RF Phase Modulation Research Articles

Three-dimensional diffusion MRI using simultaneous multislab with blipped-CAIPI in a 4D k-space framework.

To develop an efficient simultaneous multislab imaging method with blipped-controlled aliasing in parallel imaging (blipped-SMSlab) in a 4D k-space framework, and to demonstrate its efficacy in high-resolution diffusion MRI (dMRI). First, the SMSlab 4D k-space signal expression is formulated, and the phase interferences from intraslab and interslab encodings on the same physical z-axis are analyzed. Then, the blipped-SMSlab dMRI sequence is designed, with blipped-controlled aliasing in parallel imaging (blipped-CAIPI) gradients for interslab encoding, and a 2D multiband accelerated navigator for inter-kz-shot phase correction. Third, strategies are developed to remove the phase interferences, by RF phase modulation and/or phase correction during reconstruction, thus decoupling intraslab and interslab encodings that are otherwise entangled. In vivo experiments are performed to validate the blipped-SMSlab method and preliminarily evaluate its performance in high-resolution dMRI compared with traditional 2D imaging. In the 4D k-space framework, interslab and intraslab phase interferences of blipped-SMSlab are successfully removed using the proposed strategies. Compared with non-CAIPI sampling, the blipped-SMSlab acquisition reduces the g-factor and g-factor-related SNR penalty by about 12%. In addition, in vivo experiments show the SNR advantage of blipped-SMSlab dMRI over traditional 2D dMRI for 1.3-mm and 1.0-mm isotropic resolution imaging with matched acquisition time. Removing interslab and intraslab phase interferences enables SMSlab dMRI with blipped-CAIPI in a 4D k-space framework. The proposed blipped-SMSlab dMRI is demonstrated to be more SNR-efficient than 2D dMRI and thus capable of high-quality, high-resolution fiber orientation detection.

Study of the third-order parametric resonance induced by RF phase modulation and its effectiveness in improving injection efficiency

The on-axis swap-out injection scheme is promising for diffraction-limited storage rings, mainly because it can significantly reduce the requirement of dynamic aperture. However, this scheme requires the injection of full-charge bunches. Therefore, it may suffer from the reduction of injection efficiency caused by the so-called “injection transient instability” when high-charge bunches are needed. The idea of implementing RF modulation in a booster before extraction, driving the second-order parametric resonance to suppress the “injection transient instability” in the storage ring, was proposed and demonstrated previously. Here, we mainly present studies of third-order parametric resonance driven by RF phase modulation. Derivation of the modulated Hamiltonian around the third-order parametric resonance, the coordinates of both stable and unstable fixed points, and the ‘island tune’ are presented in detail. To double check the correctness of the theoretical results, numerical tests and tracking studies were carried out and presented. Furthermore, the results from comprehensive simulations are presented to demonstrate the improvement of injection efficiency by the proper settings of the RF phase modulation.

Increasing the Single-Bunch Instability Threshold by Bunch Splitting Due to RF Phase Modulation

RF phase modulation at twice the synchrotron frequency can be used to split a stored electron bunch into two or more bunchlets orbiting each other. We report on time-resolved measurements at the KArlsruhe Research Accelerator (KARA), where this bunch splitting was used to increase the threshold current of the microbunching instability, happening in the short-bunch operation mode. Switching the modulation on and off, reproducibly influences the sawtooth behaviour of the emitted coherent synchrotron radiation.

A 1–3 GHz Delta–Sigma-Based Closed-Loop Fully Digital Phase Modulator in 45-nm CMOS SOI

This paper presents a new fully digital architecture for an RF phase modulator with significantly improved phase resolution. The modulator utilizes 32 variable delay-lines in a delay-locked loop (DLL) configuration to provide 1–3 GHz operation with coarse 5-bit resolution. A 5-bit low-glitch multiplexer with accurate delay control on the control lines is used to select different taps of the DLL according to the baseband digital phase data to generate the desired phase modulated signal at the output. To further increase the effective resolution, a high speed 10-bit input, 5-bit output digital delta–sigma modulator (DSM) is added in front of the multiplexer. The DSM compensates for the phase truncation occurring in the 5-bit DLL. The impact of delay mismatch and phase offset in the DLL on the phase modulator output performance are studied. The phase modulator IC is implemented in 45-nm CMOS SOI and achieves <2% rms EVM together with 55-dB rejection of close-to-carrier emissions for an 8-Mb/s GMSK signal at 2.3 GHz, with power consumption below 35 mW.

RF Photonic Link With an MQW Phase Modulator Transmitter and an ACP-OPLL Receiver

A phase modulated (PM) RF photonic link with a multiple quantum well (MQW) phase modulator transmitter and an attenuating-counter-propagating optical phase lock loop (ACP-OPLL) receiver photonic IC is presented. The nonlinearity of the MQW phase modulator was used to cancel the residual nonlinear distortions of the ACP-OPLL receiver. This enables the demonstration of the highest dynamic range performance among the PM RF photonic links.

Method of phase space beam dilution utilizing bounded chaos generated by rf phase modulation

Method of phase space beam dilution utilizing bounded chaos generated by rf phase modulation

Photonic microwave phase shifter based on dual-sideband phase-control technique.

An all-optical photonic microwave phase shifter that can realize a continuous 0°-360° phase shift is presented. The phase-shifting operation is implemented by controlling the phase of the two RF phase-modulation sidebands while keeping the optical carrier phase fixed. The use of two RF modulation sidebands, instead of a single sideband used in most conventional phase shifters, has the advantage of high-output RF signal power, and consequently high signal-to-noise ratio performance. Experimental results demonstrate the full -180° to +180° phase shift over a wide microwave frequency range from 11 to 26.5 GHz, and 14 dB increase in the output RF signal power compared to a conventional phase shifter.

Long-range vibration detection system using heterodyne interferometry.

We present the design and performance of an extremely sensitive coherent remote vibration detection system using optical heterodyne vibration of phase shifts produced by laser light scattered off a remote target. The resulting phase-modulated intermediate RF of 200MHz, which carries the vibrational motion of the target, is demodulated down to baseband using an RF in-phase and quadrature demodulator. Acquisition and calculation of the target phase angle is carried out on a custom-made control board which utilizes high-resolution A/D converters, variable gain amplifiers, and a Spartan-6 field programmable gate array.

All-Optical Continuously Tunable Flat-Passband Microwave Photonic Notch Filter

A new all-optical microwave photonic notch filter (MPNF) is presented. It is based on controlling the amplitude and phase of the optical carriers and RF phase modulation sidebands via a diffraction-based Fourier-domain optical processor. It has the ability of realizing a flat-passband, narrow-notch, and large-free-spectral-range amplitude response and a group delay response with very few ripples. The carrier and sideband optical phase controls enable a continuous notch frequency tuning operation to be realized without altering the response shape. The filter has a simple structure and a wide bandwidth as it only involves optical components. Experimental results demonstrate an MPNF that exhibits a flat passband with <; 1 dB ripples, a deep notch of > 35 dB, and low group delay ripples of <; ±25 ps, together with the continuous notch frequency tunability and excellent long-term stability and repeatability.

Phasorial differential pulse-width pair technique for long-range Brillouin optical time-domain analysis sensors.

We introduce a novel phasorial differential pulse-width pair (PDPP) method for Brillouin optical time-domain analysis (BOTDA) sensors that combines spatial resolution enhancement with increased tolerance to non-local effects. It is based on the subtraction of the complex time-domain traces supplied by a sensor configuration that uses a phase-modulated probe wave and RF demodulation. The fundamentals of the technique are first described theoretically and using numerical simulation of the propagating waves. Then, proof-of-concept experiments demonstrate the measurement of the Brillouin frequency shift distribution over 50-km. The system is shown to withstand large variations of the pump power generated by its interaction with a powerful probe wave along the fiber; hence, highlighting the potential of the PDPP technique to increase the detected signal-to-noise ratio in long-range BOTDA. Moreover, the PDPP is also shown to increase the measurement contrast by allowing the use of relatively long duration pulses while retaining 1-m spatial resolution.

Polar Transmitter with Differential DSM Phase and Digital PWM Envelope

A low-power low-cost polar transmitter for EDGE is designed in 0.18μm CMOS. A differential delta-sigma modulator (DSM) tunes a three-terminal voltage-controlled oscillator (VCO) to perform RF phase modulation, where the VCO tuning curve is digitally pre-compensated for high linearity and the carrier frequency is calibrated by a dual-mode lowpower frequency-locked loop (FLL). A digital intermediate-frequency (IF) pulse-width5 modulator (PWM) drives a complementary power-switch followed by an LC filter to achieve envelope modulation with high efficiency. The proposed transmitter with 9mW power dissipation relaxes the time alignment between the phase and envelope modulations, and achieves an error vector magnitude (EVM) of 4% and phase noise of ?123dBc/Hz at 400kHz offset frequency.

Filtering properties of the tunable microwave photonic filter with stimulated Brillouin scattering

The filtering properties of a continuously tunable single-passband microwave photonic filter based on stimulated Brillouin scattering (SBS) are investigated. The filter utilizes the advantage of combining phase-modulated RF signal and dual-sideband suppressed-carrier pump signal to achieve the SBS-based tunable narrowband filtering. The effects of pump power on the out-of-band rejection (OBR) and 3-dB bandwidth, the optical fiber structure on the resonant sideband, and input RF signal power on the OBR and 3-dB bandwidth are analyzed theoretically and experimentally. The results show that the pump power has the potential of increasing the OBR and tuning 3-dB bandwidth, whereas the RF signal power has nearly no influence on the two parameters.

A Low-Noise Delta-Sigma Phase Modulator for Polar Transmitters

A low-noise phase modulator, using finite-impulse-response (FIR) filtering embedded delta-sigma (ΔΣ) fractional-N phase-locked loop (PLL), is fabricated in 0.18 μm CMOS for GSM/EDGE polar transmitters. A simplified digital compensation filter with inverse-FIR and -PLL features is proposed to trade off the transmitter noise and linearity. Experimental results show that the presented architecture performs RF phase modulation well with 20 mW power dissipation from 1.6 V supply and achieves the root-mean-square (rms) and peak phase errors of 4° and 8.5°, respectively. The measured and simulated phase noises of −104 dBc/Hz and −120 dBc/Hz at 400-kHz offset from 1.8-GHz carrier frequency are observed, respectively.

BOTDA measurements tolerant to non-local effects by using a phase-modulated probe wave and RF demodulation

We demonstrate a Brillouin optical time domain analysis sensor based on a phase-modulated probe wave and RF demodulation that provides measurements tolerant to frequency-dependent variations of the pump pulse power induced by non-local effects. The tolerance to non-local effects is based on the special characteristics of the detection process, which provides an RF phase-shift signal that is largely independent of the Brillouin gain magnitude. Proof-of-concept experiments performed over a 20-km-long fiber demonstrate that the measured RF phase-shift spectrum remains unaltered for large frequency-dependent deformations of the pump pulse power. Therefore, it allows the use of a higher optical power of the probe wave, which leads to an enhancement of the detected signal to noise ratio. This can be used to extend the sensing distance, to improve the accuracy of the Brillouin frequency shift measurements, and to reduce the measurement time.

Performance analysis and experimental study on Flat Optical Comb Generation

The performance of the optical frequency comb generation based on the re-circulating frequency shifter has been analyzed and demonstrated in this paper. We have theoretically analyzed the condition for flatness of the optical frequency comb and the relative intensity noise influence. We find out the influence to the flatness of optical comb owing to amplifier relative intensity noise and modulator relative factors imperfect, such as input RF signals amplitude and phase deviation and modulator defect owing to manufacture for the first time. Moreover, to verify the theoretical analysis, a 16 comb lines and spacing 12.5 GHz RFS generation system have also been carried out, and the results are in good agreement with the theoretical analysis results. DOI: http://dx.doi.org/10.11591/telkomnika.v11i1.1867

An Economic Phase-Mdulation to Intensity-Modulation Converter

A novel phase-modulation to intensity-modulation (PM-to-IM) converter is proposed and experimentally demonstrated basing on a vertical-cavity surface-emitting laser (VCSEL). Comparing with the published schemes, in which the employed DI, FBG, OBPF or dispersion devices can only process a certain phase-modulated RF signal, the proposed scheme can achieve the conversion process in an economic and resourceful manner. To be the first one of achieving such PM-to-IM conversion process by a VCSEL, the feasibility of the proposal is experimentally demonstrated with an open eye diagram when it is employed to convert phase-modulated RF signal.

Theoretical and Experimental Study on Flat Optical Comb Generation Based on Re-Circulating Frequency Shifter

A complete analysis of flat and stable optical comb generation based on the re-circulating frequency shifter has been analyzed and demonstrated in this paper. We find out the influence to the flatness of optical comb owing to amplifier relative intensity noise and modulator relative factors imperfect, such as input RF signals amplitude and phase deviation and modulator defect owing to manufacture for the first time. Moreover, to verify the theoretical analysis, a 16 comb lines and spacing 12.5 GHz RFS generation system have also been carried out, and the results are in good agreement with the theoretical analysis results.

High-Gain and High-Efficiency EER/Polar Transmitters Using Injection-Locked Oscillators

The envelope elimination and restoration (EER) approach developed by Kahn and its modern derivative, a polar transmitter, are well recognized as highly efficient amplification schemes. This paper presents an EER/polar dual-mode transmitter using injection-locked oscillators (ILOs). For an EER operation, an ILO that is combined with a mixer and a low-pass filter in the proposed architecture extracts an envelope signal and a phase-modulated RF signal from an input RF signal with complex modulation. The phase-modulated RF signal is then amplified efficiently by a class-E power amplifier (PA). Additionally, the envelope signal is reconstructed at the PA output by modulating the supply voltage of the PA. For a polar operation, the necessary phase modulation and envelope modulation are generated in the digital domain instead. Moreover, the phase-modulated RF signal is injected into an ILO and the ILO output is amplified by a class-E PA while supply-modulated with the envelope signal. For wideband code-division multiple access (WCDMA) signals, the implemented prototype transmitter achieves a 20.8-dB gain and 44% power-added efficiency (PAE) at an average output power of 25.8 dBm. For enhanced data rates for GSM evolution signals, it delivers 26.6 dB of gain and 48.7% PAE at an average output power of 26.6 dBm. Furthermore, to compensate for the AM-AM and AM-PM distortions of the PA, the linearity is improved using static digital predistortion. Experimental results demonstrate that the proposed EER/polar transmitter using ILOs has a high gain, high efficiency, and good linearity.

Photonic Generation of Phase-Modulated RF Signals for Pulse Compression Techniques in Coherent Radars

A novel and flexible photonics-based scheme is proposed for generating phase-coded RF pulses suitable for coherent radar systems with pulse compression techniques. After selecting two modes from a mode-locked laser (MLL), the technique exploits an optical in-phase/quadrature modulator driven by a low-sample rate and low-noise direct digital synthesizer to modulate the phase of only one mode. The two laser modes are then heterodyned in a photodiode, and the RF pulse is properly filtered out. The scheme is experimentally validated implementing a 4-bit Barker code and a linear chirp on radar pulses with a carrier frequency of about 25 GHz, starting from an MLL at about 10 GHz. The measures of phase noise, amplitude- and phase-transients, and autocorrelation functions confirm the effectiveness of the scheme in producing compressed radar pulses without affecting the phase stability of the optically generated high-frequency carriers. An increase in the radar resolution from 150 to 37.5 m is calculated. The proposed scheme is capable of flexibly generating software-defined phase-modulated RF pulses with high stability, even at very high carrier frequency, using only a single commercial device with potentials for wideband modulation. It can therefore allow a new generation of high-resolution coherent radars with reduced complexity and cost.

Response of colliding beam-beam system to harmonic excitation due to crab-cavity rf phase modulation

During 2008 and 2009 dedicated beam experiments with crab cavities were performed in the KEKB. The goal was to measure the impact of crab-cavity radio frequency (rf) noise on the beam quality. These experiments were performed as a validation of the crab-cavity beam dynamics models in view of the possible use of crab cavities in the upgrade of the CERN Large Hadron Collider (LHC). An unexpected strong beam-beam instability was observed during the course of the experiments as a kind of frequency response. Understanding this finding required extensive multiparticle and single particle simulations plus an extra experimental session to consolidate the observations.