resonant slot. A low-frequency radiation null at 1.68 GHz and a high-frequency radiation null at 3.19 GHz are generated. These two radiation nulls enable the proposed antenna to achieve excellent filtering performance. A prototype was fabricated and measured. The measured results are in good agreement with the simulated ones. The measurements show that the proposed three-slot filtering antenna exhibits a relative impedance bandwidth of 39.1%. The out-of-band suppression levels reach 12.5 dB and 14.8 dB in the lower and upper sidebands, respectively. The proposed three-slot filtering antenna is suitable for applications in wireless communication systems. Full article

This paper proposes an optoelectronic oscillator (OEO)-based scheme for generating frequency-doubled binary phase-coded microwave pulses. The architecture employs a cascaded dual-polarization quadrature phase shift keying modulator (DP-QPSK) and a polarization modulator (PolM) to generate carrier-suppressed ±2nd-order sidebands and an orthogonally polarized optical carrier. By applying opposite phase modulation to the two polarization components and subsequently converting them into the same polarization state using a polarization controller (PC) and a polarizer, frequency-doubled phase-coded microwave pulses are obtained after photodetection. The operating principle of the scheme is theoretically analyzed and experimentally validated. A 5 GHz OEO signal is successfully converted into a 10 GHz phase-coded microwave pulse without the use of an external electronic frequency multiplier or an additional intensity modulator for pulse carving. Binary phase-coded pulses with coding rates of 0.1 Gb/s and 0.25 Gb/s are experimentally demonstrated. The measured temporal waveforms, recovered phase information, and autocorrelation results agree well with theoretical predictions. The proposed scheme provides a structurally simple and frequency-doubling solution for OEO-based phase-coded microwave pulse generation with reduced system complexity. Full article

Noise elimination in current signals of three-phase induction motors, considered as energy systems for electromechanical conversion, is a critical preprocessing step for reliable condition monitoring and fault diagnosis. However, conventional wavelet-based denoising approaches often treat noise suppression as a generic filtering task, which may distort diagnostically relevant spectral components and inter-phase relationships. To address this limitation, this paper presents a physically constrained denoising framework that integrates the Clarke transformation with dyadic wavelet analysis to enable diagnostic-safe noise attenuation. The proposed method explicitly preserves frequency bands associated with supply harmonics, mechanical phenomena, and fault-related sidebands, while enforcing inter-phase coherence and zero-sequence stability in the Clarke domain. Wavelet parameters are selected through a diagnostic-oriented multi-criteria framework that jointly balances disturbance attenuation, harmonic fidelity, coherence retention, zero-sequence stability, and time-domain waveform integrity. Experimental validation using real three-phase induction motor current measurements under steady-state conditions shows that the proposed framework achieves noise reduction ratios of approximately 8–10 dB, while preserving the amplitudes of the main harmonic components with deviations below ${10}^{-3}$ dB. These results demonstrate that the proposed method provides a robust and physically consistent preprocessing stage for current-based monitoring of three-phase AC machines. Full article

Differential light shift (DLS) is an important error term that limits the atom interferometer’s measurement precision, especially for the case of the electro-optic modulator (EOM)-based scheme, where multiple laser sidebands exist, and their ratios are hard to control synchronously. This article carried out an experimental and theoretical study on this subject. By conducting long-term gravity measurement, we find that the gravity exhibits drifts of about 13.13 μGal, and is strongly correlated to the Raman laser’s sidebands. A model of the DLS-induced gravity error is established and a DLS compensation method is proposed to suppress the gravity drift to 2.54 μGal. Besides the compensation method, we propose a Dual-Sideband Ratio Locking scheme to more robustly eliminate the gravity measurement drift. By feeding back to both the EOM microwave power and the tapered amplifier’s temperature, this method locks both the ±1 order sideband to a stability level of ${10}^{-5}$, which corresponds to a gravity error of less than 0.1 μGal. Long-term gravity measurement is carried out after the locking method, showing a long-term stability of 1.6 μGal. The proposed methods will benefit the suppression of the DLS effect for high-precision atom interference measurement. Full article

We present a time-dependent nonperturbative theory of the reconstruction of attosecond beating by interference of multiphoton transitions (RABBIT) for photoelectron emission from hydrogen atoms in the transverse direction relative to the laser polarization axis. Extending our recent semiclassical strong-field approximation (SFA) model developed for parallel emission, we deduce analytical expressions for the transition amplitudes and demonstrate that the photoelectron probability distribution can be factorized into interhalf- and intrahalfcycle interference contributions, the latter modulating the intercycle pattern responsible for sideband formation. We identify the intrahalfcycle interference arising from trajectories released within the same half cycle as the mechanism governing attosecond phase delays in the perpendicular geometry. Our results reveal the suppression of even-order sidebands due to destructive interhalfcycle interference, leading to a characteristic spacing between adjacent peaks that doubles the standard spacing observed along the polarization axis. Comparisons with numerical calculations of the SFA and the ab initio solution of the time-dependent Schrödinger equation confirm the accuracy of the semiclassical description. This work provides a unified framework for understanding quantum interferences in attosecond chronoscopy, bridging the cases of parallel and perpendicular electron emission in RABBIT-like protocols. Full article

This work proposes a photonics-aided W-band integrated sensing and communication (ISAC) system using photonics-aided frequency multiplication to suppress phase noise. Conventional dual-laser architectures suffer from phase noise accumulation, degrading both communication reliability and sensing resolution. To address this, we integrate photonics-aided frequency multiplication with orthogonal frequency-division multiplexing (OFDM), enabling a unified signal structure that simultaneously encodes communication data and radar waveforms without redundant resource allocation. Theoretical analysis reveals phase noise cancellation through coherent beating of symmetrically filtered sidebands in the photodetector (PD). Results demonstrate concurrent delivery of probability shaping (PS)-256QAM OFDM signals with a symbol error rate below 4.2 × 10⁻² and radar sensing with a 13.6 dB peak-to-sidelobe ratio (PSLR). Under a 1 MHz laser linewidth, the system achieves a 3.2 dB PSLR improvement over conventional methods, validating its potential for high-performance ISAC in beyond-5G networks. Full article

Stimulated Brillouin scattering (SBS) suppression and phase demodulation are two fundamental issues in remote interferometric fiber sensing systems. A method is proposed for achieving simultaneous SBS suppression and phase-generated carrier (PGC) demodulation in remote interferometric fiber sensing systems, with only the use of an electro-optic phase modulator (PM). A single-frequency laser is phase-modulated by a PM to generate multi-sideband light, which can suppress SBS in long-haul fibers and generate PGC combined with the optical fiber interferometer. Then, the phase signal of the optical fiber interferometer can be demodulated by the PGC demodulation method. A detailed theoretical analysis and the experimental results are presented to confirm the feasibility of the method. The results show that the proposed method can achieve high-performance PGC demodulation with much higher bandwidth and larger dynamic range than the conventional method. Meanwhile, the SBS and its induced phase noise can be suppressed effectively. This work presents a simple setup for SBS suppression and PGC demodulation in a remote interferometric fiber sensing system. The proposed method shows great potential for application in remote and large-scale interferometric fiber sensing systems. Full article

Interferometric signals in space-borne Gravitational Wave Detectors are measured by digital phasemeters. The phasemeter processes signals generated by multiple interferometers, with its primary function being micro-radian level phase measurements. The Science Interferometer is responsible for inter-spacecraft measurements, including relative ranging, absolute ranging, laser communication, and clock noise transfer. Since the scientific interferometer incorporates multiple functions and various signals are simultaneously coupled into the heterodyne signal, establishing a suitable evaluation environment is a crucial foundation for achieving micro-radian level phase measurement during ground testing and verification. This paper evaluates the phase measurement noise of the science interferometer by simulating the heterodyne signal and establishing a test environment. The experimental results show that when the simulated heterodyne signal contains the main beat-note, upper and lower sideband beat-notes, and PRN modulation simultaneously, the phase measurement noise of the main beat-note, upper and lower sideband beat-notes all reach 2π μrad/Hz^1/2@(0.1 mHz–1 Hz), meeting the requirements of the space gravitational wave detection mission. An experimental verification platform and performance reference benchmark have been established for subsequent research on the impact of specific noise on phase measurement performance and noise suppression methods. Full article

Space-borne gravitational wave (GW) detection is poised to significantly advance the frontiers of astrophysics, gravitation, and cosmology, which might make it possible to measure the fundamental symmetries of space-time. A critical component in GW detection is the employment of ultra-stable oscillators (USOs) on each satellite, serving as precision timing references to drive analog-to-digital converters (ADCs) for digital sampling of GW signals. Achieving the required sensitivity in GW detection hinges on highly accurate clock timing. However, the challenges posed by ADC aperture jitter and sampling clock jitter cannot be overlooked. They disrupt sampling timing, introduce clock noise, and distort the digitized signal, thus limiting the effectiveness of GW detection in space. To overcome this problem, researchers have developed pilot tone correction techniques and proposed innovative clock noise calibrated time-delay interferometry (TDI), optical comb TDI techniques, and sideband arm locking techniques that effectively suppress the effects of clock noise. This study provides an in-depth and comprehensive summary of the current status of clock noise and its suppression techniques in the space-borne GW detection. Through a systematic review and analysis, the aim is to provide theoretical and experimental technical support and optimization suggestions for the implementation of China’s space-borne GW detection mission. Full article

Conventional space vector pulse width modulation (CSVPWM) with the fixed switching frequency generates significant sideband harmonics in the three-phase voltage. Discrete random switching frequency SVPWM (DRSF-SVPWM) methods have been widely applied in motor control systems for the suppression of tone harmonic energy. To further reduce the amplitude of the high-frequency harmonic with a limited switching frequency variation range, this paper proposes a time-division subbands beta distribution random SVPWM (TSBDR-SVPWM) method. The overall frequency band of the switching frequency is equally divided into N subbands, and each fundamental cycle of the line voltage is segmented into 2*(N-1) equal time intervals. Additionally, within each time segment, the switching frequency is randomly selected from the corresponding subband and follows the optimal discrete beta distribution. The switching frequency harmonic energy in the line voltage spectrum spreads across multiple frequency subbands and discrete frequency components, thereby forming a more uniform power spectrum of the line voltage. Both simulation and experimental results validate that, compared with CSVPWM, the sideband harmonic amplitude is reduced by more than 8.5 dB across the entire range of speed and torque conditions in the TSBDR-SVPWM. Furthermore, with the same variation range of the switching frequency, the proposed method achieves the lowest switching frequency harmonic amplitude and flattest line voltage spectrum compared with several state-of-the-art random modulation methods. Full article

We investigate steady-state entanglement in a hybrid optomechanical cavity coupled to a Rydberg atomic ensemble confined within a single blockade region. The ensemble behaves as one superatom due to the rigid dipole blockade effect. Through optomechanical coupling, three types of bipartite entanglement emerge among the cavity, the Rydberg superatom, and the movable mirror. As the principal quantum number of the Rydberg atoms increases (leading to reduced atomic decay rates), the direct cavity–mirror coupling entanglement is redistributed into direct cavity–superatom coupling entanglement and indirect superatom–mirror coupling entanglement. Counterintuitively, this redistribution culminates in the complete suppression of two direct coupling entanglements, leaving only the indirect coupling entanglement persistent under resonant Stokes sideband conditions. Systematic parameter tuning reveals entanglement transfer pathways and establishes the preference of the superatom–mirror entanglement for specific principal quantum numbers. Furthermore, we demonstrate the thermal robustness of the surviving entanglement up to experimentally accessible temperatures. These findings advance the understanding of quantum entanglement in hybrid quantum systems and suggest applications in quantum information processing. Full article

This letter presents a scheme for obtaining a microwave photonic frequency multiplier with low phase noise, in which an optoelectronic oscillator (OEO) is integrated with a directly modulated laser (DML)-based injection-locking technique. The system achieves frequency multiplication factors of 10 and 20, producing 10.01009 and 19.99095 GHz microwave signals with high side-mode suppression ratios of 62.0 and 50.2 dB. The measured single-sideband phase noise values are −121.87 and −111.95 dBc/Hz@10 kHz, which are 34.9 and 31.0 dB lower than those of traditional electronic frequency multiplication methods for 1 GHz signals. By utilizing the nonlinear characteristics of the DML, combined with injection locking and the OEO system, this cost-effective scheme reduces the system complexity while enhancing the stability and phase noise performance, offering a highly efficient solution for microwave frequency multiplication. Full article

We report a photonic-assisted method for measuring the frequencies of a multi-tone microwave with high accuracy based on pulse identification. The unknown microwave signal and a linearly chirped signal are modulated to an optical carrier using a dual-polarization Mach–Zehnder modulator. Carrier-suppressed single-sideband modulation avoids the generation of undesired frequency components after photodetection. An electrical bandpass filter with a narrow bandwidth selects the beat signal between the unknown signal and the linearly chirped optical tone. A pulse, generated by the beat signal, can be observed using an oscilloscope (OSC). By identifying the beating pulse position, we can accurately determine the frequency of the unknown signal. The single-tone and multi-tone microwave signal ranges of 6–16 GHz and 26–36 GHz are successfully measured, respectively. The measurement errors for single-tone and multi-tone signals are both less than ±1 MHz. Full article

A filter-free, image-reject, sub-harmonic downconverted RoF link is proposed based on a dual-polarization quadrature phase-shift keying (DP–QPSK) modulator. At the remote antenna unit, the receiving radio frequency signal is applied to the upper QPSK modulator to achieve carrier-suppressed single-sideband (CS–SSB) modulation. The local oscillator (LO) is applied to the lower QPSK modulator, achieving sub-harmonic single-sideband (SH–SSB) modulation. The I/Q mixing is realized by exploiting a two-channel photonic microwave phase shifter, which mainly consists of a modulator, two polarization controllers, and two polarizers. The image interference signal can be rejected when combing the I and Q IF signals through a 90° electrical hybrid. Because the scheme is simple and filter-free, it has a good image-reject capability over a large frequency tunable range. Moreover, due to the special SH-SSB modulation, the modulated signals are immune to the chromatic dispersion-introduced power fading effect. Last, the sub-harmonic downconverter can decrease the frequency requirement of the LO signal. Experimental results show that an image rejection ratio (IRR) greater than 50 dB can be achieved when transmitted through a 25 km single-mode fiber (SMF). Simultaneously, under different RF signals and IF signals, the IRR has no periodic power fading, only small fluctuations. Image rejection capability of the scheme for the 50-MBaud 16-QAM wideband vector signal is also verified and the demodulation of the desired IF signal with a good EVM of less than 5% is realized. Full article