Coherent terahertz wireless communication using dual-parallel MZM-based silicon photonic integrated circuits.

Coherent terahertz (THz) wireless communication using silicon photonics technology provides critical solutions for achieving high-capacity wireless transmission beyond 5G and 6G networks and seamless connectivity with fiber-based backbone networks. However, high-quality THz signal generation and noise-robust signal detection remain challenging owing to the presence of inter-channel crosstalk and additive noise in THz wireless environments. Here, we report coherent THz wireless communication using a silicon photonic integrated circuit that includes a dual-parallel Mach-Zehnder modulator (MZM) and advanced digital signal processing (DSP). The structure and fabrication of the dual-parallel MZM-based silicon photonic integrated circuit are systematically optimized using the figure of merit (FOM) method to improve the modulation efficiency while reducing the overall optical loss. The advanced DSP compensates for in-phase and quadrature (IQ) imbalance as well as phase noise by orthogonally decoupling the IQ components in the frequency domain after adaptive signal equalization and carrier phase estimation. The experimental results show a reduction in phase noise that induces degradation of transmission performance, successfully demonstrating error-free 1-m THz wireless transmission with bit-error rates of 10-6 or less at a data rate of 50 Gbps.

Spread spectrum SERS allows label-free detection of attomolar neurotransmitters.

The quantitative label-free detection of neurotransmitters provides critical clues in understanding neurological functions or disorders. However, the identification of neurotransmitters remains challenging for surface-enhanced Raman spectroscopy (SERS) due to the presence of noise. Here, we report spread spectrum SERS (ss-SERS) detection for the rapid quantification of neurotransmitters at the attomolar level by encoding excited light and decoding SERS signals with peak autocorrelation and near-zero cross-correlation. Compared to conventional SERS measurements, the experimental result of ss-SERS shows an exceptional improvement in the signal-to-noise ratio of more than three orders of magnitude, thus achieving a high temporal resolution of over one hundred times. The ss-SERS measurement further allows the attomolar SERS detection of dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and glutamate without Raman reporters. This approach opens up opportunities not only for investigating the early diagnostics of neurological disorders or highly sensitive biomedical SERS applications but also for developing low-cost spectroscopic biosensing applications.

Effect of Sex Difference on Discordance Between Instantaneous Wave-Free Ratio and Fractional Flow Reserve.

BACKGROUND: Physiology-guided percutaneous coronary intervention (PCI) has demonstrated to improve clinical outcomes. Previous trials showed the agreement between iFR and FFR is approximately 80%, however the details of discordance pattern remain to be elucidated. METHODS: We retrospectively reviewed 1024 consecutive intermediate stenotic lesions for which functional evaluation using both iFR and FFR were performed between January 2015 and June 2016. The lesions were classified into 4 groups according to iFR and FFR concordance [(iFR+/FFR+) and (iFR-/FFR-)] or discordance [(iFR+/FFR-) and (iFR-/FFR+)]. RESULTS: Our study evaluated 451 lesions, 264 lesions (58.5%) from men and 187 lesions (41.5%) from women. iFR was similar between women and men, however FFR was significantly higher in women than men. The rate of discordance between iFR and FFR was 21.3% (iFR+/FFR- 12.4% and iFR-/FFR+ 8.9%) in overall cohort. The prevalence of overall concordance and discordance were similar between men and women, however iFR+/FFR- discordance was significantly higher in women (17.1% vs. 9.1%) whereas iFR-/FFR+ discordance was significantly higher in men (11.3% vs. 4.8%). In multivariable analysis, female sex and older age were significantly associated with iFR+/FFR- discordance (odds ratio 1.88 and 1.48, respectively). Conversely, younger age, higher stenosis, and concomitant chronic total occlusion were independent predictors for iFR-/FFR+ discordance (odds ratio 0.67, 1.82, and 4.32, respectively). CONCLUSIONS: Despite similar prevalence of overall concordance and discordance between men and women, iFR+/FFR- discordance was higher in women and iFR-/FFR+ discordance was higher in men. Multivariable analysis showed female sex to be independent predictor of iFR+/FFR- discordance.

Demonstration of photonics-aided terahertz wireless transmission system with using silicon photonics circuit: erratum.

We present an erratum for our recent paper [Opt. Express 28, 23397 (2020)] to include funding information in the funding section.

Demonstration of photonics-aided terahertz wireless transmission system with using silicon photonics circuit.

We experimentally demonstrate the use of silicon photonics circuit (SPC) in the simple and cost-effective photonics-aided Terahertz (THz) wireless transmission system. We perform theoretical investigation (with experimental confirmation) to understand that the system performance is more sensitive to the free space path loss (FSPL) at the THz wireless link than the SPC's insertion loss. The SPC, we design and fabricate, combines two incident optical carriers at different wavelengths and modulates one of two optical carriers with data to transfer, consequently reducing the system footprint that is indeed one of the key challenges that must be tackled for better practicability of the THz communication system. We perform experimental verification to show the feasibility of 40 Gb/s non-return-to-zero (NRZ) on-off-keying (OOK) signal transmission over 1.4 m wireless link for possibly its application in short-reach indoor wireless communication systems utilizing (sub-)THz frequency band such as, e.g., indoor WiFi, distributed antenna/radio systems, rack-to-rack data delivery, etc. The SPC could be further integrated with various photonic elements such as semiconductor optical amplifiers, laser diodes, and photo-mixers, which will enable the path towards all-photonic THz-wave synthesizers.

Nanoislands as plasmonic materials.

Subwavelength metal nanoislands thermally dewetted from a thin film emerge as a powerful and cost-effective photonic material, due to the formation of substantially strong nano-gap-based plasmonic hot spots and their simple large-area nanofabrication. Unlike conventional nanostructures, nanoislands dewetted from thin metal films can be formed on a large scale at the wafer level and show substrate-dependent plasmonic phenomena across a broad spectral range from ultraviolet to infrared. Substrate-selective dewetting methods for metal nanoislands enable diverse nanophotonic and optoelectronic technologies, underlining mechanical, structural, and material properties of a substrate. Emerging bioplasmonic technology using metal nanoislands also serves as a high-throughput and surface-sensitive analytical technique with wide-ranging application in rapid, real-time, and point-of-care medical diagnostics. This review introduces an assortment of dewetting fabrication methods for metal nanoislands on distinct substrates from glass to cellulose fibers and provides novel findings for metal nanoislands on a substrate by three-dimensional numerical modeling. Furthermore, the plasmonic properties of metal nanoislands and recent examples for their photonic applications, in particular, biological sensing, are technically summarized and discussed.

Fiber-optic plasmonic probe with nanogap-rich Au nanoislands for on-site surface-enhanced Raman spectroscopy using repeated solid-state dewetting.

We report a fiber-optic plasmonic probe with nanogap-rich gold nanoislands for on-site surface-enhanced Raman spectroscopy (SERS). The plasmonic probe features nanogap-rich Au nanoislands on the top surface of a single multimode fiber. Au nanoislands were monolithically fabricated using repeated solid-state dewetting of thermally evaporated Au thin film. The plasmonic probe shows 7.8 × 106 in SERS enhancement factor and 100 nM in limit-of-detection for crystal violet under both the excitation of laser light and the collection of SERS signals through the optical fiber. The fiber-through measurement also demonstrates the label-free SERS detection of folic acid at micromolar level. The plasmonic probe can provide a tool for on-site and in vivo SERS applications.

Identification method of non-reflective faults based on index distribution of optical fibers.

This paper investigates an identification method of non-reflective faults based on index distribution of optical fibers. The method identifies not only reflective faults but also non-reflective faults caused by tilted fiber-cut, lateral connector-misalignment, fiber-bend, and temperature variation. We analyze the reason why wavelength dependence of the fiber-bend is opposite to that of the lateral connector-misalignment, and the effect of loss due to temperature variation on OTDR waveforms through simulation and experimental results. This method can be realized by only upgrade of fault-analysis software without the hardware change, it is, therefore, competitive and cost-effective in passive optical networks.