Alexander Denisov

Possibilities to Make Panoramic Receiver–Frequency Meter in Terahertz Band Based on Josephson Junctions

Based on previous theoretical and experimental investigations, possibilities of using Josephson junctions (JJs) to realize a new type of wideband frequency meter integrated with panoramic receiver (PRF) in terahertz band in a single unit were described in this paper. The suggested device can be particularly valuable for experimental purposes in terahertz band, where available equipment for frequency-domain measurements are usually of narrow band and expensive. It will be particularly useful to measure, for instance, the operating frequency of new generators in terahertz band whose radiation power is small, and operating frequency may deviate significantly from its design specification. Such a device can be realized by integrating two circuits in a single unit based on the JJ. The first circuit is a receiver based on JJ operating in a self-pump-mode regime, whereas the second one is a super wideband frequency meter using JJ operating as its natural measuring device.

MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier

Chirped pulse monolithic fiber amplifier based on a newly developed tapered polarization maintaining Yb-doped fiber has been developed and optimized. A novel amplification regime in a relatively long (220 cm) tapered fiber of improved design, which has been theoretically predicted, allowed us to achieve an ultimate high peak power. In this regime, the signal propagates most of the fiber without amplification and growths very rapidly only in the last 80 cm of the tapered fiber, which has a mode field area of approximately 1000 μm2 near the output. We have demonstrated amplification of 20 ps chirped pulses centered at 1056-nm with spectral width of 20 nm to 0.7 MW peak power directly from the tapered fiber amplifier. The pulses had a diffraction limited quality (M2 ~ 1.124) and could be compressed down to 350 fs with 50% efficiency. In addition, amplification of narrow-band 9 ps pulses centered at 1064 nm to a peak power of 1.8 MW directly from the tapered fiber amplifier was demonstrated.

Radiometric Imaging for Monitoring and Surveillance Issues

This paper deals with the recent advances performed by State Research Center “Iceberg” (SRC) in the field of the passive imaging at millimeter wavelengths. In particular, first the paper describes the design and the realization of two systems working in 3u2009mm and 8u2009mm wave bands, respectively. Second, the measurements collected by the two systems are enhanced by means of simple data processing strategies developed by the Institute for Electromagnetic Sensing of the Environment (IREA-CNR).

Monolithic sub-MW peak power tapered ytterbium-doped fiber amplifier

ABSTRACT In this study, we present a novel monolithic ytterbium-doped fiber amplifier with more than 0.5 MW peak power output power. The amplifier is based on a 2.1 m long tapered fiber with core/cladding diameters changing from 10/80 µm (at the signal input end) to 50/430 µm (signal output, pump input). The fiber has all-glass polarization-maintaining design, that make possible utilization of conventional FC adapter and standard angle polishing to 7° for thick end. Pump absorption was measured to be 8 dB at 915 nm for the whole fiber length. Despite a very large mode area (~30 µm) the tapered fiber demonstrates low bend sensitivity (it is possible to coil tapered fiber with 9 cm radius) and a diffraction limited beam quality. In the amplifier the pump power was coupled through the thick end by means of collimating and focusing lenses. Dichroic mirror employed to separate output signal and counter-propagating pump power. We obtained 3.5 W of average output power for a 5 mW seed signal (coupled by usual fusion splicing through a thin end) corresponding to a 28 dB gain. The amplified pulses have duration of about 5 ps and energy of about 3.3 µJ that corresponding to over 0.5 MW peak power. The spectral width was 28 nm operating with center wavelength of 1057 nm.To the best of our knowledge it is the highest peak power obtained directly from the all-fiber amplifier.. Keywords: Yb-doped tapered fiber, all-fiber megawatt system, low bend sensitive tapered fiber, ultrashort pulses amplification 1. INTRODUCTION The very rapid power scaling of both pulsed and cw Yb-doped fiber lasers dictates stringent requirements on the utilized fibers, mainly in terms of nonlinear effects threshold. Conventional single-mode Yb-doped fibers exhibit a relatively low threshold for nonlinear effects since the light is confined in a small core (6-10 µm in diameter) and propagates along long distances (above 10 m in some cases). The increasing of nonlinearity threshold is the urgent problem in the case of pulsed fiber systems, which have been demonstrated to reach power levels of several hundreds of kW and even approach MW power level. The most simple and obvious way to solve this problem is the enlargement of core diameter resulting in the enlarged mode filed diameter of the fundamental mode. In the same time, this approach has so me drawbacks: the fiber becomes a multimode, leading to degradation of output beam quality, and extremely bend-sensitive, resulting in requirement to keep the fiber straight, i.e. the system becomes cumbersome. The main goal of this work was to develop a novel approach based on utilizing of so-called tapered fibers that allows one to obtain large mode field areas and maintain an acceptable bend-loss sensitivity at the same time. The fiber parameters optimization and its using in the final amplification stage of picosecond chirped-pulse amplification system have been demonstrated. The obtained output peak power was record for all-fiber amplifying systems and approached by power level of microstructured fibers based systems.

Microstructured fiber with high-birefringence and low mode field non-circularity

A novel design of polarization-maintaining microstructured fiber is presented. A solid core is surrounded by two or more concentric rings of holes of constant diameter. The distance between adjacent holes in the first ring is constant except for one or two pairs of holes, for which the spacing is increased. It is found that the fiber of such a design can demonstrate high birefringence (up to 5x10-3) and simultaneously low azimuthal asymmetry of the mode shape. An experimental sample was fabricated. The measured value of birefringence is in excellent agreement with the calculated one. The results of the h-parameter measurement demonstrate the capability of the novel fiber to maintain the polarization state of the guided light along the fiber length.

A planar printed quasi-Yagi antenna with a parabolic reflector for WLAN

The simplicity and intuitive design of traditional planar printed quasi-Yagi antennas has led to its widespread popularity for its good directivity. In this paper, a planar printed Quasi-Yagi antenna with 3 directors and 1 concave parabolic reflector, operating in S-band, is proposed. The impedance and radiation characteristic are simulated with CST-Microwave Studio, and the antenna is fabricated and measured. The measured results indicate that the antenna which operates at 2.25-2.63GHz can achieve an average gain of 9.45 dBi within the operating frequency range, especially a highest gain of 10.3dBi at 2.45GHz, which can be widely used in WLAN.

Passive microwave remote discriminator for the marine applications

The specially calculated and prepared antiradar surfaces on special ships is very good for detecting them by the microwave radiometers. It is interesting to evaluate the possibility of using a passive millimeter wave (PMMW) radiometric discriminator for the remote controlling and finding such objects at real distances and also for environmental monitoring.

Matched loading for calibration of passive matrix millimeter wave imaging system

Passive microwave imaging system are widely designed for the remote sensing, radio-astronomical observation and especially for the detection of weapons and contraband concealed on persons under clothing in the special control devices for public security. This system must have various special calibration at the used temperatures. There described in technical details simple square matched loading for the calibration matrix radiometric 8 mm receiving array which has VSWR not pure than 1,10.

A high gain printed antenna with parabolic metal grid reflector based on SIW technology

A printed parabolic antenna is proposed in this paper. The antenna is loaded with a parabolic cylinder reflector which is composed of a series of metal-via arrays in order to improve the gain of H-plane horn antenna based on substrate integrated waveguide (SIW). The final simulation results by CST Microwave Studio indicate that this antenna has the effect of high gain, the reflection coefficient of the antenna in 36.04–36.35GHz is lower than −10dB, the gain is 13.12dBi at 36.2GHz. This type of antenna solves the difficulty in integrating reflector antenna.

A broadband and high gain yagi antenna with complex parabolic boundary reflector

A kind of broadband and high gain printed Yagi antenna with complex parabolic boundary reflector is proposed. This kind of antenna has low profile, wide bandwidth and high gain, as well as simple feeding and so on. The commercial simulation software, CST Microwave Studio® has been used to analyze the surface current on the metal radiator of antenna. The model of dipole array, which is equal with the antennas radiation characteristic, is also established and antennas radiation mechanism can be explained. Finally, antenna prototype has been manufactured according to the simulated results. Experimental results show that the reflection coefficient of this antenna is less than −10dB in 2.12–3.37GHz, and the gain in working band can stably achieve 4.0–5.4dBi. Besides, the size of the antenna is only 120mm×50mm, which can be used in the field of WLAN.