Renpu Li

We propose a rotation-controlled nonreciprocal quantum cooling scheme based on a Brillouin-assisted optomechanical system comprising a rotating whispering-gallery-mode(WGM) resonator, a backward Brillouin acoustic mode, and two mechanical oscillators. By incorporating the rotation-induced Fizeau frequency shift and backward stimulated Brillouin scattering(BSBS), we establish a linearized optomechanical model for controlling the cooling of multiple mechanical modes. The rotation-induced effective optical detuning modifies the optomechanical coupling strength and enables directional control of the cooling conditions. The cooling performance can be further regulated by the driving strength and Brillouin coupling, while remaining robust over a broad range of initial thermal occupations. This scheme provides a controllable platform for nonreciprocal quantum cooling of multiple mechanical modes.

Subject of study . Autocollimation measurement systems are the main means to realize precision angle measurement, but multifaceted error sources limit the further improvement of autocollimator angle measurement accuracy. The purpose of the work. This paper focuses on a kind of reflection noise induced from the non-working optical structure surface inside the autocollimator. This noise source can lead to errors in the detection of the target image by the image sensor. Method. Combined with the principle of Hough transform image recognition, we propose to utilize the Retinex theory to compensate the reflection noise inside the autocollimator. Main results. It is experimentally verified that this compensation algorithm can effectively suppress the influence of noise on imaging detection, and the measurement accuracy of the autocollimator around the X -axis and Y -axis can be improved from 4.29 ^{′ ′} and 3.87 ^{′ ′} to 3.59 ^{′ ′} and 3.15 ^{′ ′} . The system measurement stability performance is also improved, about 11.99% and 15.75% in the X -axis and Y -axis directions, as well. Practical significance. Therefore, this algorithmic compensation method can effectively enhance the measurement performance of the autocollimator.

Subject of study. The design concept of fiber metal ion detectors and wind-blast pressure in water flow is studied. Purpose of the work. The purpose is to sensitize a fiber sensor in relation to the concentration of metal ions in a fluid and pressure due to water flow. Method. Through theoretical analyses and computer and physical simulations, the sensitivity of a sensor consisting of a metal ion concentration meter, transitive D-shaped fiber module, and fluid flow pressure meter based on a fiber grating is investigated. Main results. As a result of metal ion concentration measurement experiments, it has been proved that the device reaches a response sensitivity of metal ion concentration of the order of 10 ⁵ nm⋅ml/mol. In addition, the sensitivity of the metal ion concentration response is ensured to be of the order of 10 ⁵ nm⋅ml/mol, and the device is experimentally investigated for sensing characteristics of axial strain and bending deformation. Practical significance. The design concept and calculation methods of a metal ion concentration and fluid flow pressure stress sensor have been developed; the sensor can be used for ecological monitoring of natural water environments.

The simultaneous ground-state cooling and the quantum synchronization of multiple mechanical oscillators are very important in the study of the quantum coherence of the optomechanical system with multiple mechanical modes. In this paper, we propose a scheme for investigating the simultaneous ground-state cooling and the quantum synchronization of two mechanical oscillators based on an optomechanical system via backward stimulated Brillouin scattering. A photon-phonon interaction via the backward stimulated Brillouin scattering process is introduced in this scheme, which is beneficial for cooling the optomechanical system. It is found that simultaneous ground-state cooling and quantum synchronization of two mechanical oscillators can be achieved when a suitable photon-phonon coupling via the backward stimulated Brillouin scattering process is chosen. Quantum synchronization is enhanced with the help of the photon-phonon coupling via the backward stimulated Brillouin scattering process. In addition, the relation between simultaneous ground-state cooling and quantum synchronization is discussed. It turns out that the appearance of simultaneous ground-state cooling is accompanied by quantum synchronization, but simultaneous ground-state cooling may not be realized when quantum synchronization is achieved. Our scheme paves a new way for the control of the quantum properties of the mechanical oscillators based on optomechanical system.

This paper proposes a terahertz absorber based on a U-shaped metal patch that exhibits both narrowband and wideband absorption characteristics. The absorber comprises a metal–medium–metal structure, with a U-shaped metal patch as the top layer, a lossy medium as the middle layer, and a fully covered metal base plate at the bottom. There are two narrowband absorption peaks at 1.368 THz and 2.648 THz and a broadband absorption band from approximately 4 to 5 THz. The formation of resonance frequencies was elucidated by analyzing the current and electric field distributions at the resonance frequency. The resonant mechanism of the U-shaped patterned structure was clarified using equivalent circuit models to evaluate the resonant frequencies of different absorption peaks. Subsequently, the absorber’s characteristics were examined under varying structural parameters. Dual-function terahertz absorbers are applicable in terahertz communications, imaging, and various other fields.

This paper proposes a triple-frequency terahertz amplitude modulator that utilizes an I-shaped strip and four U-shaped metal patches within a common metal-substrate configuration. The top metal layer consists of an I-shaped strip and four U-shaped metal patches, while the bottom substrate layer is made of polyimide. Amplitude modulation is achieved through adjusting the plasma frequency of the high-electron-mobility transistors, resulting in a modulation depth of nearly 93% at resonance frequencies of 0.26 and 0.49 THz. At 0.6 THz, the modulation depth reaches 65%, demonstrating excellent performance. Resonance frequencies are determined by electric field and surface current distribution. The triple-frequency terahertz amplitude modulator is applicable in various fields, including terahertz communications and imaging.