Frequency controlled energy absorption in parametric mixing

A Superconducting QUantum Interference Device (SQUID) modulated by a fast oscillating magnetic flux can be used as a parametric amplifier, providing gain with very little added noise. Here, we develop linearized models to describe the parametrically flux-pumped SQUID in terms of an impedance. An unpumped SQUID acts as an inductance, the Josephson inductance, whereas a flux-pumped SQUID develops an additional, parallel element which we have coined the ``pumpistor.'' Parametric gain can be understood as a result of a negative resistance of the pumpistor. In the degenerate case, the gain is sensitive to the relative phase between the pump and signal. In the nondegenerate case, gain is independent of this phase. We develop our models first for degenerate parametric pumping in the three-wave and four-wave cases, where the pump frequency is either twice or equal to the signal frequency, respectively. We then derive expressions for the nondegenerate case where the pump frequency is not a multiple of the signal frequency, where it becomes necessary to consider idler tones which develop. For the nondegenerate three-wave case, we present an intuitive picture for a parametric amplifier containing a flux-pumped SQUID where current at the signal frequency depends upon the load impedance at an idler frequency. This understanding provides insight and readily testable predictions of circuits containing flux-pumped SQUIDs.

An analysis is presented of variable-capacitance parametric amplifiers for the case where there is a loss resistance in series with the capacitance. Such a resistance provides the major form of loss in a reverse-biased semiconductor diode. It is shown that the coupling of two circuits by a pumped variable capacitance can be described by a simple equivalent circuit which has a direct physical interpretation. The characteristics of regenerative amplifiers and convertors, and of non-inverting convertors, are deduced from the equivalent circuits. The gain, bandwidth and noise properties of these amplifiers or convertors are shown to depend on two parameters of the pumped variable capacitance C, the mean Q at the signal frequency and the normalized amplitude of the variation of 1/C at the pump frequency. The noise temperature in each case is a function only of the product of these two parameters and the ratio of signal to idler (or output) frequencies. Particular attention is given to finding the optimum operating conditions and a brief discussion is given of the effects of variations of the capacitance at harmonics of the pump frequency, and of higher sidebands.

There have been impressive advances in the area of microresonator-based frequency combs (microcombs) during the last decade, making their way into applications in a wide variety of fields [1]. Although microcombs are commonly generated making use of third-order ( χ (3) ) nonlinear processes, several groups have recently started to investigate frequency comb generation based on the second-order ( χ (2) ) nonlinearity as it bears potential benefits like the linear electro-optic effect for either tuning or stabilization, or the possibility to convert light into more challenging spectral regions like the UV or mid-infrared [2] , [3]. For the latter, one approach is to start with optical parametric oscillation (OPO) and to operate it close to degeneracy. Then, a series of second-order nonlinear processes takes place, generating equidistant comb lines around both the pump frequency and the sub-harmonic frequency [2] , [4] . A promising χ (2) material to move into the mid-infrared region is cadmium silicon phosphide (CdSiP 2 ) which is transparent from 1 to 6.5 µm and has a high nonlinearity of 84.5 pm/V. Furthermore, OPO has already been shown for a CdSiP 2 mm-sized whispering gallery resonator pumped at telecom wavelength [5]. Based on these observations, we investigate OPO operation close to the point of degeneracy and this way, the possibility to generate frequency combs both around 1.5 µm and 3 µm. In this work, we have observed OPO with thresholds below 100 µW and conversion efficiencies of around 17 %. We could tune the OPO output wavelengths from 2.3 to 5 µm by coupling the pump light into different modes of the resonator and by controlling its temperature. One of the pump modes investigated enabled operation near degeneracy. Measured signal and idler wavelengths for this pump mode are plotted in figure 1a ) for different temperatures. However, OPO near degeneracy is prone to instabilities, as several parametric oscillations can be excited under similar conditions. Here, by tuning the temperature in the mK range and the pump detuning with respect to the resonance in the MHz range, the minimum obtained difference between signal and idler frequencies was 120 GHz (4 FSRs). Nonetheless, in this state we have already observed sidebands generated around the pump corresponding to SHG as shown in figure 1b ). Why operation closer to the point of degeneracy is hampered, is currently under investigation. A possibility to gain further insight and control on OPO operation might be to make use the linear electro-optic effect for fine tuning of the relative position of the resonances between the pump and the sub-harmonic frequencies.

Unusually low noise, combined with high stable gain over fairly wide bands, has been obtained with electron beam amplifiers of a new kind. This paper explains how this performance is achieved by the action of a transverse quadrupole field upon a fast cyclotron wave. The first two sections give a qualitative description of the device and of the amplifying mechanism. A physical picture of the fast cyclotron wave is used to explain the interchange of signal and noise in the input coupler and the mechanism of parametric amplification in the quadrupole region. The third section presents a detailed analysis of the amplification process. It shows that the fast cyclotron wave is amplified in accordance with a cosh function of distance traveled through the quadrupole, and that a new cyclotron wave at idler frequency (difference between pump and signal frequencies) is generated which grows as a sinh function of distance. The fourth section describes experimental tubes built to date. These operate on frequency bands between 400 and 800 mc. Typical bandwidth is 40 to 50 mc independent of gain, which may be adjusted to 20 or 30 db. Residual noise temperature of the electron beam in good specimens within this experimental lot is 70°K; input coupler loss raises this figure to about 100°K. This is equivalent to a noise figure of 1.4 db if the device is used, for instance, in radio astronomy.

Active optical processes such as amplification and stimulated emission promise to play just as important a role in nanoscale optics as they have in mainstream modern optics. The ability of metallic nanostructures to enhance optical nonlinearities at the nanoscale has been shown for a number of nonlinear and active processes; however, one important process yet to be seen is optical parametric amplification. Here, we report the demonstration of surface plasmon-enhanced difference frequency generation by integration of a nonlinear optical medium, BaTiO3, in nanocrystalline form within a plasmonic nanocavity. These nanoengineered composite structures support resonances at pump, signal, and idler frequencies, providing large enhancements of the confined fields and efficient coupling of the wavelength-converted idler radiation to the far-field. This nanocomplex works as a nanoscale tunable infrared light source and paves the way for the design and fabrication of a surface plasmon-enhanced optical parametric amplifier.

A theoretical analysis on coherent double resonant absorptive lineshape in closely spaced transitions for λ − type five level system

Using a numerical approach we report on the cloning dynamics of simultaneous self-induced transparency (SIT) and nonlinear Schrödinger (NLS) solitons in a doped nonlinear dispersive medium. This technique involves a three-level atomic system interacting resonantly with two optical fields within a Lambda scheme. As a result, a pulse in the signal frequency is transformed into a replica of the pulse in the pump frequency. The atomic population evolution shows that the basic mechanism behind the cloning process is the coherent population trapping effect. Furthermore, it is shown that the signal clone presents characteristics of both the SIT soliton and NLS soliton.

Experimental results are reported demonstrating the possibility of achieving parametric gain in an inverted paramagnetic medium. In this case the parametric pump frequency may be lower than the signal frequency. The authors used chromium-doped rutile as the active material, a pump frequency of 150 MHz, and a signal frequency of 4.25 GHz. The parametric effect is strongly supported by adjusting the idling circuit for high master gain.

A reactance amplifier has been constructed which is capable of low-noise amplification at audio and subaudio frequencies [1]. Stable voltage amplification of 20-30 db and noise figures as low as 0.16 db (50-K source resistance) have been observed for signal frequencies between 2 and 50 cps. The circuit configuration is a double sideband up-converter or modulator in which a band of frequencies from dc to several hundred cycles is used to modulate a 150-kc carrier. An analysis for noise and gain is presented which considers the average, fundamental, and second-harmonic components of the time-varying diode capacitance. The amplifier input is a signal at low audio frequency, while the output is composed of the sum and difference sidebands of the pump. Gain is realized through up-converter action associated with the frequency shift from signal frequency to near pump frequency; the sum and difference sidebands are further amplified in the output tank by the negative resistance resulting from the action of the component of time-varying capacitance at the second harmonic of the pump frequency. Gain and equivalent input noise resistance are discussed as functions of detuning in the passive output tank; measured and calculated results are compared. A scheme is also presented for stabilizing the amplifier at high values of negative resistance gain.

PROTOTYPE SECTIONS of a low-noise-solid-state maser amplifier have been operated at signal frequencies up to 40 kMc. This Ka band maser, of the traveling-wave type, has an extremely large tuning range, incorporates ferrite isolators to obtain high gain stability, and use pump frequencies in the 75-kMc region.

Josephson traveling wave parametric amplifiers can have high gain and wide frequency range, high sensitivity, and low noise, which makes them promising for quantum computing, array receiver readout systems, spectroscopy, single-photon detectors, etc. In this paper, the authors investigate samples of traveling wave parametric amplifiers based on a three-layer Nb/AlOx/Nb superconductor–insulator–superconductor (SIS) structure with a SNAIL (Superconducting Nonlinear Asymmetric Inductive Elements) series array. Each SNAIL cell consists of the kinetic inductance of four SIS junctions and the nonlinear inductance of a smaller SIS junction. The cells are alternately connected in antiphase with respect to the magnetic flux, which ensures a change in the sign of the Kerr nonlinearity and a reduction in the phase mismatch for the pump frequency, signal frequency, and idler frequency. The transmission spectra of the samples were measured at temperatures of 4.2 and 2.8 K in the frequency range of 0.1–6 GHz.

The necessary conditions for parametric amplification obtained by Penfield for the series nonlinear capacitive-linear resistive element are extended to the case when the resistive element is also nonlinear. The role played by the phase angle between the capacitive and resistive modulation, first considered by Engelbrecht for the frequency converter and the special case of quadrature pumping, is also taken into account. On the basis of the gain criteria, a figure of merit of a parametric element applicable to the pumped condition is also extended to include the type of element considered. It is demonstrated that, all things being equal, the most favorable pumping phase is that for which the capacitive variation at the pump frequency lags the resistive variation by 90° in phase. It is shown that of the nonlinear elements now being used for parametric applications, none satisfy the favorable phase condition. A convenient gain-frequency graph summarizing most of the theoretical conclusions is presented. Finally, it is also proved that for the case where the signal frequency is lower than the idler frequency, the highest frequency of operation obtainable with an existing series capacitive-resistive element can never be increased by the addition of a passive series nonlinear resistor, regardless of the pumping phase achievable by this addition.

This thesis presents the development and the additive manufacturing of smart antennas and frequency selective surfaces (FSS) for microwave, millimetre wave, and low-Terahertz applications. Numerous fabrications techniques such as etching, low-cost inkjet-printing, Fused Filament Fabrication (FFF) and Aerosol Jet Printing are employed to fabricate the antennas and FSS. Firstly, frequency reconfigurable antennas with close-coupled biasing technique are developed using double-sided etching on a thin mylar substrate for smart current and voltage sensing applications. The frequency tunable antenna also acts as a novel current sensing antenna in a smart sensing system that can sense the alternating current passing through a wire. The design is followed by introducing a low-cost inkjet-printed industry ready solution for frequency reconfigurable antennas where a single antenna aperture solution is utilised to demonstrate frequency reconfigurability in both switching and tuning configurations. Development of Frequency Selective Surfaces using low-cost printing machine is demonstrated in which FSS structures are inkjet-printed as wallpaper posters for Radio Frequency (RF) shielding and signal enhancements for 4G and 5G applications. A novel approach for fully 3D printing an FSS structure is also demonstrated using a low-cost open-source printer, which was modified to print the filament and the conductive inks simultaneously. Widespread investigation of industry-grade Aerosol Jet printing is utilised for additive manufacturing of bandstop and bandpass FSS designs for RF shielding and signal filtering. The bandstop designs are developed for microwave and millimetre-wave applications. The bandpass slot FSS designs are developed for millimetre wave and low-Terahertz applications for futuristic Beyond 5G and 6G systems.

Fractal geometries have been extensively implemented in the design of multiband antenna and frequency selective surface (FSS). For example, convoluted and Hilbert patch elements were first proposed to reduce the unit cell size of FSS (Parker and El Sheikh, IEE Proc.-H, 138, 19–22, 1991.) A fractal FSS with self-similar Sierpinski dipole array was shown to have two stop bands (J. Romeu and Y. Rahmat-Samii, IEEE Trans., AP-48, 1097–1104, 2000). However, its resonant frequencies are rather sensitive to incident angles and polarizations. Minkowski patch FSS and Sierpinski carpet fractals have been shown to provide two or three stop bands with dual polarization capability (J.P. Gianvittorio, et. al., IEEE Trans., AP-51, 3088–3096, 2003.) Recently miniature band-pass FSS with fractal antenna-filter-antenna arrays was designed and demonstrated with good frequency selectivity (S. Zheng, et. al., IEEE AWPL, 11, 240–243, 2012.) A dual band fractal FSS with a 3:1 reflection to pass band ratio and significantly improved resonant frequency stability was proposed by the author (T.K. Wu, Microwave Optical Tech. Letters, 54, 833–835, 2012).

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> × 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> with a thickness of 0.006 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems.