Phase-locked Source Research Articles

Direct Conversion of Static Voltage to a Steerable RF Radiation Beam Using an Active Metasurface

A low-profile, directive, high-power, simple radio frequency (RF) source can play a crucial role in long-distance communication, sensing, and anti-interference research. Conventional approaches to achieving high-power radiation require a microwave source, an amplifier, and a separate radiating structure. In this article, we transform a static voltage to electromagnetic radiation, which can be electronically steered, using only a thin sheet of metasurface. The proposed approach can be scaled in both power and frequency. The concept makes use of the k = 0 mode in a periodic resonant surface to excite a series of phase-locked individual sources on the surface. The phase-locked sources create an overall coherent mode in the far-field toward the desired direction. The proposed idea is inspired by spark-gap transmitters, pulsed ring-down sources, and antenna arrays to provide a novel and highly scalable electromagnetic source. We envision that the proposed active metasurface for converting a static field to electromagnetic radiation can be potentially used in long-range communication, sensing devices, and radars.

Broadband extreme ultraviolet interferometry and imaging

Using a pair of phase-locked high-harmonic generation sources, we demonstrate Fourier transform interferometry at extreme-ultraviolet (EUV) wavelengths between 17 and 55 nm. This is made possible by the adaptation of a birefringence-based ultrastable interferometer for infrared femtosecond pulses. Since we measure the interference with an EUV-sensitive CCD camera, this enables a wide range of spatially and spectrally resolved measurements at extreme ultraviolet wavelengths. We demonstrate the capabilities of this technique by performing wavelength-resolved high-resolution coherent diffractive imaging and by measuring the spatially resolved spectral absorption of a thin structured titanium film.

Multi-channel poloidal correlation reflectometry on experimental advanced superconducting tokamak.

A new multi-channel poloidal correlation reflectometry is developed at Experimental Advanced Superconducting Tokamak. Eight dielectric resonator oscillators with frequencies of 12.5 GHz, 13.5 GHz, 14.5 GHz, 15 GHz, 15.5 GHz, 16 GHz, 17 GHz, and 18 GHz are used as sources. Signals from the sources are up-converted to V band using active quadruplers and then coupled together. The output waves are launched by one single antenna after passing through a 20 dB directional coupler which can provide the reference signal. Two poloidally separated antennae are installed to receive the reflected waves from plasma. The reference and reflected signals are down-converted by mixing with a quadrupled signal from a phase-locked source with a frequency of 14.2 GHz and the IF signals pass through the filter bank. The resulting signals from the mixers are detected by I/Q demodulators. The setup enables the measurement of density fluctuation at 8 (radial) × 2 (poloidal) spatial points. A coherent mode with an increasing velocity from 50 kHz to 100 kHz is observed by using the system. The mode is located in the steep gradient region of the pedestal.

Separation of phase-locked sources in pseudo-real MEG data

This article addresses the blind separation of linear mixtures of synchronous signals (i.e., signals with locked phases), which is a relevant problem, e.g., in the analysis of electrophysiological signals of the brain such as the electroencephalogram and the magnetoencephalogram (MEG). Popular separation techniques such as independent component analysis are not adequate for phase-locked signals, because such signals have strong mutual dependency. Aiming at unmixing this class of signals, we have recently introduced the independent phase analysis (IPA) algorithm, which can be used to separate synchronous sources. Here, we apply IPA to pseudo-real MEG data. The results show that this algorithm is able to separate phase-locked MEG sources in situations where the phase jitter (i.e., the deviation from the perfectly synchronized case) is moderate. This represents a significant step towards performing phase-based source separation on real data.

SIW-Based Low Phase-Noise Millimeter-Wave Planar Dual-Port Voltage-Controlled Oscillator

In this paper, a low phase-noise millimeter-wave planar dual-port voltage-controlled oscillator (VCO) using a novel electronically tunable substrate integrated waveguide (SIW) resonator is proposed. The VCO operates in the Ka- and E-band simultaneously. At the fundamental-wave port, the VCO achieves a tuning rang of more than 120MHz by varying the varactor tuning voltage from 0 to 11V, spurious output less than −40 dBc, and a phase-noise of −114.7 dBc/Hz at 1MHz offset from 32 GHz carrier frequency. Meanwhile, at the harmonic port, a tuning rang of more than 240MHz around 64GHz carrier frequency is achieved. The measured output power varies from 6.04 to 8.75 dBm and 7.2 to 9.46 dBm within the fundamental-wave and second harmonic tuning ranges, respectively. This type of low phase-noise planar dual-port VCO is very suitable for millimeter-wave applications in high stable phase-locked sources or FMCW radars.

Source Separation and Clustering of Phase-Locked Subspaces

It has been proven that there are synchrony (or phase-locking) phenomena present in multiple oscillating systems such as electrical circuits, lasers, chemical reactions, and human neurons. If the measurements of these systems cannot detect the individual oscillators but rather a superposition of them, as in brain electrophysiological signals (electro- and magneoencephalogram), spurious phase locking will be detected. Current source-extraction techniques attempt to undo this superposition by assuming properties on the data, which are not valid when underlying sources are phase-locked. Statistical independence of the sources is one such invalid assumption, as phase-locked sources are dependent. In this paper, we introduce methods for source separation and clustering which make adequate assumptions for data where synchrony is present, and show with simulated data that they perform well even in cases where independent component analysis and other well-known source-separation methods fail. The results in this paper provide a proof of concept that synchrony-based techniques are useful for low-noise applications.

Experimental study of the coherence of a terahertz-separated metastable-state qubit inC40a+

Relaxation of the off-diagonal density-matrix elements between the metastable $3\text{ }{^{2}D}_{3/2}$ and $3\text{ }{^{2}D}_{5/2}$ states in a single ${^{40}\text{C}\text{a}}^{+}$, which are separated from each other by 1.82 THz, is studied experimentally by using the Ramsey method of separated oscillating fields. The two metastable states are connected with a stimulated Raman transition by using two infrared lasers, which are phase locked with their frequency difference bridged by an optical frequency comb. By performing Ramsey measurements for two Zeeman components of the stimulated Raman transition with different sensitivities to magnetic fields, the coherence is investigated quantitatively and the effect of magnetic-field fluctuations on that is evaluated. By using a spin-echo $\ensuremath{\pi}$ pulse in a Ramsey sequence which is effective for inhomogeneous broadening processes, a visibility decay time of 5.1 ms is obtained. This is more than twice as long as that for normal sequences. This work is an essential step for realization of a qubit using the two metastable states and demonstrates coherent manipulation of the internal states separated by around a terahertz using phase-locked light sources.

Frequency hopping millimeter-wave reflectometry in ASDEX upgrade

Millimeter-wave reflectometers for performing density fluctuations have traditionally used either tunable fixed frequency (heterodyne and homodyne) systems or multichannel fixed frequency arrangements. Only recently novel systems were brought into operation with the ability to hop from one frequency to another over a large bandwidth, during each plasma discharge, while retaining the quality of fixed frequency phase locked sources. The new broadband fast hopping millimeter-wave reflectometer incorporates frequency synthesizers for both plasma signal and local oscillators, and the receivers are heterodyne producing full phase/amplitude outputs. Two identical systems were recently installed in (ASDEX upgrade tokamak - IPP-MPG Germany) covering the Q band (33–50 GHz) and the V band (50–75 GHz). In the present article the system is described and the particular implementation on ASDEX, using monostatic antenna system, is presented showing the possibility of correlation studies in fully optimized antenna scenarios. With both Q and V channels in operation it was possible to devise several operation schemes that are described here and a result showing the radial localization of magnetohydrodynamic activity is also presented.

High Quality On-Chip Long Annular Josephson Junction Clock Source for Digital Superconducting Electronics

We have developed clock sources for rapid single flux quantum (RSFQ) digital circuits using high-quality long Josephson junction (LJJ) resonant oscillators of annular geometry. Being a topologically closed system and unperturbed by reflections from boundaries and collisions among the fluxons (flux quanta), the annular LJJ oscillator has demonstrated a high quality factor. The novel design of an annular junction clock that allows easier interface with RSFQ circuitry has been realized. Magnetic fluxons are inserted into an annular LJJ by local injection of current into the control line of the junction. This technique resolves the long-standing problem of achieving superior stability of the fluxon state for application as a clock source. The linewidth of the phase-locked clock source is measured as low as 24 Hz relative to a reference oscillator at 40 GHz. The cycle-to-cycle jitter was measured to be 9 fs at a frequency of 36 GHz, or 0.04% of the clock period which is in good agreement with theoretical estimation.

Phase Noise Analysis and Estimate of Millimeter Wave PLL Frequency Synthesizer

Phase noise is an important index in evaluating the performance of millimeter wave (MMW) frequency source. Because of the high frequency, it is difficult to measure its phase noise directly. So it is very necessary to find new methods for estimating it effectively and easily. In this paper, the main factors affecting phase noise of MMW PLL frequency source are analyzed, and then a new method to estimate the phase noise is presented, which is based on the comparison of the phase noise of microwave phase-locked frequency source with phase-locked intermediate frequency in MMW phase-locked loop. In order to demonstrate the validity of this method of phase noise estimate, it is applied to estimate the phase noise of 95GHz double PLL frequency synthesizer. The result shows that the theoretical estimate value is well coincident with the experimental value.

Phase Locking of 2-mm Wave Sources Upon High-Order IMPATT Multipliers

We describe experiments resulting in the phase locking of two electrically tunable 2-mm wave sources based on active high-order IMPATT multipliers. Phase locking modes were tested on a pair of identical multiplying sources (master and slave) with the tuning ranges 138.5+/−1.5 GHz (master) and 140.0+/− GHz (slave). The phase lock loop (PLL) system is used to lock the slave source to the master source. The multipliers of this type can translate the spectra of highly stable centimeter-wave oscillators to any part of the millimeter range with the output power 100÷20 mW over the 30 to 140 GHz range without additional amplification. The phase locked sources operate over a 3% frequency band with low phase noise and rapid frequency tuning. The amplitude-frequency characteristics of the sources are presented with the locking-mode signal spectra.

Millimeter-wave cavity ringdown spectroscopy

Laser-based cavity ringdown techniques have demonstrated ultrahigh sensitivities for trace gas detection in the optical and infrared wavelength regions. We have investigated the applicability of the cavity ringdown technique in the millimeter wave region, which is rich in the rotational spectra of molecules. The millimeter-wave system uses a tunable Fabry–Perot cavity that is excited by a continuous-wave, phase-locked source at the W band; a fast PIN diode switch that turns off the excitation after the cavity is tuned to resonance; and a diode detector that records the resonance decay. Proof of concept has been established by measuring the ringdown times with absorbing materials in the cavity and comparing them with theoretical prediction.

Coherence properties of high-order harmonics: Application to high-density laser–plasma diagnostic

We present two interferometry schemes in the extreme ultraviolet, based on either the wave-front division of a unique harmonic beam (1st scheme) or two spatially separated, phase-locked harmonic sources (2nd scheme). In the first scheme using a Fresnel bimirror interferometer, we measure the degree of spatial coherence of the 13th harmonic generated in xenon, as a function of different parameters. A high degree of coherence, larger than 0.5, is found for the best conditions in almost the full section of the beam. Then, we demonstrate that the second scheme can be used for interferometry measurements with an ultrahigh time resolution. The 11th harmonic is used to study the spatial variation of the electron density of a laser-produced plasma. Electronic densities higher than 2.1020 cm−3 are measured.

Q-band injection-locked gunn diode oscillator

The configuration and performance of a Q-band injection-locked Gunn oscillator are presented whose outport is connected with a phase-locked reference source by a circulator. The output power of the oscillator is more than 60mW at 46.1GHz. The single-sideband phase noise (SSB) is less than-71.7dBc/Hz offset 10KHz from the carrier, and the spectrum of clutter signal is less than -40dB.

Broadband heterodyne reflectometer at the W7-AS stellarator

A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz in extraordinary mode polarization, has been installed and operated at the Wendelstein 7-AS stellarator for the study of density fluctuations and density profile determination. At 2.5 T it covers the density range between 5×1018 and 5×1019 m−3. The system differs from the usual setup as it combines the advantages of heterodyne detection with broadband capability avoiding the limitations of phase-locked sources and permits the unambiguous determination of the phase delay independent of amplitude fluctuations in the reflected beam. After a first downconversion to an intermediate frequency of about 6 GHz, two additional mixing steps lead to an intermediate frequency of 60 MHz, which carries the phase delay from the plasma as a phase modulation. The phase information is yielded numerically from sin/cos detection at 60 MHz. Due to the balanced detection scheme, the drift as well as the broadband noise of the signal and local oscillators are canceled. The system has a dynamic range of about 60 dB and is within this range almost insensitive to amplitude fluctuations of the reflected beam. Examples are given demonstrating the potential of the system installed.

A highly sensitive millimeter wave quasi-optical FM noise measurement system

A highly sensitive, tunable, low-loss quasi-optical millimeter wave FM noise measurement system using a matched, easily tunable quasi-optical cavity in reflection, to act as a carrier suppression filter, is described. This can operate with matched cavity Q's of several hundred thousand with almost zero insertion loss to provide an extremely high discriminator slope at low power levels. The FM noise measurement system can allow direct measurement of phase-locked sources at low input power levels over ultra-wideband frequency ranges.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development and evaluation of a GaAs MMIC phase-locked loop chip set for space applications

GaAs monolithic microwave integrated circuit (MMIC) chips designed for a phase-locked loop frequency source to be used in space applications have been developed. The chip set includes a three-stage resistive feedback amplifier with 13-dB gain in a 275 MHz to 5.85 GHz bandwidth, a 2.0-GHz voltage-controlled oscillator, a 2.8-GHz digital prescaler, and a VHF/UHF digital phase/frequency discriminator. Both analog and buffered-FET logic digital circuits were fabricated on the same wafer. The MMIC process which was developed for this application comprises molecular beam epitaxial deposition of the active layer, proton isolation, submicron gates, thin film TaN resistor deposition, and silicon nitride passivation. The chip set was used successfully to implement a 2.0 GHz all-GaAs phase-locked loop. >

Phase locking of stimulated emission from arrays of stripe GaAIAs/GaAs lasers using active directional couplers

An experimental study was made of the characteristics of radiation emitted by arrays of stripe injection lasers in the form of coupled symmetric active Y couplers. An output power of 300 mW in one direction was achieved under cw emission conditions. The periodicity of lobes in the angular distribution corresponded to diffraction of radiation from phase-locked sources and the presence of a peak in the direction of the normal to the emitting surface indicated that the radiation from the individual sources was in phase. An output power of 72.5 mW was obtained in the case of single-frequency cw emission (in an external dispersive resonator).

35 GHz phase-locked Gunn source based on current hump phase detection

The letter describes the implementation of a phase-locking scheme described earlier to a 35 GHz Gunn solid-state source (SSS). The CLTF is developed, a loop filter is chosen and the response to a step disturbance is measured. This response is compared to the theoretical response obtained by a Runge-Kutta simulation.

Mini-Asynthesizer as the Reference forS-Band (1.7 To 2.1 GHz) Phase-Locked Oscillators

Instead of a Single Crystal Oscillator reference to an S-Band (1.7 to 2.1 GHz) microwave phase-locked source, a mini-synthesizer is used. As the mini-synthesizer, driven from a single highly-stable 1 MHz source can generate a number of frequencies in the range 90 to 100 MHz with 100 kHz spacing, the total number of output frequencies from the P.L.O. (Phase Locked Oscillator) has been increased from 5 to 350. The mini-synthesizer has been built using the ordinarily available TTL & ECL ICs. The whole system of synthesized P.L.O. has been tested and found to give satisfactory performance.