Applied optics最新文献

A photonic method for generating complicated microwave waveforms is proposed and experimentally demonstrated. Assisted by two easy-to-operate time-domain operations of differentiation and odd-order components elimination, two independent sets of frequency components, including odd-order and even-order components, can be conveniently obtained. Some complicated waveforms, such as a full-duty-cycle sinc waveform with varying sidelobes, a full-duty-cycle sinc² waveform with varying sidelobes, and a dark parabolic (or bright parabolic) waveform, are flexibly synthesized, which are validated by the theoretical analysis, simulations, and experimental demonstrations. Benefiting from the convenience of time-domain processing, the proposed scheme is easily implemented and offers relatively high precision in microwave waveform generation.

The aperture-divided optical system is a significant imaging technique that enables real-time imaging with multiple channels. However, an increasing demand for multi-channel optics presents a substantial challenge for current refractive optical systems with complex structures and a narrow wavelength band. In this paper, we propose a modified design method that combines the strengths of an off-axis reflective system and an aperture-divided optical system to achieve high levels of integration and simplified structure. A design concept of integrated optical layout and local detail optimization is proposed here. We present an analysis showing how local sub-channels' distribution affects the imaging characteristics. An integrated optical system, including a relay group constructed based on the Wassermann-Wolf differential equations and a telescope objective, is built first. The sub-aperture system utilizing distinct local surface regions is gradually established with a close connection. To demonstrate the feasibility and efficiency of the method, an integrated system with an F-number of 1.6 and an entrance pupil of 130 mm is presented with its design strategies. The aperture-divided system illustrates well imaging performance close to the diffraction limit in 3-5 µm at 33 lp/mm. The design strategy we have proposed not only has a broad application to multi-channel imaging but also provides valuable insight into to our knowledge, the new imaging technology.

This study presents the wavelength conversion facilitated by the interplay between a co-propagating triangular signal and a Gaussian pump by analyzing the nonlinear phase shift in highly nonlinear silicon-core rib waveguides, marking the first report of its kind, to our knowledge. The interaction between the pump and the signal enables possible amplification driven by cross-phase modulation and stimulated Raman scattering. To substantiate these findings, four waveguides are designed and optimized. Numerical solutions of the coupled amplitude equations result in a Raman gain of ∼18-22dB within a compact size, achieving performance comparable to or exceeding previously reported results. As predicted by the analytical model, spectral intensity doublets emerge, with their wavelength shifts and peak power ratios showing strong dependence on pump power and signal pulse width. Higher pump power causes larger wavelength shifts, while broader signal pulses expedite spectral splitting. The observed red-shift ranges from 65 to 81 nm, while the blue-shift spans 54 to 64 nm. Additionally, TPA and FCA play a crucial role in shaping the spectral doublet, particularly in highly nonlinear silicon waveguides. This work represents the first systematic exploration of wavelength conversion through pump-signal interaction in silicon rib waveguides, incorporating carrier lifetime effects and offering valuable insights into controlling spectral doublet generation for integrated photonic applications.

This study investigates a fast-switching photodetector based on heterostructure TiO₂/SnO₂ nanowire (NW), synthesized by using the GLAD-assisted e-beam evaporation technique. For performance comparison, a heterostructure TiO₂/SnO₂ thin-film (TF) device was also fabricated. Both the NW and TF heterostructure devices were synthesized on n-type silicon (n-Si) substrates, with gold (Au) as the top contact. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and chemical mapping were employed to conduct morphological and elemental analysis. Characterization of structural properties was accomplished by using X-ray diffraction (XRD). Optical measurements indicated that with two broad visible absorption peaks at 430 nm and 673 nm, the heterostructure TiO₂/SnO₂ NW sample demonstrated a 2.18-fold enhancement in ultraviolet (UV) absorption and a 1.22-fold enhancement in visible light absorption when compared to its thin-film counterpart. The heterostructure TiO₂/SnO₂ NW device demonstrated a ∼10-fold photosensitivity enhancement in comparison to the TF device. In addition, it obtained a higher detectivity of 1.193×10¹⁰ Jones and a lower noise equivalent power (NEP) of 1.114×10^-11W. Fast switching behavior was demonstrated by the current-time (I-T) characteristics, with a rise time of 0.23 s and a fall time of 0.31 s. This confirms the device's potential for high-performance photodetection applications.

A holographic display is a promising visual technology that provides intuitive and natural image observation. Particularly, a binary phase-only holographic display has the capability of high-speed switching, enabling the realization of a high-frame-rate holographic display. However, the reconstructed image quality is extremely low due to noise caused by the lack of amplitude information, hologram binarization, and speckle. To solve the problem of the image quality, temporal multiplexing of multiple reconstructed images due to the persistence of vision can be used. In this paper, an intensity compensation method based on temporal multiplexing is proposed, which efficiently reduces the noise in the reconstructed images. To achieve this reduction, multiple holograms are generated according to the residuals between the reconstructed images and the desired object. Numerical simulations and optical experiments confirm that the accumulated image quality efficiently improves by the proposed method.

To enhance the recovery performance of underwater image clarification algorithms based on polarization technology in scattering underwater environments, a multi-wavelength polarization constrained underwater image clarification method is proposed. This method takes into account the varying polarization characteristics across different wavelengths. The image is processed by separating it into three RGB color channels (red, green, and blue). Initially, the Stokes vectors of the backscattered light for each of the three channels are individually analyzed. From this analysis, a pair of orthogonally polarized images with identical backscatter intensity is derived for each color channel. Next, the histograms of these orthogonally polarized image pairs are stretched, ensuring that the polarization relationship between them is preserved. Finally, polarization differencing is applied to the orthogonally polarized images in each channel, which are then converted into grayscale images to achieve improved image clarity. The effectiveness of the proposed method has been validated through a series of polarization de-scattering experiments conducted in water with varying turbidity levels. These experiments demonstrate the method's superior performance in image restoration, particularly in scenarios with high polarization characteristics when compared to other similar approaches.

This paper discusses the application of the photomodulation method based on thin holographic films and the laser speckle correlation method for remote optical vibration monitoring of various parts of liquid pumping systems. The paper considers the microstructure of the surface relief of the holographic films used for the photomodulation method and the optical diffraction phenomenon of multi-component light on a refractive cross-grating. The results of monitoring the vibration of the pipeline, pillar, and pump housing of the water pumping system and the pipeline of the technical oil pumping system in various operation modes using the proposed methods are given. The results of experiments aimed at determining the resolution of the oscillation frequency for the photomodulation method are also presented. The achieved maximum difference in the readings of both methods for determining the first harmonic of oscillations was 0.103 Hz. The results obtained by the photomodulation method demonstrated high convergence with similar results obtained by the laser speckle correlation method. A conclusion is made about the possibility of applying the photomodulation method based on thin holographic films as a vibration visualization technique for technological equipment monitoring.

In the frequency range of 90-110 GHz, we show a dynamically tunable terahertz directional coupler based on the phase transition properties of vanadium dioxide, allowing for a continuous coupling ration adjustment from -3 to -5dB. To validate the concept experimentally, we created two metallic-dielectric hybrid counterparts that mimic the coupling effects of the VO₂ film in both its metallic (shielded branches) and extremely insulating (fully conductive branches) phase states. For -3 and -5dB coupler configurations, respectively, simulation results in the 90-110 GHz range show a coupling degree of -2.1 (0.7 dB imbalance) and -3.8dB (1.0 dB imbalance). The mode coupling dynamics in terahertz directional couplers were investigated through the branch-line waveguide theory, revealing the underlying transmission mechanism. The experimental results for the coupler's S-parameters were in relatively good agreement with the theoretical predictions. The switchable directional coupler proposed in this paper has applications in dynamic terahertz power allocation, terahertz imaging, and electromagnetic stealth.

Practical defects in parallel-plate interferometers reduce instrument finesse, compromising spectral resolution, and can distort measured spectral lineshapes. The effect of imperfect mirror parallelism is usually described by a single broadened instrument response function and diminished finesse value. However, such a characterization fails to capture spatial field effects from dispersive interferometers, such as the virtually imaged phased array (VIPA). To explore these effects, a model is developed to compute fringe patterns formed by VIPAs with nonparallel mirrors and imaged along planes at specifiable distances from the paired imaging lens. Following validation against an established VIPA model and standard etalon theory with ideal parallel-plate configurations, the new model is used to examine the effects of mirror nonparallelism. While it captures the general loss of instrument performance in spectral resolution and finesse, it also reveals fringe lineshape distortions and nonuniformity of resolution and intensity scaling across the measurement field. Furthermore, when the measurement plane is decoupled from the back focal plane of the lens, there is an evolution of field behavior, and near-ideal instrument performance is recovered within a limited region of the measurement field. Results compare favorably to Zemax simulations and experimental data. This work identifies and characterizes nonideal optical behavior arising from practical defects in mirror parallelism, thereby enabling recognition of measurement artifacts, and imparts remedial measures for selective recovery of instrument finesse.

Accurate estimation of the optical feedback coupling factor C is essential for the reliable operation of laser-based self-mixing interferometry (SMI) sensors, particularly in variable feedback conditions. In this work, we present a novel deep learning-based method, to the best of our knowledge, to estimate the time-varying C factor from SMI signals under strong, moderate, and weak feedback conditions. The proposed approach leverages a transformation of one-dimensional (1D) SMI signals into two-dimensional (2D) image representations, allowing convolutional neural networks to extract context-rich features that enhance estimation performance. Unlike traditional image-processing tasks, this method formulates the problem as a signal-to-image translation, tailored for sensor parameter inference. Experimental results demonstrate that this 2D-based approach outperforms state-of-the-art recurrent neural network models, including LSTM and transformer architectures, particularly in terms of robustness to changes in sampling frequency, displacement amplitude, and feedback regime. The methodology is generic and applicable to a wide range of sensor signal analysis tasks. To support reproducibility and practical adoption, we provide a publicly available implementation of our approach.