查看更多>>摘要：In this paper, we compare the performances of conventional CMA, two-stage CMA and constrained CMA, from cases of fixed-point, parallelization and delay periods which are necessary in real-time system. We implement an 112Gbit/s dual polarization channel model to simulate conventional CMA and other modified CMAs. When OSNR (Optical Signal to Noise Ratio) and PDL do not vary, compared with float-point case, reducing bit width of input data can worsen singularity problem of these three equalizers. Besides, when OSNR and PDL do not vary, compared with serial case, increasing parallels number can reduce singularity probabilities of these three equalizers. Then, when PDL does not change, increasing delay periods can deteriorate singularity problem. Furthermore, in float-point case, fixed-point case, serial case, parallels case and delay periods case, compared with other two equalizers, constrained CMA all shows best performances to decrease singularity probabilities. Therefore, among these three equalizers, constrained CMA is the most suitable to be employed in real-time system.
查看更多>>摘要：The fifth generation (5G) mobile fronthaul transmission system is being investigated, and one potential solution is to use 1-bit bandpass delta-sigma modulation, thus a bandpass filter (BPF) can be used to convert a digital 1-bit signal back to original analog RF signal at remote radio units. It is inevitable that this bandpass filter can induce phase and amplitude distortion to the signal, which may severely distort the signal integrity. In this work, two novel delta sigma modulators (DSM), called pre-filtered and post-filtered DSM, are proposed to compensate for the above both phase and amplitude distortion. The two designs are verified by using both simulation and experimentation with radio-over-fiber (RoF) links up to 20 km. The 5G signal used in the simulation and experimentation is a 200 MHz 64-QAM orthogonal frequency-division multiplexing signal centered at 2.5 GHz. An error vector magnitude is improved by up to similar to 19 dB using the above two DSMs.
查看更多>>摘要：We demonstrate that the deep learning algorithm can considerably simplify the design and characterization of high efficient self-focusing varied line-spaced gratings. Our neural network is implemented with a recovery rate of up to 94% for the transmission function parameters. With numerical simulations, and optical experiments, we show that the self-focusing varied line-spaced gratings designed in such a way are endowed with enhanced functionalities, such as the intensity of first-order diffraction peak being enhanced with around a factor of 30 compared with the incident intensity, and a high ratio (about 60) between the peak intensity of the first order and the intensity of the zero-order. Our results allow the rapid design and characterization of self-focusing varied line-spaced gratings as well as optimal microstructures for targeted far-field diffraction patterns, which are playing key roles in spectroscopy and monochromatization applications.
查看更多>>摘要：We present a dynamically switchable broadband dual-mode polarization conversion metasurface in the terahertz (THz) regime, which consists of double-layer graphene grating, metal resonator, and gold-vanadium dioxide (VO2) alternating grating and silicon dioxide (SiO2) dielectric spacer. The phase transition capability of VO2 is utilized to realize the switching of polarization conversion between transmission mode and reflection mode, and the design of double-layer graphene grating can enhance the transmittance in transmission mode. When VO(2 )is in the insulating state, by increasing the Fermi level of the double-layer graphene, linear polarization conversion in transmission mode can be achieved in 0.52~1.74 THz with the relative bandwidth of about 107.9%; when VO2 is in the metallic state and the Fermi level of graphene is 0 eV, the metasurface works in reflection mode, achieving the reflective linear polarization conversion in the range of 0.62~1.70 THz with relative bandwidth of up to 93.1%. The PCR in the two modes can be dynamically adjusted by changing the Fermi level of graphene and the conductivity of VO2. The proposed dual-mode metasurface is a potential in the design of optical polarization control devices for spectroscopy, imaging etc.
查看更多>>摘要：The lasing process emerges from an amplified spontaneous emission (ASE) when an optical resonator is present. The ASE is often observed during the laser emission, especially in random lasing studies. The differentiation between ASE and random lasing is difficult, particularly considering coherent and incoherent random lasing from polymeric dye-doped systems. In this article, we present the straightforward procedure of differentiation of both processes, in order to simultaneously designate the ASE and lasing emission properties and performance.
查看更多>>摘要：Wheat leaf is a natural material having abundant gaps between micro-protrusions and flat structures. Magnetron sputtering method is used to sputter Ag film on wheat leaves and Rhodamine 6G (R6G) is used to detect the SERS difference caused by different structures of the same material. The SERS signal shows that the Raman intensity of the micro-protrusions is stronger than that of the flat parts. The results shows that there are more gaps in the protrusion structure per unit area, thereby providing more "hot spots", which plays an important role in improving the SERS signal. Therefore, this low-cost and high-performance SERS system shows excellent application prospects and provides a new idea to improve SERS signal by using natural biomaterials as SERS substrate.
查看更多>>摘要：Orbital angular momentum (OAM) presents an additional degree of freedom for enhancing the information capacity in optical communications. To make full use of the OAM states, mode-division multiplexing (MDM) technology based on multiplexing multiple OAM modes has been adopted. However, numerous recent studies indicate that the recognition of multiplexed optical vortices is sensitive to the misalignment and requires complicated calculations, which severely restricts the decoding efficiency of a communication system. In this paper, a novel optical lattice that contains spatial positions and modes information is specially-designed and applied for short-haul free-space optical communications. Specifically, at the transmitter, the lattices with four different superposition modes (+/- 1, +/- 2, +/- 3, +/- 4) and positions information are obtained and utilized to code the 8-bit length sequences into each 256-ary symbol. And at the receiver side, the initial information sequences can be decoded by directly identifying the captured intensity patterns (i.e., incoherent detection method). In the proof-of-concept experiment, a 64 x 64 pixel Lena gray image is successfully transmitted over a 3 m indoor optical communication link. The bit error among all received symbol sequences is evaluated, and zero bit error rate (BER) is observed, showing favorable link communication performance. Due to the mode and spatial paralleling, this work exhibits great potential in the future high-dimensional large capacity optical communications.
True, Timothy M.Pitz, Greg A.Rice, Christopher A.Perram, Glen P....
8页
查看更多>>摘要：The rubidium 5(2) S-1/2 -> 5(2) D-3/2 and 5(2) S-1/2 -> 5(2) D-5/2 two-color two-photon transitions were examined with a variety of detunings in the region 758-798 nm to reveal the transition rates. Two cw lasers with crossed linear polarizations were overlapped and counterpropagated through a vapor cell, with the transition rate monitored by side fluorescence from 6P. Resonant enhancement via the 5P states results in intensity variations of over 6 orders of magnitude across the detuning range. No destructive interference zeros were seen, as expected from the polarization dependent calculation of the third-order susceptibility. Zeros occur from interference between two intermediate states, but due to the contributions from both symmetric and antisymmetric susceptibility tensors the zero of one is hidden by a non-zero value of the other. The polarization dependence was explicitly seen by fixing the detuning and iterating the linear polarizations from crossed to parallel.
查看更多>>摘要：We numerically demonstrate the ultranarrow high-order Fano resonance generated by the plasmonic coupling between graphene quadrupole dark mode and metallic bright magnetic dipole mode due to structural symmetry breaking effect in asymmetric hybrid metamaterials, consisting of periodic arrays of graphene nanoribbon and gold split-ring resonators. The graphene quadrupole Fano curve presents an ultranarrow lineshape with quality (Q) factor of 40. The proposed metamaterial shows the obvious dependence of the structural parameters and Fermi energy. Our designed asymmetric hybrid metamaterials shows a high sensitivity of 4.2 mu m/RIU and figure of merit (FOM) of 30, which could pave way for in label-free biomedical sensing.
查看更多>>摘要：Hyperthermia treatment technology has been widely used to accelerate the dissipation of inflammation and cancer, however, it is remain a great challenge to explore second near-infrared (NIR) nanothermometer with high sensitivity. In this work, the positive and negative thermal quenching effect were integrated to realize NIR nanothermometer with high sensitivity. For the NaNdF4:Yb@NaYF4 and NaNdF4:Yb@NaYF4 nanoparticles involved transparent film, the Yb3+ emission intensity at similar to 975 nm decreases while that of Er3+ ions at similar to 1532 nm increases with the rising of temperature upon 808 nm laser excitation. These opposite temperaturedependent emission intensity variations give out a maximum absolute temperature sensitivity (S-a) of 0.18 K-1 and a relative sensitivity (Sr) of 3.1% K-1. Moreover, the calculated minimum S-a and S-r are up to 0.04 K-1 and 1.55% K-1, respectively.
NSTL
Elsevier