Optics letters最新文献

Wavefront manipulation and correction using feedback-based optimization have long been employed in optical applications such as microscopy, optical sensing, astronomical imaging, and communication. With recent advances in quantum optics, wavefront correction has become a crucial tool in quantum imaging, quantum communication, and efficient photon coupling. Consequently, understanding the performance of optimization algorithms under low-photon conditions is essential for the effective deployment of quantum optical systems. This study investigates the performance of two algorithms in the photon-counting regime across varying mean photon rates through experiments and numerical simulations. Furthermore, we propose, simulate, and implement a novel, to the best of our knowledge, augmented algorithm that combines the strengths of both methods and is particularly well suited for quantum applications.

Optical crosstalk plays a key role in degrading the color accuracy and contrast of GaN-based micro-light emitting diodes (micro-LEDs) in display applications, and a comprehensive solution to this issue remains elusive. In this Letter, we propose a micro-LED array structure featuring individual pixels surrounded by a circular wall deposited with silver (Ag) as a reflective medium, and the effect of crosstalk reduction is well demonstrated. Compared to the conventional micro-LED devices, the luminous intensity distribution mapping indicated that the proposed micro-LED structure achieves a significant light spot reduction under the injection current of about 0.5 mA, and a low-crosstalk display is achieved through a 16 × 16 array. Furthermore, the optical field distribution of the proposed micro-LED structure was studied based on finite-difference time-domain (FDTD) simulation. The results reveal that when the height and gap width of the reflective wall are 5 µm respectively, more than 55% of the light emission is effectively limited within the ±45^∘ divergence angle. This work presents a promising solution for mitigating optical crosstalk in micro-LED displays, thereby enhancing their performance for high-quality display applications.

Quasi-periodicity has numerous applications in various fields, such as the discovery and study of quasicrystals. In the region of manipulating vector optical fields (VOFs), the periodicity is very common, but the quasi-periodicity is rarely seen. Here, we propose a kind of two-dimensional quasi-periodic VOF, introducing the concept of quasi-periodicity into the region of manipulating VOFs. We then study the optical information encoding and transmission. It is demonstrated that the information can be accurately recovered even when up to 75% of the spectrum is obstructed by sector-shaped obstacle. The information remains highly robust under random interference affecting 90% of the wave front during propagation. This work demonstrates the convolution-based construction scheme of the quasi-periodic VOF, along with the explicit information-encoding protocol and experimental demonstration. The quasi-periodic VOF opens an avenue for robust optical information transmission over long-distances.

This study leverages the tunable competition between optical and fluidic forces in a cascaded microcavity optical tweezer structure to establish a single-wavelength particle manipulation method governed by the coordinated tuning of structural coupling and optical power. By establishing distinct coupling conditions and introducing slight power perturbations, an adjustable mechanical competitive state is formed, enabling controlled transitions of particles between the capture and transportation modes. Numerical analysis reveals how this competitive state evolves with the coupling condition, and experiments in the power-sensitive critical-coupling state confirm the feasibility of the approach. The method offers a new pathway for non-contact precision manipulation in optofluidic microsystems.

A compact phase-engineering method for generating zero-order Bessel beams with uniform on-axis intensity from femtosecond lasers exhibiting asymmetric Gaussian inputs (w_x ≠ w_y) is presented. An axicon phase combined with Gaussian phase modulation (GPM) was encoded on a spatial light modulator (SLM) to correct beam ellipticity and axial decay. Analytical expressions derived using the stationary-phase method reveal the effects of asymmetry, while numerical GPM tuning ensures axial uniformity. Theoretical, simulated, and experimental results at 1030 nm show strong agreement, even for a small asymmetry (δ_w= w_y/w_x ≈ 0.95-1.05). The technique provides a simple and practical route to high-fidelity Bessel beams for ultrafast laser microfabrication.

An n-type Al_0.15Ga_0.85N hole current confinement layer (HCCL) was designed and incorporated in GaN-based vertical-cavity surface-emitting lasers (VCSELs) to alleviate the insufficient carrier confinement-induced hole leakage outside the aperture region. The simulation results show that the hetero-structure formed by p-GaN and n-Al_0.15Ga_0.85N builds the highest energy barrier for holes both in the lateral and vertical directions and has the smallest valence band bending. The higher barrier potential and smoother valence band in the p-type region favors hole confinement, thus improving the carrier injection and recombination in the active region. Under a 10 mA injection current, the proposed structure shows an increase of 37.8% in optical output power, a reduction of 0.6 mA in threshold current, and an enhancement of 32% wall-plug efficiency. The results demonstrate that the n-AlGaN HCCL can effectively regulate the band structure and improve carrier confinement capabilities in the p-type region, thus providing an effective pathway for enhancing the performance of GaN-based VCSELs.

We report on a diode-pumped passively Q-switched Tm:YLF laser emitting at 2.3 µm. To promote emission at this wavelength, a cascade laser scheme is implemented, combining the consecutive ³H₄ → ³H₅ and ³F₄ → ³H₆ transitions in the Tm³⁺-doped material. In this configuration, laser operation at 1.9 µm is deliberately isolated from the Cr:ZnSe saturable absorber avoiding undesired saturation of the absorber. The 1.9-µm laser then runs alone in continuous-wave (cw) regime and the 2.3 µm laser in passively Q-switched regime. The Q-switch laser dynamics reveal intrinsic instabilities, which are further analyzed using Poincaré maps to uncover the underlying structures of an atypical Q-switched behavior. A detailed study demonstrates that these instabilities originate from the slightly multimode nature of the beam. Therefore, a stabilization process is settled by spatial filtering of the laser mode to reach a stable regime. In this stable regime, we obtain 1.5 µs pulses with an energy of 4 µJ with a repetition rate up to 5 kHz. Finally, the dynamics correlation between the two lasers of the cascade is also studied.

This study proposes a fiber-optic xenon (Xe) sensor with photothermally tunable gas concentration sensitivity (PTGCS). A polymer microtip doped with Xe-selective material MOF-1 and photothermal material MOF-2 on the single-mode fiber (SMF) end face acts as a Fabry-Pérot (FP) sensor for Xe gas detection. MOF-2 can control the temperature of the polymer microtip by adjusting the power of the 808 nm laser. Based on the adsorption law of MOF-1, we establish the "laser power/temperature-gas concentration-spectral response" model of the sensor. Meanwhile, an ultra-compact plasmonic grating embedded between the optical fiber core and the polymer microtip serves as the temperature indicator. The research results show that when the excitation power of the 808 nm laser is 5 mW (50 °C) and 10 mW (70 °C), the PTGCS values of the sensor are 0.191 nm/ppb and 0.106 nm/ppb, respectively. The ratio of the two PTGCS values is 1.8, which can serve as the identification parameter for Xe gas to distinguish it from other gases, particularly krypton (Kr) gas. This sensor overcomes the limitation of relying solely on the selectivity of sensitive materials to identify Xe and can self-adjust the temperature to resist temperature interference.

Propagation-based X-ray phase-contrast imaging (PB-XPCI) can produce high-resolution images of soft tissue. However, this usually requires extracting the phase shift from intensity measurement at a single propagation distance through phase retrieval-an underdetermined nonlinear inverse problem. Conventional single-distance phase retrieval methods usually rely on multiple approximation conditions. Deep learning (DL)-based phase retrieval methods often rely on high-quality data for training or lengthy physics model iterative computations to optimize network parameters. In order to surmount the aforementioned limitations, this study proposes a physics-inspired phase retrieval network for propagation-based X-ray phase-contrast imaging (PIPN) and an acceleration strategy for the PIPN. It can achieve phase retrieval based solely on a single approximation condition and a physics imaging model, without the need for any training data. Experiments demonstrate that the PIPN can quickly reconstruct high-quality retrieved phase projections by using the acceleration strategy, and remain stable under different propagation distances.

The single-cavity dual-repetition-frequency self-mode-locked Tm,Ho:YLF laser is first demonstrated. Combining the natural birefringence characteristic and the soft-hole Kerr lens effect of gain medium itself, the orthogonally polarized dual-repetition-frequency self-mode-locked Tm,Ho:YLF laser with a single cavity was successfully realized. For the π-polarized and σ-polarized pulse lasers, the balanced average output powers of 282 mW and 298 mW were attained at an absorbed pump power of 2.16 W, the pulse repetition frequencies were 1.7148 GHz and 1.7173 GHz, and the output wavelengths were 2065.3 nm and 2063.8 nm. To the best of our knowledge, this is the first single-cavity dual-repetition-frequency self-mode-locked solid-state laser in the 2 µm waveband.