An object experiences an enhanced local electric field (E-field), due to the combined effects of microsphere focusing and surface plasmon excitation, leading to evanescent illumination. By augmenting the local electric field, a near-field excitation source is created, increasing the scattering of the object, resulting in an improvement of the imaging resolution.
Liquid crystal (LC) terahertz phase shifters, owing to the need for substantial retardation, frequently employ thick cell gaps, thus compromising the speed of LC response. Improving the response, we virtually demonstrate a novel liquid crystal (LC) switching approach that facilitates reversible transitions between three orthogonal orientations (in-plane and out-of-plane), thus broadening the spectrum of continuous phase shifts. LC switching is achieved via two substrates, each featuring two pairs of orthogonal finger electrodes and a single grating electrode for in- and out-of-plane control. this website The application of a voltage produces an electric field that governs the switching procedures among the three different orientations, enabling a swift response.
Within this report, we investigate the suppression of secondary modes in 1240nm single longitudinal mode (SLM) diamond Raman lasers. We achieved stable SLM output within a three-mirror V-shape standing-wave cavity, featuring an intra-cavity LBO crystal for suppressing secondary modes. The output power reached a maximum of 117 W, and the slope efficiency was 349%. We establish the required level of coupling to suppress secondary modes, including those produced by stimulated Brillouin scattering (SBS). Studies show that SBS-generated modes frequently appear in conjunction with higher-order spatial modes within the beam's profile, and this presence can be reduced by implementing an intracavity aperture. this website By employing numerical methods, it is established that the probability for these higher-order spatial modes is greater in an apertureless V-cavity than in two-mirror cavities, a consequence of its distinct longitudinal mode profile.
We propose, to our knowledge, a novel driving scheme for suppressing the stimulated Brillouin scattering (SBS) effect in master oscillator power amplification (MOPA) systems, employing an externally applied high-order phase modulation. The consistent, uniform broadening of the SBS gain spectrum, achieved by seed sources with linear chirps and exceeding a high SBS threshold, has inspired the development of a chirp-like signal. This signal is a result of further signal editing and processing applied to a piecewise parabolic signal. The chirp-like signal, unlike the traditional piecewise parabolic signal, shares comparable linear chirp characteristics. This results in decreased driving power and sampling rate requirements, facilitating a more efficient spectral spreading approach. The theoretical underpinnings of the SBS threshold model are derived from the three-wave coupling equation. Evaluating the chirp-like signal's impact on the spectrum, relative to flat-top and Gaussian spectra, in terms of SBS threshold and normalized bandwidth distribution demonstrates a significant improvement. this website The experimental validation procedure is conducted on a watt-class amplifier, employing the MOPA design. For a seed source modulated by a chirp-like signal at a 3dB bandwidth of 10GHz, the SBS threshold is enhanced by 35% compared to the flat-top spectrum and 18% compared to the Gaussian spectrum. This configuration also exhibits the highest normalized threshold. Our investigation reveals that the suppression of SBS is not solely contingent upon spectral power distribution but can also be enhanced through temporal domain optimization, thereby offering novel insights into boosting the SBS threshold of narrow linewidth fiber lasers.
Forward Brillouin scattering (FBS), induced by radial acoustic modes within a highly nonlinear fiber (HNLF), has, to the best of our knowledge, enabled acoustic impedance sensing for the first time, achieving a sensitivity exceeding 3 MHz. HNLFs, leveraging high acousto-optical coupling, yield radial (R0,m) and torsional-radial (TR2,m) acoustic modes with superior gain coefficients and scattering efficiencies as compared to standard single-mode fibers (SSMFs). The enhanced signal-to-noise ratio (SNR) achieved by this method leads to greater measurement precision. Employing HNLF's R020 mode yielded a heightened sensitivity of 383 MHz/[kg/(smm2)], demonstrably superior to the 270 MHz/[kg/(smm2)] attained using R09 mode in SSMF, despite the latter's near-maximal gain coefficient. The sensitivity, determined by using the TR25 mode in HNLF, stood at 0.24 MHz/[kg/(smm2)], a value 15 times higher than the sensitivity observed when employing the same mode in SSMF. Greater accuracy in detecting the external environment is assured by FBS-based sensors with improved sensitivity.
Short-reach applications, such as optical interconnections, stand to gain significantly from the use of weakly-coupled mode division multiplexing (MDM) techniques, which support intensity modulation and direct detection (IM/DD) transmission. The need for low-modal-crosstalk mode multiplexers/demultiplexers (MMUX/MDEMUX) is paramount in these applications. This paper details an all-fiber, low-modal-crosstalk orthogonal combining reception scheme designed for degenerate linearly-polarized (LP) modes. The scheme demultiplexes signals in both degenerate modes into the LP01 mode of single-mode fibers before multiplexing into mutually orthogonal LP01 and LP11 modes of a two-mode fiber for concurrent detection. Subsequently, a pair of 4-LP-mode MMUX/MDEMUX devices, constructed from cascaded mode-selective couplers and orthogonal combiners, were fabricated using side-polishing techniques. These devices demonstrate exceptionally low back-to-back modal crosstalk, below -1851 dB, and insertion loss below 381 dB across all four modes. Experimental results confirm the stable real-time transmission of 4-mode 410 Gb/s MDM-wavelength division multiplexing (WDM) over 20 km of few-mode fiber. The proposed scheme is scalable, enabling additional operational modes and laying the groundwork for the practical implementation of IM/DD MDM transmission applications.
A Kerr-lens mode-locked laser, whose active component is an Yb3+-doped disordered calcium lithium niobium gallium garnet (YbCLNGG) crystal, is presented in this work. The YbCLNGG laser, pumped by a spatially single-mode Yb fiber laser at a wavelength of 976nm, achieves soliton pulses of a duration as short as 31 femtoseconds at 10568nm. This output is supported by an average output power of 66 milliwatts and a pulse repetition rate of 776 megahertz through soft-aperture Kerr-lens mode-locking. A Kerr-lens mode-locked laser's maximum output power, 203mW, was achieved for 37 fs pulses, slightly longer than others, at an absorbed pump power of 0.74W. This translates to a peak power of 622kW and an optical efficiency of 203%.
Remote sensing technology's development has placed true-color visualization of hyperspectral LiDAR echo signals at the forefront of both academic inquiry and commercial endeavors. Hyperspectral LiDAR's emission power limitations result in the loss of spectral reflectance information in certain channels within the hyperspectral LiDAR echo signal. The color reconstruction process, based on the hyperspectral LiDAR echo signal, is highly susceptible to color cast issues. This study proposes a spectral missing color correction approach, utilizing an adaptive parameter fitting model, to address the existing problem. Acknowledging the gaps in the spectral reflectance bands, the colors produced from the incomplete spectral integration are modified to accurately restore the desired target colors. The proposed color correction model, when applied to hyperspectral images of color blocks, yields a smaller color difference compared to the ground truth, resulting in enhanced image quality and accurate target color reproduction, as evidenced by the experimental results.
This paper examines steady-state quantum entanglement and steering within an open Dicke model, incorporating cavity dissipation and individual atomic decoherence. Specifically, we posit that each atom interacts with independent dephasing and squeezing environments, rendering the commonly employed Holstein-Primakoff approximation inapplicable. In studying quantum phase transitions within decohering environments, we mainly find: (i) In both normal and superradiant phases, cavity dissipation and individual atomic decoherence boost entanglement and steering between the cavity field and the atomic ensemble; (ii) individual atomic spontaneous emission establishes steering between the cavity field and the atomic ensemble, but the steering in opposite directions is not concurrent; (iii) the maximum achievable steering within the normal phase is greater than in the superradiant phase; (iv) the entanglement and steering between the cavity output field and the atomic ensemble are considerably stronger than those with the intracavity field, and simultaneous steering in two directions is achievable even with the same parameters. Our findings elucidate unique features of quantum correlations present in the open Dicke model, specifically concerning individual atomic decoherence processes.
The lower resolution of polarized imagery complicates the identification of fine polarization details and limits the ability to detect small, faint targets and signals. Employing polarization super-resolution (SR) is a possible solution for this problem, the intention being to obtain a high-resolution polarized image from a low-resolution one. Whereas intensity-based super-resolution (SR) methods are more straightforward, polarization super-resolution (SR) poses a significant hurdle. Polarization SR requires the reconstruction of both polarization and intensity data, the incorporation of numerous channels, and careful consideration of the non-linear interactions between channels. Using a deep convolutional neural network, this paper addresses polarization image degradation by proposing a method for polarization super-resolution reconstruction, based on two degradation models. The network structure and its associated loss function demonstrate a successful balance in restoring intensity and polarization information, allowing for super-resolution with a maximum scaling factor of four.