Over the recent years, a huge interest has grown for curved electronics, particularly for opto-electronics systems. Indeed, curved sensors help the correction of off-axis aberrations, such as Petzval Field Curvature and astigmatism. In this paper, we describe benefits of curvature and tunable curvature on an existing fish-eye lens. We proposed a new design architecture, compact and with a high resolution, developed specifically for a curved image sensor. We discuss about aberrations and effect of higher sensor curvature on third order aberrations. Besides, we show results of sensors’ mechanical limits and its electro-optical characterization. Finally, all these experiments and optical results demonstrate the feasibility and high performances of systems with curved sensors.
In the present work we discuss a possibility to build an instrument with two operation modes - spectral and imaging
ones. The key element of such instrument is a dispersive and filtering unit consisting of two narrowband volume-phase
holographic gratings. Each of them provides high diffraction efficiency in a relatively narrow spectral range of a few tens
of nanometers. Besides, the position of this working band is highly dependent on the angle of incidence. So we propose
to use a couple of such gratings to implement the two operational modes. The gratings are mounted in a collimated beam
one after another. In the spectroscopic mode the gratings are turned on such angle that the diffraction efficiency curves
coincide, thus the beams diffracted on the first grating are diffracted twice on the second one and a high-dispersion
spectrum in a narrow range is formed. If the collimating and camera lenses are corrected for a wide field it is possible to
use a long slit and register the spectra from its different points separately. In the imaging mode the gratings are turned to
such angle that the efficiency curves intersect in a very narrow wavelength range. So the beams diffracted on the first
grating are filtered out by the second one except of the spectral component, which forms the image. In this case the
instrument works without slit diaphragm on the entrance. We provide an example design to illustrate the proposed
concept. This optical scheme works in the region around 656 nm with F/# of 6.3. In the spectroscopic mode it provides a
spectrum for the region from 641 to 671 nm with reciprocal linear dispersion of 1.4 nm/mm and the spectral resolving
power higher than 14000. In the imaging mode it covers linear 12mm x 12mm field of view with spatial resolution of 15-
We describe a dispersive unit consisting of cascaded volume-phase holographic gratings for spectroscopic applications. Each of the gratings provides high diffractive efficiency in a relatively narrow wavelength range and transmits the rest of the radiation to the 0th order of diffraction. The spectral lines formed by different gratings are centered in the longitudal direction and separated in the transverse direction due to tilt of the gratings around two axes. We consider a technique of design and optimization of such a scheme. It allows to define modulation of index of refraction and thickness of the holographic layer for each of the gratings as well as their fringes frequencies and inclination angles. At the first stage the gratings parameters are found approximately using analytical expressions of Kogelnik’s coupled wave theory. Then each of the grating starting from the longwave sub-range is optimized separately by using of numerical optimization procedure and rigorous coupled wave analysis to achieve a high diffraction efficiency profile with a steep shortwave edge. In parallel such targets as ray aiming and linear dispersion maintenance are controlled by means of ray tracing. We demonstrate this technique on example of a small-sized spectrograph for astronomical applications. It works in the range of 500-650 nm and uses three gratings covering 50 nm each. It has spectral resolution of 6130-12548.Obtaining of the asymmetrical efficiency curve is shown with use of dichromated gelatin and a photopolymer. Change of the curve shape allows to increase filling coefficient for the target sub-range up to 2.3 times.
Our intention is to develop high-resolution stigmatic spectral imaging in the XUV (2 – 40 nm). We have designed, aligned and tested a broadband stigmatic spectrometer for a range of 12–30 nm, which makes combined use of a normalincidence multilayer mirror (MM) (in particular, a broadband aperiodic MM) and a grazing-incidence plane varied linespace (VLS) reflection grating. The concave MM produces a slightly astigmatic image of the radiation source (for instance, the entrance slit), and the VLS grating produces a set of its dispersed stigmatic spectral images. The multilayer structure determines the spectral width of the operating range, which may amount to more than an octave in wavelength (e.g. 12.5–30 nm for an aperiodic Mo/Si MM), while the VLS grating controls the spectral focal curve. The stigmatism condition is satisfied simultaneously for two wavelengths, 14 and 27 nm. In this case, the condition of non-rigorous stigmatism is fulfilled for the entire wavelength range. A LiF laser plasma spectrum was recorded in one 0.5 J laser shot. A spatial resolution of 26 μm and a spectral resolution of 900 were demonstrated in the 12.5 – 25 nm range. We also report the design of a set of flat-field spectrometers of Harada type with VLS gratings. VLS gratings were made by ebeam and interference lithography. A technique (analytical + numerical) was developed for calculating optical schemes for writing plane and concave VLS gratings with predefined line density variation.
In the present work we consider optical design of a multi-slit astronomic spectrograph for UV domain with freeform reflective elements. The scheme consists of only two reflective elements – a holographic grating imposed on freeform surface and a freeform mirror. The freeforms are described by standard Zernike polynomials and the hologram is recorded by two coherent point sources. We demonstrate that in such a scheme it’s possible to obtain quite high optical quality for an extended field of view and relatively high dispersion on a curved image surface. The spectrograph works with linear field of view of 76x32 mm and provides reciprocal linear dispersion equal to 0.5 nm/mm and typical resolving power of 15 000 over the UV range of 100-200 nm. Feasibility of the optical components is discussed and coupling of the spectrograph with a TMA telescope is demonstrated.
We present an optical design of astronomic spectrograph based on a cascade of volume-phase holographic gratings. The cascade consists of three gratings. Each of them provides moderately high spectral resolution in a narrow range of 83nm. Thus the spectrum image represents three lines covering region 430-680nm. Two versions of the scheme are described: a full-scale one with estimated resolving power of 5300-7900 and a small-sized one intended for creation of a lab prototype, which provides the resolving power of 1500-3000. Diffraction efficiency modeling confirms that the system throughput can reach 75%, while stray light caused by the gratings crosstalk is negligible. We also propose a design of image slicer and focal reducer allowing to couple the instrument with a 6m-telescope. Finally, we present concept of the instrument’s optomechanical design.
In this article, we present the information and telecommunications system that allows to carry out real-time monitoring of the quality and quantity of hydraulic engineering structures in order to reduce the risk of emergencies caused by environmental damage.
Different ways to increase dispersion and spectral resolution of a fiber-fed spectrograph working in NIR range are considered. Optical schemes with composite diffractive units are investigated in details. The first discussed option is use of a pair of volume-phase transmission gratings and the second one is use of combination of a reflective grating and a prism. For each of them a certain optical scheme designed and modeled and comparison of key properties is provided.
An optical scheme of a fiber-fed spectrometer for the near-IR region around 1.5 um is presented. The scheme is based on transmission holographic gratings with aberration correction. Such question as optimization of the diffraction efficiency for the working range and its polarization dependence are considered. All the results are proved by numerical modeling.
In the paper an approach to improve diffraction efficiency of a transmission concave holographic grating for a flat-field
spectrograph is presented. The proposed method is based on numerical optimization of a merit function. Each iteration of
the procedure includes definition of the grating recording parameters and the spectrum position from conditions of
aberration correction, estimation of the diffraction efficiency by means of the Kogelnik coupled-wave theory equations,
and checking boundary conditions. It’s shown on a certain example that the technique allows to obtain high spectral
resolution and increase the diffraction efficiency. Modeling results and comparison with accurate RCWA computation
are provided as well.
In this paper an experience of an inter-institutional collaboration in teaching optics and photonics at Kazan National
Research Technical University - KAI is described. Cooperation with international scientific societies is especially
emphasized among other directions. Particularly, such a new form of the cooperation as establishment of a local student
chapter of the societies is considered. The main possibilities of students’ professional development provided by this
program are listed. Individual and collective activities are distinguished and described in details. We also represent our
view on creation and management of such chapter. It is concluded that the student chapter program can help to enhance
an optics and photonics teaching system.