Hybrid Method to Identify Second-trip Echoes Using Phase Modulation and Polarimetric Technology

For pulse Doppler radars,the widely used method for identifying second-trip echoes(STs)in the signal processing level yields significant misidentification in regions of high turbulence and severe wind shear.In the data processing level,although the novel algorithm for ST identification does not yield significant misidentification in specific regions,its overall identification performance is not ideal.Therefore,this paper proposes a hybrid method for the identification of STs using phase modulation(signal processing)and polarimetric technology(data processing).Through this approach,most of the STs are removed,whereas most of the first-trip echoes(FTs)remain untouched.Compared with the existing method using a signal quality index filter with an optimized threshold,the hybrid method exhibits superior performance(Heidke skill scores of 0.98 versus 0.88)on independent test datasets,especially in high-turbulence and severe-wind-shear regions,for which misidentification is significantly reduced.

Dual-Use Signal Design for Radar and Communication via Joint Orthogonal Signal and Phase Modulation

This paper proposes a new information modulation resorting to orthogonal signal and its phase for dual-function radar communication(DFRC)systems.Focusing on the standardized linear frequency modulation(LFM)signal by additional phase,a bank of signals enjoying satisfactory autocorrelation and cross-correlation characteristics,are generated.Then,these signals map the different information as well as their phases are also modulated to increase the communication bit rate,thus yielding a series of dual-use signals.Finally,the radar detection and communication performance of dual-use signals are also provided through numerical simulation and half-physical platform verification,confirming the effectiveness of the designed signals compared with the existing design strategy.

Nanoscale spatial phase modulation of GaAs growth in V-grooved trenches on Si(001) substrate

This letter reports the nanoscale spatial phase modulation of GaAs growth in V-grooved trenches fabricated on a Si （001） substrate by metal-organic vapor-phase epitaxy, Two hexagonal GaAs regions with high density of stacking faults parallel to Si {111 } surfaces are observed. A strain-relieved and defect-free cubic phase GaAs was achieved above these highly defective regions. High-resolution transmission electron microscopy and fast Fourier transforms analysis were performed to characterize these regions of GaAs/Si interface. We also discussed the strain relaxation mechanism and phase structure modulation of GaAs selectively grown on this artificially manipulated surface.

Effective improvement of beam lifetime based on radiofrequency phase modulation at the HLS-II storage ring

A radiofrequency(RF)phase modulation method is applied to the Hefei Light Source II storage ring to deeply investigate its longitudinal beam characteristics and improve the beam lifetime.A theoretical analytical model and corresponding experimental measurements of single bunch length and island phenomena are examined.From a series of online machine experiments,we demonstrate that the suitable phase modulation amplitude is 0.02 rad,corresponding to an optimum modulation frequency ranging from 19.6 to 20.7 kHz of the RF system.Furthermore,the overall beam lifetime can be increased by a factor of 2.38 as a result of the beam dilution effect.

Improved dichotomous search frequency offset estimator for burst-mode continuous phase modulation

A data-aided technique for cartier frequency offset estimation with continuous phase modulation （CPM） in burst- mode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio （SNR） required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods： it eliminates the need for fast Fourier transform （FFT） and modulation removal, and exhibits faster convergence rate without accuracy degradation.

Comprehensive research on self phase modulation based optical delay systems

This paper comprehensively investigates the properties of self phase modulation based optical delay systems consisting of dispersion compensation fibre and highly nonlinear fibres. It researches into the impacts of power level launched into highly nonlinear fibres, conversion wavelength, dispersion slope, modulation format and optical filter bandwidth on the overall performance of optical delay systems. The results reveal that, if the power launched into highly nonlinear fibres is fixed, the time delay generally varies linearly with the conversion wavelength, but jumps intermittently at some conversion wavelengths. However, the time delay varies semi-periodically with the power launched into highly nonlinear fibres. The dispersion slope of highly nonlinear fibres has significant influence on the time delay, especially for the negative dispersion slope. The time delay differs with modulation formats due to the different combined interaction of nonlinearity and dispersion in fibres. The bandwidth of the optical filters also greatly affects the time delay because it determines the bandwidth of the passed signal in the self phase modulation based time delay systems. The output signal quality of the overall time delay systems depends on the conversion wavelength and input power level. The optimisation of the power level and conversion wavelength to provide the best output signal quality is made at the end of this paper.

Phase modulation pseudocolor encoding ghost imaging

We present a ghost imaging scheme that can obtain a good pseudocolor image of black-and-white objects.The essential idea is to use a multi-wavelength thermal light source and the phase modulation pseudocolor encoding technique,which overcomes the disadvantages of other methods involved spatial filtering.Therefore,the pseudocolor ghost image achieved by this imaging scheme is better than that obtained by other methods in terms of brightness,color,and signal-tonoise ratio.

A low noise, high fidelity cross phase modulation in multi-level atomic medium

We develop a hybrid scheme of cross phase modulation based on electromagnetically induced transparency(EIT)and active Raman gain(ARG)in a multi-level atomic medium.The cross phase modulation,with low loss and without noise,is demonstrated in a room-temperature ^(85)Rb vapor.We show that a p radian nonlinear Kerr phase shift of the signal light relative to a reference light is observed when the signal light is modulated by the phase control field with the low light intensity.We also show that the linear and the third-order absorption can be eliminated via the Raman gain,and the phase noise of the signal light can be ignored when the phase control light is applied in this hybrid scheme.

Effect of Phase Modulation on Electromagnetically Induced Grating in a Five-Level M-Type Atomic System

We theoretically investigate the phenomena of electromagnetically induced grating in an M-type five-level atomic system. It is found that a weak field can be effectively diffracted into high-order directions using a standing wave coupling field, and different depths of the phase modulation can disperse the diffraction light into different orders. When the phase modulation depth is approximated to the orders of π, 2π and 3π, the first-, second- and third-order diffraction intensity reach the maximum, respectively. Thus we can take advantage of the phase modulation to control the probe light dispersing into the required high orders.

Effect of stimulated Brillouin scattering on the gain saturation of distributed fiber Raman amplifier and its suppression by phase modulation

For distributed fiber Raman amplifiers（DFRAs）, stimulated Brillouin scattering（SBS） can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 m W forward pump is as low as 0 d Bm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 d B, and the correction factor is 0.25 d B, in which the modulation frequency is high enough. Additionally, the factor is 1.767 d B for the modulation frequency of 25 MHz. On this basis,phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.

Optimizing effective phase modulation in coupled double quantum well Mach–Zehnder modulators

We report optimal phase modulation based on enhanced electro–optic effects in a Mach–Zehnder（MZ） modulator constructed by AlGaAs/GaAs coupled double quantum well（CDQW） waveguides with optical gain. The net change of refractive indexes between two arms of the CDQW MZ modulator is derived by both the electronic polarization method and the normal-surface method. The numerical results show that very large refractive index change over 10^（-1） can be obtained, making the phase modulation in the CDQW MZ modulator very highly efficient. It is desirable and important that a very small voltage-length product for π phase shift, V_π× L_0= 0.0226 V · mm, is obtained by optimizing bias electric field and CDQW structural parameters, which is about seven times smaller than that in single quantum-well MZ modulators.These properties open an avenue for CDQW nanostructures in device applications such as electro–optical switches and phase modulators.

dispersion grating;frequency modulation-to-amplitude modulation conversion;high-power laser facility;inertial confinement fusion;phase modulation

Frequency modulation(FM)-to-amplitude modulation(AM) conversion is an important factor that affects the time±power curve of inertial confinement fusion(ICF) high-power laser facilities. This conversion can impact uniform compression and increase the risk of damage to optics. However, the dispersive grating used in the smoothing by spectral dispersion technology will introduce a temporal delay and can spatially smooth the target. The combined effect of the dispersive grating and the focusing lens is equivalent to a Gaussian low-pass filter, which is equivalent to 8 GHz bandwidth and can reduce the intensity modulation on the target to below 5% with 0.3 nm @ 3 GHz + 20 GHz spectrum phase modulation. The results play an important role in the testing and evaluating of the FM-to-AM on the final optics and the target, which is beneficial for comprehensively evaluating the load capacity of the facility and isentropic compression experiment for ICF.

Integrated Fabry–Perot interferometer based on Er/Yb co-doped fiber for all-optical phase modulation

Fast and stable phase control is essential for many applications in optics. Here, we propose an all-fiber all-optical phase modulation scheme based on a Fabry–Perot interferometer(FPI) and an Er/Yb co-doped fiber(EYDF). By using the EYDF as an F-P cavity via rational design, a phase shift with a modulation sensitivity of 0.0312π/mW is introduced to the modulator.The phase shifts in the EYDF consist of a thermal phase shift and a nonlinear phase shift with a ratio of 19:1, and the corresponding temporal responses of the modulation are 204 ms and 2.5 ms, respectively. In addition, the compact FPI is encapsulated to provide excellent stability for the modulator.

Stepped frequency chirp signal imaging radar jamming using two-dimensional nonperiodic phase modulation

Stepped frequency chirp signal obtains high-resolution radar images by synthesizing multiple narrowband chirp pulses.It has been one of the most commonly used wideband radar waveforms due to its lower demand for radar instant bandwidth.In this paper,we propose a radar jamming method using two-dimensional nonperiodic phase modulation against stepped frequency chirp signal imaging radar.Using the unique property of nonperiodic phase modulation,the proposed method can generate high-level sidelobes that perform as a special blanket jamming along both the range and azimuth directions and make the target unrecognizable.Then,the influence of different modulation parameters,such as the code width and duty ratio,are further discussed.Based on this,the corresponding parameter design principles are presented.Finally,the validity of the proposed method is demonstrated by the Yake-42 plane data simulation and measured unmanned aerial vehicle data experiment.

Nonreciprocal microwave transmission under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect

Nonreciprocal microwave devices,in which the transmission of waves is non-symmetric between two ports,are indispensable for the manipulation of information processing and communication.In this work,we show the nonreciprocal microwave transmission in a cavity magnonic system under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect.In contrast to the schemes based on the standard phase modulation or magnon Kerr nonlinearity,we find that the joint mechanism enables the nonreciprocal transmission even at low power and makes us obtain a high nonreciprocal isolation ratio.Moreover,when two microwave modes are coupled to the magnon mode via a different coupling strength,the presented strong nonreciprocal response occurs,and it makes the nonreciprocal transmission manipulating by the magnetic field within a large adjustable range possible,which overcomes narrow operating bandwidths.This study may provide promising opportunities to realize nonreciprocal structures for wave transmission.

Hermite-Gaussian beams with sinusoidal vortex phase modulation

In this Letter,vortex phase and sinusoidal phase modulations of Hermite-Gaussian beams are studied theoretically and experimentally.The coding method of the experiment is introduced in detail,and the evolution law of focus under different beam order(m,n)and topological charge(l)is given.In order to verify the accuracy of the generation experiment,the optical field distribution under sinusoidal vortex modulation is analyzed deeply.The relevant analysis and methods provided in this Letter have certain practical significance for the development of laser mode analysis,optical communication,and other fields.

Research on stimulated Brillouin scattering suppression based on multi-frequency phase modulation

The method of generating equal-amplitude spectral lines by multi-frequency phase modulation is used in stimulated Brillouin scattering （SBS） suppression. The spectra of three, five, seven, and eleven equalamplitude spectral lines are obtained in experiment with flatnesses less than 0.3 dB. Theoretical research on SBS suppression shows that the threshold power after modulation is in reverse proportion to the maximum square of amplitude moduli of fundamental frequency and the nth harmonic wave. The threshold powers of three, five, seven, and eleven equal-amplitude spectral lines are improved by 5.21, 8.36, 9.39, and 10.76 dB, respectively.

Effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation instability in optical fibers

The synthetic effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation induced modulation instability in loss single-mode optical fibers have been numerically investigated. The results show that the quintic nonlinearity plays a role similar to the case of neglecting the group-velocity mismatch in modifying the modulation instability, namely, the positive and negative quintic nonlinearities can still enhance and weaken the modulation instability, respectively. The group-velocity mismatch can considerably change the gain spectrum of modulation instability in terms of its shape, peak value, and position. In the normal dispersion regime, with the increase of the group-velocity mismatch parameter, the gain spectrum widens and then narrows, shifts to higher frequencies, and the peak value gets higher before approaching a saturable value. In the abnormal dispersion regime, two separated spectra may occur when the group-velocity mismatch is taken into account. With the increase of the group-velocity mismatch parameter, the peak value of the gain spectrum gets higher and shorter before tending to a saturable value for the first and second spectral regimes, respectively.

Cross-phase modulation-induced penalties in multichannel DWDM optical transport networks

In dense wavelength division multiplexing (DWDM) optical transmission systems, cross-phase modulation (XPM) due to Kerr effect causes phase shift on each channel, which will ultimately be transformed to amplitude noise that leads to power penalties. In this letter, the XPM-induced penalty in multi-channel DWDM systems is investigated theoretically and an applied algorithm that can be practically used in engineering design is proposed.

A method of multichannel chaotic phase modulation spread spectrum and its application in underwater acoustic communication

Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in conventional DSSS communications, possess peri- odic character and binary value. In hostile environments, these distinct characters may lead to some important parameters of signals being estimated accurately, and then lead to the leakage of transmitted information. To solve the problem, we propose the chaotic phase modulation （CPM） sequence alternating the PN sequences. CPM sequence has complex values and constant envelope, and also possesses large quantity and good correlation characteristics. Moreover, it has more hidden features than conventional sequences by modulating its phases using chaotic sequence. To improve the data rate, we apply it into the technique of multichannel communica-tion. Simulation results show this scheme＇s superior bit error ratio （BER） performance, which demonstrates its feasibility in underwater acoustic communications.