Residual Phase Noise Research Articles

Real-Time Mitigation of Short-Range Leakage in Automotive FMCW Radar Transceivers

Frequency-modulated continuous wave radar systems suffer from permanent leakage of the transmit signal into the receive path. Besides leakage within the radar device itself, an unwanted object placed in front of the antennas causes so-called short-range (SR) leakage. In an automotive application, for instance, it originates from signal reflections of the car’s own bumper. Particularly the residual phase noise of the downconverted SR leakage signal causes a severe degradation of the achievable sensitivity. In an earlier work, we proposed an SR leakage cancellation concept that is feasible for integration in a monolithic microwave integrated circuit. In this brief, we present a hardware prototype that holistically proves our concept with discrete components. The fundamental theory and properties of the concept are proven with measurements. Further, we propose a digital design for real-time operation of the cancellation algorithm on a field programmable gate array. Ultimately, by employing measurements with a bumper mounted in front of the antennas, we show that the leakage canceller significantly improves the sensitivity of the radar.

Original Ti:Sa 10 kHz front-end design delivering 17 fs, 170 mrad CEP stabilized pulses up to 5 W.

We present a compact 10kHz Ti:Sa front end relying on an original double-crystal regenerative amplifier design. This new configuration optimizes the thermal heat load management, allowing the production of a 110nm large spectrum and maintaining a good beam profile quality. The front end delivers up to 5W after compression, 17fs pulses with a 170mrad shot-to-shot residual carrier-envelope phase noise.

A CNTFET Oscillator at 461 MHz

This letter presents design, implementation, and characterization of the first reported carbon nanotube field-effect transistor (CNTFET) RF oscillator. The circuit is implemented with discrete CNTFETs mounted on standard FR-4 substrate with off-the-shelf surface-mount-device components. The oscillator topology is similar to the phase shifter oscillator and uses two cascaded common source stages to provide enough gain for self-sustained and self-startup oscillation. The oscillator tank is merged with the matching network between two stages. The circuit oscillates at the frequency of 461 MHz with a phase noise of −115 dBc/Hz at 1 MHz and power consumption of 60 mW. While limited in output power by the driving capabilities of prototype CNTFETs, which still have a large density of residual metallic tubes, both power consumption and phase noise compare well with established and mature technologies. Moreover, the presented phase noise measurements provide a useful benchmark for the physical noise models being currently developed for this category of devices.

A novel pulse swallow based frequency divider circuit for a phase-locked loops

A new and unique frequency divider circuit has been proposed for this work. In this paper, we have implemented a $$\varDelta \varSigma$$ΔΣ fractional-N PLL using a proposed pulse swallow based frequency divider and a programmable prescaler divider circuit. Advantages of the proposed pulse swallow based frequency divider circuit have been illustrated and its usefulness are described in details. This novel pulse swallow based frequency divider technique does not include any reset or reload signal for the swallow counter as it is normally triggered by the SR latch output signal in conventional pulse swallow based frequency divider circuit. Insertion of a variable delay element at the output of the program counter can be eliminated which is normally used to settle the problem of arrival of the falling edge of the swallow counter pulse. In addition, preset enable signal can be generated without any frequency dependent delay generation block and in few cases without selection of any frequency dependent RC network block. The residual phase noise output of the divider at 1 MHz offset frequency is $$-174.5$$-174.5 dBc/Hz for a carrier signal frequency of 4.7 GHz and power consumption is 9 mW from a 1.2 V power supply. The design of the fractional-N PLL has been carried out in 130 nm standard CMOS process. There is no zero division in the proposed frequency divider's swallow counter for any counting state due to the novel mathematical calculating algorithm for the pulse swallow divider circuit.

Phase locking of a mode-locked titanium–sapphire laser-based optical frequency comb to a reference laser using a fast piezoelectric actuator

We phase lock an octave-spanning optical frequency comb, generated using a mode-locked titanium-sapphire laser and a photonic-crystal fiber, to a continuous-wave laser line-narrowed to a reference cavity. To phase lock the pulse-repetition frequency, the cavity length of the mode-locked laser is controlled by using a fast piezoelectric-actuated mirror of a servo bandwidth up to 80 kHz. The residual phase noise is 0.35 rad, and 89% of the power is concentrated to the carrier. To apply the system to optical frequency-ratio measurements and to evaluate the phase locking, a simultaneous frequency measurement of the beat between the other mode of the comb and another laser line-narrowed to a different resonance of the common reference cavity is demonstrated.

Low Phase Noise Frequency Synthesis for Ultrastable $X$ -Band Oscillators

In this letter, the design of a low phase noise frequency synthesizer is presented. The synthesizer was designed to produce four frequencies: 10 MHz, 100 MHz, 1 GHz and 10 GHz. The 1-GHz signal is produced by frequency division whereas the 100-MHz output is generated by phase-locking a low phase noise oscillator to the 1-GHz signal, hence significantly reducing its phase noise. Both residual and total phase noise measurements are presented.

Magneto-optic modulator for high bandwidth cavity length stabilization.

We propose a novel magneto-optical approach for the repetition frequency stabilization of optical frequency combs. We developed a Yb:fiber mode-locked laser with a fiber-based magneto-optic modulator used to stabilize one of the longitudinal modes to an optical reference with sub-hundred mrad residual phase noise. This modulator does not induce mechanical resonances and as such has the potential to achieve much broader feedback bandwidths than conventional modulators used for cavity length stabilization.

Towards chip-scale optical frequency synthesis based on optical heterodyne phase-locked loop.

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of -80 dBc/Hz at an offset of as low as 200 Hz.

Distribution of a phase-stabilized 100.02 GHz millimeter-wave signal over a 160 km optical fiber with 4.1 × 10-17 instability.

We report a long-distance phase-stabilized millimeter-wave distribution over optical fibers, where the optical-link-induced phase noise is compensated with a high-precision photonic-generated millimeter-wave (mm-wave) voltage-controlled oscillator (VCO). The mm-wave VCO is realized based on pre-filtering and re-modulating optical spectral lines of an optical frequency comb (OFC). By adjusting the frequency spacing of the optical spectral lines extracted from the OFC, the phase error of the transmitted optical mm-wave signal can be compensated precisely. Using the mm-wave VCO, we demonstrate a distribution of a 100.02 GHz signal over spooled optical fibers and the fractional frequency instability of the system at different transmission distances is exhibited. The residual phase noise of the remote mm-wave signal after being transferred through a 160-km fiber link is measured to be -59 dBc/Hz at 1 Hz frequency offset from the carrier, and the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches 62 fs. The long-term fractional frequency instability of 4.1 × 10-17 at 10000 s averaging time is achieved, and the maximum timing drift is within 0.93 ps (peak to peak) during 4 hours.

Phase Noise Suppression Algorithm Based on Modified LLR Metric in SC-FDMA System

In single-carrier frequency-division multiple-access (SC-FDMA) receivers in the long-term evolution uplink, phase noise is one of the major radio-frequency front-end impairments that degrade system performance. To address this issue, we propose a new log-likelihood ratio (LLR) computation algorithm. A signal model with residual phase noise is considered in the algorithm. Based on this model, we derive a closed-form expression of the likelihood function of the received symbol and calculate more accurate LLR information. Thus the accuracy of the decoder is increased and the performance of the SC-FDMA system is improved. Simulation results show that our proposed algorithm achieves superior bit error rate (BER) performance compared with the existing LLR calculation algorithms in high-order quadrature amplitude modulations (QAM).

A full spectrum resamping method in polygon tunable laser-based swept-source optical coherence tomography

Swept-source optical coherence tomography (SS-OCT) has high sensitivity and signalnoise ratio compare with time-domain optical coherence tomography and spectral-domain optical coherence tomography. Therefore, SS-OCT is the form of Fourier domain optical coherence tomography predominantly used in experimental research and biomedical image. However, polygon tunable laser-based SS-OCT suffers sweep range fluctuation and spectral misplacement. Under certain circumstances, in the current resampling methods cross-correlation is widely used to align spectrum misplacement, and truncate A-lines in order to ensure the consistency of frequency-scanning range, which, however, degrades the image SNR and resolution. We use the Mach-Zehnder interference (MZI) signal to quantify and analyze this problem in two typical polygon tunable lasers. The periodical change of sweep range and spectrum misplacement show the instability derived from polygon mirror. The parallelism among unwrapped phase curves indicates that polygon tunable laser output spectra have consistent wavelength distributions, and thus it is suited to implement cross-correlation between MZI signals in time domain, and an unwrapped phase curve can represent the wavelength distribution of all A-lines.According to the above conclusions, we demonstrate a resampling method in which the zero-padding interpolation and cross-correlation are used to align A-lines in time domain and eliminate the residual phase noise caused by integer shift. Then the unwrapped phase curve that has a largest sweep range is used to resample all the aligned A-lines, and the interference signals can be fully utilized. The experiments for signal truncation and Pomelo fruit flesh indicate that the proposed method can improve image SNR but does not make the intensity image dislocated. The phase noise (3.9 mrad for a 49 dB SNR) from static mirror is close to theory limit after resampling, thus showing good phase stability and resampling precision. The proposed resampling method also needs less computational work than one-to-one resampling method because it only fits unwrapped phase curve and calculates interpolation coefficient once.

Frequency flicker of 2.3 GHz AlN-sapphire high-overtone bulk acoustic resonators

We report the detailed characterization of 2.3 GHz AlN-Sapphire high-overtone bulk acoustic resonators (HBARs), with a typical loaded Q-factor of 25–30 × 103, 15–20 dB insertion loss, and resonances separated by about 10 MHz. The temperature coefficient of frequency of HBARs is measured to be about −25 ppm/K. We observe at high-input microwave power a significant distortion of the HBAR resonance lineshape, attributed to non-linear effects. The power-induced fractional frequency variation of the HBAR resonance is measured to be about −5 × 10−10/μW. The residual phase noise of a HBAR is measured in the range of −110 to −130 dBrad2/Hz at 1 Hz Fourier frequency, yielding resonator fractional frequency fluctuations at the level of −205 to −225 dB/Hz at 1 Hz and an ultimate HBAR-limited oscillator Allan deviation about 7 × 10−12 at 1 s integration time. The 1/f noise of the HBAR resonator is found to increase with the input microwave power. A HBAR resonator is used for the development of a low phase noise 2.3 GHz oscillator. An absolute phase noise of −60, −120, and −145 dBrad2/Hz for offset frequencies of 10 Hz, 1 kHz, and 10 kHz, respectively, in excellent agreement with the Leeson effect, is measured.

RF-subcarrier-assisted four-state continuous-variable QKD based on coherent detection.

We theoretically investigate and experimentally demonstrate a RF-assisted four-state continuous-variable quantum key distribution (CV-QKD) system. Classical coherent detection is implemented with a simple digital phase noise cancelation scheme. In the proposed system, there is no need for frequency and phase locking between the quantum signals and the local oscillator laser. Moreover, in principle, there is no residual phase noise, and a mean excess noise of 0.0115 (in shot-noise units) can be acquired experimentally. In addition, the minimum transmittance of 0.45 is reached experimentally for secure transmission with commercial photodetectors, and the maximum secret key rate (SKR) of >12 Mbit/s can be obtained. The proposed RF-assisted CV-QKD system opens the door of incorporating microwave photonics into a CV-QKD system and improving the SKR significantly.

Dual-Carrier Noncontact Vital Sign Detection With a Noise Suppression Scheme Based on Phase-Locked Loop

We present a dual-carrier vital sign detection scheme based on phase-locked loop to automatically reduce the noise introduced by residual phase noise and transmission paths. Two phase-locked microwave signals at 5.76 and 5.68 GHz are adopted to suppress noise and extract the vital sign, respectively. When the feedback beat signal is locked to the highly stable low-noise reference, the residual phase noise and path noise of the corresponding 5.76-GHz wave are reduced, providing low-noise circumstances for the 5.68-GHz carrier, which has the same path. Additionally, the 5.68-GHz carrier is phase modulated by the vital sign, thus its demodulation leads to a vital sign of low noise level and high spectral purity. The experimental results show that our system based on discrete components introduces no extra noise, has a 12-dB improvement in the signal to noise ratio at the 10-Hz frequency offset, and can effectively measure both respiration and heartbeat signals in four physical orientations at a distance of 50 cm. In addition, by suppressing the residual phase noise and path noise, the detection distance of the weak heartbeat signal from the front of the human subject is extended to at least 250 cm, which is more than double the distance of a system without the noise suppression scheme.

Ultra-low-noise monolithic mode-locked solid-state laser

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.

Low noise electro-optic comb generation by fully stabilizing to a mode-locked fiber comb.

A fully stabilized EO comb is demonstrated by phase locking the two degrees of freedom of an EO comb to a low noise mode-locked fiber comb. Division/magnification of residual phase noise of locked beats is observed by measuring an out-of-loop beat. By phase locking the 200 th harmonics of the EO comb and a driving cw frequency to a fiber comb, a record low phase noise EO comb across +/- 200 harmonics (from 1544.8 nm to 1577.3 nm) is demonstrated.

Gigahertz frequency comb offset stabilization based on supercontinuum generation in silicon nitride waveguides.

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.

Frequency comb metrology with an optical parametric oscillator.

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Monolithic CEO-stabilization scheme-based frequency comb from an octave-spanning laser**Project supported by the National Basic Research Program of China (Grant No. 2012CB821304) and the National Natural Science Foundation of China (Grant Nos. 11078022 and 61378040).

We demonstrate a carrier-envelope phase-stabilized octave-spanning oscillator based on the monolithic scheme. A wide output spectrum extending from 480 nm to 1050 nm was generated directly from an all-chirped mirror Ti:sapphire laser. After several improvements, the carrier-envelope offset (CEO) beat frequency accessed nearly 60 dB under a resolution of 100 kHz. Using a feedback system with 50-kHz bandwidth, we compressed the residual phase noise to 55 mrad (integrated from 1 Hz to 1 MHz) for the stabilized CEO, corresponding to 23-as timing jitter at the central wavelength of 790 nm. This is, to the best of our knowledge, the smallest timing jitter achieved among the existing octave-spanning laser based frequency combs.

微波光链路和光电探测器残余相位噪声的测量

微波光链路和光电探测器残余相位噪声的测量