Sergey Fomchenkov

E-beam lithography exposure conditions for the fabrication of RGB filter based on metal/dielectric subwavelength grating

The main idea of this work was to determine the optimized parameters of E-beam lithography to obtain metal grating over dielectric thin film. This combination of metal/dielectric can provide high transmission spectrum of RGB colors. Different electric flux densities were used during E-beam writing and the best resolution and symmetric periodicity was obtained at 53 μC/cm2 dose.

Indium phosphide all air-gap Fabry-Pérot filters for near-infrared spectroscopic applications

Food quality can be characterized by noninvasive techniques such as spectroscopy in the Near Infrared wavelength range. For example, 930 -1450 nm wavelength range can be used to detect diseases and differentiate between meat samples. Miniaturization of such NIR spectrometers is useful for quick and mobile characterization of food samples. Spectrometers can be miniaturized, without compromising the spectral resolution, using Fabry-Perot (FP) filters consisting of two highly reflecting mirrors with a central cavity in between. The most commonly used mirrors in the design of FP filters are Distributed Bragg Reflections (DBRs) consisting of alternating high and low refractive index material pairs, due to their high reflectivity compared to metal mirrors. However, DBRs have high reflectivity for a selected range of wavelengths known as the stopband of the DBR. This range is usually much smaller than the sensitivity range of the spectrometer detector. Therefore, a bandpass filter is usually required to restrict wavelengths outside the stopband of the FP DBRs. Such bandpass filters are difficult to design and implement. Alternatively, high index contrast materials must be can be used to broaden the stopband width of the FP DBRs. In this work, Indium phosphide all air-gap filters are proposed in conjunction with InGaAs based detectors. The designed filter has a wide stopband covering the entire InGaAs detector sensitivity range. The filter can be tuned in the 950-1450 nm with single mode operation. The designed filter can hence be used for noninvasive meat quality control.

Formation of hybrid higher-order cylindrical vector beams using binary multi-sector phase plates

Nowadays, the well-known cylindrical vector beams (CVBs) – the axially symmetric beam solution to the full-vector electromagnetic wave equation – are widely used for advanced laser material processing, optical manipulation and communication and have a great interest for data storage. Higher-order CVBs with polarisation order greater than one and superpositions of CVBs of various orders (hybrid CVBs) are especially of interest because of their great potential in contemporary optics. We performed a theoretical analysis of the transformation of first-order CVBs (radially and azimuthally polarised beams) into hybrid higher-order ones using phase elements with complex transmission functions in the form of the cosine or sine functions of the azimuthal angle. Binary multi-sector phase plates approximating such transmission functions were fabricated and experimentally investigated. The influence of the number of sectors and a height difference between neighbouring sectors, as well as the energy contribution of the different components in the generated hybrid higher-order CVBs were discussed in the context of polarisation transformation and vector optical field transformation in the focal region. The possibility of polarisation transformation, even in the case of weak focusing, is also demonstrated. The simple structure of the profile of such plates, their high diffraction efficiency and high damage threshold, as well as the easy-to-implement polarisation transformation principle provide advanced opportunities for high-efficient, quickly-switchable dynamic control of the generation of structured laser beams.

A modified Gerchberg-Saxton algorithm for design diffractive optical elements generating light distributions with submicron features

The well-known Gerchberg-Saxton (GS) algorithm allows the reconstruction of an unknown wave front from known intensity distributions on a few planes of an optical system, for example, in the input plane and the focal plane. It is also the method of choice for the production of computer-generated holograms and calculation of the transmission function of diffractive optical elements (DOEs) generating so-called structured laser beams. Such ‘unconventional’ laser beams have unique features of an amplitude/phase/polarisation distribution, significantly extending opportunities for application of laser optics in many fields of modern science. Here, we propose a new modification of the basic GS algorithm that can be used to calculate a pure-phase transmission function of DOEs which generate complex intensity distributions with submicron features. DOEs designed in this way can be used in the field of laser fabrication of nano- and micropatterns, allowing the high-performance single-step fabrication of nanostructures for real applications in nanophotonics and optical manipulation.

Diffractive optical elements for generation and transformation of structured laser beams

In this paper, we consider methods of design and manufacture of diffractive optical elements (DOEs), generating socalled structured laser beams with predetermined amplitude/phase/polarisation distributions and perform transformation of those laser beams. Diffraction optics makes it possible to implement generation and control of the structured laser beams via single DOE and their combinations. We demonstrate several traditional methods that can be used to calculate a pure-phase transmission function of DOEs, both iterative and non-iterative. In addition, different technological processes for the manufacture of DOEs are used, including direct laser writing in thin films and lithography combined with plasma etching. The structured laser beams generated using DOEs provide new opportunities for large-scale highrate laser fabrication of nano- and microscale functional elements, as well as for the laser manipulation of microscale objects. The use of the structured laser beams in these applications (for example, radially/azimuthally polarised laser beams, optical vortex beams or beams with complex-shape transverse intensity distributions) allows advanced control..

Modeling and manufacture of an interference filter with a defective layer for narrow spectral selection

We manufactured and investigated narrow spectral selection filter with a defect layer. Design of the filter was performed based on results of modeling. The main idea of that filter is sandwich structure of 5 layers with high aspect ratio between refractive indices of two different layers and phase diffractive optical element in the central layer. The structure was manufactured for operation at wavelength of 532 nm. The ZnO (n=2.03) and TiO2 (n=2.67) thin films were chosen as materials for the designed sandwich structure. The thin films were deposited by the magnetron sputtering system “Caroline D12A”. The thickness of each ZnO layer is 50 nm, the thickness of each TiO2 layer is 65 nm. The central defective layer was fabricated with the help of a plasma-chemical etching system through a hard mask of chromium. The chromium hard mask was manufactured by direct laser writing. The central TiO2 layer was etched in a SF6 gas. Then the mask was removed by liquid chemical etching. The influence of the multilayer structure properties and parameters of defective layer on the spectral characteristics of the optical filter was investigated. This filter shows very narrow spectrum selection and high efficiency. The possibility of the use of such filters for selecting a narrow range of wavelengths that can find various applications in the field of information transfer and medical devices was shown.

Multilayer dielectric stack Notch filter for 450-700 nm wavelength spectrum

In this work, a multilayer dielectric optical notch filters design is proposed based on TiO2 and SiO2 alternating layers. Titanium dioxide (TiO2) is selected for its high refractive index value (2.5) and Silicon dioxide (SiO2) as a low refractive index layer (1.45). These filters are conventionally envisioned for overpowering of powerful laser beams in research experiments, to obtain good signal-to-noise ratios in Raman laser spectroscopy. It is precarious that light from the pump laser should be blocked. This is attained by inserting a notch filter in the detection channel of the setup. In addition to spectroscopy, notch filters are also useful in laser-based florescence instrumentation and biomedical laser systems. The designed filter shows a high quality with an average transmission of more than 90% in 450-535 and 587-700 nm bandwidths. And a stop band region between 536-586 nm shows a transmission of 3% only with an optical density of greater than 3, which makes it a promising element to be used as a notch filter.

Biomedical bandpass filter for fluorescence microscopy imaging based on TiO2/SiO2 and TiO2/MgF2 dielectric multilayers

We report a design for creating a multilayer dielectric optical filters based on TiO2 and SiO2/MgF2 alternating layers. We have selected Titanium dioxide (TiO2) for high refractive index (2.5), Silicon dioxide (SiO2) and Magnesium fluoride (MgF2) as a low refractive index layer (1.45 & 1.37) respectively. Miniaturized visible spectrometers are useful for quick and mobile characterization of biological samples. Such devices can be fabricated by using Fabry-Perot (FP) filters consisting of two highly reflecting mirrors with a central cavity in between. Distributed Bragg Reflectors (DBRs) consisting of alternating high and low refractive index material pairs are the most commonly used mirrors in FP filters, due to their high reflectivity. However, DBRs have high reflectivity for a selected range of wavelengths known as the stopband of the DBR. This range is usually much smaller than the sensitivity range of the spectrometer range. Therefore a bandpass filters are required to restrict wavelength outside the stopband of the FP DBRs. The proposed filter shows a high quality with average transmission of 97.4% within the passbands and the transmission outside the passband is around 4%. Special attention has been given to keep the thickness of the filters within the economic limits. It can be suggested that these filters are exceptional choice for florescence imaging and Endoscope narrow band imaging.

Reactive ion etching of indium-tin oxide films by CCl4-based Inductivity Coupled Plasma

Indium tin oxide (ITO) films have been a subject of extensive studies in fabrication of micro-electronic devices for opto-electronic applications ranging from anti-reflection coatings to transparent contacts in photovoltaic devices. In this paper, a new and effective way of reactive ion etching of a conducting indium-tin oxide (ITO) film with Carbon tetrachloride (CCl4) has been investigated. CCl4 plasma containing an addition of gases mixture of dissociated argon and oxygen were used. Oxygen is added to increase the etchant percentage whereas argon was used for stabilization of plasma. The etching characteristics obtained with these gaseous mixtures were explained based on plasma etch chemistry and etching regime of ITO films. An etch rate as high as ~20 nm/min can be achieved with a controlled process parameter such as power density, total flow rate, composition of reactive gases gas and pressure. Our Investigation represents some of the extensive work in this area.