Showing papers on "Phase noise published in 2016"
TL;DR: An atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold) is demonstrated, limited by the phase noise of the microwave source.
Abstract: Quantum metrology uses quantum entanglement--correlations in the properties of microscopic systems--to improve the statistical precision of physical measurements. When measuring a signal, such as the phase shift of a light beam or an atomic state, a prominent limitation to achievable precision arises from the noise associated with the counting of uncorrelated probe particles. This noise, commonly referred to as shot noise or projection noise, gives rise to the standard quantum limit (SQL) to phase resolution. However, it can be mitigated down to the fundamental Heisenberg limit by entangling the probe particles. Despite considerable experimental progress in a variety of physical systems, a question that persists is whether these methods can achieve performance levels that compare favourably with optimized conventional (non-entangled) systems. Here we demonstrate an approach that achieves unprecedented levels of metrological improvement using half a million (87)Rb atoms in their 'clock' states. The ensemble is 20.1 ± 0.3 decibels (100-fold) spin-squeezed via an optical-cavity-based measurement. We directly resolve small microwave-induced rotations 18.5 ± 0.3 decibels (70-fold) beyond the SQL. The single-shot phase resolution of 147 microradians achieved by the apparatus is better than that achieved by the best engineered cold atom sensors despite lower atom numbers. We infer entanglement of more than 680 ± 35 particles in the atomic ensemble. Applications include atomic clocks, inertial sensors, and fundamental physics experiments such as tests of general relativity or searches for electron electric dipole moment. To this end, we demonstrate an atomic clock measurement with a quantum enhancement of 10.5 ± 0.3 decibels (11-fold), limited by the phase noise of our microwave source.
451 citations
07 Jul 2016
TL;DR: The potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.
Abstract: This paper reviews the state of the art in spin-torque and spin-Hall-effect-driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.
306 citations
TL;DR: In this paper, a nonlinear state-space model for nonlinearity mitigation, carrier recovery, and nanoscale device characterization is proposed, which allows for tracking and compensation of the XPM induced impairments by employing approximate stochastic filtering methods such as extended Kalman or particle filtering.
Abstract: Machine learning techniques relevant for nonlinearity mitigation, carrier recovery, and nanoscale device characterization are reviewed and employed. Markov Chain Monte Carlo in combination with Bayesian filtering is employed within the nonlinear state-space framework and demonstrated for parameter estimation. It is shown that the time-varying effects of cross-phase modulation (XPM) induced polarization scattering and phase noise can be formulated within the nonlinear state-space model (SSM). This allows for tracking and compensation of the XPM induced impairments by employing approximate stochastic filtering methods such as extended Kalman or particle filtering. The achievable gains are dependent on the autocorrelation (AC) function properties of the impairments under consideration which is strongly dependent on the transmissions scenario. The gain of the compensation method are therefore investigated by varying the parameters of the AC function describing XPM-induced polarization scattering and phase noise. It is shown that an increase in the nonlinear tolerance of more than 2 dB is achievable for 32 Gbaud QPSK and 16-quadratic-amplitude modulation (QAM). It is also reviewed how laser rate equations can be formulated within the nonlinear state-space framework which allows for tracking of nonLorentzian laser phase noise lineshapes. It is experimentally demonstrated for 28 Gbaud 16-QAM signals that if the laser phase noise shape strongly deviates from the Lorentzian, phase noise tracking algorithms employing rate equation-based SSM result in a significant performance improvement ( $>$ 8 dB) compared to traditional approaches using digital phase-locked loop. Finally, Gaussian mixture model is reviewed and employed for nonlinear phase noise compensation and characterization of nanoscale devices structure variations.
199 citations
TL;DR: In this article, a wavefront engineering mechanism was proposed to generate high purity orbital angular momentum (OAM) modes of high purity by virtue of spin-orbit interaction in continuously shaped plasmonic metasurfaces.
Abstract: Traditional technologies to generate and manipulate the orbital angular momentum (OAM) suffer from bulky size and do not lend themselves to nanophotonic systems. An ultrathin metasurface based on abrupt phase shift has recently been proposed as an alternative method. Nevertheless, gradient phase was generally approximated by multiple meta-atom/molecules with discrete levels of abrupt phase shift, which not only increases the design and fabrication complexity but also causes difficulties in obtaining simultaneous electrical and optical functionality. Furthermore, a discontinuous phase profile would introduce phase noise to the scattering fields and deteriorate the purity of the OAM beams. Here, we propose a wavefront engineering mechanism by virtue of the spin–orbit interaction in continuously shaped plasmonic metasurfaces, which offers a new approach to generate OAM modes of high purity. Equally important, a method producing arbitrary OAM topological charge, integral and fractional, is demonstrated by mer...
178 citations
TL;DR: A fully stabilized all polarization-maintaining Er frequency comb with a nonlinear amplifying loop mirror with below 0.2 rad carrier-envelope-offset frequency phase noise is demonstrated.
Abstract: A fully stabilized all polarization-maintaining Er frequency comb with a nonlinear amplifying loop mirror with below 0.2 rad carrier-envelope-offset frequency phase noise is demonstrated. The integrated timing jitter is measured as 40 attosecond from 10 kHz to 10 MHz, which is the lowest value of any Er fiber frequency comb to date.
177 citations
TL;DR: This work presents a highly integrated 57-64 GHz 4-channel receiver 2-channel transmitter chip targeting short range sensing and large bandwidth communications that is housed in an embedded wafer level ball grid array package.
Abstract: This work presents a highly integrated 57–64 GHz 4-channel receiver 2-channel transmitter chip targeting short range sensing and large bandwidth communications. The chip is housed in an embedded wafer level ball grid array package. The package includes 6 integrated patch antennas realized with a metal redistribution layer. The receiver patch antennas have a combined antenna gain of $\approx 10$ dBi while each transmitter antenna has a gain of $\approx ~6$ dBi. The chip features a wide tuning range integrated VCO with a measured phase noise lower than −80 dBc/Hz at 100 kHz offset. Each of the differential transmitter channels shows a measured output power of 2–5 dBm over the complete frequency range. In addition, one transmitter channel features a modulator that can be digitally programmed to operate in either radar or communication mode. Each of the receiver channels has a measured conversion gain of 19 dB, a single-sideband noise figure of less than 10 dB and an input referred 1 dB compression point of less than 10 dBm. With all channels turned on the chip consumes a current of 300 mA from a 3.3 V supply. The functionality of the chip is demonstrated for both sensing and short range wireless communications.
147 citations
TL;DR: A method to reduce a flicker (1/f) noise upconversion in voltage-biased RF oscillators by exploiting different behaviors of inductors and transformers in differential-and common-mode excitations is proposed.
Abstract: In this paper, we propose a method to reduce a flicker (1/f) noise upconversion in voltage-biased RF oscillators. Excited by a harmonically rich tank current, a typical oscillation voltage waveform is observed to have asymmetric rise and fall times due to even-order current harmonics flowing into the capacitive part, as it presents the lowest impedance path. The asymmetric oscillation waveform results in an effective impulse sensitivity function of a nonzero dc value, which facilitates the 1/f noise upconversion into the oscillator’s 1/f3 phase noise. We demonstrate that if the $\omega _{0}$ tank exhibits an auxiliary resonance at 2 $\omega _{0}$ , thereby forcing this current harmonic to flow into the equivalent resistance of the 2 $\omega _{0}$ resonance, then the oscillation waveform would be symmetric and the flicker noise upconversion would be largely suppressed. The auxiliary resonance is realized at no extra silicon area in both inductor- and transformer-based tanks by exploiting different behaviors of inductors and transformers in differential- and common-mode excitations. These tanks are ultimately employed in designing modified class-D and class-F oscillators in 40 nm CMOS technology. They exhibit an average flicker noise corner of less than 100 kHz.
127 citations
TL;DR: A mm-wave frequency generation technique that improves its phase noise (PN) performance and power efficiency and third-harmonic boosting and extraction techniques are proposed and applied to the frequency generator.
Abstract: This paper proposes a mm-wave frequency generation technique that improves its phase noise (PN) performance and power efficiency. The main idea is that a fundamental 20 GHz signal and its sufficiently strong third harmonic at 60 GHz are generated simultaneously in a single oscillator. The desired 60 GHz local oscillator (LO) signal is delivered to the output, whereas the 20 GHz signal can be fed back for phase detection in a phase-locked loop. Third-harmonic boosting and extraction techniques are proposed and applied to the frequency generator. A prototype of the proposed frequency generator is implemented in digital 40 nm CMOS. It exhibits a PN of $-100\;\text{dBc/Hz}$ at 1 MHz offset from 57.8 GHz and provides 25% frequency tuning range (TR). The achieved figure-of-merit (FoM) is between 179 and 182 dBc/Hz.
109 citations
TL;DR: It is demonstrated that it is possible to extract the phase and timing signals of a multiheterodyne spectrum completely computationally, without any extra measurements or optical elements.
Abstract: Dual-comb spectroscopy allows for high-resolution spectra to be measured over broad bandwidths, but an essential requirement for coherent integration is the availability of a phase reference. Usually, this means that the combs’ phase and timing errors must be measured and either minimized by stabilization or removed by correction, limiting the technique’s applicability. We demonstrate that it is possible to extract the phase and timing signals of a multiheterodyne spectrum completely computationally, without any extra measurements or optical elements. These techniques are viable even when the relative linewidth exceeds the repetition rate difference and can tremendously simplify any dual-comb system. By reconceptualizing frequency combs in terms of the temporal structure of their phase noise, not their frequency stability, we can greatly expand the scope of multiheterodyne techniques.
103 citations
TL;DR: This paper proposes a method to use geometric constraints of digital fringe projection system to substantially reduce the noise impact by allowing the use of more than one period of equivalent phase map for temporal phase unwrapping.
Abstract: One of the major challenges of employing a two-frequency (or two-wavelength) phase-shifting algorithm for absolute three-dimensional shape measurement is its sensitivity to noise. Therefore, three- or more-frequency phase-shifting algorithms are often used in lieu of a two-frequency phase-shifting algorithm for applications where the noise is severe. This paper proposes a method to use geometric constraints of digital fringe projection system to substantially reduce the noise impact by allowing the use of more than one period of equivalent phase map for temporal phase unwrapping. Experiments successfully verified the enhanced performance of the proposed method without increasing the number of patterns.
98 citations
TL;DR: This paper applies an idea of coupling multiple oscillators to reduce phase noise (PN) to beyond the limit of what has been practically achievable so far in a bulk CMOS technology to demonstrate for the first time an RF oscillator that meets the most stringent PN requirements of cellular basestation receivers while abiding by the process technology reliability rules.
Abstract: In this paper, we exploit an idea of coupling multiple oscillators to reduce phase noise (PN) to beyond the limit of what has been practically achievable so far in a bulk CMOS technology. We then apply it to demonstrate for the first time an RF oscillator that meets the most stringent PN requirements of cellular basestation receivers while abiding by the process technology reliability rules. The oscillator is realized in digital 65-nm CMOS as a dual-core LC-tank oscillator based on a high-swing class-C topology. It is tunable within 4.07–4.91 GHz, while drawing 39–59 mA from a 2.15 V power supply. The measured PN is $-$ 146.7 dBc/Hz and $-$ 163.1 dBc/Hz at 3 MHz and 20 MHz offset, respectively, from a 4.07 GHz carrier, which makes it the lowest reported normalized PN of an integrated CMOS oscillator. Straightforward expressions for PN and interconnect resistance between the cores are derived and verified against circuit simulations and measurements. Analysis and simulations show that the interconnect resistance is not critical even with a 1% mismatch between the cores. This approach can be extended to a higher number of cores and achieve an arbitrary reduction in PN at the cost of the power and area.
TL;DR: The first successful frequency comb offset stabilization that utilizes a Si3N4 waveguide for octave-spanning supercontinuum generation and achieve the lowest integrated residual phase noise of any diode-pumped gigahertz laser comb to date is demonstrated.
Abstract: Silicon nitride (Si3N4) waveguides represent a novel photonic platform that is ideally suited for energy efficient and ultrabroadband nonlinear interactions from the visible to the mid-infrared. Chip-based supercontinuum generation in Si3N4 offers a path towards a fully-integrated and highly compact comb source for sensing and time-and-frequency metrology applications. We demonstrate the first successful frequency comb offset stabilization that utilizes a Si3N4 waveguide for octave-spanning supercontinuum generation and achieve the lowest integrated residual phase noise of any diode-pumped gigahertz laser comb to date. In addition, we perform a direct comparison to a standard silica photonic crystal fiber (PCF) using the same ultrafast solid-state laser oscillator operating at 1 µm. We identify the minimal role of Raman scattering in Si3N4 as a key benefit that allows to overcome the fundamental limitations of silica fibers set by Raman-induced self-frequency shift.
TL;DR: This paper introduces an integer-N synthesizer that employs a type-I loop to achieve a wide bandwidth, allowing the use of ring oscillators, and a master-slave sampling loop filter along with harmonic traps to suppress spurs.
Abstract: The high phase noise of ring oscillators has generally discouraged their use in RF synthesis. This paper introduces an integer-N synthesizer that employs a type-I loop to achieve a wide bandwidth, allowing the use of ring oscillators, and a master-slave sampling loop filter along with harmonic traps to suppress spurs. A 2.4 GHz prototype fabricated in 45 nm digital CMOS technology provides a loop bandwidth of 10 MHz and a spur level of $-\text{65}\;\text{dBc}$ . The phase noise is $-\text{114}\;\text{dBc}/\text{Hz}$ at 1 MHz offset.
TL;DR: The novel closed-form expressions for the evaluation of the detection and false alarm probabilities are provided, assuming Rayleigh fading, and the analysis is extended to the case of CR networks with cooperative sensing, where the secondary users suffer from different levels of RF imperfections.
Abstract: Direct-conversion radio (DCR) receivers can offer highly integrated low-cost hardware solutions for spectrum sensing in cognitive radio (CR) systems. However, the DCR receivers are susceptible to radio frequency (RF) impairments, such as in-phase and quadrature-phase imbalance, low-noise amplifier nonlinearities, and phase noise, which limit the spectrum sensing capabilities. In this paper, we investigate the joint effects of RF impairments on energy detection-based spectrum sensing for CR systems in multi-channel environments. In particular, we provide the novel closed-form expressions for the evaluation of the detection and false alarm probabilities, assuming Rayleigh fading. Furthermore, we extend the analysis to the case of CR networks with cooperative sensing, where the secondary users suffer from different levels of RF imperfections, considering both scenarios of error free and imperfect reporting channel. Numerical and simulation results demonstrate the accuracy of the analysis as well as the detrimental effects of RF imperfections on the spectrum sensing performance, which bring significant losses in the spectrum utilization.
TL;DR: This Letter presents a widely tunable, low phase noise microwave source based on a photonic chip using on-chip stimulated Brillouin scattering as a narrowband active filter and shows very low close-to-carrier phase noise.
Abstract: Spectrally pure microwave sources are highly desired for several applications, ranging from wireless communication to next generation radar technology and metrology. Additionally, to generate very pure signals at even higher frequencies, these advanced microwave sources have to be compact, low in weight, and low energy consumption to comply with in-field applications. A hybrid optical and electronic cavity, known as an optoelectronic oscillator (OEO), has the potential to leverage the high bandwidth of optics to generate ultrapure high-frequency microwave signals. Here we present a widely tunable, low phase noise microwave source based on a photonic chip. Using on-chip stimulated Brillouin scattering as a narrowband active filter allows single-mode OEO operation and ultrawide frequency tunability with no signal degeneration. Furthermore, we show very low close-to-carrier phase noise. This Letter paves the way to a compact, fully integrated pure microwave source.
TL;DR: In this paper, a phase-noise-compensated optical time-domain reflectometry (φ$ -OTDR) was proposed for distributed fiber-optic vibration sensors.
Abstract: Distributed fiber-optic vibration sensors based on phase-sensitive optical time-domain reflectometry ( $\phi$ -OTDR) have found many applications in various fields. In this paper, we analyze the phase noise of $\phi$ -OTDR, which is the main limiting factor of the measurement range. We found that the laser phase noise and phase extraction error caused by the intensity noise in photodetection contribute to the total phase noise. By introducing a series of auxiliary weak reflection points along the fiber, we develop a phase-noise-compensated $\phi$ -OTDR and realize a long-range distributed vibration sensing based on the phase extraction. Furthermore, a statistical analysis was proposed to maintain the vibration measurement sensitivity along the whole fiber. In the experiment, vibrations at 30 km were measured with a linear response, which confirmed the validity of our proposed system.
TL;DR: This paper presents a low-power low-noise 60 GHz frequency synthesizer using a 20 GHz subsampling phase-locked loop (SS-PLL) and a 60 GHz tail-coupling quadrature injection-locked oscillator (QILO) which results in a lower in-band phase noise and out-of- band phase noise, respectively.
Abstract: This paper presents a low-power low-noise 60 GHz frequency synthesizer using a 20 GHz subsampling phase-locked loop (SS-PLL) and a 60 GHz tail-coupling quadrature injection-locked oscillator (QILO) which results in a lower in-band phase noise and out-of-band phase noise, respectively. To save battery life, dual-step-mixing injection-locked frequency divider (ILFD) enhances locking range for high division ratio. Moreover, tail cross-coupling technique in a QILO helps boost negative transconductance $({{-g}}_{m})$ of the 60 GHz QILO which allows the use of larger inductance for power reduction. Implemented in 65 nm CMOS, it can cover required channels from 58.32 to 64.80 GHz with quadrature outputs. It consumes 24.2 and 7.8 mW from 20 GHz SS-PLL and QILO, respectively. The proposed synthesizer achieves $-78.5\; \text{dBc/Hz}$ at 100 kHz offset, $-122\text{dBc/Hz}$ at 10 MHz offset, and a figure-of-merit (FoM) of $-236\text{dB}$ .
TL;DR: In this article, the impact of phase noise on the downlink performance of a multiuser multiple-input-multiple-output (MIMO) system was studied. But the authors focused on the impact on the quality of the channel state information (CSI) available at the BS when compared with a system without phase noise.
Abstract: We study the impact of phase noise on the downlink performance of a multiuser multiple-input–multiple-output (MIMO) system, where the base station (BS) employs a large number of transmit antennas $M$ . We consider a setup where the BS employs $M_{\mathrm{osc}}$ free-running oscillators, and $M/M_{\mathrm{osc}}$ antennas are connected to each oscillator. For this configuration, we analyze the impact of phase noise on the performance of zero forcing (ZF), regularized ZF, and matched filter precoders when $M$ and the number of users $K$ are asymptotically large, whereas the ratio $M/K=\beta$ is fixed. We analytically show that the impact of phase noise on the signal-to-interference-plus-noise ratio (SINR) can be quantified as an effective reduction in the quality of the channel state information (CSI) available at the BS when compared with a system without phase noise. As a consequence, we observe that as $M_{\mathrm{osc}}$ increases, the SINR performance of all considered precoders degrades. On the other hand, the variance of the random phase variations caused by the BS oscillators reduces with increasing $M_{\mathrm{osc}}$ . Through Monte Carlo simulations, we verify our analytical results and compare the performance of the precoders for different phase noise and channel noise variances. For all considered precoders, we show that when $\beta$ is small, the performance of the setup where all BS antennas are connected to a single oscillator is superior to that of the setup where each BS antenna has its own oscillator. However, the opposite is true when $\beta$ is large and the signal-to-noise ratio (SNR) at the users is low.
TL;DR: This work paves the way to generate high-quality low phase noise ultrashort pulses in passively mode-locked fiber lasers.
Abstract: Low phase noise mode-locked fiber laser finds important applications in telecommunication, ultrafast sciences, material science, and biology, etc. In this paper, two types of carbon nano-materials, i.e. single-wall carbon nanotube (SWNT) and graphene oxide (GO), are investigated as efficient saturable absorbers (SAs) to achieve low phase noise mode-locked fiber lasers. Various properties of these wall-paper SAs, such as saturable intensity, optical absorption and degree of purity, are found to be key factors determining the performance of the ultrafast pulses. Reduced-noise femtosecond fiber lasers based on such carbon-based SAs are experimentally demonstrated, for which the phase noise has been reduced by more than 10 dB for SWNT SAs and 8 dB for GO SAs at 10 kHz. To the best of our knowledge, this is the first investigation on the relationship between different carbon material based SAs and the phase noise of mode-locked lasers. This work paves the way to generate high-quality low phase noise ultrashort pulses in passively mode-locked fiber lasers.
TL;DR: In this article, the impact of turbulence on coherent detection and the related phase noise that restricts time and frequency transfer precision was evaluated for a two-way cancellation of atmospheric effects despite the asymmetry between up-and downlink that limits the link reciprocity.
Abstract: Bidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study the impact of turbulence on coherent detection and the related phase noise that restricts time and frequency transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up- and downlink that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end-to-end simulations under realistic turbulence and wind conditions as well as satellite kinematics. These temporally resolved simulations allow characterizing the coherent detection in terms of time series of heterodyne efficiency and phase noise for different system parameters. We show that tip-tilt correction on ground is mandatory at reception for the downlink and as a pre-compensation of the uplink. Besides, thanks to the large tilt angular correlation, the correction is shown to be efficient on uplink despite the point-ahead angle. Very good two-way compensation of turbulent effects is obtained even with the asymmetries. The two-way differential phase noise is reduced to $1{\mathrm{rad}}^{2}$, with the best fractional frequency stability below $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ after 1-s averaging time.
TL;DR: In this paper, an ultra-high-speed fractional-N$ frequency divider and a highly linear phase-frequency detector (PFD) are integrated into a high-frequency SiGe bipolar technology.
Abstract: A millimeter-wave (mm-wave) frequency synthesizer is presented focusing on an ultra-high-speed fractional- ${ N}$ frequency divider and a highly linear phase-frequency detector (PFD). All circuits are integrated into a high-frequency SiGe bipolar technology. The programmable frequency divider can be operated at input frequencies between dc and 57 GHz for division factors in the entire integer range from 12 to 259. The PFD is optimized for fractional- ${ N}$ synthesis, which requires an extremely linear characteristic due to the modulation of its input frequency. The frequency divider and the PFD are used together with an 80-GHz wideband voltage-controlled oscillator (VCO) and transceiver for a high precision mm-wave frequency-modulated continuous-wave (FMCW) radar sensor. As shown by the experimental results the realized circuits stabilize the mm-wave VCO with an extremely low phase noise below $-{\hbox{97 dBc/Hz}}$ at 10-kHz offset around its center frequency of 80 GHz and can generate a highly linear frequency ramp with a bandwidth of 24 GHz. Furthermore, the accuracy of the synthesizer is demonstrated by FMCW radar distance measurements inside a waveguide and in free space. Inside the waveguide a standard deviation of the phase of the target below 0.0018 $^{\circ }$ (which corresponds to 9.4 nm) was measured.
TL;DR: A maximum-likelihood (ML) approach to jointly estimate the self-interference and intended channels by exploiting its own known transmitted symbols and both the known pilot and unknown data symbols from the other intended transceiver is proposed.
Abstract: Operation of full-duplex systems requires efficient mitigation of the self-interference signal caused by the simultaneous transmission/reception. In this paper, we propose a maximum-likelihood (ML) approach to jointly estimate the self-interference and intended channels by exploiting its own known transmitted symbols and both the known pilot and unknown data symbols from the other intended transceiver. The ML solution is obtained by maximizing the ML function under the assumption of Gaussian received symbols. A closed-form solution is first derived, and subsequently, an iterative procedure is developed to further improve the estimation performance at moderate-to-high signal-to-noise ratios (SNRs). We establish the initial condition to guarantee the convergence of the iterative algorithm to the ML solution. In the presence of considerable phase noise from the oscillators, a phase noise estimation method is proposed and combined with the ML channel estimator to mitigate the effects of the phase noise. Illustrative results show that the proposed methods offer good cancelation performance close to the Cramer–Rao bound (CRB).
TL;DR: In this paper, the frequency ramp nonlinearity is investigated with the modified short-time Fourier transform method by using the short time Chirp-Z transform method with high accuracy.
Abstract: One of the main disturbances in a frequency-modulated continuous wave radar system for range measurement is nonlinearity in the frequency ramp. The intermediate frequency (IF) signal and consequently the target range accuracy are dependent on the type of the nonlinearity present in the frequency ramp. Moreover, the type of frequency ramp nonlinearity cannot be directly specified, which makes the problem even more challenging. In this paper, the frequency ramp nonlinearity is investigated with the modified short-time Fourier transform method by using the short-time Chirp-Z transform method with high accuracy. The random and periodic nonlinearities are characterized and their sources are identified as phase noise and spurious. These types of frequency deviations are intentionally increased, and their influence on the linearity and the IF-signal is investigated. The dependence of target range estimation accuracy on the frequency ramp nonlinearity, phase noise, spurious, and signal-to-noise ratio in the IF-signal are described analytically and are verified on the basis of measurements.
20 Jul 2016
TL;DR: In this article, the authors presented an audio band squeezed vacuum source with 1.3−0.5+0.7 mrad of phase noise, which is a nearly tenfold improvement over previously reported measurements, improving prospects for squeezing enhancements in current and future gravitational wave detectors.
Abstract: Squeezed states of light are a valuable resource for reducing quantum noise in precision measurements. Injection of squeezed vacuum states has emerged as an important technique for reducing quantum shot noise, which is a fundamental limitation to the sensitivity of interferometric gravitational wave detectors. Realizing the most benefit from squeezed-state injection requires lowering optical losses and also minimizing squeezed quadrature fluctuations—or phase noise—to ensure that the large noise in the anti-squeezed quadrature does not contaminate the measurement quadrature. Here, we present an audio band squeezed vacuum source with 1.3−0.5+0.7 mrad of phase noise. This is a nearly tenfold improvement over previously reported measurements, improving prospects for squeezing enhancements in current and future gravitational wave detectors.
20 Sep 2016
TL;DR: In this paper, the authors present an approach for producing highly stable pulse trains with a record-low residual integrated offset frequency phase noise of 14 mrad at 1 GHz fundamental repetition rate using a monolithic mode-locked solid-state laser.
Abstract: Low-noise, high-repetition-rate mode-locked solid-state lasers are attractive for precision measurement and microwave generation, but the best lasers in terms of noise performance still consist of complex, bulky optical setups, which limits their range of applications. In this Letter, we present an approach for producing highly stable pulse trains with a record-low residual integrated offset frequency phase noise of 14 mrad at 1 GHz fundamental repetition rate using a monolithic mode-locked solid-state laser. The compact monolithic design simplifies implementation of the laser by fixing the cavity parameters and operates using just 265 mW of 980 nm pump light.
TL;DR: Based on an optically injected semiconductor laser (OISL) operating at period-one (P1) nonlinear dynamical state, high-purity millimeter-wave generation at 60 GHz band is experimentally demonstrated via 1/4 and 1/9 subharmonic microwave modulation.
Abstract: Based on an optically injected semiconductor laser (OISL) operating at period-one (P1) nonlinear dynamical state, high-purity millimeter-wave generation at 60 GHz band is experimentally demonstrated via 1/4 and 1/9 subharmonic microwave modulation (the order of subharmonic is with respect to the frequency fc of the acquired 60 GHz band millimeter-wave but not the fundamental frequency f0 of P1 oscillation). Optical injection is firstly used to drive a semiconductor laser into P1 state. For the OISL operates at P1 state with a fundamental frequency f0 = 49.43 GHz, by introducing 1/4 subharmonic modulation with a modulation frequency of fm = 15.32 GHz, a 60 GHz band millimeter-wave with central frequency fc = 61.28 GHz ( = 4fm) is experimentally generated, whose linewidth is below 1.6 kHz and SSB phase noise at offset frequency 10 kHz is about −96 dBc/Hz. For fm is varied between 13.58 GHz and 16.49 GHz, fc can be tuned from 54.32 GHz to 65.96 GHz under matched modulation power Pm. Moreover, for the OISL operates at P1 state with f0 = 45.02 GHz, a higher order subharmonic modulation (1/9) is introduced into the OISL for obtaining high-purity 60 GHz band microwave signal. With (fm, Pm) = (7.23 GHz, 13.00 dBm), a microwave signal at 65.07 GHz ( = 9fm) with a linewidth below 1.6 kHz and a SSB phase noise less than −98 dBc/Hz is experimentally generated. Also, the central frequency fc can be tuned in a certain range through adjusting fm and selecting matched Pm.
01 Sep 2016
TL;DR: The main contribution of this work is to introduce designs for LLO CV-QKD based on self-coherence phase sharing, in which the phase reference information and the quantum information are coherently obtained from a single optical wavefront.
Abstract: We develop a comprehensive framework to model and optimize the performance of continuous-variable quantum key distribution (CV-QKD) with a local local oscillator (LLO), when phase reference sharing and QKD are jointly implemented. We first analyze the limitations of the only existing approach, called LLO-sequential, and show that it requires high modulation dynamics and can only tolerate small phase noise. Our main contribution is to introduce two designs to perform LLO CV-QKD, respectively called LLO-delayline and LLO-displacement, and to study their performance. Both designs rely on a self-coherent approach, in which phase reference information and quantum information are coherently obtained from a single optical wavefront. We show that these designs can lift some limitations of the existing LLO-sequential approach. The LLO-delayline design can in particular tolerate much stronger phase noise and thus appears to be an appealing alternative to LLO-sequential in terms of network integrability. We also investigate, with the LLO-displacement design, how phase reference information and quantum information can be multiplexed within a single optical pulse. By studying the trade-off between phase reference recovery and phase noise induced by displacement, we, however, demonstrate that this design can only tolerate low phase noise. On the other hand, the LLO-displacement design has the advantage of minimal hardware requirements and provides a simple approach to multiplex classical and quantum communications, opening a practical path towards the development of ubiquitous coherent classical-quantum communications systems compatible with next-generation network requirements.
TL;DR: This paper seeks to close this performance gap by extending PLL bandwidth (BW) using quantization noise cancellation techniques and by employing a dual-path digital loop filter to suppress the detrimental impact of DAC quantization Noise.
Abstract: Phase noise performance of ring oscillator based digital fractional-N phase-locked loops (FNPLLs) is severely compromised by conflicting bandwidth requirements to simultaneously suppress oscillator phase and quantization noise introduced by the time-to-digital converter (TDC), $\Delta \Sigma $ fractional divider, and digital-to-analog converter (DAC). As a consequence, their figure-of-merit (FoMJ) that quantifies the power–jitter tradeoff is at least 25 dB worse than their LC-oscillator-based FNPLL counterparts. This paper seeks to close this performance gap by extending PLL bandwidth (BW) using quantization noise cancellation techniques and by employing a dual-path digital loop filter to suppress the detrimental impact of DAC quantization noise. Fabricated in 65 nm CMOS process, the proposed FNPLL operates over a wide frequency range of 2.0–5.5 GHz using a modified extended range multi-modulus divider with seamless switching. The proposed digital FNPLL achieves 1.9 psrms integrated jitter while consuming only 4 mW at 5 GHz output. The measured in-band phase noise is better than −96 dBc/Hz at 1 MHz offset. The proposed FNPLL achieves wide BW up to 6 MHz using a 50 MHz reference and its FoMJ is −228.5 dB, which is the best among all reported ring-based FNPLLs.
TL;DR: Benefits in terms of flexibility, spectral containment, low latency, and robustness to Doppler spread and phase noise are discussed in the article.
Abstract: This article introduces G-DFT-s-OFDM as a potential 5G waveform candidate. G-DFT-sOFDM replaces the CP with a sequence having a tunable length; this sequence is part of the IFFT output rather than being appended to it. Benefits in terms of flexibility, spectral containment, low latency, and robustness to Doppler spread and phase noise are discussed in the article.
TL;DR: This paper presents an all-digital phase-locked loop (AD-PLL) using a voltage-domain digitization realized by an analog-to-digital converter (ADC) instead of adopting a traditional time- to- digital converter (TDC) which usually suffers from a tradeoff in resolution and power consumption.
Abstract: This paper presents an all-digital phase-locked loop (AD-PLL) using a voltage-domain digitization realized by an analog-to-digital converter (ADC) instead of adopting a traditional time-to-digital converter (TDC) which usually suffers from a tradeoff in resolution and power consumption. It consists of an 18 bit class-C digitally controlled oscillator (DCO), a 4 bit comparator, a digital loop filter (DLF), and a frequency-locked loop (FLL). Implemented in 65 nm CMOS technology, the proposed PLL reaches an in-band phase noise of $- 112\; \text{dBc/Hz}$ and an RMS jitter of 380 fs at a carrier frequency of 2.2 GHz. A figure of merit (FoM) of $-242 \; \text{dB} $ was achieved with a power consumption of only 4.2 mW.