Optics express最新文献

Optical frequency domain reflectometry (OFDR) is a research hotspot in fiber optic sensing technology. This technology can be used for strain, vibration and temperature sensing and has great application prospects in fields such as deformation analysis of aerospace components and bridge monitoring. This article analyzes the reasons for strain demodulation errors under large strains. In response to the problem of reduced similarity between the reference state signal and the measured state signal, a strain measurement method based on the similarity feature of a double-segment Rayleigh scattering spectrum is proposed. Local segments at both ends of the reference state signal are used as new fingerprint spectra, and the offset of the measured state signal similarity spectrum is synchronously searched after extension. At the same time, by revealing the mechanism of strain edge demodulation errors, a strain edge optimization method based on automatic adjustment of the sliding window center position is proposed. A comparison experiment was conducted with traditional methods to verify the effectiveness of the above method. Finally, a sensing unit length of 32.6 mm was achieved with a frequency modulation bandwidth of 5 nm, and the measurement range was from ± 2000 µɛ to ± 2500 µɛ. The measurable spectral offset was increased from 48% to 60%, with a maximum standard deviation of 1.9 µɛ.

High-field THz sources with peak field strengths exceeding MV/cm are essential for nonlinear THz spectroscopy and coherent control of matter on ultrafast time scales. Two-color femtosecond laser plasma sources employing long filamentation have been reported as providing single-cycle, >MV/cm fields, with multi-decade spanning bandwidth and polarization control, making them promising sources for such experiments. In this work, we report the observation of spatiotemporal spreading of the THz pulse when standard off-axis parabolic mirrors are used for collection and focusing of long filament plasma-based THz pulses. This produces a flying focus for THz light, with the axial focal region propagating at a velocity of 1/3 the speed of light. The THz emission is then subsequently spread over a temporal width of ∼10 ps, approximately 100 times the THz pulse duration detected by electro-optic sampling at any single point along the focus. The consequences of this non-ideal focusing are a potential and drastic overestimation of the peak THz electric field based on energy measurements, as well as significant phase noise arising from beam pointing fluctuations. We show that this spatiotemporal spreading can be minimized using a simple axicon lens that perfectly collimates the extended filament source, resulting in improved spatial and temporal focusing of the THz pulse.

Metamaterial absorption technology plays an increasingly important role in military and civilian sectors, serving crucial functions in communication, radar technology, and electromagnetic cloaking. However, traditional metamaterial absorbers are predominantly composed of periodic structures, thus limiting their absorption bandwidth, polarization, and angular flexibility. This study employs disordered structures, utilizing their randomness and diversity, to optimize and enhance the performance of periodic structure metamaterial absorbers. Building upon a well-designed periodic perfect absorption structure, a uniform distribution function is introduced to analyze the effects of positional and size disorder on the absorptive properties of the metamaterial. The mechanisms of the disorder are further investigated through simulation analysis. Subsequently, an innovative approach based on disorder engineering for broadband enhancement of metamaterial absorbers is proposed. Numerical simulation results and experimental validations demonstrate that absorbers constructed using this method significantly broaden the absorption bandwidth while maintaining excellent angular and polarization stability. This research not only offers a new method for the design and performance optimization of metamaterial absorbers but also provides a theoretical foundation for the development of metamaterial self-assembly techniques.

Light induced self-assembly's non-contact and non-invasive nature, along with its versatility and dynamic assembly capabilities, make it particularly well-suited for the self-organization of particles. Previous self-assembly configurations are either in a static equilibrium state or in a dynamic equilibrium state driven by a pushing force. In this study, we introduce a one-dimensional parity-time symmetric (PT-symmetric) multilayer optical system consisting of balanced gain and loss, enabling the generation of a total pulling force on the structure. By conducting molecular dynamics simulations, we achieve the self-organized structure exhibiting pulling force. Furthermore, by reversing the direction of the incident light, we realized pushing force induced binding. The stability of the bound structure is also analyzed using linear stability analysis. Additionally, the light induced self-assembly exhibiting pulling and pushing force is achieved in the one-dimensional multilayer system with unbalanced gain and loss. This work provides an additional degree of freedom in the self-organization of particles.

A deep learning-based phase modulation method for liquid crystal (LC) devices was demonstrated. For LC devices with a single-electrode structure, achieving complex phase distributions is highly challenging. Meanwhile, multi-electrode LC devices, as pixel resolution increases and electrode size decreases, encounter issues of cumbersome modulation steps and reduced modulation accuracy during the phase modulation process. This method uses the concept of field to modulate the phase of the LC device, providing an effective phase modulation scheme. By establishing a deep learning model, it maps the phase retardation distribution of LC devices onto the electric field distribution. This method effectively mitigates the phase modulation issues arising from the fringe field effect, enabling an accurate and precise phase modulation distribution.

Classical and quantum nonreciprocity have important applications in information processing due to their special one-way controllability for physical systems. In this paper we investigate the nonreciprocal transmission and quantum correlation by introducing the dissipative coupling into a linear coupling system consisting of two microdisk resonators. Our research results demonstrate that even in the case of a stationary resonator, dissipative coupling can effectively induce nonreciprocity within the system. Moreover, the degree of nonreciprocity increases with the dissipative coupling strength. Importantly, the phase shift between the dissipative coupling and coherent coupling serves as a critical factor for controlling both nonreciprocal transmision and one-way quantum steering. Consequently, the introduction of dissipative coupling not only enhances the nonreciprocal transmission and nonreciprocal quantum correlation but also enables on-demand manipulation of nonreciprocity. This highlights dissipation as an effective means for manipulating classical and quantum nonreciprocity, thus playing a favorable role in chiral quantum networks.

In the field of topological photonics, one goal is to seek specialized structures with topological protection that can support the stable propagation of light. We have designed a topological configuration featuring a broad channel to sustain edge or interface states. The topological properties are elucidated by analyzing the energy spectrum, eigenstates, and winding numbers. Furthermore, the propagation characteristics of light within our structure are examined through the computation of intensities derived from the coupled mode equations. Our findings reveal that the structure is capable of confining light to the central region, facilitating stable and robust propagation for large-sized beams. Additionally, simulations conducted using commercial software have substantiated the theoretical analysis. Our finding may have significant implications for the modulation of structured light and the development of photonic devices with wide channel capabilities.

This study proposes what we believe to be a novel high-spectral-resolution three-frequency Rayleigh lidar for simultaneously measuring middle atmosphere temperature and wind. The temperature and wind could be retrieved without assuming an external reference temperature, as typical for a traditional Rayleigh Doppler lidar. Adopting a similar idea used in sodium temperature/wind lidar, this system alternatively emits laser pulses at three frequencies. It receives the corresponding Rayleigh backscattered signals filtered by an iodine cell as a frequency discriminator. The three frequencies are optimized based on the spectral characteristics resulting from the convolution of the pulse laser lineshape convolved Rayleigh scattering signal with iodine molecular absorption spectrum. A two-dimensional calibration curve for temperature and wind ratio is then generated from the theoretical calculation of the final convoluted spectra and used to retrieve temperature and wind simultaneously. Simulated with the return signals collected by a current broadband Rayleigh lidar (30-inch telescope and 15 W output laser power), the temperature and wind uncertainties with resolutions of 1 km and 1 hr are estimated to be 0.4 K and 0.35 m/s, respectively, at 30 km and increase to 16.3 K and 8.1 m/s at 70 km.

Generating multiple local oscillator (LO) beams by beam splitters is a crucial aspect of large heterodyne array receivers operating at terahertz (THz) frequencies, with over 100 pixels. Metasurfaces have received considerable attention due to their unique and flexible wavefront modulation capabilities. Nevertheless, the design of beam-splitting metasurfaces faces significant challenges in increasing the number of diffraction beams, improving power efficiency, and achieving greater homogeneity. A SA-GS-based design model for beam-splitting metasurfaces is proposed to achieve multi-beam with high power efficiency and homogeneity. As a proof of concept, we have designed and optimized a 16-beam splitting metasurface from 0.82 THz to 1.6 THz. The objective is to develop large-pixel THz multi-beam heterodyne array receivers and optical systems. The number of beams is also extended to 100-, 144-, 225-, and 289-beam configurations, with power efficiencies of 93.55%, 93.92%, 96.01%, and 96.18% at 0.85 THz, respectively. Moreover, the main beams exhibit excellent homogeneity. This model can be employed in the design of multi-beam metasurfaces with variable deflection angles and intensity ratios. Finally, the multi-beam splitting metasurface is fabricated, and the experimental measurement agrees with the simulation. This work presents an effective approach for the inverse design of beam splitters or holographic imaging devices.

High optical complexity caused by the variability of marine particles poses a major challenge to the development of bio-optical algorithms for particulate organic carbon (POC) concentration retrievals from optical measurements in coastal waters. Here, we developed a particle composition-specific approach to estimate POC off the coastal areas of Guangdong and eastern Hainan Island, China. The ratio of phytoplankton absorption to detritus absorption coefficient aph(443)/ad(443) was used to optically discriminate water types. The samples with aph(443)/ad(443) ≤ 4.9 showed a significant correlation between POC and absorption line height at 676 nm aLH(676) (R2 = 0.75, n = 70, p < 0.01). In contrast, aph-dominant samples with aph(443)/ad(443) > 4.9 had a high covariance between POC and particle scattering coefficient at 675 nm bp(675) (R2 = 0.85, n = 37, p < 0.01). Validation with an independent dataset yielded a small positive bias (R2 = 0.81, APD = 23.10%, RMSE = 29.01 mg m^-3, RPD = 16.31%). The approach provided a better estimation of POC concentration in coastal waters compared with univariate algorithms. A depth-resolved index aLH(676)/bbp(442) was defined as the ratio of absorption line height to particle backscattering coefficient. Using the depth-resolved index instead of aph(443)/ad(443) for optical water type classification can be utilized to represent the vertical variations of POC in 1 m bins, and can complement remote sensing observations to accurately characterize the three-dimensional structure of POC distribution in the oceans.