Sensitivity improvement of dual-comb spectroscopy using mode-filtering technique

In this study, we demonstrated an improvement in the detection sensitivity of dual-comb spectroscopy using the repetition rate multiplication of optical frequency combs. We compared the dual-comb signals in three dual-comb setups consisting of combinations of two combs with and without mode-filtering, and investigated how the repetition rate influences the signal-to-noise ratio (SNR) of dual-comb measurements. The dual-comb setups using high-repetition-rate combs enabled the absorption lines of HCN gas to be measured with a high SNR in a short averaging time, and real-time spectral data acquisition was realized using a low-sensitivity and low-resolution RF spectrum analyzer

FPGA Implementation of Hierarchical Subcarrier Rate and Distribution Matching for up to 1.032 Tb/s or 262144-QAM

A novel hierarchical subcarrier rate and distribution matching has been implemented in an FPGA at 1.032 Tb/s. The implemented subsystem achieves seamless data flow among subcarriers at a resolution < 0.01 bit per channel use

Open Semiclassical Strings and Long Defect Operators in AdS/dCFT Correspondence

We consider defect composite operators in a defect superconformal field theory obtained by inserting an AdS_4 x S^2-brane in the AdS_5 x S^5 background. The one-loop dilatation operator for the scalar sector is represented by an integrable open spin chain. We give a description to construct coherent states for the open spin chain. Then, by evaluating the expectation value of the Hamiltonian with the coherent states in a long operator limit, a Landau-Lifshitz type of sigma model action is obtained. This action is also derived from the string action and hence we find a complete agreement in both SYM and string sides. We see that an SO(3)_H pulsating string solution is included in the action and its energy completely agrees with the result calculated in a different method. In addition, we argue that our procedure would be applicable to other AdS-brane cases.Comment: 22 pages, 1 figure, LaTeX, minor corrections and references added. v3) some new results added. shortened and accepted version in PR

Compact and scalable polarimetric self-coherent receiver using dielectric metasurface

The polarimetric self-coherent system using a direct-detection-based Stokes-vector receiver (SVR) is a promising technology to meet both the cost and capacity requirements of the short-reach optical interconnects. However, conventional SVRs require a number of optical components to detect the state of polarization at high speed, resulting in substantially more complicated receiver configurations compared with the current intensity-modulation-direct-detection (IMDD) counterparts. Here, we demonstrate a simple and compact polarimetric self-coherent receiver based on a thin dielectric metasurface and a photodetector array (PDA). With a single 1.05-$\mu$m-thick metasurface device fabricated on a compact silicon-on-quartz chip, we implement functionalities of all the necessary passive components: a 1$\times$3 splitter, three polarization beam splitters with different polarization bases, and six focusing lenses. Combined with a high-speed PDA, we demonstrate self-coherent transmission of 20-GBd 16-ary quadrature amplitude modulation (16QAM) and 50-GBd quadrature phase-shift keying (QPSK) signals over a 25-km single-mode fiber. Owing to the surface-normal configuration, it can easily be scaled to receive spatially multiplexed channels from a multicore fiber or a fiber bundle, enabling compact and low-cost receiver modules for the future highly parallelized self-coherent systems.Comment: 10 pages, 6 figures (main manuscript) + 2 pages, 2 figures (supplementary info

Dual-comb spectroscopy for rapid characterization of complex optical properties of solids

We demonstrate rapid characterization of complex optical properties of solids via dual-comb spectroscopy (DCS) in the near-infrared region. The fine spectral structures in the complex refractive index of an Er:YAG are successfully deduced using the developed system and Fourier analysis. Moreover, simultaneous determination of the refractive index and the thickness is demonstrated for a silicon semiconductor wafer through the use of multireflected echo signals. The results indicate the potential of DCS as a powerful measurement tool for the rapid and full characterization of solid materials

Reprocessable Aliphatic Polydithiourethanes Based on the Reversible Addition Reaction of Diisothiocyanates and Dithiols

Aliphatic polydithiourethanes (PDTUs) were successfully synthesized from diisothiocyanates and dithiols having different values of the carbon atom number. The thermal properties and hydrogen-bonding behavior of PDTUs were studied in detail by using differential scanning calorimetry, thermal gravimetric analysis, temperature dependence nuclear magnetic resonance, Fourier transform infrared-attenuated total reflection, and density functional theory and semiempirical molecular orbital methods. In this work, we demonstrated that the thermal decomposition of PDTUs happened from the cleavage of the C–S bond of the dithiocarbamate moiety in the main chain and also that the active isothiocyanate and thiol groups were reprepared in the terminal of the decomposed polymer (i.e., oligomer). Furthermore, we found that the thermal depolymerization of PDTUs and the repolymerization of dithiourethane oligomers at room temperature proceeded repeatedly a few times

Synthesis and decrosslinking of networked polymers having zwitterion structure consisted by cyclic amidine and isothiocyanate

We have already found that the polymers, which are obtained by the polymerization of 4‐vinylphenyl isothoiocyanate after the zwitterion formation with cyclic amidines, are networked through the ionic interaction among the zwitterions becoming insoluble to various solvents. We report here on the results of the reaction of nucleophilic reagents such as amines and alcohols with the zwitterionic adduct to investigate about the decrosslinking through the resolution of ionic interactions. In the model reactions of amines and alcohols with the zwitterion compounds, which were consisted of the phenyl isothiocyanate and cyclic amidines, the reaction of nucleophilic reagents and zwitterionic adducts having methyl group at the 2‐position of the amidine proceed quantitatively. Based on the model reaction, such nucleophilic addition was applicable to decrosslinking reaction of the networked polymers containing the zwitterion structure in the side‐chain