Phase Noise Research Articles

A frequency servo SoC with output power stabilization loop technology for miniaturized atomic clocks

A frequency servo system-on-chip (FS-SoC) featuring output power stabilization technology is introduced in this study for high-precision and miniaturized cesium (Cs) atomic clocks. The proposed power stabilization loop (PSL) technique, incorporating an off-chip power detector (PD), ensures that the output power of the FS-SoC remains stable, mitigating the impact of power fluctuations on the atomic clock's stability. Additionally, a one-pulse-per-second (1PPS) is employed to synchronize the clock with GPS. Fabricated using 65 nm CMOS technology, the measured phase noise of the FS-SoC stands at −69.5 dBc/Hz@100 Hz offset and −83.9 dBc/Hz@1 kHz offset, accompanied by a power dissipation of 19.7 mW. The Cs atomic clock employing the proposed FS-SoC and PSL obtains an Allan deviation of 1.7 × 10−11 with 1-s averaging time.

A Progressive-Learning-Based Channel Prediction Within Phase Noise of Independent Oscillators

A Progressive-Learning-Based Channel Prediction Within Phase Noise of Independent Oscillators

Realisation of High-Frequency DRO Oscillators with Mosfet Transistors for Sub-MMWAVE Band

Abstract In high-frequency electronics, optimizing RF oscillators performance is essential, especially as applications reach into wide frequency bands. This article describes proposed clock generators for UWB sensor systems based on oscillators with dielectric resonator (DRO). Evaluation boards with different sizes of microstrip conductors were developed and tested, based on which new versions of boards were created. Improvements were made to integrate the DRO into a shielded box to ensure minimal external interference. The final designs demonstrated stable operation with low phase noise λ (1 MHz) = -108.805 dBc at fc = 21.732 GHz, sufficient power (3.65 dBm) and low power consumption(56 mW).

Spectral Analysis of Nonlinear Phase Noise Arising in Coherent Fiber-Optic Transmission Systems of OFDM Signals

Spectral Analysis of Nonlinear Phase Noise Arising in Coherent Fiber-Optic Transmission Systems of OFDM Signals

Synchronization and Equalization for Joint Close-In and Reciprocal Mixing Phase Noise Distortion Compensation in Packet-Based OFDM Systems

Synchronization and Equalization for Joint Close-In and Reciprocal Mixing Phase Noise Distortion Compensation in Packet-Based OFDM Systems

Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator

Photonics integration of an optoelectronic oscillator (OEO) on a chip is attractive for fabricating low cost, compact, low power consumption, and highly reliable microwave sources, which has been demonstrated recently in silicon on insulator (SOI) and indium phosphide (InP) platforms at X-band around 8 GHz. Here we demonstrate the first integration of OEOs on the thin film lithium niobate (TFLN) platform, which has the advantages of lower V π , no chirp, wider frequency range, and less sensitivity to temperature. We have successfully realized two different OEOs operating at Ka-band, with phase noises even lower than those of the X-band OEOs on SOI and InP platforms. One is a fixed frequency OEO at 30 GHz realized by integrating a Mach–Zehnder modulator (MZM) with an add-drop microring resonator (MRR), and the other is a tunable frequency OEO at 20–35 GHz realized by integrating a phase modulator (PM) with a notch MRR. Our work marks the first step of using TFLN to fabricate integrated OEOs with high frequency, small size, low cost, wide range tunability, and potentially low phase noise.

A 65-nm duty-cycle corrector achieving 10% to 90% duty-correction range with [formula omitted]0.86% duty-cycle error

This brief introduces a dual-loop analog duty-cycle corrector (DCC) designed to enhance the in-band phase noise performance of phase-locked loops (PLLs) by achieving precise duty cycle correction over a wide input duty cycle range. The proposed DCC incorporates a duty-cycle adjustor (DCA) within each loop, working in conjunction with a low-pass filter (LPF) and a duty-control amplifier to regulate the feedback control voltage. The feedback control voltage within each loop fine-tunes the timing delay of input pulse, ensuring that the output duty cycle of each loop is adjusted to 50%. Consequently, the proposed DCC demonstrates an expanded duty correction range. The proposed DCC was fabricated in a 65-nm standard CMOS process with an active area of 0.078 mm2. Measurement results validate the efficiency of the proposed DCC in correcting a wide range of input duty cycles (i.e., 10% to 90%) to an output duty cycle of 50% with a maximum duty cycle error of <0.86% for an input clock frequency ranging from 1 MHz to 100 MHz. To further showcase its effectiveness, the duty-corrected clock was supplied to a commercially available PLL (ADF4351). This demonstrated a noteworthy reduction of approximately 19 dB in reference spurs and a 10 dBc/Hz in the in-band phase noise.

Quantum state tomography in a third-order integrated optical parametric oscillator.

We measured the covariance matrix of the fields generated in an integrated third-order optical parametric oscillator operating above threshold. We observed up to (2.3 ± 0.3) dB of squeezing in amplitude difference and inferred (4.9 ± 0.7) dB of on-chip squeezing, while an excess of noise for the sum of conjugated quadratures hinders the entanglement. The degradation of amplitude correlations and state purity for increasing the pump power is consistent with the observed growth of the phase noise of the fields, showing the necessity of strategies for phase noise control aiming at entanglement generation in these systems.

Robust, wide-range, and precise transmitter IQ impairment monitoring scheme for coherent digital subcarrier multiplexing systems.

In this Letter, we present a robust, wide-range, and precise monitoring scheme for transmitter (Tx) impairments in coherent digital subcarrier multiplexing (DSCM) systems. The proposed scheme employs frequency-domain pilot tones (FPTs) to compensate for frequency offset (FO), polarization aliasing, and carrier phase noise, thus isolating Tx impairments from channel distortions. It then implements 4 × 4 real-valued MIMO to compensate for Tx impairments by equalizing symmetric subcarriers. Tx impairment monitoring is derived from the equalizer coefficients. By considering the phase shift caused by Tx impairments, a wide-range and precise monitoring of Tx impairments including IQ skew, IQ phase, and gain imbalances is achieved. We experimentally validated our approach using a 48-GBaud, four-subcarrier, dual-polarization coherent DSCM system. The results confirm the method's capability for a wide-range, robust, and precise Tx impairment monitoring in coherent DSCM systems, maintaining performance even in the presence of ultra-fast polarization variation.

Phase noise suppression of optic flexural disk accelerometer by studying the thermal stability of optical fiber ring

As the core sensing elements of ultra-long fiber interferometer, the distributed thermal strain difference of the fiber rings can cause extra noise of the flexural disk, resulting in a penalty of the deterioration accuracy. In this paper, the thermal strain distribution characteristics of the fiber ring are firstly analyzed by the finite element method (FEM), and the distribution result is consistent with that demonstrated by the Rayleigh optical frequency-domain reflectometry (R-OFDR) strain measurement. The interferometer phase noise caused by the distributed strain difference is further studied by constructing a fully symmetric polarization-maintaining fiber-ring Mach-Zehnder interferometer (MZI) with an arm length of over 100 meters. The results show that the distributed thermal strain difference of two fiber rings will cause additional phase fluctuation, which leads to higher low-frequency noise. Therefore, a dual-fiber-ring MZI with matched distributed thermal strains is proposed to suppress the phase noise caused by the thermal strain, and the best suppression is as high as 45.6 dB. This is very important for the research and design of low noise fiber seismometer.

Passively stabilized Brillouin fiber laser frequency combs for ultralow-noise microwave generation

Ultralow-noise microwaves are essential in a wide variety of scientific and technological applications, such as metrology, radars, and communications. Here, we propose and demonstrate a scheme for generating an ultralow-noise microwave signal using a Brillouin optical frequency comb (OFC), which is based on the stimulated Brillouin scattering in combination with a frequency-shifted optical injection locking mechanism. The generated two intra-cavity Brillouin lasers are used as the intra-cavity pump for the eventual formation of the OFC and thus the microwave signal via the cascaded four-wave mixing process. Exploiting the cascaded narrowing effect in the Brillouin cavity assisted by the frequency-shifted optical injection locking, the proposed microwave signal source exhibits ultralow phase noise. Experimental results show that the phase noise of the microwave signal is equivalent to below −115 dBc/Hz for a 200-GHz carrier at 10 kHz offset. The system can work in stable operation without the need for any active feedback loop.

Phase tracking using a Kalman filter based on probability density distribution in frequency-scanning interferometry

Frequency-scanning interferometry (FSI) utilizing external cavity diode lasers (ECDL) stands out as a potent technique for absolute distance measurement. Nevertheless, the inherent scanning nonlinearity of ECDL and phase noise pose a challenge, as it can compromise the accuracy of phase extraction from interference signals, thereby reducing the measurement accuracy of FSI. In this study, we propose a composite algorithm aimed at mitigating non-orthogonal errors by integrating the least-squares and Heydemann correction technique. Furthermore, we employ Kalman filtering for precise phase tracking. We introduce a parameter selection strategy based on the statistical distribution of instantaneous frequency to achieve the fusion estimation of phase observation values and theoretical models, which starts a new perspective for the application of multi-dimensional data fusion in FSI measurement. Through simulation and experimental validation, the efficacy of this approach is confirmed. The experimental results show promising outcomes: with an average phase error of 0.12%, a standard deviation of less than 1.7 µm in absolute distance measurement, and an average positioning accuracy error of 0.29 µm.

Phase Noise in Real‐World Twin‐Field Quantum Key Distribution

AbstractThe impact of noise sources in real‐world implementations of twin‐field quantum key distribution (TF‐QKD) protocols is investigated, focusing on phase noise from photon sources and connecting fibers. This work emphasizes the role of laser quality, network topology, fiber length, arm balance, and detector performance in determining key rates. Remarkably, it reveals that the leading TF‐QKD protocols are similarly affected by phase noise despite different mechanisms. This study demonstrates duty cycle improvements of over a factor of two through narrow‐linewidth lasers and phase‐control techniques, highlighting the potential synergy with high‐precision time and frequency distribution services. Ultrastable lasers, evolving toward integration and miniaturization, offer promising solutions for agile TF‐QKD implementations on existing networks. Properly addressing phase noise and practical constraints allows for consistent key rate predictions, protocol selection, and layout design, crucial for establishing secure long‐haul links for the quantum communication infrastructures under development in several countries.

Wideband Low Phase-Noise Signal Generation Using Coaxial Resonator in Cascaded Phase Locked Loop

The generation of high-quality wideband frequency sweeps presents a significant challenge, particularly in modern telecommunication, radar, and measurement systems where miniaturization is paramount. While phase-locked loops (PLLs) have become the dominant technique for signal generation, their application in broadband sweeps necessitates fractional-N operation. This, in turn, degrades phase noise and introduces unwanted spurs. This paper proposes a novel approach for broadband signal generation. By cascading two PLLs and utilizing a coaxial resonator, we achieve a high-performance oscillator that operates without the excessive fractional spurs, maintaining their level below −80 dBc across the entire frequency band. The prototype demonstrates non-degraded phase noise performance, reaching −102 dBc/Hz at 100 kHz offset and −121 dBc/Hz at 1 MHz offset for signals at 10 GHz. Despite significant frequency jumps, our design achieves lock times below 41 µs. These results, supported by theoretical analysis, validate the proposed method’s effectiveness in generating low-noise broadband frequency sweeps, ideal for local oscillator applications.

Receiver in-phase and quadrature skew tolerant baud-rate timing recovery scheme for short-reach coherent optical interconnection.

A baud-rate sampling timing recovery (TR) scheme with receiver IQ skew tolerance is proposed and experimentally demonstrated. The proposed scheme performs independent TR for the in-phase and quadrature (IQ) tributary signals, thereby tracking the sampling phase error while naturally compensating for receiver IQ skew. The robustness of the IQ-independent TR to frequency offset (FO) and phase noise is theoretically analyzed. To address IQ misalignment caused by the IQ-independent TR, the use of pseudo-noise (PN) sequences for IQ frame synchronization is proposed. The proposed scheme achieves accurate timing recovery with hardware-efficient baud-rate sampling in the presence of receiver IQ skew, laying the foundation for stable performance of subsequent baud-rate equalization. The performance of the scheme is validated in a 56 GBaud polarization division multiplexed (PDM) 16QAM coherent experimental system. Experimental results demonstrate that the proposed scheme achieves similar BER performance to the modified Gardner + real-valued multiple-input multiple-output (RVMIMO) (@2 SPS) scheme. Moreover, the proposed scheme exhibits robustness to arbitrary IQ skew compared to the ABSPD + RVMIMO (@1 SPS) scheme.

Dual‐Comb Interferometry for Coherence Analysis of Tightly Locked Mid‐Infrared Quantum Cascade Laser Frequency Combs

Frequency combs are powerful tools for many applications and high performances are achieved by stabilizing these lasers. For operation in the mid‐infrared, quantum cascade lasers (QCL) are ideal candidates as they present numerous advantages. However, stabilized QCL‐combs lack a detailed characterization of their noise properties due to the sensitivity limits of current analyzing techniques. To overcome these challenges, what is believed to be the first tightly locked dual QCL‐comb system is developed. Its use is twofold. First, phase noise analysis of the dual‐comb signal shows residual phase noise below 600 mrad for all comb lines, and the comb coherence as well as the performances of the repetition frequency locking mechanism is characterized. Second, coherent averaging with a 7 × 105 Hz1/2 figure‐of‐merit system is demonstrated, which is compatible with high‐precision spectroscopy.

Optimizing Ti/TiN Multilayers for UV, Optical and Near-IR Microwave Kinetic Inductance Detectors

Microwave Kinetic Inductance Detectors (MKIDs) combine significant advantages for photon detection like single photon counting, single pixel energy resolution, vanishing dark counts and µs time resolution with a simple design and the feasibility to scale up into the megapixel range. But high quality MKID fabrication remains challenging as established superconductors tend to either have intrinsic disadvantages, are challenging to deposit or require very low operating temperatures. As alternating stacks of thin Ti and TiN films have shown very impressive results for far-IR and sub-mm MKIDs, they promise significant improvements for UV, visible to near-IR MKIDs as well, especially as they are comparably easy to fabricate and control. In this paper, we present our ongoing project to adapt proximity coupled superconducting films for photon counting MKIDs. Some of the main advantages of Ti/TiN multilayers are their good control of critical temperature (Tc) and their great homogeneity of Tc even over large wafers, promising improved pixel yield especially for large arrays. We demonstrate the effect different temperatures during fabrication have on the detector performance and discuss excess phase noise observed caused by surface oxidization of exposed Si. Our first prototypes achieved photon energy resolving powers of up to 3.1 but turned out to be much too insensitive. As the work presented is still in progress, we also discuss further improvements planned for the near future.

Optically synchronized unidirectional optical amplifier-based coherent optical fiber links.

We report on the realization of a unidirectional transmission-based bidirectional erbium-doped fiber amplifier (UTB-EDFA) for the coherent optical fiber links. By applying an optical phase-locked loop (OPLL) between the two unidirectional EDFA (Ui-EDFA) paths, the annoying uncorrelated phase noise between the two paths can be largely suppressed. Promisingly, we can independently optimize the gains of the UTB-EDFAs for bidirectional transmissions, resulting in higher net gain acquired compared with the conventional single-path bidirectional EDFA (SPBA)-based ones. We demonstrate that the fractional frequency instability of the UTB-EDFA-based scheme can be decreased by 26.3% over the most asymmetrical 100 km two-way optical frequency comparison (TWC) system compared with the SPBA-based ones and, more importantly, can acquire higher net gain for unevenly distributed sub-links over ultra-long fiber links, such as 1000 km, by independently optimizing the gains. This technique paves the way for the applications of large-scale fiber networks.

Multi-gigabit X-band transmitter for satellite communication using the optical phase-locked loop.

Optical generation of microwave signals using photonic techniques offers benefits of frequency agility, ease of frequency scaling, and reduced hardware complexity. We demonstrate the generation and detection of QPSK modulated with symbol rates up to 5 GBaud at carrier frequencies of 8-12 GHz through optical heterodyning of two-phase-locked lasers. The received data is demodulated through appropriate post-processing to correct for the phase noise and IQ imbalance. The approach is scalable to mmWave and THz communication.

Theoretical analysis of the buried heterostructure laser for stable dual-wavelength generation

Stable dual-wavelength emission from a laser is desirable for microwave signal generation using the optical heterodyning method. As both optical wavelengths are generated from the same cavity, the phase noise of the generated microwave signal is minimized. In this work, we exploit the inherent birefringence in the buried heterostructure semiconductor laser to generate dual polarized modes. We carefully analyze the mode competition between various modes in the cavity and propose the desirable gain modification conditions for stable dual mode oscillations when the laser is operating near the threshold. We show that the required asymmetry in the gain for two stable modes can be obtained from the mode confinement factors and facet losses. We also show the applicability of our results to a homogeneously broadened multimode laser.