Evgeny G. Mironov

Composite chromium and graphene oxide as saturable absorber in ytterbium- doped Q-switched fiber lasers

In recent years, graphene and its compounds (e.g., oxides) have been used as saturable absorbers in passive Q-switched and mode-locked lasers, leading to the fabrication of compact pulsed fiber lasers. In this article, we study the operation of a Q-switched ytterbium-doped fiber ring laser based on a composite saturable absorber made of graphene oxide and chromium. We show that the addition of a thin layer of chromium can lead to pulse durations ranging from 3.5 to 9.4 μs and subsequently increasing the laser peak power.

Temperature Control of Terahertz Metamaterials With Liquid Crystals

We design and experimentally characterize terahertz (THz) electric split-ring-resonator metamaterials infiltrated with nematic liquid crystals (LCs). We demonstrate that the resonant response of such metamaterials can be tuned by temperature due to the change of the LC arrangement from nematic to isotropic phase. In particular, we show that the frequency tuning is strongly dependent on the initial LC orientation, with resonant frequency shifting towards lower frequencies for LC director perpendicular to the gap and towards higher frequencies for LC director parallel to the gap of the electric split ring resonators. Our results open new opportunities for the design of tunable THz filters based on LCs.

Enhancing Weak Optical Signals Using a Plasmonic Yagi—Uda Nanoantenna Array

Nanoantennas have been used in a wide range of applications in sensing, spectroscopy, and imaging-in general, the antennas can enhance physical phenomena such as the local electric field or concentrate light in a certain direction. We have fabricated an array of 80 plasmonic Yagi-Uda nanoantennas on the cladding of an optical fiber and, by doing this, we show that the signal reaching the fast detector can be increased by a factor of 5 dB. The experiment demonstrates that plasmonic directive nanoantennas can indeed collect and concentrate electromagnetic radiation along a certain direction and eventually could be used to enhance weak signals.

Titanium Nano-Antenna for High-Power Pulsed Operation

While plasmonic nano-antennas can produce intense electric fields in a very small area, in general, these devices cannot handle high power, because of their small footprints. In order to increase the maximum peak power that these devices can withstand, they can be driven by nano-second pulses from a larger diameter Q-switched laser, which reduces the fluence reaching the devices, thus avoiding their destruction. Furthermore, we show that an increase in the power density capacity of the nano-antennas can be achieved by replacing gold with titanium: more than 18 dB greater power density can be handled by titanium based nano-antennas without significant reduction in their electric field enhancement capabilities.

Analysis of silica-filled slot waveguides based on hyperbolic metamaterials

We have theoretically studied the optical properties of a filled slot metamaterial waveguide with lateral slab regions consisting of alternating silver–silica multilayers. It is shown that this geometry improves the subwavelength confinement of guided light and that the particular metal–dielectric ratio of 15  nm/10  nm results in substantially enhanced transmission, as compared with metal–dielectric–metal slot waveguides having similar dimensions.

Thick multilayered (silica/gold) dipole nano-antenna

Nano-antennas are the optical equivalent of antennas that are used to transmit and receive information at radio frequencies. These antennas have been used in different applications in photonics such as optical imaging, particle manipulation, bio-sensing, and improvement of the performance of solar cells. In this article we study composite nano-antennas made of alternating layers of silica and gold. We show that a 50% filling factor leads to a 2.0 times increase in the electric-field enhancement factor when compared with a pure-gold antenna.

Charnia-like broadband plasmonic nano-antenna

Charnia was a pre-Cambrian life-form that exhibited a fractal structure to improve the extraction of nutrients from the pre-historic seas. Inspired by its fractal structure, this paper studies the potential application of these self-similarity fractal structures to create a plasmonic nano-antenna that can operate over a large linewidth. These devices are studied both theoretically and experimentally. It is shown that these nano-antennas can produce electric field enhancements above 8 over 200 nm range and surface enhanced Raman scattering (SERS) enhancements higher than 105.

Integration of bow-tie plasmonic nano-antennas on tapered fibers

In this article, a new and flexible approach to control the electric field enhancement of bow-tie nano-antennas by integrating them on the lateral of a tapered optical fiber is proposed. The device is driven by a Q-switched laser and the performance of a fabricated nano-antenna in a quartz slide is tested by a Surface Enhanced Raman Scattering (SERS) experiment. A refractive index sensing experiment is also performed and a sensitivity of (240 ± 30) nm/RIU is found in the 1.33-1.35 index range.

Fishnet metamaterials with incorporated titanium absorption layer

Some metamaterial applications require the use of high-power lasers, but the incoming radiation may damage the metamaterials. In addition to that, the presence of an absorptive material placed close to metamaterial surface can lead to quick heating of the surrounding area, resulting in serious thermal damage or melting of the fabricated pattern. We study the impact of a titanium absorptive layer on top of a conventional fishnet structure and we show that due to increased absorption the melting power is reduced by nearly 50% and thermal damage leads to the formation of microbumps on the exposed surface.

Strong electric field enhancement in a gold/silica bow-tie nano-antenna

Bow-tie nano-antennas are the kind of plasmonic structures that are widely used in optical applications to obtain strong electric fields in a limited volume. Their capability to enhance the incident light can be greatly improved by constructing these structures from several alternating metal/dielectric layers. Following this approach, we introduce and then analyze the performance of a multilayered Au/SiO2 bow-tie nano-antenna in the finite-difference time-domain software. We show that the gold/silica thickness ratio of 50% leads to the improvement of the electric field enhancement on almost 50%, when compared to a monolithic gold device, which makes the proposed design attractive for various sensing applications.