Optics express最新文献

This paper presents a design of a large imaging plane wide-band zoom optical system, by analyzing the Gaussian principle of the mechanically compensated zoom system, the initial structural parameters are determined. The optimized system has a zoom range of 18-35.5 mm and distortion is less than 2%. It achieves wide-band parfocality (400-850 nm), meeting the usage requirements for 4 K resolution sensors. The system is designed with a spherical lens, and tolerance analysis indicates its suitability for mass production. Experimental results show that the system achieves a center resolution of 174 lp/mm and 104 lp/mm in the visible spectrum and NIR-I band, respectively, which significantly improves the resolution and sensitivity of the endoscope adapters.

We present a wideband rectifying metasurface (RMS) with enhanced system efficiency for wireless power transmission and energy harvesting. The RMS consists of periodic arrays with integrated diodes, with a high input impedance matched with the diodes, thus eliminating the matching network between metasurface (MS) and rectifier. Besides, a unique harmonic feedback network is embedded in each unit cell, rectifying the high-order harmonic generated by the diode repeatedly, improving the total efficiency over a wide bandwidth. The converted DC power is channeled to one single load through the DC-paths formed by the branches of MS and a series of inductors, avoiding additional DC-combination networks. The MS can effectively capture EM energy at an operating band of 2-3.5 GHz, and the simulated radiation-AC efficiency is up to 99% at 2.8 GHz. A finite 8 × 8 array is fabricated and measured. The total conversion efficiency reaches a peak value of 60.5% at 2.7 GHz when the power density is 25dBm/m², and is greater than 40% from 2.3 GHz to 2.9 GHz, exhibiting a wide bandwidth of 23.1% compared with existing state-of-the-art studies. The integrated MS-based RF energy harvester with the advantages of a simple structure is of great significance for wireless power transfer and energy harvesting applications.

In this paper, an optically transparent dual-band microwave chiral metamaterial based on indium tin oxide (ITO) strips is proposed. The rotation angle and length of the three ITO strips on the structural layer can be varied to generate two independent frequency bands in the circular dichroism (CD) spectrum. The maximum CD value is 0.72, and the optical transmittance reaches 64%. The experimental and simulation results are largely in agreement. Moreover, a designed optically transparent 2D microwave image encoder is proposed as a potential application. The proposed device has considerable potential for application in the fields of signal transmission, information coding, and homeland security.

In this paper, we studied the sidewall conditions of 28 × 52 µm² InGaN-based blue and green micro-LEDs with different sidewall angles and their effects on external quantum efficiency (EQE). Our findings indicate that steeper sidewall mesas can reduce non-radiative recombination and leakage current, which is beneficial for achieving high internal quantum efficiency (IQE). However, as the sidewall angle increases, the light output from the micro-LED tends to concentrate in the internal region, leading to a decrease in light extraction efficiency (LEE). Using microscopic hyperspectral imaging, we observed distinct chromaticity characteristic distributions in the internal area of mesas with different sidewall angles, compared to the entire micro-LEDs. Mesas with gentler sidewalls exhibited lower chromaticity stability. For both blue and green micro-LEDs, the optimal sidewall tilt angle was found to be 48°, yielding the highest EQE. This result reflects a trade-off between LEE and IQE. Notably, the improvement in IQE for green micro-LEDs was not as significant as that for blue micro-LEDs, likely due to the higher indium content in green InGaN micro-LEDs, which results in deeper localized potential wells and a higher dislocation density. This work demonstrates the variation of IQE and LEE for blue and green micro-LEDs fabricated on mesas with different sidewall angles, aimed at achieving the highest EQE.

In this paper, we demonstrate a high-contrast front-end laser system based on Yb: YAG solid-state laser for Ti: sapphire terminal amplification. An ultrafast Yb: YAG solid-state laser is used to generate a broad-spectrum seed through white light generation (WLG), and then the signal light near 1600 nm is amplified by three-level colinear optical parametric chirped pulse amplification (OPCPA). Finally, a fs second harmonic generation (SHG) is used to obtain a laser output with a central wavelength of 795 nm, a pulse width of 40.2 fs, a contrast baseline of nearly 10^-12 within 1 ns, and almost no ps pedestal. We used this laser system as a seed to amplify it to about the theoretical estimated 30 TW level, showing good dispersion properties and contrast preservation capabilities.

For what we believe to be the first time, we propose a general design method for ultralong optical path length (OPL) multipass matrix cells (MMCs) based on the multicycle mode of two-sided field mirrors. Based on the classical Pickett Bradley White cell (PBWC), the design idea of the dual-circulation mode based on two-sided field mirrors is described in detail, with the example of the MMC based on the PBWC-PBWC. Its simple design method and optical stability analysis are given. The other three MMCs based on the dual-circulation mode using the PBWC and Bernstein Herzberg White cell (BHWC) are given. Furthermore, we propose a general design method for ultralong OPL MMCs with multicycle mode by adding cyclic elements. The OPL of the MMCs designed via this method can reach the order of kilometers or even tens of kilometers. To verify the effectiveness of the design method, a CH₄ detection system with an MMC based on PBWC-PBWC-PBWC was constructed. The OPL of the MMC is 1,138 m. Allan deviation analysis reveals that the minimum detection limit of methane is 367 ppt. The design method proposed in this paper provides a new idea for the design of multipass cells (MPCs), and the new MMCs have great potential application value in the field of high-precision trace gas monitoring.

A high-power laser beam profiling system was set up to investigate the influence of the interaction between the laser beam and the process emissions during welding with a shaped beam profile. A positional instability of the beam on the workpiece in the order of magnitude of tens of µm and noticeable distortions of the beam shape were observed when no cross jet was used. Both perturbations were reduced when a cross jet was applied to remove the process emissions from the beam path and minimized when the cross jet was positioned closest to the workpiece.

Holographic displays have the potential to reconstruct natural light field information, making them highly promising for applications in augmented reality (AR), head-up displays (HUD), and new types of transparent three-dimensional (3D) displays. However, current spatial light modulators (SLMs) are constrained by pixel size and resolution, limiting display size. Additionally, existing holographic displays have narrow viewing angles due to device diffraction limits, algorithms, and optical configurations. To overcome these obstacles, we propose a transparent large-size light-field holographic display system. This system utilizes a spectrum-expanded light-field holography algorithm that decomposes the light field in the spectrum domain according to each viewing angle. The spectrum is expanded by a factor of 3. The proposed algorithm widens the viewing angle of the holographic display and utilizes the full spectrum of the display device to support smooth motion parallax as well as the natural depth of field of the light field. Furthermore, we further enlarge the display size by introducing waveguides, and optimize the far-field display performance of the waveguide. The display size is enlarged to 100 mm compared to the general method. The extended spectrum enhances the diffraction angle on the waveguide's grating, resolving content discontinuity in far-field views. The proposed method allows for a more vivid perception of light fields with motion parallax and depth effects on a large transparent screen.

Broadband microwave signals with customized chirp shapes are highly captivating in practical applications. Compared with electronic technology, photonic solutions are superior in bandwidth but suffer from flexible and rapid manipulation of chirp shape or frequency. Here, we demonstrate a concept for generating broadband microwave signals with programmable chirp shapes. Our realization is based on a recirculating phase-modulated optical loop to ultrafast manipulate the laser frequency, which breaks the limitation of the buildup time of the laser from spontaneous emission. Through heterodyne beating the frequency-agile lasers with a continuous-wave laser, microwave signals with ultrafast and programmable chirp shapes are generated. Besides, signal parameters, such as bandwidth, center frequency, and temporal duration, can be reconfigured. In the experiment, highly coherent microwave signals with various customized chirp shapes are generated, where the time resolution for programming the chirp shape is 649 ps. This flexible frequency manipulation characteristic holds promise for many applications, including LiDAR, broadband radar systems, and spectroscopy.

A three-sectioned, bidirectionally coupled, tunable, optical comb source is presented. The photonic integrated circuit (PIC) consists of a gain section, a slotted mirror section and a Fabry-Perot (FP) section. Optical frequency combs (OFCs) are produced by gain switching the FP section via a high power radio frequency (RF) signal. An investigation into the effect of the RF frequency on the quality of the OFC is performed. Multimode behavior is observed with OFCs produced in multiple modes as well as the overall degradation in the quality of the combs in each mode. A minimal extension multimode rate equation model is presented that reproduces the experimental results extremely well using experimentally determined values for numerical parameters. The appearance of multimode behavior is interpreted as relating to the modified relaxation oscillation frequency of the bidirectionally coupled system.