Phase Noise Reduction Research Articles

Optimal modified lateral shearing interferometer with axial range extension by using a dual optical plate.

We present a method to extend the axial range of digital holographic microscopy based on the optimal modified lateral shearing interferometer (MLSI). The proposed system can extend the axial range by using a dual optical plate. The interference pattern with two spatial wavelengths is generated by the plate with different thicknesses. These spatial wavelengths transfer a dual spatial frequency into the Fourier plane by using FFT. Two phases are extracted by a dual spatial frequency and combined to create a synthetic wavelength, which is applied to measure the micrometer-scale object without phase unwrapping. Also, the noise-reducing algorithm is used to reduce phase noise caused by the amplified noise of the synthetic wavelength. The experimental result confirms the feasibility of the optimal MLSI by using a dual optical plate.

A Wireless-Frequency-Locked-Loop-Based Vital Sign Sensor With Quadrature Tracking and Phase-Noise Reduction Capability

Most conventional continuous wave (CW) vital sign sensors suffer from the phase noise of the voltage-controlled oscillator (VCO). This work develops a novel wireless-frequency-locked-loop (FLL)-based sensor to overcome this issue. This technology uses the propagation delay of the sensor signal to make the entire sensing circuit and the subject under test (SUT) a wireless FLL. The wireless FLL uses a quadrature-tracking technique to track the phase of the propagation signal and the phase variation that is caused by the vibration of the SUT. This technique thus enables the wireless FLL not only to reduce the phase noise of the VCO but also to sense the vital signs of the SUT. Moreover, the phase-noise reduction of the wireless FLL increases with the sensing distance. The signal-to-noise ratio (SNR) of the proposed wireless-FLL-based sensor in vital sign sensing is therefore much higher than that of a conventional CW sensor. The SNR performance of the wireless-FLL-based sensor is further optimized using a highly sensitive VCO. Experimental results demonstrate that the SNR of the wireless-FLL-based sensor is around 16 dB better than that of the conventional CW sensor at a detection distance of 4 m. The SNR enhancement increased by approximately 6.6 dB when the detection distance is doubled. With this SNR enhancement, the heart-rate measurement accuracy of the developed 2.4 GHz wireless-FLL-based sensor is 90.5 % at a detection distance of 8 m.

Process variation tolerant wide-band fast PLL with reduced phase noise using adaptive duty cycle control strategy

ABSTRACT This paper presents the effects of manufacturing process variations on the phase-locked loop (PLL) performances like lock time, lock range and phase noise. At higher operating frequencies, due to process variations, there is a shift in the duty cycle of the divider output to phase-frequency detector, which leads to lock failure. To alleviate this problem an adaptive duty cycle control (ADCC) strategy is proposed and used in the frequency divider present in the feedback path of PLL. The proposed technique makes the PLL process variation tolerant and lock at higher frequencies where otherwise PLL was out of lock. It assists the PLL to lock faster and achieve low phase noise at all frequencies under nominal conditions. The operating temperature range is also enhanced to −50° to 50o C. Simulation studies in Cadence design environment on a 3.5 GHz PLL reveals the lock range improvement of 40% and phase noise improvement of 15%.

Phase noise reduction in wavelength scanning interferometry using a phase synthesis approach

We proposed a method to reduce the phase noise in wavelength scanning interferometry (WSI). The method utilizes the two different mechanisms of Fourier transform and the least squares algorithm to produce a synthetic phase map. For validation, the deformation of a fiberglass reinforced resin matrix composite specimen under mechanical loading was measured using a self-built WSI system. The results demonstrate the decrease of phase noise points by more than 20% without sacrificing spatial resolution. The reduction of phase noise can provide high quality phase unwrapping and increase the accuracy of deformation measurements.

Stable period-one oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating.

Period-one (P1) oscillations in a semiconductor laser under optical feedback from a narrowband fiber Bragg grating (FBG) are numerically investigated. FBG feedback enhances the stability of P1 oscillations compared to the conventional mirror feedback in the form of P1 microwave linewidth and phase noise reduction and residual noise peaks suppression. In the proposed scheme, the FBG has a narrow bandwidth smaller than the laser relaxation oscillation frequency. Then it effectively suppresses the coherence collapse of the laser by filtered feedback. Hence it can keep the laser in P1 operation even under relatively strong feedback. Besides, a uniform FBG has a comb-filtered reflectivity spectrum with a main lobe surrounded by several side lobes. Hence it can limit the external cavity modes by each lobe. As a result, FBG feedback can reduce microwave linewidth and phase noise by sustaining stronger feedback power and improve side-peak suppression ratio (SPSR) by filtering external cavity modes. The effects of stabilization are enhanced by properly increasing grating bandwidth. By fine-tuning the feedback delay time, the microwave linewidth can be reduced to a local minimum which reveals the optimal locking between P1 frequency and one of the external cavity modes. Increasing the feedback delay time, the local minimum linewidth can be further reduced. FBG feedback reduces the microwave linewidth by up to more than an order of magnitude and improves the SPSR by up to more than two orders of magnitude than mirror feedback using the same delay time.

Mode Locked Laser Phase Noise Reduction Under Optical Feedback for Coherent DWDM Communication

Single section quantum dash (QDash) mode locked lasers (MLL) can provide a flat and broadband optical frequency comb with low energy consumption, operational simplicity and large-scale low-cost production possibilities. MLL longitudinal modes can be employed as single carriers with a regular spectral spacing in a dense wavelength division multiplexing (DWDM) link, making them promising components for next generation DWDM transceivers. However, individual modes of a MLL suffer from relatively high phase noise while high capacity coherent transmission requires carriers with low phase noise. Optical feedback, which is a well-known method to reduce the linewidth of a single mode laser, can be used to stabilize comb lasers. This article reports on the investigation of phase noise properties of comb lines delivered from a single section QDash MLL under optical feedback and shows that each MLL longitudinal mode optical linewidth can be drastically narrowed. It enables coherent transmission with extended link budget over 50 km at Tbit/s line rates.

Oscillator Stabilization Through Feedback With Slow Wave Structures

This article presents a new formulation to predict the steady-state, stability, and phase-noise properties of oscillator circuits, including either a self-injection network or a two-port feedback network for phase-noise reduction. The additional network contains a slow wave structure that stabilizes the oscillation signal. Its long delay inherently gives rise to multivalued solutions in some parameter intervals, which should be avoided for a reliable operation. Under a two-port feedback network, the circuit is formulated extracting two outer-tier admittance functions, which depend on the node-voltage amplitudes, phase shift between the two nodes, and excitation frequency. Then, the effect of the slow wave structure is predicted through an analytical formulation of the augmented oscillator, which depends on the numerical oscillator model and the structure admittance matrix. The solution curves are obtained in a straightforward manner by tracing a zero-error contour in the plane defined by the analysis parameter and the oscillation frequency. The impact of the slow-wave structure on the oscillator stability and noise properties is analyzed through a perturbation method, applied to the augmented oscillator. The phase-noise dependence on the group delay is investigated calculating the modulation of the oscillation carrier. The various analysis and design methods have been applied to an oscillator at 2.73 GHz, which has been manufactured and measured, obtaining phase-noise reductions of 13 dB, under a one-port load network, and 18 dB, under a feedback network.

Non-Common Band SAR Interferometry Via Compressive Sensing

To avoid decorrelation, conventional synthetic aperture radar interferometry (InSAR) requires that interferometric images should have a common spectral band and the same resolution after proper preprocessing. For a high-resolution (HR) image and a low-resolution (LR) one, the interferogram quality is limited by the LR one since the non-common band (NCB) between two images is usually discarded. In this article, we try to establish an InSAR method to improve interferogram quality by means of exploiting the NCB. To this end, we first define a new interferogram, which has the same resolution as the HR image. Then we formulate the interferometric relationship between the two images into a compressive sensing (CS) model, which contains the proposed HR interferogram. With the sparsity of interferogram in appropriate domains, we model the interferogram formation as a typical sparse recovery problem. Due to the speckle effect in coherent radar imaging, the sensing matrix of our CS model is inherently random. We theoretically prove that the sensing matrix satisfies restricted isometry property, and thus the interferogram recovery performance is guaranteed. Furthermore, we provide a fast interferogram formation algorithm by exploiting computationally efficient structures of the sensing matrix. Numerical experiments show that the proposed method provides better interferogram quality in the sense of reduced phase noise and obtain extrapolated interferogram spectra with respect to CB processing.

Self-Forced Opto-Electronic Oscillators Using Sagnac-Loop PM-IM Convertor

Efficient phase to intensity conversion is key in Sagnac-loop based opto-electronic oscillators ( OEO). This paper features analytical modeling of phase to intensity conversion in practical Sagnac-loop interferometers, with practical coupling imbalance in 3-dB optical coupler, polarization imbalance of the non-reciprocal optical phase shifter (NRPS), and cross-talk ratio in polarization maintaining fiber (PMF). Single-sideband (SSB) phase noise of self-forced frequency stabilization technique of this OEO is also modelled using self-injection locked (SIL) and dual self-phase locked loop (DSPLL); the free-running and forced modeling results of Sagnac-loop based OEO matches with experimentally measured phase noise results. The measured phase noise of the SILDPLL based OEO at 10 GHz is −131 dBc/Hz at offset frequency of 10 kHz with approximately 11 dB phase noise reduction compared to the results of free-running OEO. Self-forced stabilization of OEO results in timing jitter of 19.5 fs, a factor of 6 times reduction in the free-running performance.

Robust and fast filtering method for enhancement of two-dimensional quality-guided path unwrapping algorithms.

This paper presents a new filtering algorithm for reducing phase noise based on the bicubic interpolation method (BIM). The unwrapped phase map accuracy is enhanced by the combination of BIM with a conventional unwrapping algorithm. The bicubic interpolation filtering (BIF) and bicubic interpolation smoothed filtering (BISF) methods are two powerful low-pass filters. The simulation shows that the BIF and BISF convert the initial noise distribution to Gaussian distribution. The Mirau interferometer is used to improve the performance of the proposed filtering algorithms. The root mean square error between two quality-guided path unwrapping algorithms and BISF method is estimated at approximately 31 nm.

Photonic frequency-octupling scheme for stable microwave generation based on two incoherent optical sources

In this paper, a real-time frequency-octupling photonic generator scheme that can realize stable microwave signal generation by using two incoherent optical sources without the support of phase-locked loops is successfully demonstrated, which proves that the improved feed-forward modulation is a feasible method for reducing phase noise. The principle of the proposed generator is illustrated by theory, simulation, and experiment. A 16GHz stable microwave signal with a bandwidth less than 0.2MHz is generated by using a 2GHz driving signal, and a 64GHz optical millimeter wave signal is obtained by using an 8GHz driving signal. Furthermore, a purity 320GHz terahertz wave signal is obtained by simulation based on the same principle and setup. The results show that the terahertz signal has good transmission characteristic and fine eye diagram in the 40.5km fiber link. In addition, to enhance the flexibility and feasibility of the generator, the feasible range of the modulation index and a signal enhancement method are also explored.

300-GHz-band wireless communication using a low phase noise photonic source

AbstractThe implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on–off keying is crucial to further boost the terahertz (THz) communications speed. Thereby, carrier phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, the photonic-based THz sources and the phase noise problem are briefly summarized. Then, a low phase-noise photonic source based on the stimulated Brillouin scattering (SBS) optical fiber cavity is first applied for a 300-GHz-band QPSK wireless communication link. The highest data rate at forward-error-correction limited condition was 15 Gbaud utilizing the SBS-based photonic source with a small transmit power of ~ −36 dBm. Its transmission characteristics are evaluated and compared with the conventional optical frequency comb generator (OFCG)-based source at 5 Gbaud. The proposed SBS-based photonic source has been proven to offer better performances than the OFCG-based source with respect to the phase noise, optical carrier to noise ratio, and bit error rate in communications.

A Phase Noise Reduction Technique in LC Cross-coupled Oscillators with Adjusting Transistors Operating Regions

In this paper, an intuitive analysis of a phase noise reduction technique is done, and then a modified structure is proposed to achieve higher phase noise reduction than the original one. This method reduces the impact of noise sources on the phase noise by decreasing closed-loop gain in zero-crossings points and moving this high closed-loop gain to the non-zero-crossings points. This reduction tested on different scales and all of them showed improvement in the phase noise performance. In other words, this method reduces the phase noise by manipulating the operation region. Impulse sensitivity function (ISF) for the proposed structure shows degradation in comparison to the original structure. We have designed the proposed oscillator in 0.18 μm using CMOS TSMC standard technology. The proposed oscillator operates on 900 MHz, moreover, phase noise is -138.4 dBc/Hz at 1 MHz offset frequency while it consumes 3.11 mA from 1.8 V supply voltage. Keywords. LC cross-coupled oscillator. Phase noise reduction. ISF reduction.

Utilization of Multi-Resonant Defected Ground Structure Resonators in the Oscillator Feedback for Phase Noise Reduction of K-Band VCOs in 0.18-$\mu$ m CMOS Technology

This work proposes a new theory to reduce the phase noise of K-band Voltage-Controlled Oscillators (VCOs) in Complementary Metal Oxide Semiconductor (CMOS) process by introducing one or more transmission poles around the parallel resonance of an LC-tank circuit. Introduction of transmission poles beside the parallel resonance of the LC-tank circuit sharpens the skirt characteristics of the Scattering ( $\vert \text{S}\vert$ ) parameters of the resonators. In return, sharp $\vert \text{S}\vert $ -parameters slope enhances the resonator loaded quality (Q) factor without compromising the unloaded Q-factor. In addition, the transmission pole can be realized near the second harmonic of the oscillation. This allocation of the transmission pole leads to the cancellation of this second harmonic and a further reduction of the phase noise. The proposed theory is verified by three different designs based on defected ground structure (DGS) resonators. These designs realized a low-band transmission pole before the parallel resonance, a high-band transmission pole after the parallel resonance, and dual-band transmission poles around the parallel resonance. First, each design is verified and compared to the others using circuit and electromagnetic simulations to establish the Q-factor improvement. Then, each of the resonators is utilized in a differential VCO topology and the phase noise reduction in post-layout simulations is confirmed. Finally, two chips are fabricated in 0.18- $\mu $ m CMOS technology and measured. The measurement results are in good agreement with the simulations, which confirm our claim about the proposed theory.

A 17.6-to-24.3 GHz −193.3 dB figure-of-merit LC voltage-controlled oscillator using layout floorplan optimization technique for Q-factor enhancement

This paper presents a 20 GHz low-phase-noise low-power LC voltage-controlled oscillator (VCO). It adopts a fully differential tuning varactor, a coarse and a fine capacitor array to cover wide tuning range with a small tuning gain to reduce the amplitude-to-phase noise conversion. A layout floorplan is proposed to reduce the impact of the parasitic resistance of the interconnect and thus improve the Q of the LC tank in the VCO. Hence, the phase noise can be reduced without increasing power consumption. Post-layout simulation results show that the VCO with the proposed layout floorplan can get the phase noise reduction from 1.6 to 3.3 dB compared to the VCO with other layout floorplans in the case of the same power consumption. Implemented in a 65 nm CMOS process, the prototype achieves 17.6–24.3 GHz frequency range, −124 dBc/Hz@10 MHz phase noise at 20.1 GHz carrier frequency, 4.9 mW DC power, and −193.3 dB figure-of-merit.

Low-Noise Voltage Controlled Oscillator with Coupled Microstrip Lines of Different Lengths

Introduction. Coupled two- or three-wire microstrip lines are often used to reduce a phase noise of voltage-controlled oscillators (VCOs). Unfortunately, the phase noise was not optimized depending on the lengths of a three-wire coupled microstrip lines. Aim. For the three-wire coupled microstrip structure, the task of determining of the optimal lengths of its stabs was set. The stabs were corresponded to the reduced phase noise of the selected VCO. Materials and methods . In the oscillator example, the resonator model with three electromagnetically coupled microstrip lines was studied. Herein the second line from the first and the third from the second line differed by the same physical length. The widths of the first and of the third lines were the same, and their coupling clearances with the second line were the same too. On the one hand, in this three-wire microstrip line short-end modes with a common ground electrode were implemented. On the other, at the ends of the first and of the third lines open-end modes were implemented. The free end of the second line is line input. Results. For the considered oscillator, the basic formulas for calculating its frequency-setting elements and resonator model parameters were obtained. By these formulas the estimation of base contours impedances for two oscillators with three-coupled microstrip lines of the same and different lengths, and also for the oscillator using a two-coupled microstrip line was given. For comparison, the proposed VCO near the optimal difference in the three-wire line microstrips lengths had the base contour impedance phase steepness 2...4 times greater, as well as its modules graphs had the width 4...10 times less. Conclusion. In comparison with the known VCOs, the possibility of obtaining lower phase noise spectrum levels at 6...10 dB/Hz in the designed oscillator with the calculated lengths of the selected three-coupled line microstrips was experimentally confirmed.

Improvements in a 20-kW Phase-Locked Magnetron by Anode Voltage Ripple Suppression

Microwave devices based on high-power magnetrons are currently used widely and there is a strong demand for phase-controlled magnetrons. In this work, the performance of a 20-kW $S$ -band continuous-wave magnetron with varied anode voltage ripple is studied. The anode voltage ripple is introduced to an equivalent model of the magnetron to evaluate the system’s performance theoretically. The effects of the anode voltage ripple and the injection parameters on the magnetron’s output are thus analyzed numerically. Furthermore, experiments are performed while the anode voltage ripple is varied from 4.2% to 0.6% using a shunt capacitance-adjustable ripple filter module. A nearly tripled locking bandwidth is observed under a constant injection ratio at 0.1 with decreasing ripple. The ripple-suppressed system pulls its sideband energy to the locking frequency and thus achieves a spectral intensity increment of 0.9 dB, phase noise reduction of 13 dB at an offset of 100 kHz, and phase jitter convergence from ±1.8° to ±0.9°. The experimental features validate the results obtained from the theoretical analyses. The results of this investigation also provide guidance for future industrial applications of phase-locked magnetron arrays.

Stabilizing DFB laser injection-locked to an external fiber-optic ring resonator

Self-injection locking to an external fiber cavity is an efficient technique enabling drastic linewidth narrowing and self-stabilization of semiconductor lasers. The main drawback of this technique is its high sensitivity to fluctuations of the configuration parameters and surroundings. In the proposed laser configuration, to the best our knowledge, for the first time the self-injection locking mechanism is used in conjunction with a simple active optoelectronic feedback, ensuring stable mode-hopping free laser operation in a single longitudinal mode. Locking to 4-m length fiber resonator causes a drastic narrowing of the DFB laser linewidth down to 2.8 kHz and a reduction of the laser phase noise by three orders of magnitude. We have explored key features of the laser dynamics with and without active feedback, revealing stability and tunability of the laser linewidth as an additional benefit of the proposed technique.

Interferometric Phase Retrieval for Multimode InSAR via Sparse Recovery

Modern spaceborne synthetic aperture radar (SAR) features a capacity of multiple imaging modes. It comes with Earth-observation data archives consisting of SAR images acquired in various modes with different resolutions and coverage. In this context, in addition to using single-mode images for SAR interferometry (InSAR), exploiting images acquired in different imaging modes for InSAR can provide extra interferograms and, thus, favors the retrieval of interferometric information. The interferometric processing of multimode image pairs requires special considerations due to significant variations in the Doppler spectra. Conventionally, the InSAR technique only uses the spectral band common in both master and slave images, and the remaining band is discarded before interferogram formation. Therefore, conventional processing cannot make full use of the observed data, and the interferogram quality is limited by the common band spectra. In this article, by exploiting the conventionally discarded spectrum, we present a new interferometric phase retrieval method for multimode InSAR data to improve interferogram quality. To this end, first, we propose a linear model to characterize the interferometric phase of a multimode image pair based on image spectral relation. Second, we adopt a sparse recovery method to inverse the linear model for the retrieval of the interferometric phase. Finally, we present real-data experiments on TerraSAR-X staring spotlight to sliding spotlight interferometry and Sentinel-1 strip map to Terrain Observation by Progressive Scan (TOPS) interferometry to test the proposed method. The experiment results show that the proposed method can provide interferograms with reduced phase noise and defocusing effect for multimode InSAR.

An Interferometric Phase Noise Reduction Method Based on Modified Denoising Convolutional Neural Network

The traditional interferometric synthetic aperture radar denoising methods normally try to estimate the phase fringes directly from the noisy interferogram. Since the statistics of phase noise are more stable than the phase corresponding to complex terrain, it could be easier to estimate the phase noise. In this article, phase noises rather than phase fringes are estimated first, and then they are subtracted from the noisy interferometric phase for denoising. The denoising convolutional neural network is introduced to estimate the phase noise and then a modified network called IPDnCNN is constructed for the problem. Based on the IPDnCNN, a novel interferometric phase noise reduction algorithm is proposed, which can reduce the phase noise while protecting fringe edges and avoid the use of filter windows. The experimental results using the simulated and real data are provided to demonstrate the effectiveness of the proposed method.