Sensors based on different types of guiding modes have been used for sensor applications for a long time. Those technologies were commercialized and actively used in different sensing applications. However, new challenges in biomedical research are requiring even better sensors. One of those new perspective technologies is plasmonic hyperbolic metamaterials. It was shown that those structures have a big potential for sensing. In order to compare these new guiding structures with traditional ones, we performed the analysis of sensitivity for different guiding structures: optical dielectric waveguide, surface-plasmon polaritons, long-range surface plasmon polaritons (LRSPP), plasmonic hyperbolic materials with a combination of metal and dielectric layers. All structures were placed on the BK7 glass substrate and we set wavelength at 1550 nm. We used the Si3N4 layer a waveguiding medium for the dielectric waveguide, we used gold for all plasmonic structures. The water layer on the top of all structures was used as a sensing area. For guiding modes coupling we used diffraction gratings for a few reasons. Firstly, there are no materials with a refractive index capable to couple guiding modes. Secondly, diffraction gratings provide compact, a planar design which is easier to keep the structure in the thermostatic condition And last but not least, we used coupling gratings with the same grating profile (sinusoidal) and the same corrugation depth so all guiding modes will be coupled the same way. Our results showed that plasmonic hyperbolic structures indeed have much higher sensitivity comparing with the traditional guided wave sensors based on dielectric waveguides and surface plasmon-polaritons.
There are many applications which require high sensitivity spectral detection. In some cases, you need the wavelength range to be extended to cover all necessary spectral fingerprints. We are proposing a broadband spectrometer for ultrasensitive detection based on plasmonic hyperbolic metamaterials and diffraction gratings. Using variety of materials in fabrication of the hyperbolic metamaterials, we can cover the wide spectral range from near UV (~250 nm) to IR (~2 μm). In our spectrometer, the diffraction gratings have two functions. One is coupling the incident light source with the plasmonic guiding modes, which have a very high effective refractive index (≥8.1), much higher than the refractive index of germanium (4.05), the natural material with the highest refractive index. While a prism can also be used for coupling guiding modes with incident light, a diffraction grating is the only way to excite the guiding modes because of the plasmonics modes with very high effective refractive index. The second function of the diffraction gratings is their natural role in spectrometers. We demonstrated based on numerical simulations that we could reach high detection spectral sensitivity using compact diffraction gratings combined with hyperbolic metamaterials; the huge “n-meter” spectrometer is not necessary.
Plasmonic structures for biomedical sensing are in use for a long time. However, there is a fundamental limitation of their sensitivity due to low effective refractive index of layered plasmonic structures. We are proposing a hyperbolic metamaterial (HMM) structure which is a combination of surface plasmon Polaritons (SPPs) and long-range surface plasmon Polaritons (LRSPPs) modes. The result of the interaction between these modes leads to plasmonic modes with ultra-high effective refractive index. We calculated and optimized plasmonic HMM structure with effective refractive index equal to 8.1, i.e. twice as much as that of germanium, a natural material with the highest refractive index. We simulated these structures for gold, silver, copper and aluminum. The best way to use these structures for protein sensing is to use diffraction gratings – there is no natural material which can be used as a prism. By optimizing layer parameters and diffraction grating we were able to build a model of the structure with sensitivity as 10-9 for refractive index. We are hoping to achieve sensitivity up to 10-11, so this structure can be used for different protein sensing application including detection of metastatic cells spreading the human body.
AlN films deposited on sapphire substrates were damaged by single UV nanosecond (at 248 nm) and IR femtosecond
(at 775 nm) laser pulses in air at normal pressure. The films had high (27-35 atomic %) concentration of oxygen
introduced into thin surface layer (5-10 nm thickness). We measured damage threshold and studied morphology of the
damage sites with atomic force and Nomarski optical microscopes with the objective to determine a correlation between
damage processes and oxygen content. The damage produced by nanosecond pulses was accompanied by significant
thermal effects with evident signatures of melting, chemical modification of the film surface, and specific redistribution
of micro-defect rings around the damage spots. The nanosecond-damage threshold exhibited pronounced increase with
increase of the oxygen content. In contrast to that, the femtosecond pulses produced damage without any signs of
thermal, thermo-mechanical or chemical effects. No correlation between femtosecond-damage threshold and oxygen
content as well as presence of defects within the laser-damage spot was found. We discuss the influence of the oxygen
contamination on film properties and related mechanisms responsible for the specific damage effects and morphology of
the damage sites observed in the experiments.
We present results of comparative study of laser-induced ablation of AlN films with variable content of oxygen as a
surface-doping element. The films deposited on sapphire substrate were ablated by a single nanosecond pulse at
wavelength 248 nm, and by a single femtosecond pulse at wavelength 775 nm in air at normal pressure. Ablation craters
were inspected by AFM and Nomarski high-resolution microscope. Irradiation by nanosecond pulses leads to a
significant removal of material accompanied by extensive thermal effects, chemical modification of the films around the
ablation craters and formation of specific defect structures next to the craters. Remarkable feature of the nanosecond
experiments was total absence of thermo-mechanical fracturing near the edges of ablation craters. The femtosecond
pulses produced very gentle ablation removing sub-micrometer layers of the films. No remarkable signs of thermal,
thermo-mechanical or chemical effects were found on the films after the femtosecond ablation. We discuss mechanisms
responsible for the specific ablation effects and morphology of the ablation craters.
Diffraction gratings used in various applications for compact optical devices. We used different technologies
for this task: deep-UV lithography, FIB milling, e-beam lithography, and hot embossing/nanoimprinting technology. We
analyzed advantages and disadvantages of each fabrication technology.
In this work we developed new type of biosensors based on nanolayered metal-dielectric structure. It was found that
using the combination of nano-size (from 15 to 25 nm) layers of gold and dielectric support a new type of plasmon
modes: bulk plasmon-polariton (BPP). In this work the role of corrugation for different nano-layers has been
investigated. Thus, it was found that even corrugation of one 25 nm nano-layer results in effective coupling of BPP
modes. The coupling efficiency as a function of corrugation depth, corrugation profile has been investigated. Diffraction
gratings were fabricated by hot embossing technology.
Optical multiplexers/demultiplexers developed for the telecommunication industry, at the level of the basic principles,
perform essentially the same functions as general-use optical spectrometers. The spectrometer design inspired by the
telecom devices would represent an extremely compact device compatible with the manufacturing procedures in
integrated optoelectronics and micro-optics. In this paper we summarize our recent results on development of a
miniature optical spectrometer. The spectrometer uses a diffractive optical element integrated with a planar optical
waveguide. It is designed to provide spectral resolution of at least 2nm in the entire visible spectral range from 400nm-
700nm, and simultaneously resolve spectra from up to 35 independent optical inputs. The optical part of the
spectrometer fits volume below 10mm3. The spectrometer is designed for on-chip diagnostic systems, in particular for
fluorescence detection of hazardous materials. A device prototype with diffractive optical element fabricated using
electron beam lithography is manufactured and tested.
Abnormal reflecting mirror (ARM) structures, consisting of a corrugated optical waveguide structure, can serve as a narrow band reflection filter in which strong field enhancement may occur by excitation of the guided mode. The latter is quite interest for SHG. We report experimental results of a first prototype, which exhibits CSHG in the ARM structure.
A new, high efficiency diffraction grating configuration for use in the situation of grazing incidence is proposed and analyzed. The structure consists of a flat mirror plane, a thin dielectric film with a grating at the air-film interface. It can advantageously replace corrugation metal gratings in all applications, particularly in high power laser applications using the Littman-Metcalf mounting.
The influence of titanium and lead dopants on the waveguide fabrication by ion exchange process and photoinduced second harmonic generation has been investigated. The similar effect of the glass composition on photoinduced second order nonlinearity and refractive index increment by ion exchange has been observed. The obtained results made it possible to rule out the influence of the glass structure on the charge transfer processes in lead silicate glasses.