Vibration-induced Phase Noise Research Articles

Effect and mitigation of oscillator vibration-induced phase noise on carrier phase tracking

The influence of vibration-induced oscillator phase noise on carrier phase tracking of a GNSS receiver is analyzed. We show that when the oscillator is vibrating, the vibration-induced oscillator noise is increased and the carrier phase tracking is affected. In order to mitigate the influence of the vibration-induced oscillator phase noise on carrier phase tracking, a vector tracking structure based on an extended Kalman filter called vector phase tracking loop (VPLL) is proposed. In this method, an individual phase lock loop (PLL) for each channel is used to track the satellite-dependent parameters such as atmospheric delay, and a common vector loop is integrated for common parameters tracking such as the receiver clock. The performance of the conventional PLL and the proposed VPLL under oscillator vibration is compared using data collected from a simulator and from a field test. Different PLL bandwidths are tested in order to consider different operating conditions. The test results show that when similar thermal noise error is present, the proposed method can improve the carrier phase tracking compared to conventional PLL.

Novel Gyroscopic Mounting for Crystal Oscillators to Increase Short and Medium Term Stability under Highly Dynamic Conditions.

In this paper, a gyroscopic mounting method for crystal oscillators to reduce the impact of dynamic loads on their output stability has been proposed. In order to prove the efficiency of this mounting approach, each dynamic load-induced instability has been analyzed in detail. A statistical study has been performed on the elevation angle of the g-sensitivity vector of Stress Compensated-cut (SC-cut) crystals. The analysis results show that the proposed gyroscopic mounting method gives good performance for host vehicle attitude changes. A phase noise improvement of 27 dB maximum and 5.7 dB on average can be achieved in the case of steady state loads, while under sinusoidal vibration conditions, the maximum and average phase noise improvement are as high as 24 dB and 7.5 dB respectively. With this gyroscopic mounting method, random vibration-induced phase noise instability is reduced 30 dB maximum and 8.7 dB on average. Good effects are apparent for crystal g-sensitivity vectors with low elevation angle φ and azimuthal angle β. under highly dynamic conditions, indicating the probability that crystal oscillator instability will be significantly reduced by using the proposed mounting approach.

Proportional-scanning-phase method to suppress the vibrational noise in nonisotope dual-atom-interferometer-based weak-equivalence-principle-test experiments

Vibrational noise is one of the most important noises that limits the performance of the nonisotopes atom-interferometers (AIs) -based weak-equivalence-principle (WEP) -test experiment. By analyzing the vibration-induced phases, we find that, although the induced phases are not completely common, their ratio is always a constant at every experimental data point, which is not fully utilized in the traditional elliptic curve-fitting method. From this point, we propose a strategy that can greatly suppress the vibration-induced phase noise by stabilizing the Raman laser frequencies at high precision and controlling the scanning-phase ratio. The noise rejection ratio can be as high as ${10}^{15}$ with arbitrary dual-species AIs. Our method provides a Lissajous curve, and the shape of the curve indicates the breakdown of the weak-equivalence-principle signal. Then we manage to derive an estimator for the differential phase of the Lissajous curve. This strategy could be helpful in extending the candidates of atomic species for high-precision AIs-based WEP-test experiments.

Vibration sensitivity reduction of two microwave oscillators using inter‐injection locking technique

Phase noise is one of the most important specifications of microwave oscillators. External factors such as mechanical vibrations increase the phase noise of the oscillator. A novel technique is introduced to reduce vibration-induced phase noise using inter-injection locking of two coupled oscillators. Two similar oscillators with equal free running frequencies are chosen and are subjected to sinusoidal vibration. The mechanical configuration is such that vibration sensitivity vector increases the frequency of one oscillator and decreases the other one's frequency of oscillation. Coupling these two oscillators using inter-injection locking, the common after-lock frequencies of both oscillators would be equal to the free running frequency of oscillation; as such the influence of vibration on the oscillators is reduced. Experimental measurements are carried out to confirm the proposed technique.

Heterodyne measurement of resonant elastic scattering from epitaxial quantum dots.

Resonant elastic scattering from InAs quantum dots (QDs) is studied by heterodyne spectroscopy. We show theoretically that heterodyne spectroscopy of a two-level quantum emitter is not sensitive to the inelastic fluorescence component. In practice, we easily measure the elastic emission even when the fluorescence is dominated by inelastic scattering. We are able to distinguish the resonant elastic fluorescence from a large background of scattered pump light by modulating the QD transition frequency with a surface acoustic wave. The signal linewidth is 250 Hz, limited by vibration-induced phase noise in the optical fibers used for resonant optical drive and fluorescence collection.

Modeling phase noise in multifunction subassemblies

Obtaining requisite phase noise performance in hardware containing multifunction circuitry requires accurate modeling of the phase noise characteristics of each signal path component, including both absolute (oscillator) and residual (non-oscillator) circuit contributors. This includes prediction of both static and vibration-induced phase noise. The model (usually in spreadsheet form) is refined as critical components are received and evaluated. Additive (KTBF) phase noise data can be reasonably estimated, based on device drive level and noise figure. However, accurate determination of component near-carrier (multiplicative) and vibration-induced noise usually must be determined via measurement. The model should also include the effects of noise introduced by IC voltage regulators and properly discriminate between common versus independent signal path residual noise contributors. The modeling can be easily implemented using a spreadsheet.

Common-Arm Counterpropagating Interferometer for Measurement of Vibration-Induced Noise in Fibers

We propose and demonstrate a novel technique to measure the vibration sensitivity of fiber-based optical components. It uses a common-arm counterpropagating frequency-shifted interferometer that reduces the vibration-induced phase noise of the interconnecting fibers feeding the signal to and from the vibrating device under test. The noise introduced by the vibrating fibers can be excessive, and measurements of a given device cannot be made with assurance. The proposed technique improves the vibration-induced phase noise floor by more than 30 dB compared to a conventional frequency-shifted Mach-Zehnder interferometer and allows measurement of low vibration sensitive devices. A phase sensitivity of 1 mrad/g at 192 Terahertz (THz) is achieved with this method. We also present results of vibration sensitivity of an assortment of commonly used fiber-based optical devices.

Measurement and real-time cancellation of vibration-induced phase noise in a cavity-stabilized laser

We demonstrate a method to measure and actively reduce the coupling of vibrations to the phase noise of a cavity-stabilized laser. This method uses the vibration noise of the laboratory environment rather than active drive to perturb the optical cavity. The laser phase noise is measured via a beat note with a second unperturbed ultra-stable laser while the vibrations are measured by accelerometers positioned around the cavity. A Wiener filter algorithm extracts the frequency and direction dependence of the cavity response function. Once the cavity response function is known, real-time noise cancellation can be implemented by use of the accelerometer measurements to predict and then cancel the laser phase fluctuations. We present real-time noise cancellation that results in a 25 dB reduction of the laser phase noise power spectral density.

Acceleration insensitive encapsulated silicon microresonator

This paper presents the acceleration sensitivity and the resulting vibration-induced phase noise of an electrostatically coupled encapsulated silicon microresonator. External vibrations can produce phase noise in microresonators by generating time-varying stress in the resonant beams. A spring mounted resonator design that reduces the induced axial stress is presented here. Measurements and simulations show that the acceleration sensitivity and the vibration-induced phase noise of this device can be reduced 1000 times smaller than that of the previously published silicon microresonator and 10 times smaller than the commercially used high end SC (stress compensated)-cut quartz resonator.

Cancellation of Vibration-Induced Phase Noise in Optical Fibers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Vibration causes mechanical distortions in optical fibers that induce phase fluctuations in the transmitted optical signal. Information encoded on the optical signal by modulation, such as in a radio-frequency (RF)-photonic link also degrades. A feed-forward correction technique is described that enables 20 dB or more cancellation of vibration-induced phase fluctuations in an optical fiber wound on a spool. The scheme is also applied to an optoelectronic oscillator (OEO). The OEO has emerged as an excellent low-noise source that rivals the best electronic RF oscillators over a broad range of offset frequencies. However, close-to-carrier spectral purity of an OEO is degraded mostly by the vibration-induced phase fluctuations in optical fibers when the temperature is held constant. Implementation of feed-forward phase correction in an OEO has shown improvement by almost an order of magnitude in the vibration sensitivity of the oscillator. </para>

A novel method to suppress vibration-induced phase noise of crystal oscillators

A compensated polarization-effect tuning technique is used to suppress the mechanical vibration-induced phase noise of quartz crystal oscillators. Unlike the earlier approach, the tuning signal is filtered by a dynamic function that provides both varying magnitude and phase compensation of the nonlinear distortion of the accelerometer and the phase delay of the tuning mechanism thus improving noise cancellation. Laboratory tests demonstrate that vibration-induced phase noise of a crystal oscillator under mechanical vibration is significantly suppressed after using this approach.

Effects of random vibration in high-speed phase-shifting speckle pattern interferometry

The influence of random vibrations on the performance of a dynamic phase-shifting speckle pattern interferometer is investigated by means of experiments and numerical simulations. Two aspects are evaluated: first, temporal unwrapping reliability, second, vibration-induced phase noise. The former is found to be a significant constraint, even for peak velocities well below the Nyquist velocity limit of the interferometer. Shorter sampling windows and higher framing rates are shown to increase the unwrapping success rate, but longer windows reduce the phase error. Three analytical criteria for determining the expected unwrapping success rate are proposed and compared.

Measurement of static and vibration-induced phase noise in UHF thin-film resonator (TFR) filters.

Measurements of the static phase noise and vibration sensitivity of thin-film resonator (TFR) filters operating at 640 and 2110 MHz have been made. They show that the short-term frequency instability of the filters is small compared with that induced in the oscillator signal by the sustaining stage amplifier PM (phase modulation) noise. In-oscillator measurement of filter performance under vibration indicates that fractional frequency vibration sensitivities (deltafo/fo) are on the order of several parts in 10(-9)/g. Because the percentage bandwidth and order (number of poles) of the filters was fairly constant, so was the product of the center frequency and group delay. Thus, the fractional frequency vibration sensitivity of the filters can be expressed alternatively as carrier signal phase sensitivity to vibration. The tau-omega0 product for the filters that were tested was on the order of 300 rad, so that the equivalent phase sensitivity to vibration was approximately 1 microrad/g.