Levinedaniels9063

Our proposal is based on a dispersion-diversity receiver with an electrical bandwidth of ∼61.0% baud rate and a high tolerance to laser wavelength drift. A deep convolutional neural network enables accurate signal recovery in the presence of a strong signal-signal beat interference. Compared with the conventional method, the proposed DLEDD scheme can reduce the optimum CSPR by ∼8 dB, leading to a significant signal-to-noise ratio improvement of ∼5.8 dB according to simulation results. We experimentally demonstrate the optical field reconstruction for a 28-GBaud 16-ary quadrature amplitude modulation signal after 80-km single-mode fiber transmission based on the proposed DLEDD scheme with a 2-dB optimum CSPR. The results show that the proposed DLEDD scheme could offer a high-performance solution for cost-sensitive applications such as data center interconnects, metro networks, and mobile fronthaul systems.We introduce a class of partially coherent sources, which are capable of producing beams with radially quasi-periodic and azimuthally fully periodic intensity profiles. The physical properties of the source, as well as the propagation of the intensity distribution and the complex degree of spatial coherence of the ensuing beams are investigated and interpreted. It is shown that the shape and symmetry of the intensity and the degree of spatial coherence are generally adjustable and modulated by the parameters related to the beam source. Moreover, the periodic changes of intensity arise from the discontinuity of the phase. The results provide a method for synthesizing fields with peculiar periodic intensity distributions in polar coordinates.We present an improved color purity of additive transmissive structural color filters by controlling a resonance order and by inserting a highly absorbing material. The proposed structure consists of a single metal sandwiched by two transparent dielectric media serving as a cavity to minimize the ohmic loss in the metal mirrors, which is distinctly different from a conventional Fabry-Perot (FP) cavity that is in general designed to have two metal mirrors. Low reflections at an air-dielectric interface cause a quality-factor of a resonance to be reduced, causing a degraded color purity, which can be improved by employing a 1st order resonance that exhibits a narrower bandwidth than a fundamental FP resonant mode (0th order). For a red color with the improved purity, introducing an ultrathin absorbing layer in the middle of a top cavity enables the 1st resonance to be trivially influenced while selectively suppressing a 2nd order resonance appearing at the shorter wavelength region. Moreover, angle-insensitive performances up to 60° are attained by utilizing a cavity material with high index of refraction. Besides, the fabrication of the structural coloring devices involves a few deposition steps, thus rendering the approach suitable for applications over the large area. The described concept could be applied to diverse applications, such as colored solar panels, sensors, imaging devices, and decorations.Frequency-sensitive super-collimation (FSSC) is a novel dispersion phenomenon of photonic crystals (PhCs) that can realize the beam collimating propagation with very high frequency sensitivity. In order to deeply investigate the origin and the stability of FSSC phenomenon in a wide parameter space, we study the geometry of dispersion surface in detail. Four features for the special geometry of dispersion surface with FSSC are found for rectangular PhCs. The special geometry supports the stability of FSSC in a wide range of parameter space. Two-parameter modulation (TPM) method, in which the aspect ratio β and the dielectric constant of rods ɛr of rectangular lattice are chosen as the key parameters, is used to analyze the geometry of dispersion surface from the frequency changes at the high-symmetry points. Step by step, the origin of such geometry is revealed and the evolving process can be explained by the field distribution changes of Bloch modes at the high-symmetry points. Furthermore, we show that the geometry not only can be used to explain the origin and the stability of FSSC, but also can help us to find other FSSC phenomenons. Theoretically, we believe the geometry of dispersion surface and the TPM can be widely used on the studies of complex dispersion properties of PhCs. The FSSCs found in this work with higher sensitivity or higher stability can help us to design new on-chip PhC devices.Optical absorption and scattering result in quality degradation of underwater images, which hampers the performance of underwater vision tasks. In practice, a well-posed underwater image recovery requires a combination of scene specificity and adaptability. To this end, this paper breaks down the overall recovery process into in-situ enhancement and data-driven correction modules, and proposes a Multi-stage Underwater Image Enhancement (MUIE) method to cascade the modules. In the in-situ enhancement module, a channel compensation with scene-relevant supervision is designed to address different degrees of unbalanced attenuation, and then the duality-based computation inverts the result of running a enhancement on inverted intensities to recover the degraded textures. In response to different scenarios, a data-driven correction, encoding corrected color-constancy information under data supervision, is performed to correct the improper color appearance of in-situ enhanced results. Further, under the collaboration between scene and data information, the recovery of MUIE avoids ill-posed response and reduces the prior dependence of specific scenes, resulting in a robust performance in different underwater scenes. Recovery comparison results confirm that the recovery of MUIE shows the superiority of scene clarity, realistic color appearance and evaluation scores. With the recovery of MUIE, the Underwater Image Quality Measurement (UIQM) scores of recovery-challenging images in the UIEB dataset were improved from 1.59 to 3.92.Frequency sweep operation of directly modulated optical negative feedback lasers is numerically and experimentally investigated for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) with a high signal-to-noise ratio (SNR), particularly over a long range. Low FM noise corresponding to a spectral linewidth of ∼2.0 kHz is sustained even with injection current modulation of an optical negative feedback laser through optical feedback from a Fabry-Perot etalon, and a beat note spectrum with a 30-dB SNR is achieved even when a 300-m delay fiber is used as a ranging sample. These results encourage an approach to provide directly modulated frequency-swept lasers for long-range FMCW LiDAR.Quantum interference plays an essential role in understanding the concepts of quantum physics. Moreover, the interference of photons is indispensable for large-scale quantum information processing. With the development of quantum networks, interference of photons transmitted through long-distance fiber channels has been widely implemented. However, quantum interference of photons using free-space channels is still scarce, mainly due to atmospheric turbulence. Here, we report an experimental demonstration of Hong-Ou-Mandel interference with photons transmitted by free-space channels. Two typical photon sources, i.e., correlated photon pairs generated in spontaneous parametric down conversion (SPDC) process and weak coherent states, are employed. A visibility of 0.744 ± 0.013 is observed by interfering with two photons generated in the SPDC process, exceeding the classical limit of 0.5. Our results demonstrate that the quantum property of photons remains even after transmission through unstable free-space channels, indicating the feasibility and potential application of free-space-based quantum interference in quantum information processing.Over the last decade, free-space quantum key distribution (QKD), a secure key sharing protocol, has risen in popularity due the adaptable nature of free-space networking and the near-term potential to share quantum-secure encryption keys over a global scale. While the literature has primarily focused on polarization based-protocols for free-space transmission, there are benefits to implementing other protocols, particularly when operating at fast clock-rates, such as in the GHz. In this paper, we experimentally demonstrate a time-bin QKD system, implementing the coherent one-way (COW) at 1 GHz clock frequency, utilizing a free-space channel and receiver. We demonstrate the receiver's robustness to atmospheric turbulence, maintaining an operational visibility of 92%, by utilizing a lab-based turbulence simulator. With a fixed channel loss of 16 dB, discounting turbulence, we obtain secret key rate (SKR) of 6.4 kbps, 3.4 kbps, and 270 bps for three increasing levels of turbulence. Our results highlight that turbulence must be better accounted for in free-space QKD modelling due to the additional induced loss.Non-equilibrium Green's function (NEGF) formalism is used to optimize the gain region of a quantum cascade laser (QCL) tailored to emit radiation at ∼5 µm wavelength, originally designed by Evans et al. [Appl. Phys. Lett., 88,051105(2006)10.1063/1.2171476]. The optimization strategy uses electron-photon selfenergies to find characteristics of devices under the "operating conditions," i.e., interacting with the laser field. These conditions can be quite different from the one when the device is in no-lasing state and the unsaturated gain is being optimized. Selleck Opevesostat The saturation caused by the optical field can push the structure from strong to weak coupling conditions, what changes laser parameters in a non-linear manner. Moreover, the NEGF method does not require any phenomenological parameters (such as, e.g., the phase relaxation times), so the quantities dependent on these parameters are determined solely on physical grounds. The use of the above procedure for the structure under investigation shows that the increase of the quantum efficiency by 24% and the output power by 83% in comparison to the original design can be achieved when the widths of injection and extraction barriers are changed to their optimal values.Inspired by compressed sensing techniques, a method for significantly enhancing the maximum allowable scan rate in quasi-distributed acoustic sensing (Q-DAS) is described and studied. Matching the scan parameters to the interrogated array facilitates orders of magnitude improvement in the scan rate and a corresponding increase in the maximum slew rate (SR) of differential phase variations which can be measured without ambiguity. The method is termed array matched interrogation (AMI). To improve the method's SNR, maximum number of sensing sections and maximum range, the interrogation pulse can be replaced by a perfect periodic autocorrelation (PPA) code. This version of the method is referred to as coded array matched interrogation (C-AMI). The implementation of C-AMI is not trivial and requires special design rules which are derived and tested experimentally. The design rules ensure that the 'folding' of the returning peaks of the Q-DAS array into a scan period, which is much shorter than the fiber's roundtrip time, will not lead to overlaps.