The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne S...The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.展开更多
Integrated optical phased arrays(OPAs),owing to their high integration level and wide-angle beamsteering capability,are a key promising component for 3D/4D sensing and free-space optical communication.However,integrat...Integrated optical phased arrays(OPAs),owing to their high integration level and wide-angle beamsteering capability,are a key promising component for 3D/4D sensing and free-space optical communication.However,integrated OPAs typically employ a single-wavelength laser as the input light source,which limits their application in spectral imaging and secure communication.In this work,we propose and experimentally demonstrate a dual-wavelength coherent beam combining(CBC)scheme using a 64-element integrated OPA.A multiwavelength CBC model is established and validated with two wavelength pairs(1545/1555 and 1535∕1565 nm).Both simulation and experimental results confirm that the beam dispersion intensifies with the steering angle and wavelength separation.To overcome this inherent dispersion issue,we employ a stochastic parallel gradient descent algorithm with two avalanche photodiodes as feedback sensors,achieving an arbitrarily configurable angular separation between the two wavelength beams.Finally,we demonstrate the wide field of view beam-steering capability of the combined beam across a 60 deg(±30 deg)range.We provide a foundational framework for advancing multiwavelength OPA toward applications in spectral imaging and secure optical communications.展开更多
A novel scalable architecture for coherent beam combining with hybrid phase control involving passive phasing and active phasing in master oscillator-power amplifier configuration is presented. Wide-linewidth mutually...A novel scalable architecture for coherent beam combining with hybrid phase control involving passive phasing and active phasing in master oscillator-power amplifier configuration is presented. Wide-linewidth mutually injected passive phasing fibre laser arrays serve as master oscillators for the power amplifiers, and the active phasing using stochastic parallel gradient descent algorithm is induced. Wide-linewidth seed laser can suppress the stimulated Brillouin scattering effectively and improve the output power of the fibre laser amplifier, while hybrid phase control provides a robust way for in-phase mode coherent beam combining simultaneously. Experiment is performed by active phasing fibre laser amplifiers with passive phasing fibre ring laser array seed lasers. Power encircled in the main-lobe increases1.57 times and long-exposure fringe contrast is obtained to be 78% when the system evolves from passive phasing to hybrid phasing.展开更多
MOtion COmpensation(MOCO) is an essential step in high resolution airborne Synthetic Aperture Radar(SAR) imaging. Generally, a reference altitude level is assumed and external Digital Elevation Model(DEM) is required ...MOtion COmpensation(MOCO) is an essential step in high resolution airborne Synthetic Aperture Radar(SAR) imaging. Generally, a reference altitude level is assumed and external Digital Elevation Model(DEM) is required for the scene topography heavily varied. To overcome the shortcoming, we propose a MOCO method based on Phase Gradient Autofocus(PGA) which can obtain well focused images without DEM. In the implementation, we first compensate the normal range-invariant term. Then the data are divided into strips in range-compressed domain and PGA is applied to each substrip to extract the phase errors. Finally, the phase error surface is obtained using interpolation and then compensated. Real airborne SAR data of a UAV-SAR system experiments and comparisons demonstrate the validity and effectiveness of the proposed algorithm. The results show that our algorithm is effective.展开更多
A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scattere...A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scatterer in ISAR image. The new approach aims to choose strong scatterers for error phase averaging with a threshold rather than just simply to pick out the strongest point in each range cell, which is not necessarily real strong scatterers if in some range cells consists more than one strong scatterer and whereas in other range cells no scatterer at all. The results of processing real data are presented to confirm the validity of the proposed approach.展开更多
This paper develops a new algorithm based on the Projected Gradient Algorithm (PGA) for the design of FIR digital filters with "sum of power of two" coefficients. It is shown that the integer programming inv...This paper develops a new algorithm based on the Projected Gradient Algorithm (PGA) for the design of FIR digital filters with "sum of power of two" coefficients. It is shown that the integer programming involved in the FIR filter design can be solved by this algorithm. It is compared with the reported method for a SemiDefinite Programming (SDP) relaxation- based design. The simulations demonstrate that the new algorithm often yields the similar error performances of the FIR filter design, but the average CPU time of this approach is significantly reduced.展开更多
摘要The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.
基金supported by the National Natural Science Foundation of China(Grant Nos.62575305,62305275,12574333,11974258,and 62305388)the Natural Science Foundation of Hunan Province of China(Grant No.2024JJ6473)the Innovation Research Foundation of National University of Defense Technology(Innovation Research Foundation of(NUDT)(Grant No.24-ZZCX-JDZ-18).
摘要Integrated optical phased arrays(OPAs),owing to their high integration level and wide-angle beamsteering capability,are a key promising component for 3D/4D sensing and free-space optical communication.However,integrated OPAs typically employ a single-wavelength laser as the input light source,which limits their application in spectral imaging and secure communication.In this work,we propose and experimentally demonstrate a dual-wavelength coherent beam combining(CBC)scheme using a 64-element integrated OPA.A multiwavelength CBC model is established and validated with two wavelength pairs(1545/1555 and 1535∕1565 nm).Both simulation and experimental results confirm that the beam dispersion intensifies with the steering angle and wavelength separation.To overcome this inherent dispersion issue,we employ a stochastic parallel gradient descent algorithm with two avalanche photodiodes as feedback sensors,achieving an arbitrarily configurable angular separation between the two wavelength beams.Finally,we demonstrate the wide field of view beam-steering capability of the combined beam across a 60 deg(±30 deg)range.We provide a foundational framework for advancing multiwavelength OPA toward applications in spectral imaging and secure optical communications.
基金supported by the Innovation Foundation for Graduates in National University of Defense Technology,China (GrantNo.B080702)
摘要A novel scalable architecture for coherent beam combining with hybrid phase control involving passive phasing and active phasing in master oscillator-power amplifier configuration is presented. Wide-linewidth mutually injected passive phasing fibre laser arrays serve as master oscillators for the power amplifiers, and the active phasing using stochastic parallel gradient descent algorithm is induced. Wide-linewidth seed laser can suppress the stimulated Brillouin scattering effectively and improve the output power of the fibre laser amplifier, while hybrid phase control provides a robust way for in-phase mode coherent beam combining simultaneously. Experiment is performed by active phasing fibre laser amplifiers with passive phasing fibre ring laser array seed lasers. Power encircled in the main-lobe increases1.57 times and long-exposure fringe contrast is obtained to be 78% when the system evolves from passive phasing to hybrid phasing.
摘要MOtion COmpensation(MOCO) is an essential step in high resolution airborne Synthetic Aperture Radar(SAR) imaging. Generally, a reference altitude level is assumed and external Digital Elevation Model(DEM) is required for the scene topography heavily varied. To overcome the shortcoming, we propose a MOCO method based on Phase Gradient Autofocus(PGA) which can obtain well focused images without DEM. In the implementation, we first compensate the normal range-invariant term. Then the data are divided into strips in range-compressed domain and PGA is applied to each substrip to extract the phase errors. Finally, the phase error surface is obtained using interpolation and then compensated. Real airborne SAR data of a UAV-SAR system experiments and comparisons demonstrate the validity and effectiveness of the proposed algorithm. The results show that our algorithm is effective.
摘要A new approach to phase averaging in phase gradient algorithm (PGA) is proposed, which is based on the fundamental fact that the information of translational phase error is widely contained in every defocused scatterer in ISAR image. The new approach aims to choose strong scatterers for error phase averaging with a threshold rather than just simply to pick out the strongest point in each range cell, which is not necessarily real strong scatterers if in some range cells consists more than one strong scatterer and whereas in other range cells no scatterer at all. The results of processing real data are presented to confirm the validity of the proposed approach.
基金Supported by Shaanxi Province Natural Science Funds.
摘要This paper develops a new algorithm based on the Projected Gradient Algorithm (PGA) for the design of FIR digital filters with "sum of power of two" coefficients. It is shown that the integer programming involved in the FIR filter design can be solved by this algorithm. It is compared with the reported method for a SemiDefinite Programming (SDP) relaxation- based design. The simulations demonstrate that the new algorithm often yields the similar error performances of the FIR filter design, but the average CPU time of this approach is significantly reduced.