Efficient Generation of Intense Broadband Terahertz Pulses from Quartz

The intense terahertz (THz) pulses facilitate the observation of various nonlinear optical effects and manipulation of material properties. In this work, we report a convenient approach that can produce strong broadband terahertz pulses with center frequency tunable between 2-4 THz. The coherent THz light source with pulse energy of 1.2 microjoule can be generated from a low-cost crystalline quartz pumped by an ultrashort tilted wave-front pulse. Thanks to the wide transparent spectral window and high damage threshold, our theoretical analysis and experiment show that the optical rectification in quartz is as efficient as that in LiNbO3, but covers much broader spectral range. This work not only provides the light source that is urgently needed for nonlinear THz spectroscopy beyond 1 THz, but offers an alternative route in the selection of nonlinear optical crystals for optical frequency conversion

Integrated circularly polarized OAM generator and multiplexer for fiber transmission

Unlike linearly polarized modes in fiber, modes exploiting orbital angular momentum (OAM) are circularly polarized when propagating in fiber. The use of OAM modes for spatial multiplexing requires efficient, low cost mode generators and multiplexers. We propose such a device based on the standard 220-nm silicon-on-insulator platform, taking multiple single-mode data-modulated signals, and imprinting these signals on right- and left-circularly polarized OAM channels on a single, multiplexed output. The device is designed to easily couple to an OAM fiber with a ring shaped core. This approach treating circular polarization within the multiplexer allows us to avoid the losses associated with filtering out unwanted polarization to create a single polarization. Designing the device to have an output matched to the OAM fiber mode profile also avoids mode size conversion. We describe our design methodology and optimization techniques using a transfer-matrix model and the finite-difference time-domain method. A candidate design is simulated and modal crosstalk is examined, showing that lowcrosstalk OAM multiplexing can be achieved through direct fiberto-chip coupling

Integrated phased array for scalable vortex beam multiplexing

Orbital angular momentum (OAM) modes have low model interactions during fiber propagation at data center distances, and thus are suitable for ultra-high capacity systems at low digital signal processing. Generating OAM modes using free-space setups is useful for proof-of-concept experiments, but is not a scalable solution. We use an optical phased array (OPA) with two-dimensional antennas for on-chip circularly polarized OAM beam generation. Our previous work demonstrated an OAM multiplexer for lower-order modes. In this work, we demonstrate an OAM multiplexer that supports a record of 46 (23 per polarization) simultaneous spatial modes up to OAM order 11. We also improve the crosstalk performance of our multiplexer. We incorporate an intensity tuning capability that substantially improves the OAM quality by enabling a uniform power distribution across the antennas. The worst-case crosstalk for the supported OAM5 to OAM11 are found experimentally to be better than -12 dB, with OAM10 achieving -17.2 dB

Optimal ultra-miniature polarimeters in silicon photonic integrated circuits

Measurement of the state of polarization of light is essential in a vast number of applications, such as quantum and classical communications, remote sensing, astronomy, and biomedical diagnostics. Nanophotonic structures and integrated photonic circuits can, in many circumstances, replace conventional discrete optical components for miniature polarimeters and chip-scale polarimetry systems and thus significantly improve robustness while minimizing the footprint and cost. We propose and experimentally demonstrate two silicon photonic four-photodetector (PD) division-of-amplitude polarimeters (4PD-DOAPs) using a complementary metal–oxide–semiconductor-compatible photonic fabrication process. The first design targets minimizing the number of optical components. The second design makes use of a slightly more complex circuit design to achieve an optimal frame for measurements; this measurement frame minimizes and equalizes estimation variances in the presence of the additive white Gaussian noise and the signal dependent shot noise. Further theoretical examination reveals that within the optimal measurement frames for Stokes polarimeters, the DOAP with four PDs has the minimal equally weighted variance compared to those with a greater number of PDs

Research on Ordering Strategy of Capital-Limited Retailers under Stochastic Market Demand

Under the condition of capital constraint on retailer, the retailers can effectively alleviate the funds shortage by delay payments and financing to third party financial institutions. This method will improve the profit of retailer and the performance of the csupply chain. Newsboy model under conditions of permissible delay payments, considers the capital structure of the company in the study of financing problems, and research two-stage supply chain system consisting of suppliers and retailers. An optimal order strategy model of the retailer is constructed, and the Analytical solution of this model is obtained. Then, this paper obtains a series of useful management conclusions through sensitivity analysis

A Chip-scale, Full-Stokes Polarimeter

The polarization of light conveys unique information that can be exploited by crucial applications. The bulky and costly discrete optical components used in conventional polarimeters limit their broad adoption. A compact, low-cost polarimeter would bring this functionality into a myriad of new scenarios and revolutionize its exploitation. Here we present a high-performance, full-Stokes polarimeter on a silicon chip. A surface polarization splitter and on-chip optical interferometer circuit produce the analysis matrix of an optimally conditioned polarimeter. This solid-state polarimeter is a system-on-a-chip with exceptional compactness, stability, and speed that could be used singly or in integrated arrays. Large arrays can increase the speed and resolution of full-Stokes imaging; therefore, our design provides a scalable polarimeter solution.Comment: 5 figure

A Single Multi-Task Deep Neural Network with a Multi-Scale Feature Aggregation Mechanism for Manipulation Relationship Reasoning in Robotic Grasping

Grasping specific objects in complex and irregularly stacked scenes is still challenging for robotics. Because the robot is not only required to identify the object's grasping posture but also needs to reason the manipulation relationship between the objects. In this paper, we propose a manipulation relationship reasoning network with a multi-scale feature aggregation (MSFA) mechanism for robot grasping tasks. MSFA aggregates high-level semantic information and low-level spatial information in a cross-scale connection way to improve the generalization ability of the model. Furthermore, to improve the accuracy, we propose to use intersection features with rich location priors for manipulation relationship reasoning. Experiments are validated in VMRD datasets and real environments, respectively. The experimental results demonstrate that our proposed method can accurately predict the manipulation relationship between objects in the scene of multi-object stacking. Compared with previous methods, it significantly improves reasoning speed and accuracy

On-chip circular polarization splitter using silicon photonic nanoantenna array

Control and sorting of quantum states of photons through the manipulation of polarization and spatial modes of light in integrated photonic circuits contributes important applications in optical communications and quantum-optical systems. We design and demonstrate a novel structure for a silicon nanoantenna array that can split the circular polarization states and couple them to separate single-mode silicon waveguides. Implemented using a CMOS-compatible photonic fabrication process, the array can be monolithically integrated with other photonic components for chip-scale optical signal processing. We also show that the polarization sorting property of the nanoantenna array can be flexibly controlled (by adjusting design parameters at subwavelength scale) to split any two arbitrary orthogonal polarization states