Optics Express

Based on the theory of the microwave photonic filter (MPF), to our knowledge, a novel fiber Bragg grating (FBG) wavelength demodulation method based on time-domain detection is proposed. The method uses VNA (vector network analyzer) to measure the S21 parameter of the sensor system, and converts them to the time-domain through inverse discrete Fourier transform (IDFT), The wavelength demodulation and positioning of FBG can be realized by measuring the amplitude and position of the time-domain peak. In order to improve the number of FBG multiplexes, a method is proposed to eliminate the effect of spectrum overlap by normalization in the case of two FBGs and three FBGs...

We describe a new multiplexing technique and its application to demultiplexing in the time domain by using higher-order Hermite-Gaussian (HG) pulses, which are solutions of the Schrödinger equation. We call this technique eigen-function division multiplexing (EDM). This method enables us to further increase the total transmission capacity by superimposing many different HG pulses in the same time slot. This technique is different from a conventional optical time domain multiplexing (OTDM) technique using interleaving, where one pulse exists only in one time slot...

Simultaneous distance measurements on two or more optical wavelengths enable dispersion-based correction of deviations that result from insufficient knowledge of the refractive index along the signal propagation path. We demonstrate a supercontinuum-based approach for highly accurate distance measurements suitable for such an inline refractivity compensation. The distance is estimated from the phase delay observations on the intermode beats. We use a supercontinuum (SC) coherently broadened from a 780 nm frequency comb and spanning the spectral range of 570-970 nm...

Ghost imaging (GI) requires each echo from the object being correctly matched with the corresponding illuminiation pattern. We proposed a way for such matching with no physical synchronization towards bistatic configuration. The illumination is dually encoded in spatial and time domain. With aperiodic waveform and progressive correlation, the echoes can be correctly located and images can be obtained. In the experiments, our scheme is verified under different levels of signal to noise ratios, as well as different intensity of crosstalk...

The space time frequency transfer plays a crucial role in applications such as space optical clock networks, navigation, satellite ranging, and space quantum communication. Here, we propose a high-precision space time frequency transfer and time synchronization scheme based on a simple intensity modulation/direct detection (IM/DD) laser communication system, which occupies a communication bandwidth of approximately 0.2%. Furthermore, utilizing an optical-frequency comb time frequency transfer system as an out-of-loop reference, experimental verification was conducted on a 113 km horizontal atmospheric link, with a long-term stability approximately 8...

Organic photodetectors (OPDs) have attracted increasing attention in the future wearable sensing and real-time health monitoring, due to their intrinsic features including the mechanical flexibility, low-cost processing and cooling-free operations; while their performances are lagging as the results of inferior carrier mobility and small exciton diffusion coefficient of organic molecules. Graphene exhibits the great photoresponse with wide spectral bandwidth and high response speed. However, weak light absorption and the absence of a gain mechanism have limited its photoresponsivity...

A method based on deflectometry to measure the refractive index distribution of radial gradient refractive index (GRIN) lens is proposed in this paper. The method establishes the relationship between the refractive index distribution and the direction of light ray by deriving the propagation equation of light in a non-uniform medium. By measuring the deflection angle using the principle of deflectometry and the assumption of central refraction, the refractive index distribution of the radial GRIN lens is determined...

Virtual image lenses play essential roles in various optical devices and applications, including vision correction, photography, and scientific instruments. Here, we introduce an approach for creating virtual image Luneburg lenses (LL) on graphene. Remarkably, the graphene plasmonic lens (GPL) exhibits electrically tunable virtual focusing capabilities. The design principle of the tunability is based on the nonlinear relationship between surface plasmon polariton (SPP) wave mode index and chemical potential of graphene...

Silicon avalanche photodiode (APD) single-photon detectors in space are continuously affected by radiation, which gradually degrades their dark count performance. From August 2016 to June 2023, we conducted approximately seven years (2507 days) of in-orbit monitoring of the dark count performance of APD single-photon detectors on the Micius Quantum Science Experimental Satellite. The results showed that due to radiation effects, the dark count growth rate was approximately 6.79 cps/day @ -24 °C and 0.37 cps/day @ -55 °C, with a significant suppression effect on radiation-induced dark counts at lower operating temperature...

Virtual reality devices featuring diffractive grating components have emerged as hotspots in the field of near-to-eye displays. The core aim of our work is to streamline the intricacies involved in devising the highly efficient slanted waveguide grating using the deep-learning-driven inverse design technique. We propose and establish a tandem neural network (TNN) comprising a generative flow-based invertible neural network and a fully connected neural network. The proposed TNN can automatically optimize the coupling efficiencies of the proposed grating at multi-wavelengths, including red, green, and blue beams at incident angles in the range of 0°-15°...

According to the principle of synthetic aperture ladar, high-resolution imaging can be achieved if the relative motion exists between the target and the ladar. The imaging system has characteristics including a large field of view, narrow-band laser signals applied, and easy engineering implementation. The complex image reconstruction and the synthetic aperture laser imaging method for moving targets based on the spatial light modulator and the direct-detection detector array are proposed. The far-field simulations and the near-field experiments for the stop-and-go target and the continuous-moving target were carried out...

The physics of nonlinear optical materials is incredibly versatile, with the design of novel materials and structures offering numerous degrees of freedom. Nevertheless, weak inherent nonlinearity of conventional optical materials continues to hinder the progress of a number of important applications. In this study, we delve into the realm of broadband enhancement of nonlinearity within one-dimensional (1d) plasmonic metamaterials, exploring its intricate connection with nonlocality. Specifically, we introduce a phenomenological framework for quantifying the effective third-order nonlinear susceptibility of 1d multiphase plasmonic nanostructures, utilizing heavily doped semiconductors, and subsequently applying this approach using realistic material parameters...

Magnetorheological finishing (MRF) technology is characterized by its high convergence rate and minimal subsurface damage as advantages. However, the non-Gaussian type tool influence function (TIF) it generates may cause mid-frequency errors and oriented surface texture issues. Magnetorheological precession finishing (MRPF) technology capable of generating Gaussian-like removal functions, lacks a clearly defined removal function model. This study acquired polishing spots in tilted polishing, discrete precession, and continuous precession modes via fixed-point polishing experiments...

Diffractive optical element is advantageous for miniaturization, arraying and integration of optical systems. They have been widely used in beam shaping, diffractive imaging, generating beam arrays, spectral optimization and other aspects. Currently, the vast majority of diffractive optics are not tunable. This limits the applicability and functionality of these devices. Here we report a tunable diffractive optical element controlled by light in the visible band. The diffractive optical element consists of a square gold microarray deposited on a deformable substrate...

We demonstrate high-output-power and high-efficiency operation of 1.3-µm-wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs). By introducing a metal reflector and adjusting the phase of the reflected light via optimization of the thickness of the p-InP cladding layer, we successfully achieve an output power of approximately 400 mW with the slope efficiency of 0.4 W/A and the wall-plug efficiency of 20% under CW conditions. In addition, this PCSEL exhibits a narrow circular beam with a divergence angle below 1...

Two-photon polymerization (TPP) is an advanced 3D fabrication technique capable of creating features with submicron precision. A primary challenge in TPP lies in the facile and accurate characterization of fabrication quality, particularly for structures possessing complex internal features. In this study, we introduce an automated brightfield layerwise evaluation technique that enables a simple-to-implement approach for in situ monitoring and quality assessment of TPP-fabricated structures. Our approach relies on sequentially acquired brightfield images during the TPP writing process and using background subtraction and image processing to extract layered spatial features...

A diffuse optical tomography system with chaotic laser is proposed for the three-dimensional optical phantom. The high signal-to-noise ratio is beneficial to improve the spatial resolution of diffuse optical tomography. It is essential to drive the chaotic laser as the incident light into the optical phantom. The transmitted light emitted from phantom as the detection light and a part of the incident light as the reference light to carry out cross-correlation analysis. The high-density source-detector configuration in parallel plate structure is designed for detecting targets in the phantom...

Multi-band terahertz (THz) absorbers have recently gained attention due to their favorable application prospects in communication, imaging, detection, and other fields. However, many multi-band THz absorbers are tuned by a single method, which limits their tuning effect. To address this issue, we propose a multi-band THz absorber that can be co-modulated by thermal and electrical methods. Our proposed absorber uses vanadium dioxide (VO2 ) to achieve this co-modulation. When VO2 is insulating, the frequency of the absorbing peaks originating from the lateral Fabry-Pérot resonance mode can be changed by adjusting the VO2 width...

Quantitative phase contrast microscopy (QPCM) can realize high-quality imaging of sub-organelles inside live cells without fluorescence labeling, yet it requires at least three phase-shifted intensity images. Herein, we combine a novel convolutional neural network with QPCM to quantitatively obtain the phase distribution of a sample by only using two phase-shifted intensity images. Furthermore, we upgraded the QPCM setup by using a phase-type spatial light modulator (SLM) to record two phase-shifted intensity images in one shot, allowing for real-time quantitative phase imaging of moving samples or dynamic processes...

In this paper, we introduce a new type of controllable auto-focusing vortex beam array named annular quasi-Airy vortex beam array (QAVBA), which can reduce the crosstalk among different orbital angular momentum (OAM) modes of optical vortex. The effects of initial beam parameters of annular QAVBA and propagation conditions on the OAM mode propagation performance are investigated. The results indicate that the topological angle θ, the topological charge m, and the decay parameter α could manipulate the auto-focusing characteristics of annular QAVBA and regulate the crosstalk of OAM modes...