Diatomic metasurfaces designed for interferometric mechanisms possess significant potential for the multidimensional manipulation of electromagnetic waves,including control over amplitude,phase,frequency,and polarizat...Diatomic metasurfaces designed for interferometric mechanisms possess significant potential for the multidimensional manipulation of electromagnetic waves,including control over amplitude,phase,frequency,and polarization.Geometric phase profiles with spin-selective properties are commonly associated with wavefront modulation,allowing the implementation of conjugate strategies within orthogonal circularly polarized channels.Simultaneous control of these characteristics in a single-layered diatomic metasurface will be an apparent technological extension.Here,spin-selective modulation of terahertz(THz)beams is realized by assembling a pair of meta-atoms with birefringent effects.The distinct modulation functions arise from geometric phase profiles characterized by multiple rotational properties,which introduce independent parametric factors that elucidate their physical significance.By arranging the key parameters,the proposed design strategy can be employed to realize independent amplitude and phase manipulation.A series of THz metasurface samples with specific modulation functions are characterized,experimentally demonstrating the accuracy of on-demand manipulation.This research paves the way for all-silicon meta-optics that may have great potential in imaging,sensing and detection.展开更多
Owing to their charge-free property,magnons are highly promising for achieving dissipationless transport without Joule heating,and are thus potentially applicable to energy-efficient devices.Here,we investigate valley...Owing to their charge-free property,magnons are highly promising for achieving dissipationless transport without Joule heating,and are thus potentially applicable to energy-efficient devices.Here,we investigate valley magnons and associated valley modulations in a kagome ferromagnetic lattice with staggered exchange interaction and Dzyaloshinskii-Moriya interaction.The staggered exchange interaction breaks the spatial inversion symmetry,leading to a valley magnon Hall effect.With nonzero Dzyaloshinskii-Moriya interaction in a staggered kagome lattice,the magnon Hall effect can be observed from only one valley.Moreover,reversing the Dzyaloshinskii-Moriya interaction(D→-D)and exchanging J_(1)and J_(2)(J_(1)■J_(2))can also regulate the position of the unequal valleys.With increasing Dzyaloshinskii-Moriya interaction,a series of topological phase transitions appear when two bands come to touch and split at the valleys.The valley Hall effect and topological phase transitions observed in kagome magnon lattices can be realized in thin films of insulating ferromagnets such as Lu_(2)V_(2)O_(7),and will extend the basis for magnonics applications in the future.展开更多
Directional modulation(DM)is one of the most promising secure communication techniques.However,when the eavesdropper is co-located with the legitimate receiver,the conventional DM has the disadvantages of weak anti-sc...Directional modulation(DM)is one of the most promising secure communication techniques.However,when the eavesdropper is co-located with the legitimate receiver,the conventional DM has the disadvantages of weak anti-scanning capability,anti-deciphering capability,and low secrecy rate.In response to these problems,we propose a twodimensional multi-term weighted fractional Fourier transform aided DM scheme,in which the legitimate receiver and the transmitter use different transform terms and transform orders to encrypt and decrypt the confidential information.In order to further lower the probability of being deciphered by an eavesdropper,we use the subblock partition method to convert the one-dimensional modulated signal vector into a twodimensional signal matrix,increasing the confusion of the useful information.Numerical results demonstrate that the proposed DM scheme not only provides stronger anti-deciphering and anti-scanning capabilities but also improves the secrecy rate performance of the system.展开更多
In this paper, we investigated phase modulation-based computational ghost imaging. According to the results of numerical simulations, we found that the range of the random phase affects the quality of the reconstructe...In this paper, we investigated phase modulation-based computational ghost imaging. According to the results of numerical simulations, we found that the range of the random phase affects the quality of the reconstructed image. Besides,compared with those amplitude modulation-based computational ghost imaging schemes, introducing random phase modulation into the computational ghost imaging scheme could significantly improve the spatial resolution of the reconstructed image, and also extend the field of view.展开更多
Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induce...Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.展开更多
Recently,a Rydberg atom-based mixer was developed to measure the phase of a radio frequency(RF)field.The phase of the signal RF(SIG RF)field is down-converted directly to the phase of a beat signal created by the pres...Recently,a Rydberg atom-based mixer was developed to measure the phase of a radio frequency(RF)field.The phase of the signal RF(SIG RF)field is down-converted directly to the phase of a beat signal created by the presence of a local RF(LO RF)field.In this study,we propose that the Rydberg atom-based mixer can be converted to an all-optical phase detector by amplitude modulation(AM)of the LO RF field;that is,the phase of the SIG RF field is related to both the amplitude and phase of the beat signal.When the AM frequency of the LO RF field is the same as the frequency of the beat signal,the beat signal will further interfere with the AM of the LO RF field inside the atom,and then the amplitude of the beat signal is related to the phase of the SIG RF field.The amplitude of the beat signal and the phase of the SIG RF field show a linear relationship within the range of 0 toπ/2 when the phase of the AM is set with a differenceπ/4 from the phase of the LO RF field.The minimum phase resolution can be as small as 0.6°by optimizing the experimental conditions according to a simple theoretical model.This study will expand and contribute to the development of RF measurement devices based on Rydberg atoms.展开更多
Modulation recognition becomes unreliable at low signal-to-noise ratio(SNR)over fading channel.A novel method is proposed to recognize the digital modulated signals with frequency and phase offsets over multi-path fad...Modulation recognition becomes unreliable at low signal-to-noise ratio(SNR)over fading channel.A novel method is proposed to recognize the digital modulated signals with frequency and phase offsets over multi-path fading channels in this paper.This method can overcome the effects of phase offset,Gaussian noise and multi-path fading.To achieve this,firstly,the characteristic parameters search is constructed based on the cyclostationarity of received signals,to overcome the phase offset,Gaussian white noise,and influence caused by multi-path fading.Then,the carrier frequency of the received signal is estimated,and the maximum characteristic parameter is searched around the integer multiple carriers and their vicinities.Finally,the modulation types of the received signal with frequency and phase offsets are classified using decision thresholds.Simulation results demonstrate that the performance of the proposed method is better than the traditional methods when SNR is over 5dB,and that the proposed method is robust to frequency and phase offsets over multipath channels.展开更多
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 a...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.展开更多
This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results...This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results indicate that, in the case of high-order dispersion, the walk-off effect takes on new characteristics and will influence considerably the shape, position and especially the number of the spectral regions of the gain spectra of modulation instability. Not only the group-velocity mismatch, but also the difference of the third-order dispersion of two optical waves will alter the gain spectra of modulation instability but in different ways. Depending on the values of the walk-off parameters, the number of the spectral regions may increase from two to at most four, and the spectral shape and position may change too.展开更多
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 o...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.展开更多
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 ...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.展开更多
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 trai...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.展开更多
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 sa...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.展开更多
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 po...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.展开更多
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 ...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.展开更多
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...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.展开更多
We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state...We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated.It is found that the cavity optomechanical system can be modulated to different topological Su–Schrieffer–Heeger(SSH)phases via designing the optomechanical couplings legitimately.Meanwhile,combining the effective optomechanical couplings and the probability distributions of gap states,we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields.Moreover,we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.展开更多
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 chang...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.展开更多
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 s...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.展开更多
Utilizing the linear-stability analysis, this paper analytically investigates and calculates the condition and gain spectra of cross-phase modulation instability in optical fibres in the ease of exponential saturable ...Utilizing the linear-stability analysis, this paper analytically investigates and calculates the condition and gain spectra of cross-phase modulation instability in optical fibres in the ease of exponential saturable nonlinearity and high-order dispersion. The results show that, the modulation instability characteristics here are similar to those of conventional saturable nonlinearity and Kerr nonlinearity. That is to say, when the fourth-order dispersion has the same sign as that of the second-order one, a new gain spectral region called the second one which is far away from the zero point may appear. The existence of the exponential saturable nonlinearity will make the spectral width as well as the peak gain of every spectral region increase with the input powers before decrease. Namely, for every spectral regime, this may lead to a unique value of peak gain and spectral width for two different input powers. In comparison with the case of conventional saturable nonlinearity, however, when the other parameters are the same, the variations of the spectral width and the peak gain with the input powers will be faster in case of exponential saturable nonlinearity.展开更多
基金supports from National Key Research and Development Program of China(2021YFB2800703)Sichuan Province Science and Technology Support Program(25QNJJ2419)+1 种基金National Natural Science Foundation of China(U22A2008,12404484)Laoshan Laboratory Science and Technology Innovation Project(LSKJ202200801).
文摘Diatomic metasurfaces designed for interferometric mechanisms possess significant potential for the multidimensional manipulation of electromagnetic waves,including control over amplitude,phase,frequency,and polarization.Geometric phase profiles with spin-selective properties are commonly associated with wavefront modulation,allowing the implementation of conjugate strategies within orthogonal circularly polarized channels.Simultaneous control of these characteristics in a single-layered diatomic metasurface will be an apparent technological extension.Here,spin-selective modulation of terahertz(THz)beams is realized by assembling a pair of meta-atoms with birefringent effects.The distinct modulation functions arise from geometric phase profiles characterized by multiple rotational properties,which introduce independent parametric factors that elucidate their physical significance.By arranging the key parameters,the proposed design strategy can be employed to realize independent amplitude and phase manipulation.A series of THz metasurface samples with specific modulation functions are characterized,experimentally demonstrating the accuracy of on-demand manipulation.This research paves the way for all-silicon meta-optics that may have great potential in imaging,sensing and detection.
基金support from the Funding for School-level Research Projects of Yancheng Institute of Technology(Grant Nos.xjr2020038,xjr2022039,and xjr2022040)。
文摘Owing to their charge-free property,magnons are highly promising for achieving dissipationless transport without Joule heating,and are thus potentially applicable to energy-efficient devices.Here,we investigate valley magnons and associated valley modulations in a kagome ferromagnetic lattice with staggered exchange interaction and Dzyaloshinskii-Moriya interaction.The staggered exchange interaction breaks the spatial inversion symmetry,leading to a valley magnon Hall effect.With nonzero Dzyaloshinskii-Moriya interaction in a staggered kagome lattice,the magnon Hall effect can be observed from only one valley.Moreover,reversing the Dzyaloshinskii-Moriya interaction(D→-D)and exchanging J_(1)and J_(2)(J_(1)■J_(2))can also regulate the position of the unequal valleys.With increasing Dzyaloshinskii-Moriya interaction,a series of topological phase transitions appear when two bands come to touch and split at the valleys.The valley Hall effect and topological phase transitions observed in kagome magnon lattices can be realized in thin films of insulating ferromagnets such as Lu_(2)V_(2)O_(7),and will extend the basis for magnonics applications in the future.
基金supported by National Natural Science Foundation of China(No.62171445)。
文摘Directional modulation(DM)is one of the most promising secure communication techniques.However,when the eavesdropper is co-located with the legitimate receiver,the conventional DM has the disadvantages of weak anti-scanning capability,anti-deciphering capability,and low secrecy rate.In response to these problems,we propose a twodimensional multi-term weighted fractional Fourier transform aided DM scheme,in which the legitimate receiver and the transmitter use different transform terms and transform orders to encrypt and decrypt the confidential information.In order to further lower the probability of being deciphered by an eavesdropper,we use the subblock partition method to convert the one-dimensional modulated signal vector into a twodimensional signal matrix,increasing the confusion of the useful information.Numerical results demonstrate that the proposed DM scheme not only provides stronger anti-deciphering and anti-scanning capabilities but also improves the secrecy rate performance of the system.
基金Project supported by the National Natural Science Foundation of China(Grant No.11305020)the Science and Technology Research Projects of the Education Department of Jilin Province,China(Grant No.2016-354)the Science and Technology Development Project of Jilin Province,China(Grant No.20180520165JH)
文摘In this paper, we investigated phase modulation-based computational ghost imaging. According to the results of numerical simulations, we found that the range of the random phase affects the quality of the reconstructed image. Besides,compared with those amplitude modulation-based computational ghost imaging schemes, introducing random phase modulation into the computational ghost imaging scheme could significantly improve the spatial resolution of the reconstructed image, and also extend the field of view.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61177073)the Specialized Research Fundfor the Doctoral Program of Higher Education of China (Grant No.20104307110020)+1 种基金the Fund of Innovation of Graduate School of National University of Defense Technology, China (Grant No.B110703)the Hunan Provincial Innovation Foundation for Postgraduate, China (Grant No. CX2011B033)
文摘Four-wave mixing induced by modulation instability in a single-mode fiber is analyzed from the phase-matching point of view. For the two-channel transmission, a method is proposed to select the four-wave-mixing-induced sidebands, which is based on the proper use of a continuous-wave and a pulse as light sources. We find that a mass of sidebands are generated in the modulation instability resonance region, and the power of the sideband increases with not only the peak power of the pump pulse but also the continuous-wave power which acts as a seed. The research will provide guidance for fiber communication and sensing systems using wavelength division multiplexing technology.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0304900 and 2017YFA0402300)the Beijing Natural Science Foundation(Grant No.1212014)+3 种基金the National Natural Science Foundation of China(Grant Nos.11604334,11604177,and U2031125)the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB08-3)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics(Grant No.KF201807)the Fundamental Research Funds for the Central Universities,and Youth Innovation Promotion Association CAS.
文摘Recently,a Rydberg atom-based mixer was developed to measure the phase of a radio frequency(RF)field.The phase of the signal RF(SIG RF)field is down-converted directly to the phase of a beat signal created by the presence of a local RF(LO RF)field.In this study,we propose that the Rydberg atom-based mixer can be converted to an all-optical phase detector by amplitude modulation(AM)of the LO RF field;that is,the phase of the SIG RF field is related to both the amplitude and phase of the beat signal.When the AM frequency of the LO RF field is the same as the frequency of the beat signal,the beat signal will further interfere with the AM of the LO RF field inside the atom,and then the amplitude of the beat signal is related to the phase of the SIG RF field.The amplitude of the beat signal and the phase of the SIG RF field show a linear relationship within the range of 0 toπ/2 when the phase of the AM is set with a differenceπ/4 from the phase of the LO RF field.The minimum phase resolution can be as small as 0.6°by optimizing the experimental conditions according to a simple theoretical model.This study will expand and contribute to the development of RF measurement devices based on Rydberg atoms.
基金supported by the National Natural Science Foundation of China under Grant 62071364 and 62231027in part by the Key Research and Development Program of Shaanxi under Grant 2023-YBGY-249+1 种基金in part by the Key Research and Development Program of Guangxi under Grant 2022AB46002in part by the Fundamental Research Funds for the Central Universities under Grant KYFZ23001.
文摘Modulation recognition becomes unreliable at low signal-to-noise ratio(SNR)over fading channel.A novel method is proposed to recognize the digital modulated signals with frequency and phase offsets over multi-path fading channels in this paper.This method can overcome the effects of phase offset,Gaussian noise and multi-path fading.To achieve this,firstly,the characteristic parameters search is constructed based on the cyclostationarity of received signals,to overcome the phase offset,Gaussian white noise,and influence caused by multi-path fading.Then,the carrier frequency of the received signal is estimated,and the maximum characteristic parameter is searched around the integer multiple carriers and their vicinities.Finally,the modulation types of the received signal with frequency and phase offsets are classified using decision thresholds.Simulation results demonstrate that the performance of the proposed method is better than the traditional methods when SNR is over 5dB,and that the proposed method is robust to frequency and phase offsets over multipath channels.
基金This work was supported in part by the National Natural Science Foundation of China(61771109,U19B2017,61871080,61701088)the China Postdoctoral Science Foundation(2020M68147)。
文摘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.
基金Project supported by the Fundamental Application Research Project of the Department of Science ＆ Technology of Sichuan Province （Grant Nos 05JY029-084 and 04JY029-103）, the Key Program of Natural Science Foundation of Educational Commission of Sichuan Province （Grant No 2006A124）, and the Foundation of Science ＆ Technology Development of Chengdu University of Information Technology （Grant No KYTZ20060604）.
文摘This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results indicate that, in the case of high-order dispersion, the walk-off effect takes on new characteristics and will influence considerably the shape, position and especially the number of the spectral regions of the gain spectra of modulation instability. Not only the group-velocity mismatch, but also the difference of the third-order dispersion of two optical waves will alter the gain spectra of modulation instability but in different ways. Depending on the values of the walk-off parameters, the number of the spectral regions may increase from two to at most four, and the spectral shape and position may change too.
基金Project supported by the National Science and Technology Major Project of Science and Technology of China(Grant No.2011ZX02708)the National Natural Science Foundation of China(Grant No.61504137)
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.61178012,11204156,11304179,and 11247240)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant Nos.20133705110001 and 20123705120002)+1 种基金the Scientific Research Foundation for Outstanding Young Scientists of Shandong Province of China(Grant No.BS2013DX034)the Natural Science Foundation of Shandong Province of China(Grant No.ZR2012FQ024)
文摘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.
基金supported by the National Natural Science Foundation of China(Grant No.61301179)the Doctorial Programs Foundation of the Ministry of Education,China(Grant No.20110203110011)the Programme of Introducing Talents of Discipline to Universities,China(Grant No.B08038)
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant No.61177073)the Major Application Basic Research Project of National University of Defense Technology,China(Grant No.ZDYYJCYJ20140701)
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60978007)Open Fund of Key Laboratory of Optical Communication and Lightwave Technologies (Beijing University of Posts and Telecommunications),Ministry of Education,China
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774262 and 61975154).
文摘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.
基金This work was supported by the National Natural Science Foundation of China(Nos.12075236,11575181,11705203,51627901)the Anhui Provincial Natural Science Foundation(No.1808085QA24).
文摘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.
基金the National Natural Science Foundation of China(Grant Nos.61822114,12074330,and 62071412)。
文摘We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated.It is found that the cavity optomechanical system can be modulated to different topological Su–Schrieffer–Heeger(SSH)phases via designing the optomechanical couplings legitimately.Meanwhile,combining the effective optomechanical couplings and the probability distributions of gap states,we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields.Moreover,we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.
基金Project supported by the National Natural Science Foundation of China(Grant No.11474106)the Natural Science Foundation of Guangdong Province,China(Grant No.2016A030313439)the Science and Technology Program of Guangzhou City,China(Grant No.201707010403)
文摘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.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274112 and 11474092the Key Project of Shanghai Municipal Education Commission under Grant No 14ZZ056+1 种基金the Shanghai Natural Science Fund Project under Grant No14ZR1410300the Key Research Project of Henan Province Education Department under Grant No 13A140818
文摘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.
基金Project supported by the Key Program of the Natural Science Foundation of Sichuan Provincial Education Department (Grant No. 2006A124)the Fundamental Application Research Project of the Department of Science & Technology of Sichuan Province (Grant No. 05JY029-084)
文摘Utilizing the linear-stability analysis, this paper analytically investigates and calculates the condition and gain spectra of cross-phase modulation instability in optical fibres in the ease of exponential saturable nonlinearity and high-order dispersion. The results show that, the modulation instability characteristics here are similar to those of conventional saturable nonlinearity and Kerr nonlinearity. That is to say, when the fourth-order dispersion has the same sign as that of the second-order one, a new gain spectral region called the second one which is far away from the zero point may appear. The existence of the exponential saturable nonlinearity will make the spectral width as well as the peak gain of every spectral region increase with the input powers before decrease. Namely, for every spectral regime, this may lead to a unique value of peak gain and spectral width for two different input powers. In comparison with the case of conventional saturable nonlinearity, however, when the other parameters are the same, the variations of the spectral width and the peak gain with the input powers will be faster in case of exponential saturable nonlinearity.
