Optics express最新文献

Dual-parameter temperature and humidity sensors based on optical fiber sensing have wide applications. Among various optical fiber sensors, surface plasmon resonance (SPR) sensors exhibit excellent sensing sensitivity. To address the bandwidth issue and expand the sensitivity, this paper proposes a multimode fiber-no core fiber (MMF-NCF) SPR sensor. The humidity channel covers an Ag/PVA composite film, while the temperature channel covers an Ag/MgF₂/PDMS composite film. The MgF₂ modulates the shape of the resonance curve, shifts the resonance curve towards the infrared direction and enhancing the sensitivity by 0.245 nm/^oC. Compared with previous temperature and humidity detection ranges up to 20°C ∼ 100°C and 40% ∼ 100%, this has obvious improvement. The maximum sensitivities are -0.5683 nm/%RH and -3.259 nm/^oC. The mean temperature sensitivity is -1.88877 nm/^oC and the mean humidity sensitivity is -0.51249 nm/%RH. The polynomial fitting degrees reach 0.99914 and 0.99875, and FOM values are 2.715 × 10^-2/^oC and 4.735 × 10^-3/%RH, which is expected to be in agriculture, food industry, such as biological implementation is widely used in production activities.

Scattering-type scanning near-field optical microscopy (s-SNOM) under the excitation of single cycle picosecond (ps) pulse provides access to terahertz (THz) time-resolved nanoscopy. However, the development of THz nanoscopy has been greatly limited due to the inherently low efficiency of the scattered field and the convolution of the intrinsic material response with the extrinsic response of the cantilevered tip. In this work, we quantitatively study the near-field time-delayed pulse transients of resonant cantilevered tips, observing localized tip-enhanced coupling as well as delocalized collective charge oscillations propagating as resonant surface waves along cantilevered tips. By numerical temporal-spectral analysis, the phonon resonance of the topological insulator Bi₂Se₃ can be effectively extracted from the resonant surface waves at the end of the cantilever. We demonstrate that after propagating 600 µm, the intensity of near-field signals extracted from the resonant surface waves is about three orders higher than that from the traditional scattering field. Our research reveals the delocalized tip-enhanced light-matter interaction in propagating surface waves and proposes a promising route to non-scattering THz nanoscopy.

This paper employed a two-color double-pulse femtosecond laser (TDFL) technology for surface processing of carbon fiber reinforced polymers (CFRP). By exploring the changes in ablation thresholds for resin and carbon fiber under varying wavelengths and pulse numbers, optimal wavelength combinations were identified. Adjustments to processing parameters and pulse delay enabled precise removal of the CFRP surface, targeting resin while causing no damage to the underlying carbon fibers. After laser treatment, the CFRP surface showed modifications in surface roughness and wettability, improving adhesive bonding with binders or coatings.

As a low-energy method to increase the data rate of optical links in data centers, we propose self-homodyne Nyquist optical time division multiplexing (OTDM). In Nyquist OTDM, spectrally efficient high-baud rate signals can be generated exceeding the limit of electronic signal processing. However, full integration of OTDM systems has not been reported, mainly because of the complicated signal detection scheme, which involves demultiplexing and clock recovery. In our proposal, the Nyquist pulse train is transmitted to the receiver as a local oscillator (LO) to leverage self-homodyne detection, which allows using large linewidth lasers and a simplified digital signal processing (DSP) algorithm. As the transmitted pulse train serves as an optical clock, demultiplexing and detection of the OTDM signal can be performed without using power-intensive high-bandwidth electronics and DSP. In this method, the LO pulse train needs to enter the coherent detector in exact synchronization with the OTDM signal for detecting the individual tributary correctly. For this purpose, we present a pulse delay control method suitable for photonic integration. A Nyquist pulse train with m carriers enables m-time multiplexing of optical signals. We explain and demonstrate the proposed concept in the case of m = 2, as it is the most feasible implementation. In the O-band where the chromatic dispersion (CD) is negligible, DSP-free operation can be achieved using the QPSK format. At the band edges where CD is non-negligible, it can be compensated by the DSP as in the conventional coherent detection. We verify this numerically and in an experiment involving the transmission of a 64-Gbaud QPSK signal at 1550 nm over a single-mode fiber. In terms of low energy, self-homodyne Nyquist OTDM is advantageous in wavelength division multiplexing (WDM). Taking it into consideration, we perform 4-channel WDM transmission of the 64-Gbaud QPSK signal over a 1-km dispersion shifted fiber without CD compensation. The results demonstrate a data rate of 512 Gb/s with a BER of <1 × 10^-10.

The fiber Bragg grating (FBG) is fabricated by the femtosecond laser writing technique with a plane-by-plane (Pl-by-Pl) method in the double-cladding fiber (DCF). The refractive index modified (RIM) region formed by this method is 12 μm × 8 μm in size. Due to the Pl-by-Pl method, high-order Bragg resonances with reflectance greater than 99% can be achieved. The fabricated high-quality FBG features a narrow full width at 3 dB bandwidth of approximately 0.45 nm, a high reflectivity above 99%, and almost no side-mode peaks. To investigate the application of fabricated FBGs, we have built a thulium-doped all-fiber oscillator with purely forward-pumped structures. A thulium-doped fiber laser (TDFL) at a central wavelength of 1953.79 nm was constructed by using the prepared fiber grating. The signal-to-noise ratio (SNR) is above 56 dB. When the pump power is 19 W, the total output power of the continuous wave is 4 W, and the output efficiency is 25.6%. In addition, the numerical calculation has been carried out to further optimize the output power. This work provides a possible approach for designing and implementing a continuous Tm-doped fiber laser with enhanced output efficiency.

Nowadays, spaceborne LiDAR technology, particularly ICESat-2, has become a transformative tool in marine environmental research. Unlike traditional passive optical remote sensing methods, ICESat-2 offers detailed vertical structure mapping of oceanic optical properties. Despite the potential of ICESat-2 for observing the optical vertical structure, its application in the East China Sea with complex hydrological conditions and dynamic ecosystems remains limited. In this study, we introduce an innovative methodology for retrieving the vertical structure of subsurface optical properties in the East China Sea using ICESat-2 spaceborne LiDAR observations. After preprocessing ICESat-2 ATL03 data, we employed a 4 km × 1 m bin with a 0.15 m depth step for sliding accumulation, allowing us to capture LiDAR signals at various water depths. Following deconvolution, we proposed a method to calculate the vertical profiles of the diffuse attenuation coefficient and the particulate backscatter coefficient, thereby obtaining their vertical distributions. Our retrieval results show a high degree of consistency with MODIS products and BGC-Argo data, particularly in clearer open waters. The optical parameters in the East China Sea exhibit a distinct spatial pattern, with elevated values in the western and northern regions and lower values in the eastern and southern regions. This distribution is largely attributed to the proximity of the northern laser track segments to land and the influence of terrestrial runoff from the Yangtze River on the western side of the East China Sea. The influx of suspended particles and nutrients in this region significantly affects the magnitude of optical parameters, resulting in higher root mean square errors (RMSE) compared to the eastern waters. Moreover, our analysis reveals notable differences in the vertical distribution of the diffuse attenuation coefficient and the particulate backscatter coefficient, reflecting varying concentrations of optically active components across different water layers. These findings validate the efficacy of ICESat-2 for retrieving the vertical structure of subsurface ocean optical properties, providing a robust foundation for understanding the dynamic changes within the East China Sea ecosystem.

Recent advancements in display technology have led to the development and diversification of complex glass materials. Among them, Corning's Lotus NXT glass offers excellent optical properties, high thermal stability, and dimensional accuracy, which are crucial for display applications. However, these characteristics make it difficult to apply pre-existing machining techniques developed for conventional glass materials directly to NXT glass. In this study, we used the laser-induced deep etching (LIDE) technique to fabricate micro holes in NXT glass. Various laser, chemical, and mechanical parameters were subjected to experimental analysis and optimization to achieve higher etching speed and aspect ratio. In this study, successful etching of Corning's Lotus NXT glass was achieved by optimizing laser parameters, including a wavelength of 1030 nm, a pulse energy of 45 µJ, a pulse count of 2 × 10⁴, and a repetition rate of 40 kHz, combined with a chemical composition consisting of a 1:5 molar ratio of HF to HCl. This resulted in a high aspect ratio of ∼23:1 and an impressive etching speed of 1200 µm/h.

The recent surge of interest in moiré photonics arises from the possibility of exploring many groundbreaking physical phenomena in photonics. These phenomena include photonic topological states and magic-angle lasing, which offer an attractive platform for manipulating the flow and confinement of light from remarkably simple device geometries. In this work, we fabricate a series of metallic moiré superlattices supporting moiré plasmon polaritons and explore the moiré-potential induced plasmonic resonances. We demonstrate that two-dimensional moiré plasmonic superlattices exhibit transmittance and polarization-dependent responses because of the localized plasmonic resonances in the infrared range, whose modes have a near-flat dispersion band. Our findings hold the potential for the understanding of localized plasmonic resonances within moiré superlattices.

Dielectric waveguides are widely recognized as excellent and versatile components for integrated multifunctional photonic chips, thanks to their strong optical confinement capabilities. In this study, we present a novel semi-tapered depressed-cladding waveguide structure, designed and fabricated using femtosecond laser direct writing technology. The optical guiding performance of this semi-tapered waveguide is systematically analyzed by characterizing its loss characteristics. Leveraging the high gain and superior laser performance of the semi-tapered waveguide platform, we successfully demonstrate an efficient vortex waveguide laser. Moreover, we achieve a stable Q-switched vortex laser with short pulse duration and high repetition rate by utilizing an Sb₂Te₃ thin film as a saturable absorber. This work exemplifies the potential for developing three-dimensional waveguides for on-chip integrated pulsed lasers.

Atmospheric refraction imposes a fundamental limitation on the accuracy and precision of geodetic measurements that utilize electromagnetic waves. For terrestrial observations at optical wavelengths recorded over flat terrain, the vertical temperature gradient controls the bending of the rays thus affecting mostly the vertical angle measurement. The rules of thumb for mitigating these effects (variation ranges and short-term fluctuations) are based on intuition and practitioner experience. To address the challenge of understanding the impact of refractive index inhomogeneities on the refraction angle without additional instruments, we introduce large eddy simulations (LES) in geodesy. We use the PALM software to simulate realistic atmospheric conditions and investigate first- and second-order variations of the refraction angle using virtual measurements over a flat terrain with surface heterogeneities. We analyze the optimal measurement times to minimize refraction effects, highlighting the potential of LES to help plan measurement campaigns. Additionally, the correlating influence of atmospheric turbulence on the measurements is quantified. We propose a correction model based on the variance inflation factor as a practical tool for incorporating turbulence into a geodetic uncertainty model.