HOG-VGG:VGG Network with HOG Feature Fusion for High-Precision PolSAR Terrain Classification

This article proposes a VGG network with histogram of oriented gradient(HOG) feature fusion(HOG-VGG) for polarization synthetic aperture radar(PolSAR) image terrain classification.VGG-Net has a strong ability of deep feature extraction,which can fully extract the global deep features of different terrains in PolSAR images,so it is widely used in PolSAR terrain classification.However,VGG-Net ignores the local edge & shape features,resulting in incomplete feature representation of the PolSAR terrains,as a consequence,the terrain classification accuracy is not promising.In fact,edge and shape features play an important role in PolSAR terrain classification.To solve this problem,a new VGG network with HOG feature fusion was specifically proposed for high-precision PolSAR terrain classification.HOG-VGG extracts both the global deep semantic features and the local edge & shape features of the PolSAR terrains,so the terrain feature representation completeness is greatly elevated.Moreover,HOG-VGG optimally fuses the global deep features and the local edge & shape features to achieve the best classification results.The superiority of HOG-VGG is verified on the Flevoland,San Francisco and Oberpfaffenhofen datasets.Experiments show that the proposed HOG-VGG achieves much better PolSAR terrain classification performance,with overall accuracies of 97.54%,94.63%,and 96.07%,respectively.

High-order Autler–Townes splitting in electrically tunable photonic molecules

Whispering gallery mode optical microresonators represent a promising avenue for realizing optical analogs of coherent light–atom interactions,circumventing experimental complexities.All-optical analogs of Autler–Townes splitting have been widely demonstrated,harnessing coupled optical microresonators,also known as photonic molecules,wherein the strong coupling between resonant fields enables energy level splitting.Here,we report the characterizations of Autler–Townes splitting in waveguide-coupled microring dimers featuring mismatched sizes.By exploiting backscattering-induced coupling via Rayleigh and Mie scatterers in individual rings,high-order Autler–Townes splitting has been realized,yielding supermode hybridization in a multi-level system.Upon resonance detuning using an integrated phase shifter,intra-cavity coupling-induced splitting becomes almost indistinguishable at the zero-detuning point where the strong inter-cavity coupling counteracts the imbalance of backscattering strengths in individual rings.Through demonstrations on the maturing silicon photonics platform,our findings establish a framework of electrically tunable photonic molecules for coupling-mediated Autler–Townes splitting,offering promising prospects for on-chip signal generation and processing across classical and quantum regimes.

On-chip ultra-high rejection and narrow bandwidth filter based on coherency-broken cascaded cladding-modulated gratings

Bragg filters are of essential importance for chip-scale photonic systems.However,the implementation of filters with sub-nanometer bandwidth and rejection beyond 70 dB is hindered by the high index contrast of the siliconon-insulator platform,which makes filters prone to fabrication imperfections.In this paper,we propose to combine coherency-broken cascading architecture and cladding modulation to circumvent the intrinsic limitation.The cascading architecture effectively prevents the accumulation of phase errors,while the cladding modulation offers additional design freedom to reduce the coupling coefficient.A bimodal Bragg filter with a testingequipment-limited rejection level of 74 dB and a 40 dB bandwidth of 0.44 nm is experimentally demonstrated.The minimum feature size is 90 nm,which significantly relieves the fabrication constraints.