Tens Of GHz Research Articles

Multicharged Ion Generation in Plasma Created by Millimeter Waves and Confined in a Cusp Magnetic Trap

Modern way of ECR multicharged ion sources development is connected with increasing of microwave frequency up to tens of GHz. Millimeter wave gyrotrons are used now at a few laboratories. Traditional mirror magnetic traps with min B configuration for suppressing of MHD instabilities became too expensive because very strong magnetic field is needed. So prospection of axisymmetric plasma trap with MHD stabilization is a quite relevant subject of modern plasma physics. The simplest trap of such kind is CUSP one. The zero level of magnetic field in the center of the trap doesn’t allow to achieve a good confinement in classical regime. In a gasdynamic regime of plasma confinement was studied. The same regime may be realized in the CUSP geometry trap if plasma density is high enough. A small CUSP trap was designed for plasma creation by 37,5 GHz gyrotron radiation under ECR conditions. Temporal evolutions of plasma parameter in experiments were quite smooth and stable. Experimental ion charge state distribution corresponds with calculated one for optimal plasma conditions.

High-speed optical switching based on diffusive conduction in an optical waveguide with surface-normal optical control

We report a surface-normal optically controlled waveguide switch made of a p-i-n diode that utilizes optically induced voltage screening to turn on and diffusive conduction to turn off. We examine theoretically diffusive conduction in these switches and show that this mechanism offers the possibility of creating optical switches operating at several tens of GHz. As a proof-of-concept demonstration, we present experimental results of wavelength-converting, optical switching at frequencies up to 2.5 GHz in a multiple-quantum-well, GaAs-based waveguide device using milliwatt-level switching powers. Optimized arrays of these devices can be used for high-speed, multichannel wavelength conversion and optical regeneration in wavelength-division-multiplexed systems.

Fast relaxation in the structural glass and glassy crystal of ethanol and cyano cyclohexane: A quasielastic light scattering study

Fast relaxation processes in the structural glass and glassy crystal of ethanol as well as in the glassy crystal of cyano cyclohexane were studied by quasielastic light scattering (LS). Depolarized and polarized LS spectra together with the Brillouin line were measured applying a tandem Fabry–Perot interferometer at frequencies 1–1500 GHz. Depolarized, polarized LS and internal friction data exhibit very similar behavior, thus reflect the same relaxations. The depolarized LS spectra are described by assuming a nearly constant loss (NCL) contribution dominating in the frequency range from 1 GHz to a few tens GHz and by a fast dynamics contribution at higher frequencies. The NCL amplitude increases exponentially with temperature in a similar way as found by dielectric spectroscopy for other molecular glasses. The data cannot be described by thermally activated dynamics in double well potentials, a result contradicting the findings in inorganic glasses such as silica.

Single flux quantum signal transmission techniques in building practical RSFQ circuits

The practical implementation of rapid single flux quantum (RSFQ) technology requires much more complexity than the presently developed circuits. Multiple chips have to be integrated with a technology that is reliable at cryogenic temperatures. The interchip and intrachip data transmission speed of tens of GHz has to be supported. Also, the large RSFQ circuits need serial biasing to reduce the amount of the bias current. The test circuits were designed, simulated, fabricated with Nb technology, and tested at a temperature of 4.2 K. Test results at GHz frequencies showed that SFQ pulses can be successfully transmitted over an extensive distance in a chip, between chips, and over the circuits in different ground planes.

Passively Mode-Locked Pulse Generation at 40 GHz Repetition Rate by Semiconductor Lasers with Distributed Bragg Reflector for Oscillating Mode Control

Passively mode-locked pulse generations at a 40 GHz repetition rate were demonstrated without using any saturable absorbers. In a conventional dispersive Fabry-Perot cavity with the length corresponding to a mode-locking frequency of lower tens GHz, the phase differences between longitudinal modes become large and cause the out-of-phase mode-locking. In the present work, the gain section was restricted to a half-length of the cavity, then the phase differences were suppressed, and mode-locked pulse generations were achieved. A distributed Bragg reflector (DBR) was implemented in the cavity as an oscillating mode selector. The obtained pulses were almost transform-limited. A typical time-bandwidth product of 0.45 was obtained for a DBR length of 291 µm. By varying the DBR current, the center wavelength of mode-locked pulses was changed over 5 nm. Time-bandwidth products for pulses generated from lasers with various coupling lengths of DBR are also investigated experimentally.

BiCMOS technology for mixed-digital, analog, and RF applications

As process technology advances, we will see SoC systems with millions of digital gates combined with RF circuits operating in the tens of GHz.

D-wave induced zero-field resonances in dc pi-superconducting quantum interference devices.

A dc pi SQUID consists of a superconducting ring interrupted by two Josephson junctions, one of which carries in equilibrium a pi phase difference, caused, for example, by the d-wave pairing symmetry of the high- T(c) cuprates. If this phase shift is maintained in the voltage state, anomalous resonance currents are expected in the SQUIDs transport characteristics. Here we report the observation of such resonances for high- T(c) dc pi SQUIDs, providing evidence for the influence of the d-wave symmetry on the voltage state of a Josephson junction for frequencies of several tens of GHz.

Propagation of ultrashort acoustic wave packets in PbMoO 4 studied by Brillouin spectroscopy

We employ Brillouin spectroscopy to study the propagation in PbMoO 4 of ultrashort acoustic wave packets created by absorption of subpicosecond optical pulses in a thin-film metallic transducer. The development of the acoustic power spectrum can be studied up to several tens of GHz. We obtain information on the local propagation velocity with a sensitivity of 0.1%. Diffraction of the Fourier components of the acoustic wave packet in the crystal can be monitored in the spectral domain via the spectral width, or in real-space using scans transverse to the beam, and turns out to be anomalously small. Preliminary results at helium temperatures are presented, which show pump intensity dependent propagation effects.

Nonthermal mixing mechanism in a diffusion-cooled hot-electron detector

We present an analysis of a diffusion-cooled hot-electron detector fabricated from clean superconducting material with low transition temperature. The distinctive feature of a clean material, i.e., material with large electron mean free path, is a relatively weak inelastic electron scattering that is not sufficient for the establishment of an elevated thermodynamic electron temperature when the detector is subjected to irradiation. We propose an athermal model of a diffusion-cooled detector that relies on suppression of the superconducting energy gap by the actual dynamic distribution of excess quasiparticles. The resistive state of the device is caused by the electric field penetrating into the superconducting bridge from metal contacts. The dependence of the penetration length on the energy gap delivers the detection mechanism. The sources of the electric noise are equilibrium fluctuations of the number of thermal quasiparticles and frequency dependent shot noise. Using material parameters typical for A1, we evaluate performance of the device in the heterodyne regime at terahertz frequencies. Estimates show that the mixer may have a noise temperature of a few quantum limits and a bandwidth of a few tens of GHz, while the required local oscillator power is in the μW range due to ineffective suppression of the energy gap by quasiparticles with high energies.

The 100 GHz light switch

Escalating transmission rates in telecoms networks are the spur behind an international research effort in optical processing. The author reports on the work of the BT researchers who are laying the foundations for a new era of photon-based switching systems. The work is based on an interferometric switch known as the TOAD. The TOAD is a variant of a Mach-Zehnder interferometer. Light enters the interferometer, then passes through a 50:50 coupler which divides the input equally between the upper and lower arms. In general, the upper and lower light streams will experience different phase shifts, and these shifts will determine the way the original input is allocated between the two output ports. In particular, if the interferometer is suitably biased then all the light will appear at one or other of the outputs. Now, if a phase shift is introduced into one of the arms the output will switch between ports. This is the principle; its practical exploitation depends on the availability of a device that can effect a π phase shift at a rate of at least tens of GHz. In the TOAD this function is assigned to a semiconductor optical amplifier.

Passive optical fast frequency-hop CDMA communications system

This paper proposes an all-fiber fast optical frequency-hop code division multiple access (FFH-CDMA) for high-bandwidth communications. The system does not require an optical frequency synthesizer allowing high communication bit rates. Encoding and decoding are passively achieved by Bragg gratings, Multiple Bragg gratings replace a frequency synthesizer, achieving a hopping rate in tens of GHz. A main lobe sine apodization can be used in writing the gratings to enhance the system capacity and the spectrum efficiency. All network users can use the same tunable encoder/decoder design. The simultaneous utilization of the time and frequency domains offers notable flexibility in code selection. Simulations show that the encoder efficiently performs the FFH spread spectrum signal generation and that the receiver easily extracts the desired signal from a received signal for several multiple access interference scenarios. We measure the system performance in terms of bit error rate, as well as auto-to cross-correlation contrast. A transmission rate of 500 Mb/s per user is supported in a system with up to 30 simultaneous users at 10/sup -9/ bit error rate. We compare FFH-CDMA to several direct sequence-CDMA systems in terms of bit error rate versus the number of simultaneous users. We show that an optical FFH-CDMA system requires new design criteria for code families, as optical device technology differs significantly from that of radio frequency communications.

Temparature drift of modulation characteristics in semiconductor lasers

The temperature dependences of the basic parameters of single-mode InGaAsP semiconductor lasers have been analysed with due regard for the Auger effect. Formulas have been derived for computing the temperature drifts of amplitude-frequency and phase-frequency characteristics (AFC, PFC) under direct high-frequency modulation to construct three-dimensional amplitude and phase surfaces. On the basis of the formulas derived, an analytical method has been designed for calculating the temperature drift of the AFC and PFC of semiconductors lasers under high-frequency modulation by small signals without any optical feedback. The proposed method yields results in good agreement with the experimental data over wide frequency (tens of GHz) and temperature (δT ≃ 80 K) intervals. The PFC drifts have been studied as a function of different parameters and initial temperatures (thermostabilisation temperature) of lasers. The temperature drifts of lasers have been numerically estimated and criteria have been formulated for choosing the laser operation modes in phase stabilisation fibre-optic laser transmitter modules. The error of the AFC and PFC determination method is of the order of 0.2%/K.

Enhanced second-order optical nonlinearity using inter- and intra-band transitions in low-dimensional semiconductors

We propose a novel scheme of enhancing χ(2)(ω3;−ω1,ω2) in asymmetric quasi-low- dimensional (QLD) semiconductors. The ω1 and ω2 are tuned to exciton levels, while ω3=ω2−ω1 is tuned to an intersubband transition energy. Fairly large χ(2) is obtained when a certain asymmetry is introduced in the QLD structure by, e.g., an external electric field F. A possible application is the efficient down conversion of coherent light emitted from a laser diode(s) into an intersubband frequency ω3 via a parametric process or difference-frequency generation. It is also possible to modulate the intensity of the down-converted, long-wavelength light by modulating F at a very high frequency of several tens of GHz.

An exact expression for the noise voltage across a resistor shunted by a capacitor

The mean square voltage developed across a noisy resistor (R) with a white spectral density shunted by a capacitor (C) is known to be (kT/C), where k is Boltzmann's constant and T the absolute temperature of R. A puzzling aspect of this simple result is that the value of the resistor (which is the real source of noise) appears to play no part and gives no clue on the outcome in the limiting cases of R to 0 or C to 0. The difficulty is resolved by first noting that due to quantum effects, the simple white noise model breaks down at frequencies of 10/sup 9/ Hz or so. Using a quantum-corrected expression for the spectral density, the problem of the RC network has been reworked exactly. It is verified that the new expression yields correct results for all values of the parameters. A Taylor series expansion of the output in terms of the noise equivalent bandwidth of the RC circuit shows that the old result (kT/C) is very accurate for bandwidths of up to tens of GHz. Numerical results are illustrated graphically. >

Fibre's low loss is microwave's gain

The microwave region of the electromagnetic spectrum – frequencies between about 1 GHz and a few tens of GHz, or wavelengths in the centimetre range – is mainly used for radars, satellite links, short-haul terrestrial communications and electronic warfare equipment. And although optoelectronic components have been developed primarily for telecommunication needs, optical fibre technology is also attractive for microwave signal transmission and processing and could replace existing microwave carriers such as coaxial cable. Among the many advantages of fibres are huge bandwidth (more than several hundreds of GHzkm in single-mode fibre), low optical attenuation (less than 0.5 dBkm-1 at 1.3 μm and 0.2 dBkm-1 at 1.55 μm), low weight, small size and immunity to electromagnetic interference (EMI).

Electron pulse generation at 64 GHz in scanning electron microscope

An electron beam chopping technique has been developed which enables the generation of electron pulses at tens of GHz in an SEM. This is effected by deflecting the beam in a circle and chopping it with a multislot aperture. Electron pulses have been produced at 64 GHz and measured, and a waveform measurement at 18 GHz demonstrates its potential application to electron beam characterisation of very high speed devices and MMICS.

Measuring the ISR Impedance at Very High Frequencies by Observing the Energy Loss of a Coasting Beam

A slow energy loss of unbunched protons and antiprotons in the ISR has been observed which is larger than expected for interactions with the residual gas and for synchrotron radiation., It can be explained as a parasitic mode loss due to the wall currents induced by the longitudinal Schottky noise. This noise as seen at the wall of a circular chamber of radius a extends to a typical frequency of the order ? ~ c?/a limited by the finite opening angle of ~1/? of the fields created by a relativisitic particle. Due to the statistical longitudinal distribution of the particles the total energy loss due to the induced wall current is proportional to the total number of particles and the loss per particle becomes independent of current. This loss leads to a steady decrease of the orbit radius which can be observed for long storage times. Using these results obtained at different energies, the frequency dependence of the resistive longitudinal impedance in the range of several tens of GHz is obtained. This impedance is compared with the prediction of the diffraction theory.