Optics express最新文献

A single-longitudinal-mode (SLM) distributed Bragg reflector (DBR) fiber laser with cylindrical vector beam (CVB) output at 1064 nm was demonstrated. The SLM operation is enabled by a short DBR cavity constructed by a high-gain Yb:YAG crystal-derived silica fiber (YYCDSF), fabricated via the molten core (MC) method with a core Yb₂O₃ concentration of 7.43 wt.%. By offset-splicing a 5.4-mm segment of the YYCDSF to a few-mode fiber Bragg grating (FM-FBG) for mode excitation and selection, a stable single-longitudinal-mode cylindrical vector beam (SLM-CVB) fiber laser was achieved. The laser delivered a maximum output power of 18.08 mW, a slope efficiency of 12.3% for the absorbed pump power, and an optical signal-to-noise ratio (OSNR) of ∼56 dB. Furthermore, by adjusting the polarization controller (PC), switchable radially polarized (TM₀₁) beam and azimuthally polarized (TE₀₁) beam were generated, both exhibiting mode purities (MP) exceeding 93%. To the best of our knowledge, this is the first SLM-CVB fiber laser demonstration based on a DBR cavity structure.

The profile accuracy of arc grinding wheels directly affects the precision of complex optics during grinding. However, existing studies have yet to systematically elucidate the distinct effects of wheel profile errors across different frequency bands on workpiece form errors. In this study, the generation mechanism of workpiece form error during the arc-envelope grinding process is revealed, considering the influence of wheel profile error across different frequency bands through kinematic simulation. The mapping relationship between profile errors and form errors is further analyzed, showing that the mapping coefficient is governed by both amplitude and frequency. The effects of neglecting wheel profile errors on the compensation effectiveness are analyzed for the conventional form error reverse compensation methods, revealing that conventional approaches cannot achieve complete convergence of error profiles and magnitudes. To address this issue, what we believe to be a novel compensation method considering profile errors of arc grinding wheels is proposed. Experimental results demonstrate that the cylindrical workpiece form error was significantly reduced from 8.8 µm PV to 2.1 µm PV after only a single compensation iteration, achieving a 38.2% improvement in compensation accuracy compared to the conventional shape-correction compensation method after two iterations. This method effectively enhances the grinding precision of complex optics while reducing iteration cycles of grinding-measurement-compensation processes.

Different from the plane wave, the vortex beam passing through a Young's double slit will produce an interference pattern with lateral shear, where the degree of lateral shear is determined by the beam's topological charge, namely, providing a quantitative method for measuring the topological charge of vortex beams. However, limited by the detection efficiency, noise, and cost of infrared cameras, using Young's double-slit interference to measure infrared optical vortex modes remains relatively unexplored. Here, we construct a nonlinear Young's double slit, such that when an infrared optical vortex beam passes through it, interference fringes with lateral shear can be observed in the visible region. In our experiment, we successfully measured nine vortex modes with different topological charges using a visible camera, overcoming the performance limitations of infrared detectors. This scheme holds great promise for infrared vortex-encoded optical communications.

Absorbing aerosols, such as brown carbon (BrC) and absorbing secondary organic aerosols (SOA), have attracted broad interest due to their importance for climate and human health. The pronounced time-dependence of light absorption during aging renders the precise estimation of their impact on global warming difficult. Single particle studies of such aerosols would be very useful to better understand their aging in the atmosphere through processes such as photochemistry. Previously proposed optical traps cannot continuously trap particles whose absorption state changes from strongly absorbing to non-absorbing or vice versa. Some of the traps presented can isolate absorbing and non-absorbing particles, but require mechanical alignment of the trap depending on the strength of particle absorption. However, mechanical realignment is not compatible with continuous trapping and observation. Here, we introduce a universal optical trap which does not require mechanical realignment. The versatility of the trap relies on four trapping beams - either vortex Laguerre-Gaussian (LG) or fundamental Gaussian beams - which are modulated with a spatial light modulator (SLM). The performance of the trap is demonstrated by trapping different types of absorbing and non-absorbing particles. We also show that the trap can be used to observe the photochemical reaction of aqueous droplets containing fulvic acid, a common component of BrC. Digital holography measurements demonstrate that the confinement of the particles in the trap can be controlled by changing the orbital angular momentum (OAM) of the LG beams. Spectroscopic measurements, such as fluorescence and Raman scattering, are shown to be possible in all configurations of the proposed trap.

Corner cube retroreflectors can be used in Fourier transform interferometers to create multi-pass optical delay configurations to increase the resolution of the interferometer. This paper will present a multi-pass optical delay design using two identical retroreflectors and it will prove that this design will be the theoretically most efficient design to achieve as many passes as possible using two identical retroreflectors. A formula will be derived to calculate the relation between beam diameter, retroreflector position and the number of passes. An experiment was conducted to demonstrate this design which achieves 24 passes and the resulting interferometer has a scanning range of about 7.2 m.

InGaN-based blue micro-scale light-emitting diodes (micro-LEDs) experience a significant reduction in external quantum efficiency (EQE) as their chip size decreases. In contrast, InGaN red micro-LEDs maintain a relatively stable EQE, regardless of chip size. To understand these size-dependent efficiency characteristics for both blue and red InGaN micro-LEDs, we have developed a comprehensive model of internal quantum efficiency (IQE) including both the effects of surface recombination velocity (SRV) and diffusion length. For micro-LEDs with relatively long diffusion lengths of exceeding 1 μm, IQE decreases significantly as chip size decreases or SRV increases. In contrast, for micro-LEDs with short diffusion lengths of less than 0.1 μm, which applies to InGaN red LEDs, IQE changes only slightly with reductions in chip size or increases in SRV. Our developed IQE model is expected to provide valuable insights into the efficiency characteristics of micro-LEDs, contributing to improved efficiency.

Fringe projection profilometry (FPP) enables high-precision 3D shape measurement and is increasingly deployed with biaxial micro-electro-mechanical system (MEMS) laser-scanning projectors for large-range projection. However, the fast and slow axes of a biaxial MEMS mirror exhibit coupled and nonlinear motion, causing the actual scanning trajectory to deviate from an ideal separable sweep. Consequently, points sharing the same phase no longer lie on straight lines or planar isophase surfaces, but instead follow curved spatial loci, making accurate calibration challenging. This work introduces a phase-angle-ray model (PARM) that establishes a bivariate polynomial mapping between the phase and MEMS deflection angles, from which projected rays are analytically derived. Two calibration frameworks based on pinhole and ray-based imaging models are developed by integrating geometric constraints from a standard plane and multiple standard spheres. Experiments demonstrate that the proposed method achieves high calibration accuracy, improved metric consistency, and precise 3D reconstruction.

We present a low-noise 1123 nm laser based on a master oscillator power amplifier (MOPA) configuration. A specially coated Nd:YAG nonplanar ring oscillator (NPRO) is employed as the seed, generating single-frequency radiation at 1123 nm with low intensity and frequency noise. Two cascaded ytterbium-doped fiber amplifiers (YDFA) boost the output power to 1 W while preserving the seed's spectral purity. The combined solution of NPRO and MOPA can ensure high output power while maintaining low noise. In free-running operation the laser achieves a sub-kilohertz linewidth (834 ± 63 Hz), a signal-to-noise ratio (SNR) exceeding 50 dB, and excellent power stability (<0.5% over 4000 s). Relative intensity noise (RIN) reaches 1×10^-2 Hz^-1/2 at 1 mHz, and frequency noise is 7.9×10⁴ Hz/Hz^1/2 at 1 Hz.

Computer-generated holography (CGH) is a 3D imaging technique that faithfully reproduces visual perception cues for humans. Recently, various applications have been developed by integrating cascaded phase patterns with CGH. However, numerous CGH studies employing cascaded structures have been limited to the reconstruction of 2D planar images. In this paper, we propose a cascaded structure capable of reconstructing 3D objects through a stochastic gradient algorithm. To achieve high-quality reconstruction, we adopt a non-hogel-based light-field to CGH synthesis method, which enables holograms with high resolution in both spatial and angular domains. We validate the effectiveness of the proposed model through applications such as encryption/decryption and hologram channel multiplexing.

Suppression of stimulated Raman scattering (SRS) is essential in high-power fiber lasers. Regarding temporal intensity stability, phase-modulated single-frequency lasers (PM-SFLs) are considered the optimal seed lasers for SRS suppression in high-power fiber amplifiers. This study proposes and demonstrates a category of quasi-continuous-wave (quasi-CW) lasers with controllable temporal intensity stability, achieved by combining two PM-SFLs. The theoretical analysis reveals the potential and mechanism of the controllable quasi-CW lasers for higher Raman thresholds than PM-SFLs. Notably, the dispersion makes them close to CW pumps for Raman Stokes light, and their broadband spectrum contributes to a higher Raman threshold. The experimental results verify that an appropriate wavelength interval enables the controllable quasi-CW lasers to have slightly better SRS suppression than a single PM-SFL. This study could provide new insights for designing lasers with tunable spectral and temporal properties, especially for SRS suppression in optical fibers.