An integrated plasmonic indium-tin-oxide (ITO)-based silicon electro-optical modulator has been designed, fabricated, and characterized. A sandwich structure shows a 40 GHz bandwidth at the $-2$ dB level and an extinction ratio of about 1.8 dB. The device is fabricated on a silicon-on-insulator wafer. A silicon waveguide is excluded from the electric circuit. Instead, an ITO layer is used both as a bottom electrical contact and as an electric field-sensitive medium. As a gate oxide, we used a silicon dioxide layer capped with a gold top electrode to form a capacitor. The dielectric rib inside the ITO-Au capacitor forms a coupling interface between the TE photonic and plasmonic modes.

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for biosensing. However, SERS analysis has several concerns: the signal is limited by a number of molecules and the area of the plasmonic substrate in the laser hotspot, and quantitative analysis in a low-volume droplet is confusing due to the change of concentration during quick drying. The usage of hollow-core microstructured optical fibers (HC-MOFs) is thought to be an effective way to improve SERS sensitivity and limit of detection through the effective irradiation of a small sample volume filling the fiber capillaries. In this paper, we used layer-by-layer assembly as a simple method for the functionalization of fiber capillaries by gold nanoparticles (seeds) with a mean diameter of 8 nm followed by UV-induced chloroauric acid reduction. We also demonstrated a simple and quick technique used for the analysis of the SERS platform formation at every stage through the detection of spectral shifts in the optical transmission of HC-MOFs. The enhancement of the Raman signal of a model analyte Rhodamine 6G was obtained using such type of SERS platform. Thus, a combination of nanostructured gold coating as a SERS-active surface and a hollow-core fiber as a microfluidic channel and a waveguide is perspective for point-of-care medical diagnosis based on liquid biopsy and exhaled air analysis.

We demonstrate an optoelectronic microwave oscillator based on the integrated plasmon assisted Si-ITO electrooptical modulator on silicon-on-insulator platform. Modulator of this type has a big potential for compact low-noise microwave oscillator applications due to extremely small active length, of about several microns, and up to 40 GHz bandwidth. Microwave spectra and phase noise of the resulting signal have been measured and modeled for three different lengths of the optical fiber delay lines of 43, 93 and 193 meters. The phase noise of -62.84, -72.03 and -82.32 dBc/Hz at 10 kHz offset has been achieved at 8.251 GHz frequency, which is in good correspondence with the modeling. That paves a way for fabrication of integrated, dramatically miniaturized and broadband tunable optoelectronic oscillators by combining the modulator with silicon-based widely tunable integrated optical filters on the same chip. In addition, we believe that the demonstration of such a compact Si-ITO plasmonic modulator as a part of an optoelectronic oscillator would be an important step towards the integration of transparent conductive oxide-based modulators into more complicated systems.

В данной работе продемонстрировано сужение спектральной линии лазера с распределенной обратной связью 210 кГц до 150 Гц в режиме самозахвата частоты внешнего кремниевого резонатора на основе фотонной интегральной схемы, что открывает перспективы создания компактных узкополосных лазеров для генерации малошумных микроволновых сигналов.