Manipulating terahertz guided wave excitation with Fabry-Perot cavity-assisted metasurfaces.

Metasurfaces are emerging as powerful tools for manipulating complex light fields, offering enhanced control in free space and on-chip waveguide applications. Their ability to customize refractive indices and dispersion properties opens up new possibilities in light guiding, yet their efficiency in exciting guided waves, particularly through metallic structures, is not fully explored. Here, we present a new method for exciting terahertz (THz) guided waves using Fabry-Perot (FP) cavity-assisted metasurfaces that enable spin-selective directional coupling and mode selection.

Molecularly imprinted polymer-coated hybrid optical waveguides for sub-aM fluorescence sensing.

The sensitivity of fluorescent sensors is crucial for their applications. In this study, we propose a molecularly imprinted polymer (MIP)-coated optical fibre-hybrid waveguide-fibre sensing structure for ultrasensitive fluorescence detection. In such a structure, the MIP coated-hybrid waveguide acts as a sensing probe, and the two co-axially connected optical fibres act as a highly efficient probing light launcher and a fluorescence signal collector, respectively.

Front-face synchronous fluorescence spectroscopy: a rapid and non-destructive authentication method for Arabica coffee adulterated with maize and soybean flours.

Unlabelled: This article describes a novel front-face synchronous fluorescence spectroscopy (FFSFS) method for the fast and non-invasive authentication of ground roasted Arabica coffee adulterated with roasted maize and soybean flours. The detection was based on the different composition of fluorescent Maillard reaction products and caffeine in roasted coffee and cereal flours. For each roasted maize or soybean adulterant flour (5-40 wt%), principal component analysis coupled with linear discriminant analysis (PCA-LDA) was used for qualitative discrimination.

Fluorescence quenching by competitive absorption between solid foods: Rapid and non-destructive determination of maize flour adulterated in turmeric powder.

Fluorescence quenching induced by competitive absorption between different components of solid foods was observed for the first time. By using front-face synchronous fluorescence spectroscopy (FFSFS) and fluorescence titration, competitive absorption between maize flour and turmeric powder was proven to occur between phenolic acids in maize flour and curcumin in turmeric powder. FFSFS was applied for the rapid and non-destructive determination of maize flour adulterated in turmeric powder.

A Review on Terahertz Technologies Accelerated by Silicon Photonics.

In the last couple of decades, terahertz (THz) technologies, which lie in the frequency gap between the infrared and microwaves, have been greatly enhanced and investigated due to possible opportunities in a plethora of THz applications, such as imaging, security, and wireless communications. Photonics has led the way to the generation, modulation, and detection of THz waves such as the photomixing technique. In tandem with these investigations, researchers have been exploring ways to use silicon photonics technologies for THz applications to leverage the cost-effective large-scale fabrication and integration opportunities that it would enable.

Critical Factors for In Vivo Measurements of Human Skin by Terahertz Attenuated Total Reflection Spectroscopy.

Attenuated total reflection (ATR) geometry is a suitable choice for in vivo measurements of human skin due to the deep penetration of the field into the sample and since it makes it easy to measure the reference spectrum. On the other hand, there are several critical factors that may affect the terahertz (THz) response in these kinds of experiments. Here, we analyse in detail the influence of the following factors: the contact positions between the thumb and the prism, the contact pressure, the contact duration, and the materials of the prism.

Terahertz-frequency temporal differentiator enabled by a high-Q resonator.

Terahertz (THz) fundamental "building blocks" equivalent to those used in multi-functional electronic circuits are very helpful for actual applications in THz data-processing technology and communication. Here, we theoretically and experimentally demonstrate a THz temporal differentiator based on an on-chip high-quality (Q) factor resonator. The resonator is made of low-loss high-resistivity silicon material in a monolithic, integrated platform, which is carefully designed to operate near the critical coupling region.

Broadband achromatic metalens in terahertz regime.

Achromatic focusing is essential for broadband operation, which has recently been realised from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element.

Flexibly designed spoof surface plasmon waveguide array for topological zero-mode realization.

We propose a flexibly designed photonic system based on ultrathin corrugated metallic "H-bar" waveguide that supports spoof surface plasmon polariton (SPP) at microwave frequencies. Five designs were presented, in order to demonstrate flexibility according to varying height, period, core width, rotation, and shifting on the "H-bar" unit of the waveguide. The propagation constant between two hybrid designs of period and height structure was then shown in order to study the coupling effect.

Fano-resonance in one-dimensional topological photonic crystal heterostructure.

We theoretically realize the Fano resonance with a high quality factor of 10 using a structure, which is constructed from three one-dimensional photonic crystals and a defect layer. The emerged Fano resonance can be attributed to the weak coupling between a Fabry-Perot cavity mode and a topological edge state mode provided by the topological photonic crystal heterostructure. Moreover, we experimentally reproduce this Fano resonance in the optical communication range with a high quality of 10.

High extinction ratio electromagnetically induced transparency analogue based on the radiation suppression of dark modes.

A high extinction ratio (ER) electromagnetically induced transparency (EIT) analogue based on single-layer metamaterial is designed and experimentally demonstrated in this paper. This design involves four mirror-like symmetrically coupled split ring resonators (SRRs) that exhibit a bright-dark-dark-bright mode configuration. The EIT-like effect is realized by coupling between the bright resonators and dark resonators.

Optimization of adiabatic microring resonators with few-mode and high-Q resonances.

We present the theoretical analysis and experimental demonstration of adiabatic microring resonators. The resonators are halfway between microdisk and microring preserving the good properties of both the microdisk (high Q-factor) and the microring (internal mode rejection). Device modeling based on the coupled-mode theory suggests that both the internal and external decay rates should be low in order to obtain high-Q and high extinction ratio resonances.

Seven-bit reconfigurable optical true time delay line based on silicon integration.

We design, fabricate, and characterize a 7-bit reconfigurable optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches on the silicon photonics platform. Variable optical attenuators (VOAs) are embedded to suppress the inter-symbol crosstalk caused by the finite extinction ratio of switches. The device can provide a maximum of 1.

Selective excitation of microring resonances using a pulley-coupling structure.

We explore the selective excitation of resonances in microring resonators with a pulley-coupling structure. Due to the wavelength dispersion of coupling coefficient, only the resonances near critical coupling exhibit pronounced sharp notches in the transmission spectrum. Experimental results show that the resonance extinction ratio is a strong function of wavelength.

Continuously tunable reflective-type optical delay lines using microring resonators.

We present a reflective-type optical delay line using waveguide side-coupled 13 microring resonators terminated with a sagnac loop reflector. Light passes through the microring resonator sequence twice, doubling the delay-bandwidth product. Group delay is tuned by p-i-p type microheaters integrated directly in the microring waveguides.

CMOS-compatible temperature-independent tunable silicon optical lattice filters.

We present a CMOS-compatible athermal tunable silicon optical lattice filter composed of 10 cascaded 2 × 2 asymmetric Mach-Zehnder interferometers. Active tuning experiments show that the filter central wavelength can be red-/blue-shifted by 13.1/21.

Tunable two-stage self-coupled optical waveguide resonators.

We report tunable two-stage self-coupled optical waveguide (SCOW) resonators composed of a pair of mirror-imaged single SCOW resonators connected by a phase shifter in between. Experimental results show that the coupled-resonator-induced-transparency and high-order bandstop filtering characteristics can be obtained in the transmission spectra of the devices with two different configurations. The resonance spectrum can be tuned by using either a p-i-p microheater or a p-i-n diode in the phase shifter.

Tunable silicon Fabry-Perot comb filters formed by Sagnac loop mirrors.

We experimentally demonstrate tunable silicon comb filters based on Fabry-Perot (FP) resonators composed of two Sagnac loop mirrors. The comb filter resolves up to 54 comb lines with a 115 GHz channel spacing over a spectral range from 1510 to 1560 nm. The comb line extinction ratio is ~26.