Lowemidtgaard2914

A novel symbol division multiplexing (SDM) technology is proposed in an intensity modulation and direct detection (IM/DD) pulse amplitude modulation (PAM) optical interconnection. The SDM-PAM4 symbol is the multiplexing of two standard 3-bit PAM8 symbols based on many-to-one (MTO) mapping, increasing by an extra 50% the line rate compared with a typical PAM4 under the same symbol rate and channel bandwidth. The forward error correction (FEC) based on low-density parity-check coding establishes a mechanism between the codewords of both intra- and inter-SDM-PAM4 symbols, to theoretically support the iterative decoding of symbol de-multiplexing employing an optimized bit-interleaved coded modulation iterative decoding (BICM-ID) system. Furthermore, since SDM evidently reduces the mapping order of the PAM signal, the transmission reliability can be effectively improved by alleviating the impairments mainly caused by fiber chromatic dispersion and Kerr nonlinearity. The experimental results indicate that the SDM-PAM4 can achieve more than 5 dB superior systematic receiver power sensitivity over 10-km single mode fiber transmission, and thus represent an important development in coding and modulation multiplexing techniques for optical interconnection systems.We develop a general methodology capable of analyzing the response of Weyl semimetal (WSM) photogalvanic networks. Both single-port and multiport configurations are investigated via extended versions of Norton's theorem. An equivalent circuit model is provided where the photogalvanic currents induced in these gapless topological materials can be treated as polarization-dependent sources. To illustrate our approach, we carry out transport simulations in arbitrarily shaped configurations involving pertinent WSMs. Our analysis indicates that the photogalvanic currents collected in a multi-electrode system directly depend on the geometry of the structure as well as on the excitation and polarization pattern of the incident light. Our results could be helpful in designing novel optoelectronic systems that make use of the intriguing features associated with WSMs.Terahertz (THz) absorption spectroscopy is a powerful tool for molecular label-free fingerprinting, but it faces a formidable hurdle in enhancing the broadband spectral signals in trace-amount analysis. In this paper, we propose a sensing method based on the geometry scanning of metal metasurfaces with spoof surface polarization sharp resonances by numerical simulation. This scheme shows a significant absorption enhancement factor of about 200 times in an ultra-wide terahertz band to enable the explicit identification of various analytes, such as a trace-amount thin lactose film samples. The proposed method provides a new, to the best of our knowledge, choice for the enhancement of wide terahertz absorption spectra, and paves the way for the detection of trace-amount chemical, organic, or biomedical materials in the terahertz regime.In this Letter, an exciton absorption assumption is made to explain the mid-infrared saturable absorption performance of the 2D h-BN nanosheet. The exciton binding energy of ∼0.4 eV corresponds to the light wavelength around 3 µm, matching well with the experimental results. Experimentally, the h-BN saturable absorber (SA) shows a modulation depth of 5.3% in the wavelength region of 3 µm. By employing the h-BN SA in an ErLu2O3 laser, laser pulses with a pulse duration of 252 ns are realized at a repetition rate of 169 kHz, corresponding to a pulse energy of 3.55 µJ and peak power of 14 W. The exciton absorption assumption will help obtain a better understanding of the nonlinear optical dynamics in 2D materials from a new perspective.Here we report the demonstration of a spectral peaking phenomenon in a fiber laser oscillator. An HCN gas cell was inserted in an ultrashort-pulse Er-doped fiber laser with single-wall carbon nanotubes. Sech2-shaped ultrashort pulses with intense multiple sharp spectral peaks were stably generated. When the generated pulses were coupled into highly nonlinear fiber, enhanced multiple spectral peaks were generated by periodical spectral peaking in the optical fiber. The characteristics and physical mechanism of spectral peaking in the fiber laser were investigated via numerical simulations. As the magnitude of absorption was increased, the magnitude of the generated spectral peaks increased almost exponentially. It was clarified that the spectral peaks were generated through the accumulation of filtering components generated in each round trip.We theoretically investigate the dynamics, bifurcation structure, and stability of localized states in Kerr cavities driven at the pure fourth-order dispersion point. Both the normal and anomalous group velocity dispersion regimes are analyzed, highlighting the main differences from the standard second-order dispersion case. In the anomalous regime, single and multi-peak localized states exist and are stable over a much wider region of the parameter space. In the normal dispersion regime, stable narrow bright solitons exist. Some of our findings can be understood using a new, to the best of our knowledge, scenario reported here for the spatial eigenvalues, which imposes oscillatory tails to all localized states.Ultra-longitudinal-compact S-bends with flexible latitudinal distances (d) are proposed and experimentally demonstrated with ultralow loss and fabrication-friendly structures by three steps based on numerical optimization. During the first step (curve optimization), insertion losses (ILs) of S-bends are significantly reduced by optimizing transition curves based on Bézier curves. During the second step (shape optimization), the ILs are further minimized by varying the widths of S-bends to increase optical confinement. In the third step (curvature optimization), considering ease of fabrication, an optimization of curvature radius is used to ensure that all feature sizes for the S-bends are larger than 200 nm. Simulation results show that for S-bends with footprints of 2.5× d μm2, the ILs are less than (0.19, 0.045, 0.18, 0.27) dB in a wavelength range of 1400-1700 nm when d is set as (3, 6, 9, 12) μm, respectively. Then, the S-bends of 2.5× 3 μm2 and 2.5× 12 μm2 are fabricated on a commercial 220-nm silicon-on-insulator (SOI) platform. Experimental results show that the ILs of both are less than 0.16 dB in a wavelength range of 1420-1630 nm. The lowest ILs are 0.074 dB and 0.070 dB, respectively. Moreover, in addition to the ultralow ILs and ease of fabrication, our design is flexible for designing S-bends with a flexible value of d, which makes our approach practical in large-scale photonic integrated circuits.In this study, we developed a photonic band microscope based on hyperspectral Fourier image spectroscopy. The developed device constructs an infrared photonic band structure from Fourier images for various wavelength obtained by hyperspectral imaging, which make it possible to speedily measure the dispersion characteristics of photonic nanostructures. By applying the developed device to typical photonic crystals and topological photonic crystals, we succeeded in obtaining band structures in good agreement with the theoretical prediction calculated by the finite element method. This device facilitates the evaluation of physical properties in various photonic nanostructures, and is expected to further promote related fields.A novel, to the best of our knowledge, class of coherent structures of inseparability, incorporating phases asymmetrically cross-coupled by two position vectors, is introduced in theory and experiment. These phases disappear in the environment of complete coherence, but the vanishment is avoidable in the coexistent state of extreme incoherence and full coherence. The radiated beams intrinsically possess a controllable rotation but undergo an intermediate process quite different from the twisted Gaussian Schell-model beams. Analysis shows a novel association between the magnitude and the phase of the coherent structure which displays both synergy and opposition. Our work further reveals the inner mechanism of the inseparable coherent structures and extends a new horizon for the optical twist.Photoacoustic/ultrasound (PA/US) dual-modality imaging has been evolving rapidly for the last two decades. Handheld PA/US probes with different implementations have attracted particular attention due to their convenience and high applicability. However, developing a volumetric dual-modality PA/US imaging probe with a compact design remains a challenge. Here, we develop a handheld volumetric PA/US imaging probe with a special light-ultrasound coupling design and an internal scanning mechanism. A coaxial design for the excitation and detection paths in a customized 3D-printed housing with a size of 110 × 90 × 64 mm3 is proposed to optimize the signal-to-noise ratio (SNR) of the handheld probe for deep tissue imaging. Two parallel and synchronously rotational acoustic reflectors allow for volumetric imaging with an effective field of view (FOV) of more than 30 mm × 20 mm × 8 mm. In addition to simulation and phantom validations, in vivo human trials are successfully carried out, demonstrating the high imaging quality and stability of the system for potential clinical translations.We demonstrate all-optical mode switching with a graphene-buried polymer waveguide asymmetric directional coupler (DC) by using the photothermal effect of graphene, where TE-polarized pump light and TM-polarized signal light are employed to maximize pump absorption and minimize graphene-induced signal loss. Our experimental device, which uses a graphene length of 6.2 mm, shows a pump absorption of 3.4 dB (at 980 nm) and a graphene-induced signal loss of 0.1 dB. The device can spatially switch between the fundamental mode and the higher-order mode with extinction ratios larger than 10 dB (at 1580 nm) and switching times slightly shorter than 1 ms at a pump power of 36.6 mW. Graphene-buried polymer waveguides offer many new possibilities for the realization of low-power all-optical control devices.The recent advances in femtosecond vacuum UV (VUV) pulse generation, pioneered by the work of Noack et al., has enabled new experiments in ultrafast time-resolved spectroscopy. Expanding on this work, we report the generation of 60 fs VUV pulses at the 7th harmonic of Tisapphire with more than 50 nJ of pulse energy at a repetition rate of 1 kHz. The 114.6 nm pulses are produced using non-collinear four-wave difference-frequency mixing in argon. The non-collinear geometry increases the phase-matching pressure, and results in a conversion efficiency of ∼10-3 from the 200 nm pump beam. The VUV pulses are pre-chirp-compensated for material dispersion with xenon, which has negative dispersion in this wavelength range, thus allowing almost transform-limited pulses to be delivered to the experimental chamber.In this Letter, we report a four-wavelength quadrature phase demodulation technique for extrinsic Fabry-Perot interferometric (EFPI) sensors and dynamic signals. Four interferometric signals are obtained from four different laser wavelengths. A wavelength interval of four wavelengths is chosen according to the free spectrum range (FSR) of EFPI sensors to generate two groups of anti-phase signals and two groups of orthogonal signals. The linear fitting (LF) method is applied to two groups of anti-phase signals to eliminate the dc component and ac amplitude to obtain two normalized orthogonal signals. The differential cross multiplication (DCM) method is then used to demodulate the phase signal from these two normalized orthogonal signals. The proposed LF and DCM (LF-DCM) based four-wavelength quadrature phase demodulation overcomes the drawback of the traditional ellipse fitting (EF) and DCM (EF-DCM) based dual-wavelength demodulation method that it is not suitable for weak signal demodulation since the ellipse degenerates into a straight line, which makes the EF algorithm invalid.